Wolf Prize in Agriculture (1157 Pages)
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Ronald L. Phillips 985
some 1 as defined by groups 9 and 10 is represented by seven independent breakage events. This break is marked proximally by the SSR marker p-mmc0041 and distally by the SSR marker
the same point or very similar points indicates a preferential breakage and ͞or transmission of the chromosome segments to offspring. On the short arm, five independent events (5 of 21) demonstrate a common break in the range that is marked by the SSRs p-umc1071 and p-umc1727 defining segment 1. All other breakpoints are defined by one or two events. Most striking is that we did not observe a centric break resulting in either a telocentric maize chromosome or a centric maize–oat translo- cation. This situation left intact a large area spanning the centromere and the proximal regions on both arms, segment 7 (Fig. 2), and it is in strong contrast to earlier results from the production of maize chromosome 9 RHs (12) that showed that the level of chromosome 9 breakage across the chromosome was relatively constant. The physical sizes of the segments differ remarkably as shown by GISH experiments (Fig. 3). In the line 1.07.3-001.3-03 (a sibling from group 7), the maize chromosome shows a primary constriction that defines the deficient short arm to Ϸ80% of its regular WT metaphase length. This result would mean that the missing element (20%) represents a genetic size of at least 445 map units separated into 6 distinct segments by 8 of 10 groups. On the other hand, GISH of line 1.07.2-007.3-04 (a sibling from group 9) shows the distal maize chromosome fragment translo- cated to an oat chromosome. The fragment length corresponds to Ϸ20% of the long-arm WT length in metaphase and visualizes segment 8. Even considering that the definition of the single segment by two markers varies over a considerable genetic distance, the segment 7 spans approximately the proximal 80% of the short and the proximal 80% of the long arm of the genetic map of maize chromosome 1. The line 1.07.1-020.3-01 (sibling of group 3) shows by GISH analysis a fragment of Ϸ15% of the WT short-arm length translocated to an oat chromosome. This fragment visualizes the length of the segments 1 and 2 together marked by SSRs p-umc1397 and p-umc1479. Summary The current set of disomic oat–maize addition lines involves all maize chromosomes in different oat backgrounds with the exception of chromosome 10. The maize chromosome 10 addi- tion progeny has only the short arm; a fertile disomic telocentric addition line is available. The whole chromosome 10 added to haploid GAF-Park oat does allow the availability of DNA. Although not fertile, and therefore not capable of producing disomic addition offspring, we continue to maintain the original plant vegetatively by tiller cloning under short-day growing conditions. The leaves show remarkable somatic stability for the added maize chromosome over a period of Ͼ3 years. The plant serves as a source for chromosome 10 genomic DNA and RNA. The complete series of DNAs made from each maize chro- mosome addition has been used as a powerful tool to allocate genes and markers to chromosome. Ananiev et al. (31) used the oat–maize chromosome 9 addition line as the DNA source to construct a chromosome-specific cosmid library allowing the isolation of maize-specific repetitive DNA families. The low level of cross-hybridization under standard conditions between oat and maize genomic DNA makes it possible to screen libraries for maize species-specific sequences (31). Oat–maize addition lines are ideal for mapping gene families and markers that have more than one copy on different chro- mosomes likely because of the duplicative nature of maize. For example, Okagaki et al. (32) mapped 350 ESTs and sequence tagged sites to chromosomes by a presence vs. absence test and Fig. 2. Panel of the first RH lines for maize chromosome 1. Shown are the 15 SSR markers that frame the seven breakpoints, hence define the RH segments between p-umc1354 (most distal on the short arm) and p-umc2244 (most distal on the long arm) markers representing a genetic distance of more than 1,120 map units according to the IBM2 map. Fig. 3. GISH of metaphase chromosomes from root tips of three RH plants of the maize chromosome 1 panel. (A) Plant BC 1 F
, 1.07.3-001.3-3 (sibling of group 7), arrow points to the deficient short arm of maize chromosome 1; the chromosome lost Ϸ20% of its short arm. p-umc1626 is the most distal present marker tested (see also Fig. 2). The yellow-painted chromosome visualizes the segments 7 and 8 representing the genetic distance of 656 – 675 map units (B) Plant BC 1 F
1.07.2-007.3-4 (sibling of group 9), arrow points to the translocation fragment visualizing the RH segment 8. The translocation fragment accounts for Ϸ20% of
the long-arm length representing the genetic distance of 261–332 map units (C) Plant BC 1 F 2 1.07.1-020.3-1 (sibling of group 3), arrow points to the translocation fragment visualizing the RH segments 1 and 2 accounting for Ϸ15% of the short-arm length representing the distance of 226–257 map units. Kynast et al. PNAS
͉ June 29, 2004 ͉ vol. 101 ͉ no. 26 ͉ 9925 PLANT
BIOLOGY 38_2006-7 Phillips.p65 06-Mar-09, 7:49 PM 985 Document Outline
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