Dissection and cytological mapping of barley chromosome 2H in the genetic background of common wheat

We used gametocidal (Gc) chromosomes 2C and 3C(SAT) to dissect barley 2H added to common wheat. The Gc chromosome induces chromosomal breakage resulting in chromosomal aberrations in the progeny of the 2H addition line of common wheat carrying the monosomic Gc chromosome. We conducted in situ hybridization to select plants carrying structurally rearranged aberrant 2H chromosomes and characterized them by sequential C-banding and in situ hybridization. We established 66 dissection lines of common wheat carrying single aberrant 2H chromosomes. The aberrant 2H chromosomes were of either deletion or translocation or complicated structural change. Their breakpoints were distributed in the short arm (2HS), centromere (2HC) and the long arm (2HL) at a rough 2HS/2HC/2HL ratio of 2:1:2. We conducted PCR analysis of the 66 dissection lines using 115 EST markers specific to chromosome 2H. Based on the PCR result, we constructed a physical or cytological map of chromosome 2H that were divided into 34 regions separated by the breakpoints of the aberrant 2H chromosomes. Forty-seven markers were present in 2HS and 68 in 2HL. We compared the 2H cytological map with a previously reported 2H genetic map using 44 markers that were used in common to construct both maps. The order of markers in the distal region was the same on both maps but that in the proximal region was somewhat contradictory between the two maps. We found that the markers distributed rather evenly in the genetic map were actually concentrated in the distal regions of both arms as revealed by the cytological map. We also recognized an EST-marker or gene-rich region in the 2HL interstitial region slightly to the telomere.     

Dissection of barley chromosome 5H in common wheat

We dissected barley chromosome 5H added to common wheat by a genetic method or the gametocidal system. Firstly, we induced chromosomal breaks in the offspring of a 5H addition line of common wheat carrying a gametocidal chromosome and cytologically screened for plants with structural chromosomal changes involving 5H, such as deletions and translocations. Secondly, we screened the progeny of such plants to establish common wheat lines carrying structurally changed chromosomes containing single segments of the dissected 5H. Using 23 representative 5H dissection lines, we physically mapped 97 barley EST markers assigned to 5H. The ESTs fell into 20 regions of 5H between the breakpoints of the 23 dissected segments, distributing rather evenly along the chromosome, with significantly higher frequency in the distal region of the long arm. The ESTs, in turn, allowed us to distinguish the breakpoints of dissected 5H segments. We demonstrated by PCR (polymerase chain reaction), as well as by in situ hybridization, that these dissected 5H segments were stably transmitted in the dissection lines. We discuss the usefulness of the 5H dissection lines for physical mapping of DNA markers. These 5H dissection lines are available from National BioResource Projects-Wheat, Japan.     

Characterisation of mildew resistant wheat-rye substitution lines and identification of an inverted chromosome by fluorescent in situ hybridisation

Seven different mildew resistant wheat lines derived from crosses between triticale and bread wheat were examined by molecular cytogenetics and chromosome C-banding in order to determine their chromosomal composition. Genomic in situ hybridisation (GISH) showed the presence of rye germplasm in all the lines and identified three substitution lines, three double substitution lines and one addition-substitution line. C-banding identified rye chromosomes 1R and 4R in the addition-substitution line, rye chromosomes 1R and 6R in two substitution lines and 1R and 2R in the third line, and rye chromosome 1R in the three substitution lines. Two of the latter lines (7-102 and 7-169) contained a modified form of the chromosome; fluorescent in situ hybridisation (FISH) using five different repetitive DNA-probes showed a pericentric inversion of 1R in both lines. The breakpoints of the 1R inversion were between (1) the 5S rDNA site and the NOR-region on the satellite of the short arm, and (2) between two AAC(5) sites close to the centromere on the long arm. The role of the rye chromosomes in the mildew resistance, the utilisation of the inverted 1R and the significance of the lines in wheat breeding are discussed.     

Deletion-based physical mapping of barley chromosome 7H

Chromosomal mutations in barley (Hordeum vulgare, 2n=2x=14, HH) chromosome 7H added to the common wheat (Triticum aestivum, 2n=6x=42, AABBDD) cultivar Chinese Spring were induced genetically by the gametocidal activity of certain alien chromosomes derived from wild species of the genus Aegilops. The rearranged barley chromosomes were characterized by C-banding, FISH and GISH. Twenty two deletion or translocation chromosomes in a hemizygous condition were selected for deletion mapping of 17 AFLP and 28 STS markers that are specific to 7H. Of the 22 breakpoints in chromosome 7H, seven involved the short arm (7HS), 12 the long arm (7HL) and three were in the centromeric region. The seven 7HS breakpoints separated all four 7HS-specific AFLP markers and split the 21 STS markers into six groups. One breakpoint occurred between two STS markers formerly occupying the same position in the genetic map. All seven 7HS breakpoints were separated from each other by either the AFLP or STS markers. The 12 breakpoints in 7HL divided the 13 7HL-specific AFLP markers into seven groups, and the seven STS markers into three groups. On the other hand, the 12 breakpoints in 7HL were divided into six groups by the AFLP markers and into two groups by the STS markers. This deletion-based map was in accordance with previously published genetic and physical maps using the same STS markers. The breakpoints, AFLP markers and STS markers were arrayed in a consistent order. Received: 5 February 2001 / Accepted: 19 February 2001     

Preferential elimination of chromosome 5R of rye in the progeny of 5R5D dimonosomics

Transmission of chromosome 5R of rye (Secale cereale L.) and chromosome 5D of common wheat (Triticum aestivum L.) through gametes of 5R5D dimonosomics (2n = 42, 20W″ + 5R′ + 5D′) was studied. Chromosome 5R was found to have lower competitiveness as compared to 5D. Gametes with the rye chromosome were two times less often involved in the formation of a progeny. The combined frequency of the karyotypes of wheat (5D5D) and wheat monosomics (5D) was 11.6-fold higher than the frequency of the karyotypes of substitution lines (5R5R) and monosomics for the rye chromosome (5R). The karyotypes of 10.38% of hybrid plants had aberrant 5R chromosomes with different translocations formed as a result of breakages in the centromere and in the proximal region of the long arm. Telocentrics for the short arm t5RS, i5RS isochromosomes, and chromosomes with a terminal deletion T5RS.5RL-del were identified. The absence of amplification of SSR markers mapped on 5RS and the detection of PCR products for a number of 5RL markers (including the genome-specific rye marker Xrms115) permitted nine plants carrying only the long arm of chromosome 5R to be revealed. Since t5RL telocentrics were not detected by the cytological analysis, the results obtained allow us to suggest the presence of small intercalary translocations of the long arm of chromosome 5R in chromosome 5D or in other wheat chromosomes.     

柱穗山羊草2C染色体诱发中国春小麦背景中黑麦1R染色体结构变异的研究

当柱穗山羊草(Aegilops cylindrica Host．)2C染色体单体添加到普通小麦品种中国春和以中国春为背景的派生系时,减数分裂时,不含2C染色体的配子会发生染色体结构变异。为了制备一套黑麦1R染色体缺失系以用于定位黑麦1R染色体上的控制重要农艺性状的基因,把一条2C染色体导人到小黑麦1R二体附加系(21″ 1R″)中,然后让这些个体(21″ 1R″ 2C′,2n=45)自交,以便产生1R染色体结构变异体。实验共检测了345粒F,种子,83粒种子带有结构变异的黑麦1R染色体(24．1％)。通过C分带和原位杂交检测,对来自于23株F2的46个F3植株所带有的异常1R染色体进行了归类：其中1RL端体为39．1％,1RL等臂染色体为2．2％,1RL易位系为32．6％。1RS端体为4．3％,1RS等臂染色体为4．3％,切点在长臂上的缺失体为2．2％。在6．5％的植株中同时含有2种类型的1R染色体结构变异。其余8．7％带有异常1R染色体的个体因为没有原位杂交结果而无法判断是属于哪种类型。已获得的1R结构变异株将有可能进一步发展成为一套可用于定位黑麦1R染色体上重要功能基因的遗传材料。另外,还探讨了综合应用细胞学和分子标记方法鉴定易位染色体中小麦染色体片段的尝试,并对所获结果进行了讨论。     

Development and application of EST-based markers specific for chromosome arms of rye (Secale cereale L.)

To develop a set of molecular markers specific for the chromosome arms of rye, a total of 1,098 and 93 primer pairs derived from the expressed sequence tag (EST) sequences distributed on all 21 wheat chromosomes and 7 rye chromosomes, respectively, were initially screened on common wheat 'Chinese Spring' and rye cultivar 'Imperial'. Four hundred and fourteen EST-based markers were specific for the rye genome. Seven disomic chromosome addition lines, 10 telosomic addition lines and 1 translocation line of 'Chinese Spring-Imperial' were confirmed by genomic in situ hybridization and fluorescencein situ hybridization, and used to screen the rye-specific markers. Thirty-one of the 414 markers produced stable specific amplicons in 'Imperial', as well as individual addition lines and were assigned to 13 chromosome arms of rye except for 6RS. Six rye cultivars, wheat cultivar 'Xiaoyan 6' and accessions of 4 wheat relatives were then used to test the specificity of the 31 EST-based markers. To confirm the specificity, 4 wheat-rye derivatives of 'Xiaoyan 6 × German White', with chromosomes 1RS, 2R and 4R, were amplified by some of the EST-based markers. The results indicated that they can effectively be used to detect corresponding rye chromosomes or chromosome arms introgressed into a wheat background, and hence to accelerate the utilization of rye genes in wheat breeding.     

Production of wheat-barley recombinant chromosomes through induced homoeologous pairing

Summary Sears' phlb mutant was used successfully for the first time to induce pairing and recombination between specific barley chromosomes and their wheat homoeologues. Pairing was induced in specially constructed genetic stocks having 19 pairs of wheat chromosomes and triply monosomic for either barley chromosome arm 6HL or 3HL, a related wheat chromosome, and chromosome 5B of wheat carrying the phlb mutation. Wheat-barley recombinant chromosomes were isolated from among the progeny obtained from self-fertilization of the triple monosomic stocks, by screening for dissociation of biochemical markers on the barley arms. Glutamic oxaloacetic transaminase (GOT), aconitase hydratase (ACO), and dipeptidase (DIP) isozymes were used to select recombinants involving the 6HL arm, and esterase (EST) and malate dehydrogenase (MDH) were used for the 3HL arm. Altogether, six recombinants involving 6HL (1.4%) and six involving 3HL (1.1%) were isolated. These wheat-barley recombinant chromosomes are being used to construct a detailed gene order map of barley based on biochemical and molecular markers.     

Chromosomal assignment and deletion mapping of barley EST markers

From about 10000 PCR-based EST markers of barley we chose 1421 EST markers that were demonstrated to be amplified differently by PCR between wheat (Triticum aestivum cv. Chinese Spring) and barley (Hordeum vulgare cv. Betzes). We assigned them to the seven barley chromosomes (1H to 7H) by PCR analysis using a set of wheat-barley chromosome addition lines. We successfully assigned 701 (49.3%) EST markers to the barley chromosomes: 75 to 1H, 127 to 2H, 119 to 3H, 94 to 4H, 108 to 5H, 81 to 6H and 97 to 7H. By using a set of Betzes barley telosomic addition lines of Chinese Spring, we could successfully determine the chromosome-arm (S or L) location of at least 90% of the EST markers assigned to each barley chromosome. We conducted a trial mapping using 90 EST markers assigned to 7HS (49) or 7HL (41) and 19 wheat lines carrying 7H structural changes. More EST markers were found in the distal region than in the proximal region.     

Production of wheat-rye substitution lines and identification of chromosome composition of karyotypes using C-banding, GISH, and SSR markers

Based on the cross (Triticum aestivum L. x Secale cereale L.) x T. aestivum L., wheat-rye substitution lines (2n = 42) were produced with karyotypes containing, instead of a pair of homologous wheat chromosomes, a homeologous pair of rye chromosomes. The chromosome composition of these lines was described by GISH and C-banding methods, and SSR analysis. The results of genomic in situ hybridization demonstrated that karyotype of these lines included one pair of rye chromosomes each and lacked wheat--rye translocations. C-banding and SSR markers were used to identify rye chromosomes and determine the wheat chromosomes at which the substitution occurred. The lines were designated 1R(1D), 2R(2D)2, 2R(2D)3, 3R(3B), 6R(6A)2. The chromosome composition of lines IR(1A), 2R(W)1, 5R(W), 5R(5A), and 6R(W)1, which were earlier obtained according to the same scheme for crossing, was characterized using methods of telocentric analysis, GISH, C-banding, and SSR analysis. These lines were identified as 1R(1A), 2R(2D)1, 5R(5D), 5R(5A), and 6R(6A)1, C-banding of chromosomes belonging to line 1R(1A) revealed the presence of two translocated chromosomes (3DS.3DL-del. and 4AL.W) during simultaneous amplification of SSR markers located on 3DL and 4AS arms. The "combined" long arm of the newly derived chromosome 4A is assumed to be formed from the long arm of chromosome 4AS itself and a deleted segment 3DL. All examined lines are cytologically stable, except for 3R(3B), which does not affect the stability of rye 3R chromosome transfer. Chromosome identification and classification of the lines will permit them to be models for genetic studies that can be used thereafter as promising "secondary gene pools" for the purpose of plant breeding.     

High-resolution cytological mapping of the long arm of chromosome 5A in common wheat using a series of deletion lines induced by gametocidal (Gc) genes of Aegilops speltoides

Gametocidal (Gc) genes of Aegilops in the background of the wheat genome lead to breakage of wheat chromosomes. The Q gene of wheat was used as a marker to select 19 deletion lines for the long arm of chromosome 5A of common wheat, Triticum aestivum cv. Chinese Spring (CS). The extents of deleted segments were cytologically estimated by the C-banding technique. The DNAs of deletion lines were hybridized with 22 DNA probes recognizing sites on the long arm of the chromosome (5AL) to determine their physical order. Based on the breeding behavior of the deletion lines, the location of a novel gene (Pv, pollen viability) affecting the viability of the male gamete was deduced. The segment translocated from 4AL to 5AL in CS was cytologically estimated to represent 13% of the total length of 5AL. Although DNA markers were almost randomly distributed along the chromosome arm, DNA markers located around the centromere and C-banded regions were obtained only rarely. Some deletion lines were highly rearranged in chromosome structure due to the effect(s) of the Gc gene. Applications of Gc genes for manipulating wheat chromosomes are discussed.     

Homoeologous relationship of rye chromosome arms as detected with wheat PLUG markers

Based on the similarity in gene structure between rice and wheat, the polymerase chain reaction (PCR)-based landmark unique gene (PLUG) system enabled us to design primer sets that amplify wheat genic sequences including introns. From the previously reported wheat PLUG markers, we chose 144 markers that are distributed on different chromosomes and in known chromosomal regions (bins) to obtain rye-specific PCR-based markers. We conducted PCR with the 144 primer sets and the template of the Imperial rye genomic DNA and found that 131 (91.0 %) primer sets successfully amplified PCR products. Of the 131 PLUG markers, 110 (76.4 %) markers showed rye-specific PCR amplification with or without restriction enzyme digestion. We assigned 79 of the 110 markers to seven rye chromosomes (1R to 7R) using seven wheat–rye (cv. Imperial) chromosome addition and substitution lines: 12 to 1R, 8 to 2R, 11 to 3R, 8 to 4R, 16 to 5R, 12 to 6R, and 12 to 7R. Furthermore, we located their positions on the short or long (L) chromosome arm, using 13 Imperial rye telosomic lines of common wheat (except for 3RL). Referring to the chromosome bin locations of the 79 PLUG markers in wheat, we deduced the syntenic relationships between rye and wheat chromosomes. We also discussed chromosomal rearrangements in the rye genome with reference to the cytologically visible chromosomal gaps.     

High-resolution cytological mapping of the long arm of chromosome 5A in common wheat using a series of deletion lines induced by gametocidal (Gc) genes of Aegilops speltoides

Gametocidal (Gc) genes of Aegilops in the background of the wheat genome lead to breakage of wheat chromosomes. The Q gene of wheat was used as a marker to select 19 deletion lines for the long arm of chromosome 5A of common wheat, Triticum aestivum cv. Chinese Spring (CS). The extents of deleted segments were cytologically estimated by the C-banding technique. The DNAs of deletion lines were hybridized with 22 DNA probes recognizing sites on the long arm of the chromosome (5AL) to determine their physical order. Based on the breeding behavior of the deletion lines, the location of a novel gene (Pv, pollen viability) affecting the viability of the male gamete was deduced. The segment translocated from 4AL to 5AL in CS was cytologically estimated to represent 13% of the total length of 5AL. Although DNA markers were almost randomly distributed along the chromosome arm, DNA markers located around the centromere and C-banded regions were obtained only rarely. Some deletion lines were highly rearranged in chromosome structure due to the effect(s) of the Gc gene. Applications of Gc genes for manipulating wheat chromosomes are discussed.     

New wheat-rye 5DS-4RS·4RL and 4RS-5DS·5DL translocation lines with powdery mildew resistance

Powdery mildew is one of the serious diseases of wheat (Triticum aestivum L., 2n = 6 × = 42, genomes AABBDD). Rye (Secale cereale L., 2n = 2 × = 14, genome RR) offers a rich reservoir of powdery mildew resistant genes for wheat breeding program. However, extensive use of these resistant genes may render them susceptible to new pathogen races because of co-evolution of host and pathogen. Therefore, the continuous exploration of new powdery mildew resistant genes is important to wheat breeding program. In the present study, we identified several wheat-rye addition lines from the progeny of T. aestivum L. Mianyang11 × S. cereale L. Kustro, i.e., monosomic addition lines of the rye chromosomes 4R and 6R; a disomic addition line of 6R; and monotelosomic or ditelosomic addition lines of the long arms of rye chromosomes 4R (4RL) and 6R (6RL). All these lines displayed immunity to powdery mildew. Thus, we concluded that both the 4RL and 6RL arms of Kustro contain powdery mildew resistant genes. It is the first time to discover that 4RL arm carries powdery mildew resistant gene. Additionally, wheat lines containing new wheat-rye translocation chromosomes were also obtained: these lines retained a short arm of wheat chromosome 5D (5DS) on which rye chromosome 4R was fused through the short arm 4RS (designated 5DS-4RS·4RL; 4RL stands for the long arm of rye chromosome 4R); or they had an extra short arm of rye chromosome 4R (4RS) that was attached to the short arm of wheat chromosome 5D (5DS) (designated 4RS-5DS·5DL; 5DL stands for the long arm of wheat chromosome 5D). These two translocation chromosomes could be transmitted to next generation stably, and the wheat lines containing 5DS-4RS·4RL chromosome also displayed immunity to powdery mildew. The materials obtained in this study can be used for wheat powdery mildew resistant breeding program.     

Construction and study of leaf rust-resistant common wheat lines with translocations of Aegilops speltoides Tausch

Genotyping was performed for the leaf rust-resistant line 73/00i (Triticum aestivum x Aegilops speltoides). Fluorescence in situ hybridization (FISH) with probes Spelt1 and pSc119.2 in combination with microsatellite analysis were used to determine the locations and sizes of the Ae. speltoides genetic fragments integrated into the line genome. Translocations were identified in the long arms of chromosomes 5B and 6B and in the short arm of chromosome 1B. The Spelt1 and pSc119.2 molecular cytological markers made it possible to rapidly establish lines with single translocation in the long arms of chromosomes 5B and 6B. The line carrying the T5BS x 5BL-5SL translocation was highly resistant to leaf rust, and the lines carrying the T6BS x 6BL-6SL translocation displayed moderate resistance. The translocations differed in chromosomal location from known leaf resistance genes transferred into common wheat from Ae. speltoides. Hence, it was assumed that new genes were introduced into the common wheat genome from Ae. speltoides. The locus that determined high resistance to leaf rust and was transferred into the common wheat genome from the long arm of Ae. speltoides chromosome 5S by the T5BS x 5BL-5SL translocation was preliminarily designated as LrAsp5.     

Cytogenetic analysis of forms produced by crossing hexaploid triticale with common wheat

Summary Hexaploid triticales were crossed with common wheats, and the resultant froms were selected for either triticale (AD 213/5-80) or common wheat (lines 381/80, 391/80, 393/80). The cytogenetic analysis showed that all forms differ in their chromosome composition. Triticale AD 213/5-80 and wheat line 381/80 were stable forms with 2n = 6x = 42. Lines 391/80 and 393/80 were cytologically unstable. In triticale AD 213/5-80, a 2R (2D) chromosome substitution was found. Each of the three wheat lines had a chromosome formed by the translocation of the short arm of IR into the long arm of the IB chromosome. In line 381/80, this chromosome seems to be inherited from the Kavkaz wheat variety. In lines 391/80 and 393/80, this chromosome apparently formed de novo since the parent forms did not have it. The karyotype of line 381/80 was found to contain rye chromosomes 4R/7R, 5R and 7R/4R. About 15% of the cells in line 391/80 contained an isochromosome for the 5R short arm and also a chromosome which arose from the translocation of the long arms of the 5D and 5R chromosomes. About one-third of the cells in the common wheat line 393/80 contained the 5R chromosome. This chromosome was normal or rearranged. Practical applications of the C-banding technique in the breeding of triticale is discussed.     

Origin, structure, and behavior of a highly rearranged deletion chromosome 1BS-4 in wheat.

Wheat (Triticum aestivum L.) deletion (del) stocks are valuable tools for the physical mapping of molecular markers and genes to chromosome bins delineated by 2 adjacent deletion breakpoints. The wheat deletion stocks were produced by using gametocidal genes derived from related Aegilops species. Here, we report on the origin, structure, and behavior of a highly rearranged chromosome 1BS-4. The cytogenetic and molecular marker analyses suggest that 1BS-4 resulted from 2 breakpoints in the 1BS arm and 1 breakpoint in the 1BL arm. The distal segment from 1BS, except for a small deleted part, is translocated to the long arm. Cytologically, chromosome 1BS-4 is highly stable, but shows a unique meiotic pairing behavior. The short arm of 1BS-4 fails to pair with a normal 1BS arm because of lack of homology at the distal ends. The long arm of 1BS-4 only pairs with a normal 1BS arm within the distal region translocated from 1BS. Therefore, using the 1BS-4 deletion stock for physical mapping will result in the false allocation of molecular markers and genes proximal to the breakpoint of 1BS-4.     

Production of wheat-rye substitution lines and identification of chromosome composition of karyotypes using C-banding, GISH, and SSR markers

Based on the cross (Triticum aestivum L. × Secale cereale L.) × T. aestivum L., wheat-rye substitution lines (2n = 42) were produced with karyotypes containing, instead of a pair of homologous wheat chromosomes, a homeologous pair of rye chromosomes. The chromosome composition of these lines was described by GISH and C-banding methods, and SSR analysis. The results of genomic in situ hybridization demonstrated that karyotype of these lines included one pair of rye chromosomes each and lacked wheat-rye translocations. C-banding and SSR markers were used to identify rye chromosomes and determine the wheat chromosomes at which the substitution occurred. The lines were designated 1R(1D), 2R(2D)₂, 2R(2D)₃, 3R(3B), 6R(6A)₂. The chromosome composition of lines 1R(1A), 2R(W)₁, 5R(W), 5R(5A), and 6R(W)₁, which were earlier obtained according to the same scheme for crossing, was characterized using methods of telocentric analysis, GISH, C-banding, and SSR analysis. These lines were identified as 1R(1A), 2R(2D)₁, 5R(5D), 5R(5A), and 6R(6A)₁, C-banding of chromosomes belonging to line 1R(1A) revealed the presence of two translocated chromosomes (3DS.3DL-del. and 4AL.W) during simultaneous amplification of SSR markers located on 3DL and 4AS arms. The “combined” long arm of the newly derived chromosome 4A is assumed to be formed from the long arm of chromosome 4AS itself and a deleted segment 3DL. All examined lines are cytologically stable, except for 3R(3B), which does not affect the stability of rye 3R chromosome transfer. Chromosome identification and classification of the lines will permit them to be models for genetic studies that can be used thereafter as promising “secondary gene pools” for the purpose of plant breeding.     

Chromosome bin map of expressed sequence tags in homoeologous group 1 of hexaploid wheat and homoeology with rice and Arabidopsis

A total of 944 expressed sequence tags (ESTs) generated 2212 EST loci mapped to homoeologous group 1 chromosomes in hexaploid wheat (Triticum aestivum L.). EST deletion maps and the consensus map of group 1 chromosomes were constructed to show EST distribution. EST loci were unevenly distributed among chromosomes 1A, 1B, and 1D with 660, 826, and 726, respectively. The number of EST loci was greater on the long arms than on the short arms for all three chromosomes. The distribution of ESTs along chromosome arms was nonrandom with EST clusters occurring in the distal regions of short arms and middle regions of long arms. Duplications of group 1 ESTs in other homoeologous groups occurred at a rate of 35.5%. Seventy-five percent of wheat chromosome 1 ESTs had significant matches with rice sequences (E < or = e(-10)), where large regions of conservation occurred between wheat consensus chromosome 1 and rice chromosome 5 and between the proximal portion of the long arm of wheat consensus chromosome 1 and rice chromosome 10. Only 9.5% of group 1 ESTs showed significant matches to Arabidopsis genome sequences. The results presented are useful for gene mapping and evolutionary and comparative genomics of grasses.