Genome evolution in allotetraploid Nicotiana



Yüklə 168,04 Kb.
Pdf görüntüsü
tarix26.04.2018
ölçüsü168,04 Kb.
#40269


 

Biological Journal of the Linnean Society

 

, 2004, 



 

82

 

, 599–606. With 1 figure



© 2004 The Linnean Society of London, 

 

Biological Journal of the Linnean Society, 

 

2004, 



 

82

 

, 599–606



 

599


 

Blackwell Science, LtdOxford, UKBIJBiological Journal of the Linnean Society0024-4066The Linnean 

Society of London, 2004? 2004

824


599606

Original Article

GENOME EVOLUTION IN ALLOTETRAPLOID 

 

NICOTIANA

 

K. Y. LIM 



 

ET AL.

 

 



 

*Corresponding author. E-mail: a.r.leitch@qmul.ac.uk



 

Biological relevance of polyploidy: ecology to genomics

 

Edited by A. R. Leitch, D. E. Soltis, P. S. Soltis, I. J. Leitch and J. C. Pires

 

Genome evolution in allotetraploid 

 

Nicotiana

 

KAR YOONG LIM



 

1

 



, ROMAN MATYASEK

 

2



 

, ALES KOVARIK

 

2

 



 and ANDREW R. LEITCH

 

1



 

*

 



1

 

School of Biological Sciences, Queen Mary, University of London, London E1 4NS, UK

 

2



 

Institute of Biophysics, Academy of Sciences of the Czech Republic, CZ-61265 Brno, Czech Republic

 

Received 4 July 2003; accepted for publication 5 January 2004

 

The nuclear cytoplasmic interaction (NCI) hypothesis of genome evolution and speciation in plants states that newly



formed allopolyploids pass through a bottleneck of sterility and the fertile plants that emerge are fixed for species-

specific chromosome translocations. These translocations restore fertility and reduce negative effects of the maternal

cytoplasm on an alien paternal genome. Using fluorescent 

 

in situ

 

 hybridization and genomic 



 

in situ

 

 hybridization



and by reviewing published data, we test the NCI hypothesis using three natural 

 

Nicotiana

 

  allotetraploids (all



2

 

n

 

 



 

=

 



 4

 

x

 

 



 

=

 



 48, 

 

N. arentsii

 



 

N. rustica

 

  and several genotypes, including a feral plant and cultivars, of 



 

N. tabacum

 

(tobacco)). We compare these data with three synthetic tobacco plants (Th37) that are F3 descendent progeny of an



allotetraploid formed from 

 

Ǩ



 

 

 



N. sylvestris

 

 (2



 

n

 

 



 

=

 



 24) 

 

¥



 

 

 



ǩ

 

 



 

N. tomentosiformis

 

 (2



 

n

 

 



 

=

 



 24). No intergenomic translocations

were observed in 



 

N. arentsii

 

 and 



 

N. rustica

 

. An analysis of subtelomeric tandem repeats in these allotetraploids and



their putative parents shows minimal genetic changes; those that do occur may reflect evolution in the diploids or

the polyploids subsequent to allopolyploidy. All natural 



 

N. tabacum

 

  genotypes have intergenomic translocations.



This may reflect a large ‘genomic-shock’ generated by allopolyploidy involving widely diverged parental species. Two

of three synthetic tobacco plants had a translocation similar to that found in all cultivars of tobacco. This translo-

cation may be significant in tobacco fertility and may have been fixed early in tobacco’s evolution. But it is lacking

in the feral tobacco, which might indicate a polyphyletic origin or early divergence from all cultivars examined. Over-

all, only in tobacco is there any evidence that NCI may have influenced genome evolution, and here further data are

required to verify chromosome identity.

© 2004 The Linnean Society of London, 

 

Biological Journal of the Linnean

Society

 

, 2004, 



 

82

 

, 599–606.



 

ADDITIONAL KEYWORDS:

 

 

allopolyploid – 



 

N. paniculata

 

  – 



 

N. undulata

 

  – 



 

N. wigandioides

 

  – reticulate



 

evolution – satellite repeat.

 

INTRODUCTION



 

Gene conversion, chromosomal translocations and

sequence loss, gain, amplification and reduction have

all been associated with allopolyploidy and are per-

haps induced by allopolyploidy. But it remains unclear

whether changes are species-specific, ubiquitous,

accelerated in polyploids or simply reflect evolutionary

processes that occur in diploids and polyploids alike.

According to Gill’s (1991) nuclear cytoplasmic inter-

action (NCI) hypothesis, a newly formed polyploid

passes through a bottleneck of sterility, and the fertile

plants that emerge have ‘species-specific transloca-

tions’. These translocations, rather than ‘random

translocations’, are involved in restoring fertility and

cytoplasmic compatibility in the allopolyploid. In sup-

port of this argument, Jiang & Gill (1994a) identified

in two tetraploid wheats ‘species-specific’ transloca-

tions, and Leitch & Bennett (1997) noted that two cul-

tivars of 

 

Nicotiana tabacum

 

 (tobacco, cvs. 095-55 and



35466) analysed by Kenton 

 

et al

 

.  (1993) had several



translocations common to both.

Song 


 

et al

 

.  (1995) extended the NCI hypothesis in



studies of synthetic 

 

Brassica

 

  allopolyploids. In these



synthetic plants, restriction fragment length polymor-

phisms (RFLPs) indicated that the paternal genome

degenerates more rapidly than the maternal genome.

Downloaded from https://academic.oup.com/biolinnean/article-abstract/82/4/599/2643091

by guest

on 26 April 2018




 

600


 

K. Y. LIM 



 

ET AL

 

.



 

© 2004 The Linnean Society of London, 



 

Biological Journal of the Linnean Society, 

 

2004, 



 

82

 

, 599–606



 

However, generalizations are proving difficult to find.

Studies of synthetic hybrids and allopolyploids of 

 

Triti-

cum

 

 and 



 

Aegilops

 

 revealed fast, non-random and repro-



ducible elimination of chromosome- and genome-

specific sequences (Ozkan, Levy & Feldman, 2001;

Shaked 

 

et al

 

., 2001; Levy & Feldman, 2004 – this



issue). This elimination was associated with the acti-

vation of retroelements and the loss of uncharacterized

RNA transcripts, the latter reflecting either gene loss

or epigenetic inactivation (Kashkush, Feldman & Levy,

2002, 2003). By contrast, amplified fragment length

polymorphism (AFLP) analyses of newly synthesized



 

Gossypium

 

 allopolyploids (cotton) showed no evidence



of rapid genetic change associated with allopolyploidy

(Liu 


 

et al

 

., 2001; Adams & Wendel, 2004 – this issue).



Is there evidence for species-specific translocations

that may have been selected in early 



 

Nicotiana

 

allopolyploid evolution? The genus 



 

Nicotiana

 

  is an



ideal model to study patterns of evolution associated

with polyploidy because it has 



 

c

 

. 70 diploid and poly-



ploid species (Goodspeed, 1954; Chase 

 

et al

 

., 2003) and



provides clear examples of recurrent, including recent,

reticulate evolution (Chase 



 

et al

 

., 2003). Here we anal-



yse three natural allopolyploids, 

 

N. rustica

 



 

N. arentsii

 

and several cultivars of 



 

N. tabacum

 

, including a feral



tobacco, and synthetic tobacco plants descended from

a plant made by Burk (1973). We use fluorescent 



 

in

situ

 

 hybridization (FISH) to localize tandem repetitive



sequences and genomic 

 

in situ

 

 hybridization (GISH) to



identify intergenomic translocations, including ‘spe-

cies-specific translocations’. GISH, which uses

labelled total genomic DNA from either one or both

putative parents of the allopolyploid as a probe, is a

powerful method to identify parental chromatin in the

allopolyploid. The method has been applied to a range

of natural and cultivated allopolyploids to determine

allopolyploid parentage and to identify the occurrence,

nature, and distribution of whole parental genomes,

chromosomes and introgressed chromosome segments

(Heslop-Harrison, 1992; Jiang & Gill, 1994b; Gill &

Friebe, 1998; Heslop-Harrison, 1998). Thus, GISH is

an ideal method to search for intergenomic species-

specific translocations and the influence of NCI on

early allopolyploid evolution. The work complements

that of Kovarik 



 

et al

 

.  (2004 – this issue), who exam-



ined ribosomal DNA (rDNA) evolution in the same

material.

 

RESULTS


 

N

 

ICOTIANA

 

 

 

TABACUM

 

Nicotiana tabacum

 

  (tobacco) is an allotetraploid



(2

 

n

 

 



 

=

 



 4

 

x

 

 



 

=

 



 48) with two cytologically distinct parental

genomes, the S-genome and the T-genome (Kenton



 

et al

 

., 1993). Flower morphology, chromosome segrega-



tion patterns, GISH, chloroplast and mitochondrial

sequence data all suggest that a close relative of



 

N. sylvestris

 

  (2



 

n

 

 



 

=

 



 2

 

x

 

 



 

=

 



 24,  section 

 

Alatae

 

) is the



maternal S-genome donor (Goodspeed, 1954; Bland,

Matzinger & Levins, 1985; Kenton 



 

et al

 

., 1993;



Mosconne, Matzke & Matzke, 1996; Lim 

 

et al

 

., 2000;



Chase 

 

et al

 

., 2003). The paternal, T-genome donor of



tobacco is more controversial, with ancestors of

 

N. tomentosiformis

 



 

N. otophora

 

  (both section 



 

Tomen-

tosae

 

, 2



 

n

 

 



 

=

 



 2

 

x

 

 



 

=

 



 24) or an introgression hybrid impli-

cated (Kenton 



 

et al

 

., 1993; Parokonny & Kenton,



1995).

Lim 


 

et al

 

.  (2000) conducted a detailed karyotype



analysis of all species in 

 

Nicotiana

 

 section 



 

Tomentosae

 

using a suite of repetitive DNA probes and demon-



strated that the T-genome of tobacco was closely sim-

ilar to 


 

N. tomentosiformis

 

  and quite dissimilar from



 

N. otophora

 

. Murad 



 

et al

 

. (2002) extended the analysis



to show that the T-genome was most like one accession

of 


 

N. tomentosiformis

 

, carrying the tandem repetitive



sequences called NTRS, GRD5, GRD3 and GRD53.

Thus tobacco evolved from a particular genotype of



 

N. tomentosiformis

 

  that existed after the common



ancestor of extant 

 

N. tomentosiformis

 

.



Although 

 

N. otophora

 

  is not the T-genome donor of



 

N. tabacum

 

,  there is a possibility that 



 

N. otophora

 

DNA has introgressed into the T-genome. This would



explain Riechers & Timko’s (1999) data on putrescine

 

N

 

-methyltransferase gene families in tobacco, in



which one family member is found in tobacco and

 

N. tomentosiformis

 

  and another in tobacco and



 

N. otophora.

 

  Similarly, Ren & Timko (2001) observed



some matching AFLP bands in tobacco with

 

N. otophora

 

 and others with 



 

N. tomentosiformis.

 

 How-



ever, introgression of 

 

N. otophora

 

 DNA into tobacco is



only one possible explanation of the data; another is

that there was independent loss of sequences in the

diploids after tobacco’s formation. Certainly if

 

N. otophora

 

 is involved in tobacco’s ancestry, it has left



no cytological footprint detected to date. In addition,

there is no evidence from Tnt1 retrotransposon inser-

tion sites for introgressed N. otophora DNA (Melayah

et al., 2004 – this issue).

We  analysed published and new GISH data to

search for species-specific translocations in tobacco

cultivars SR1 and Gatersleben (Mosconne et al.,

1996), 095-55, 35455, SR1 (Kenton et al., 1993), 095-

55 (Lim et al., 2000), a feral tobacco (Fig. 1A) from

Bolivia (kindly donated by Dr S. Knapp, Natural

History Museum, London), and three synthetic

tobacco plants (Fig. 1E). The synthetic tobacco plants

are  descendant  progeny  (F3)  of  a  single  plant  made

by crossing 

Ǩ 

N. sylvestris 

(2n = 24) ¥ 

ǩ

N. tomentosiformis (2n = 24) and the F1 converted to a

fertile amphidiploid by in vitro  callus culture (F0)

(Burk, 1973). A tally of intergenomic translocations in

all tobacco allopolyploids observed is shown in Table 1.

Downloaded from https://academic.oup.com/biolinnean/article-abstract/82/4/599/2643091

by guest

on 26 April 2018




GENOME EVOLUTION IN ALLOTETRAPLOID NICOTIANA

601


© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 599–606

T

able 1.

Karyotype details and c

hromosome translocations (inc

luding nomenc

lature synonyms) that occur in different lines of tobacco

Chromosomes

(per 1C genome)

0955-55


a/b

Samsun


NN

d

35466



a

SR1


a/c

Gatersleben

c

Bolivia


e

Synthetic

Th37-1

f

Synthetic



Th37-9

g

Synthetic



Th37-8

h

Overall karyotype



No

. of S-genome c

hromosomes

9/9


10

10

10/10



10

11 (10)


11

11

12



No

. of 


T

-genome chromosomes

6/7

10

9



9/10

10

6



1

0

1



1

1

2



No

. of recombinant c

hromosomes

9/8


4

5

5/4



4

7

 (8)



3

3



Recombinant c

hromosomes

S1/t;

 ST3;


 S1/ST3;

 N

+



/+

––

–/–





S2/t;



 S2/ST1;

 ST1;


 S2/t1

+

/++



+

+

/++



++



S11/t;

 ST2;


 S11/ST2;

 S11/t2


+

/++


+

+

/++



+

–––


T1/s;

 TS1;


 T1/TS4;

 N

+



/+

––

–/–





*T4/s



–/–



–/–

++



+

T5/s;



 TS2;

 T2/TS1;


 N

+

/++



+

+

/–



–––



T6/s;

 TS4;


 T6/TS2;

 T11/t4


+

/+



++

/++


+

?

–––



T7/s/s;

 TS3;


 T7/TS5;

 N

+



/++

–/–





T9/s;



 TS5;

 T9/TS3;


 T9/t3

+

/++



+

+

/++



+

+

+



N;

 TS6;



 T11/TS6;

 N

+



/–



–/–





GISH data reveal the number of S-genome

T



-genome or recombinant c

hromosomes in different tobacco lines

, reported by 

a

K



enton 

et al

(1993



),

 

b



Lim 

et al

(2000



),

c

Mosconne 



et al

(1996



),

 

d



P

arokonny & K

enton (1995

),

 or 



e–h

shown here:

 

e

F



igure 1A;

 

f



synthetic tobacco (

F

ig



1E),


 

g

synthetic tobacco (



F

ig



1E),

 Th37-9 is aneuploid,

2

n

 =

 49 with an extra 



T

-genome chromosome;

 

h

synthetic tobacco 



Th37-8 (not shown).

 A breakdown of the recombinant c

hromosomes is given:

 (

+



) presence or (–)

absence of individual recombinants

The nomenclature of these c



hromosomes is confused between publications

. Synonyms are given 

in the order 

Lim 


et al

(2000



),

K

enton 



et al

(1993



),

 P

arokonny & K



enton (1995

),

 Mosconne 



et al

(1996



).

 N 


=

 no name for c

hromosome given.

 *T4/s is a translocation observed for the fi

rst time

here


The text of this manuscript uses the nomenc

lature of the fi

rst entry

.

Downloaded from https://academic.oup.com/biolinnean/article-abstract/82/4/599/2643091



by guest

on 26 April 2018




602

K. Y. LIM ET AL.

© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 599–606

T4/s


T4/s

S2/t


T4/s

T9/s


TH37-1

Th37-9


A

B

E



D

C

F



I

H

G



N. undulata

NUNSSP


NUNSSP

NUNSSP


N. wigandoides

NUNSSP


U-genome

W-genome


GISH

Downloaded from https://academic.oup.com/biolinnean/article-abstract/82/4/599/2643091

by guest

on 26 April 2018




GENOME EVOLUTION IN ALLOTETRAPLOID NICOTIANA

603


© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 599–606

1. A similar chromosome, identified as T9/s, is found

in all N. tabacum  allopolyploids analysed, includ-

ing the synthetic tobacco plants Th37-1 and Th37-

9. This may indicate an important translocation for

allopolyploid stability and have adaptive signifi-

cance. In each case the chromosome is identified by

the translocation. GISH reveals that the chromo-

some carries a T-genome centromere and is there-

fore, by definition, a T-genome chromosome. Its

identity can be further narrowed down by exclusion

of chromosomes with markers and by its small size.

Thus a T9 origin chromosome remains the best fit,

but the chromosomes carrying the translocation

between lines may not be homologous. Likewise,

there may be forced homology for chromosomes T6/

s and for S11/t in the natural tobacco plants (e.g.

S11/t, which carries an NOR, might be confused

with independent translocations on S10 or S12).

2. Chromosome T4/s is distinctive and carries a

marker generated by a tandem repeat in the long

arm that stains strongly by GISH. The chromosome

is found in the Bolivian tobacco (Fig. 1A) and in

synthetic plants Th37-1 and Th37-9 (Fig. 1E). This

translocation is not found in cultivated tobaccos

(Parokonny & Kenton, 1995; Mosconne et al., 1996;

Lim  et al., 2004). Its independent evolution in

Bolivian tobacco and in the synthetic tobacco sug-

gests that the translocation may be significant, per-

haps representing a hotspot of recombination.

3. Chromosome S2/t is distinctive as it carries a large

T-genome translocation. This chromosome is found

in all cultivars of tobacco, but is absent in the feral

tobacco from Bolivia. Without independent mark-

ers it cannot be demonstrated unequivocally that

the chromosome is homologous in all cultivars, but

certainly it appears similar morphologically. To our

surprise, synthetic tobacco Th37-1 and Th37-9 car-

ries a similar translocation (Fig. 1E).

4. There are discrepancies in the numbers of translo-

cations reported for cv. 095-55 (Kenton et al., 1993;

Lim  et al., 2000) and for cv. SR1 (Kenton et al.,

1993; Mosconne et al., 1996). In both instances the

discrepancies fall at easily identifiable chromo-

somes. The differences may have arisen through

cultivar divergence in the respective laboratories or

misidentification of the breeding lines.

5. There are fewer translocations in the synthetic

tobaccos compared with most cultivated varieties.

One synthetic tobacco plant (Th37.8, not shown)

had no detectable intergenomic translocations. The

Th37 population of synthetic tobacco remains het-

erozygous and is not yet fixed for any translocation.

Because of the lack of independent markers to con-

firm homology, no direct support can be given for the

NCI hypothesis and the occurrence of ‘species-specific’

translocations. Nevertheless, there does appear to be

surprising congruence in the data among tobaccos of

widely different origin, including those newly synthe-

sized. There is some evidence that GISH labelling of

the paternal T-genome is poor compared with the

labelling of the maternal S-genome in cultivated

tobacco (Parokonny & Kenton, 1995). This may sug-

gest degeneracy of the paternal genome, as inferred

from studies of synthetic Brassica allopolyploids (Song

et al., 1995). There was no reduction in the strength of

GISH labelling to the T-genome in the synthetic

tobacco (Fig. 1C).

N

ICOTIANA

 

RUSTICA

Goodspeed (1954) used morphology, karyotype analy-

ses and breeding experiments to propose that the

parents  of  N. rustica   (2n = 4x = 48)  were  ancestors

of  N. paniculata  (2n = 2x = 24)  and  N. undulata

(2n = 2x = 24). Chloroplast gene sequencing and phy-

logenetic reconstructions of Nicotiana  indicate that

Figure 1. Root tip metaphases after FISH using biotin-labelled probes (Cy3, red fluorescence) and digoxigenin-labelled

probes (FITC, green fluorescence). Blue fluorescence is the DAPI counterstain for DNA. A, GISH to N. tabacum collected

from Bolivia (N. sylvestris  genomic DNA, green; N. tomentosiformis  genomic DNA, orange). Note the numerous small S-

genome translocations to T-genome chromosomes (arrows, T4/s is identified and can be compared with the similar

chromosome in synthetic tobaccos in E) and T-genome translocations to S-genome chromosomes (arrow heads). B, GISH

to metaphase of N. rustica (N. paniculata genomic DNA, orange; N. undulata genomic DNA, green). Arrows show nucleolar

organizer regions that label with both probes (yellow). C, GISH to synthetic tobacco plant Th37-9 (N. tomentosiformis

genomic DNA, orange; N. sylvestris  genomic DNA green), and D, DAPI image of the same metaphase. E, Chromosomes

carrying intergenomic translocations in plants TH37-1 and Th37-9. The intensely stained bands labelled by GISH (arrows)

provide a useful marker to identify the chromosomes (the orange/yellow band on the short arm of one homologue of Th37-

1 is rDNA and is discussed in detail in Skalická et al. (2003). F, NUNSSP labelling to N. arentsii; G, DAPI image and H,

after GISH in a reprobing experiment to identify the genomic origin of the chromosomes in the same metaphase

(N. undulata  genomic DNA, green; N. wigandioides,  red). I, Karyotypes of N. undulata  (top),  N. wigandioides  (bottom).

The N. arentsii karyotype (rows 2–5), derived from the metaphase in F–H was split into U- and W-genomes (middle two

rows) based on the labelling patterns generated by GISH. The NUNSSP signal to these chromosomes  is shown (rows

2–5). Scale bar = 10 mm.

Downloaded from https://academic.oup.com/biolinnean/article-abstract/82/4/599/2643091



by guest

on 26 April 2018




604

K. Y. LIM ET AL.

© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 599–606

the maternal genome, the P-genome donor, may be an

ancestor of N. paniculata  and/or  N. knightiana  (sec-

tion  Paniculatae) (Aoki & Ito, 2000; Chase et al.,

2003). Phylogenies using internally transcribed

spacer sequences (ITS) of rDNA (Chase et al., 2003)

suggest that the paternal genome donor is an ancestor

of  N. undulata  and/or  N. glutinosa,  although Good-

speed (1954) placed N. glutinosa in an entirely differ-

ent section.

GISH to N. rustica metaphases, using total genomic

DNA probes from N. paniculata  and  N. undulata,

localized 24 P-genome chromosomes and 24 U-genome

chromosomes, respectively. There were no interge-

nomic translocations, nor any evidence for reduced

effectiveness of the probe labelling the paternal U-

genome compared with the labelling of the maternal

P-genome (Fig. 1B). We recently isolated three fami-

lies of repetitive sequences, two from N. paniculata

(NPAMBO and NPAMBE, both 180-bp monomer

repeats) and one from N. undulata  (NUNSSP) (Lim

et al., 2004). FISH using these probes to N. paniculata

and  N. undulata  metaphases revealed that they

hybridized only to their species of origin and to subte-

lomeric locations on most chromosome arms (Lim



et al., 2004). The pattern of probe hybridization to

N. rustica was nearly the sum of that found in the two

parents. However, NPAMBO repeats occurred in a

lower copy number and in a slightly different distri-

bution to the P-genome of N. rustica  compared with



N. paniculata.

N

ICOTIANA

 

ARENTSII

Based on flower and chromosome morphology, Good-

speed (1954) proposed that N. arentsii  is a natural

allopolyploid (2n = 4x = 48) with ancestors related to



N. undulata 

(2n = 2x = 24) 

and 

N. wigandioides

(2n = 2x = 24). Plastid gene sequencing and phyloge-

netic reconstructions of Nicotiana  indicate that the

maternal genome donor of N. arentsii is closely related

to N. undulata (section Undulatae) (Aoki & Ito, 2000;

Chase et al., 2003). An analysis of the structure of the

intergenic sequences (IGSs) that occur between 45S

rDNA subunits reveals that IGSs in N. arentsii  are

closely similar to N. undulata. Indeed all the IGSs of

N. wigandioides  origin appear to have been lost by

sequence homogenization (Kovarik et al., 2004). To

provide further evidence in support of Goodspeed’s

(1954) hypothesis that N. arentsii  is indeed an

allopolyploid derived from these parents, we used

GISH and total genomic DNA from each of the puta-

tive parents (Fig. 

1H).  To  each metaphase of



N. arentsii,  total genomic DNA from N. undulata

labelled 24 U-genome chromosomes and total genomic

DNA from N. wigandioides  labelled 24 W-genome

chromosomes (Fig. 1I). There were no intergenomic

translocations, and no evidence that the paternal W-

genome is degenerate.



Nicotiana wigandioides

N. undulata 

and


N. arentsii are closely related species in phylogenetic

reconstructions of the genus (Chase et al., 2003). The

tandem repeat NUNSSP, isolated from N. undulata

(Lim et al., 2004), labels subtelomeric regions of chro-

mosomes of N. undulata 

and 


N. wigandioides,

although the distribution of signal differs between

species (Fig. 1I). By conducting multiple labelling

strategies, it is possible to identify the genomic origin

of the chromosomes and the distribution of NUNSSP

in  N. arentsii  (Fig. 1F–H). A comparison of the U-

genome with N. undulata  and of the W-genome with

N. wigandioides  (Fig. 1I) reveals little change in the

distribution pattern of NUNSSP.

DISCUSSION

Allopolyploidy combines the genomes of two species

into a common nucleus. Subsequent evolution can

potentially result in genome re-organization and chro-

mosomal rearrangement. Gill (1991) and Jiang & Gill

(1994a) observed common translocations in Triticum

allopolyploids and breeding lines, and postulated that

species-specific translocations arise to restore fertility

in newly formed allopolyploids. These arguments have

also been applied to N. tabacum to explain the occur-

rence of intergenomic translocations (Leitch & Ben-

nett, 1997; Lim et al., 2000) and the apparent

degeneracy of the T-genome, which labels less strongly

by GISH (Parokonny & Kenton, 1995; Leitch & Ben-

nett, 1997).

GISH data on a range of natural N. tabacum geno-

types reveal that all have intergenomic translocations.

The cultivars all have a large translocation to an S-

genome chromosome (S2/t), as do two of three

synthetic tobacco plants derived from the same popu-

lation of seeds (Table 1). The feral tobacco from Bolivia

is different in that it lacks this translocation, perhaps

indicating that tobacco is polyphyletic or that this

tobacco diverged before the cultivars examined. The

synthetic tobacco plants demonstrate that interge-

nomic translocations can occur early in allopolyploid

evolution. Whether any translocations are fixed as

‘species-specific translocations’ in tobacco will remain

unclear until further analyses and more direct evi-

dence for chromosome homology is found.

Intergenomic translocations may have arisen in

tobacco  because  its  parents  are  widely  diverged

[i.e.  N. tomentosiformis  section  Tomentosae  and

N. sylvestris  section  Sylvestres,  cf. phylogenetic

schemes (Aoki & Ito, 2000; Chase et al., 2003;

Knapp, Chase & Clarkson, 2004)]. By contrast, the

parents of N. rustica  and particularly N. arentsii,

with no intergenomic translocations, are closely

Downloaded from https://academic.oup.com/biolinnean/article-abstract/82/4/599/2643091

by guest

on 26 April 2018




GENOME EVOLUTION IN ALLOTETRAPLOID NICOTIANA

605


© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 599–606

related. Similarly, Tragopogon  allotetraploids that

combine closely related diploid genomes do not dis-

play intergenomic translocations (Soltis et al., 2004 –

this issue). A hypothesis linking parental genome

divergence with intergenomic translocations runs

counter to the view that the more closely related the

parental genomes, the more likely there will be

translocations because of homoeologous chromosome

pairing and multivalent formation in meiosis. In

support of the hypothesis is that the union of

diverged genomes upon allopolyploidy can elicit

‘genomic-stress’, which in turn may activate trans-

posons and retrotransposons, DNA strand breaks

(McClintock, 1984; Melayah et al., 2004) and possi-

bly intergenomic translocations. It is conceivable

that the more similar the parental genomes, the

lower the ‘genomic-stress’. It may also be significant

that only in tobacco are the karyotypes of the

parental species substantially different, i.e.



N. tomentosiformis  lacks terminal heterochromatic

repeats found in N. sylvestris  and the karyotype is

bimodal. Perhaps this karyotype divergence gener-

ates ‘genomic-stress’ in the allopolyploid.

There are small differences in the distribution of

tandem repeats between the P-genomes of N. rustica

and the putative maternal species N. paniculata,

whereas the U-genome is nearly identical to that of



N. undulata  (Lim  et al., 2004). Similarly, there are

only minor differences between N. arentsii  and its

putative parents N. undulata  and  N. wigandioides

(Fig. 1I). These probably reflect divergence between

the diploids and the allopolyploids. Perhaps accessions

or lines of parental diploids with even more similar

banding patterns remain to be found. The distribution

of tandem repeats in N. tabacum can be accounted for

by direct inheritance from the diploid parents and by

re-organizations arising from the intergenomic trans-

locations (as determined by GISH) (Lim et al., 2000;

Murad et al., 2002). Thus, changes in the distribution

and copy numbers of tandem repeats in the three Nic-

otiana  allopolyploids compared with the putative

parental species are few. They are certainly minor

compared with the large-scale changes that occur over

time-scales of diploid Nicotiana speciation, as demon-

strated for Nicotiana  section  Tomentosae  (Lim  et al.,

2000). It is possible that molecular analyses such as

RFLP and AFLP would reveal further genetic change

associated with allopolyploidy, as has been demon-

strated for synthetic allopolyploids and hybrids of

Brassica  (Song  et al., 1995) and Triticeae (Ozkan

et al., 2001; Shaked et al., 2001).

ACKNOWLEDGEMENTS

We thank NERC and the Czech Academy of Sciences

(grants 204/01/0313 and 521/01/0037) for funding. We

thank Miss D. Saikia and Mr J. Clarkson for assis-

tance. We thank Professor V. Sissons (USDA) and Dr

Sandra Knapp (Natural History Museum, London) for

Nicotiana material.

REFERENCES



Adams KL, Wendel JF. 2004. Exploring the genomic myster-

ies of polyploidy in cotton. Biological Journal of the Linnean



Society 82: 573–581.

Aoki S, Ito M. 2000. Molecular phylogeny of Nicotiana (Solan-

aceae) based on the nucleotide sequence of the matK gene.



Plant Biology 2: 316–324.

Bland MM, Matzinger DF, Levins CS. 1985. Comparison of

the mitochondrial genome of Nicotiana tabacum with its pro-

genitor species. Theoretical and Applied Genetics  69:  535–

541.


Burk LG. 1973. Partial self-fertility in a theoretical amphi-

ploid progenitor of N. tabacumJournal of Heredity 64: 348–

350.

Chase MW, Knapp S, Cox AV, Clarkson J, Butsko Y,

Joseph J, Savolainen V, Parokonny AS. 2003. Molecular

systematics, GISH and the origin of hybrid taxa in Nicotiana

(Solanaceae). Annals of Botany 92: 107–127.

Gill BS. 1991. Nucleocytoplasmic interaction (NCI) hypothesis

of genome evolution and speciation in polyploid plants. In:

Sasakuma T, Kinoshita T, eds. Proceedings of the Kihara

memorial international symposium on cytoplasmic engineer-

ing in wheat. Yokohama, 48–53.

Gill BS, Friebe B. 1998. Plant cytogenetics at the dawn of the

21st century. Current Opinion in Plant Biology 1: 109–115.



Goodspeed TH. 1954. The genus Nicotiana.  Massachusetts,

USA: Chronica Botanica Company.



Heslop-Harrison JS. 1992. Molecular cytogenetics, cytology

and genomic comparisons in the Triticeae. Hereditas  116:

93–99.

Heslop-Harrison JS. 1998. Plant genes, genomes and chro-

mosomes. Cytogenetics and Cell Genetics 81: L3.



Jiang J, Gill BS. 1994a. Different species-specific chromo-

some translocations in Triticum timopheevii and T. turgidum

support the diphyletic origin of polyploid wheats. Chromo-

some Research 2: 59–64.

Jiang JM, Gill BS. 1994b. Nonisotopic  in-situ hybridization

and plant genome mapping – the first 10 years. Genome 37:

717–725.

Kashkush K, Feldman M, Levy AA. 2002. Gene loss, silenc-

ing and activation in a newly synthesized wheat allotetra-

ploid. Genetics 160: 1651–1659.

Kashkush K, Feldman M, Levy AA. 2003. Transcriptional

activation of retrotransposons alters the expression of adja-

cent genes in wheat. Nature Genetics 33: 102–106.

Kenton A, Parokonny AS, Gleba YY, Bennett MD. 1993.

Characterization of the Nicotiana tabacum  L. genome by

molecular cytogenetics. Molecular and General Genetics 240:

159–169.


Knapp S, Chase MW, Clarkson JJ. 2004. Nomenclature

changes and a new sectional classification in Nicotiana

(Solanaceae). Taxon 53: 73–82.

Downloaded from https://academic.oup.com/biolinnean/article-abstract/82/4/599/2643091

by guest

on 26 April 2018




606

K. Y. LIM ET AL.

© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 599–606

Kovarik A, Matyasek R, Lim KY, Skalická K, Koukalová

B, Knapp S, Chase M, Leitch AR. 2004. Concerted evolu-

tion of 18–5.8–26S rDNA repeats in Nicotiana  allotetra-

ploids.  Biological Journal of the Linnean Society  82:  615–

625.


Leitch IJ, Bennett MD. 1997. Polyploidy in angiosperms.

Trends in Plant Science 2: 470–476.

Levy AA, Feldman M. 2004. Genetic and epigenetic repro-

gramming of the wheat genome upon allopolyploidization.



Biological Journal of the Linnean Society 82: 607–613.

Lim KY, Matyasek R, Kovarik A, Fulnecek J, Leitch AR.

2004.  Molecular cytogenetics and tandem repeat sequence

evolution in the allopolyploid Nicotiana rustica  compared

with diploid progenitors N.  paniculata  and  N.  undulata.

Cytogenetics and Genome Research in press.

Lim KY, Matyasek R, Lichtenstein CP, Leitch AR. 2000.

Molecular cytogenetic analyses and phylogenetic studies in

the  Nicotiana  section Tomentosae. Chromosoma  109:  245–

258.


Liu B, Brubaker CL, Mergeai G, Cronn RC, Wendel JF.

2001.  Polyploid formation in cotton is not accompanied by

rapid genomic changes. Genome 44: 321–330.



McClintock B. 1984. The significance of responses of the

genome to challenge. Science 226: 792–801.



Melayah D, Lim KY, Bonnivard E, Chalhoub B, Dorlhac

de Borne F, Mhiri C, Leitch AR, Grandbastien M-A.

2004. Distribution of the Tnt1 retrotransposon family in the

amphidiploid tobacco (Nicotiana tabacum) and its wild Nic-



otiana  relatives.  Biological Journal of the Linnean Society

82: 639–649.

Mosconne EA, Matzke MA, Matzke AJM. 1996. The use of

combined FISH/GISH in conjunction with DAPI counter-

staining to identify chromosomes containing transgene

inserts in amphidiploid tobacco. Chromosoma 105: 231–236.



Murad L, Lim KY, Christopodulou V, Matyasek R, Lich-

tenstein CP, Kovarik A, Leitch AR. 2002. The origin of

the paternal genome of tobacco is traced to a particular lin-

eage within Nicotiana tomentosiformis (Solanaceae). Ameri-

can Journal of Botany 89: 921–928.

Ozkan H, Levy AA, Feldman M. 2001. Allopolyploidy-

induced rapid genome evolution in the wheat (Aegilops–



Triticum) group. Plant Cell 13: 1735–1747.

Parokonny AS, Kenton AY. 1995. Comparative physical

mapping and evolution of the Nicotiana tabacum  L. karyo-

type. In: Brandham PE, Bennett MD, eds. Kew chromosome

conference II. Kew, UK: Royal Botanic Gardens, 301–320.

Ren N, Timko MP. 2001. AFLP analysis of genetic polymor-

phism and evolutionary relationships among cultivated and

wild Nicotiana species. Genome 44: 559–571.

Riechers DE, Timko MP. 1999. Structure and expression

of the gene family encoding putrescine N-

methyltransferase  in  Nicotiana  tabacum:   new  clues  to

the evolutionary origin of cultivated tobacco. Plant



Molecular Biology 41: 387–401.

Shaked H, Kashkush K, Ozkan H, Feldman M, Levy AA.

2001.  Sequence elimination and cytosine methylation are

rapid and reproducible responses of the genome to wide

hybridization and allopolyploidy in wheat. Plant Cell  13:

1749–1759.



Skalická K, Lim KY, Matyasek R, Koukalová B, Leitch

AR, Kovarik A. 2003. Rapid evolution of parental rDNA in

a synthetic tobacco allotetraploid line. American Journal of



Botany 90: 988–996.

Soltis DE, Soltis PS, Pires JC, Kovarik A, Tate JA,

Mavrodiev E. 2004. Recent and recurrent polyploidy in

Tragopogon  (Asteraceae): cytogenetic, genomic and genetic

comparisons.  Biological Journal of the Linnean Society  82:

485–501.

Song KM, Lu P, Tang KL, Osborn TC. 1995. Rapid genome

change in synthetic polyploids of Brassica and  its implica-

tions for polyploid evolution. Proceedings of the National

Academy of Sciences, USA 92: 7719–7723.

Downloaded from https://academic.oup.com/biolinnean/article-abstract/82/4/599/2643091

by guest

on 26 April 2018



Yüklə 168,04 Kb.

Dostları ilə paylaş:




Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©genderi.org 2024
rəhbərliyinə müraciət

    Ana səhifə