Molecular characterization of the genomic region harboring the BYDV-resistance geneBdv2 in wheat

Barley yellow dwarf virus (BYDV) can cause significant losses of wheat worldwide. The long arm segment ofThinopyrum intermedium chromosome 7Ai#1 carrying the BYDV resistance geneBdv2 was translocated to the distal region of the long arm of wheat chromosome 7D in translocation line Yw642. In this study, 40 wheat EST sequences located in the distal region of 7DL were explored to identify specific PCR markers for theBdv2 region on the basis of the homoeologous relationship between wheat chromosome 7D and Th.intermedium chromosome 7Ai# 1. Our results revealed 8 novel EST-PCR markers specific to theBdv2 region, including 5 EST-STS markers of BE404744, BE498985, BE591497, BG606695 and BQ161842, and 3 EST-SSCP markers of BE404953, BG312663 and BE498985. These EST-PCR markers could distinguishBdv2 from another BYDV-resistance gene located onTh.intermedium chromosome 2Ai-2. These specific bands for theBdv2 region were further cloned and sequenced. The sequencing analysis indicated that the specific sequences for theBdv2 region were highly homologous with the original wheat EST sequences that were used to design primers, and encode respectively a protein kinase, P450, centrin, transducin, and a hypothetical protein. This study created a starting point for eventual cloning of theBdv2 gene and understanding the defense mechanism.     

Research progress in BYDV resistance genes derived from wheat and its wild relatives

Barley yellow dwarf virus （BYDV） may cause a serious disease affecting wheat worldwide. True resistance to BYDV is not naturally found in wheat. BYDV resistance genes are found in more than 10 wild relative species belonging to the genera of Thinopyrum, Agropyron, Elymus, Leymus, Roegneria, and Psathyrostachy. Through wide crosses combining with cell culture, use ofph mutants, or irradiation, 3 BYDV resistance genes in Th. intermedium, including Bdv2, Bdv3 and Bdv4, were introgressed into common wheat background. Various wheat-Th, intermedium addition and substitution, translocation lines with BYDV-resistance were developed and characterized, such as 7D-TAi#1 （bearing Bdv2）, 7B-7Ai#1, 7D-7E （beating Bdv3）, and 2D-2Ai-2 （bearing Bdv4） translocations. Three wheat varieties with BYDV resistance from Th. intermedium were developed and released in Australia and China, respectively. In addition, wheat-Agropyron cristatum translocation lines, wheat-Ag, pulcherrimum addition and substitution lines, and a wheat-Leymus multicaulis addition line （line24） with different resistance genes were developed. Cytological analysis, morphological markers, biochemical markers, and molecular markers associated with the alien chromatin carrying BYDV resistance genes were identified and applied to determine the presence of alien, chromosomes or segments, size of alien chromosome segments, and compositions of the alien chromosomes. Furthermore, some resistance-related genes, such as RGA, P450, HSP70, protein kinases, centrin, and transducin, were identified, which expressed specifically in the resistance translocation lines with Bdv2. These studies lay the foundations for developing resistant wheat cultivars and unraveling the resistance mechanism against BYDV.     

The use of cell culture for subchromosomal introgressions of barley yellow dwarf virus resistance from Thinopyrum intermedium to wheat.

Barley yellow dwarf virus (BYDV) resistance has been transferred to wheat from a group 7 chromosome of Thinopyrum (Agropyron) intermedium. The source of the resistance gene was the L1 disomic addition line, which carries the 7Ai-1 chromosome. The resistance locus is on the long arm of this chromosome. BYDV resistant recombinant lines were identified after three or more generations of selection against a group 7 Th. intermedium short arm marker (red coleoptile) and selection for the presence of BYDV resistance. One recombinant line produced by ph. mutant induced homoeologous pairing and 14 recombinant lines induced by cell culture have been identified. Resistance in seven of the cell culture induced recombinants has been inherited via pollen according to Mendelian segregation ratios for up to eight generations. Meiotic analysis of heterozygotes indicates that the alien chromatin in the cell culture induced recombinants is small enough to allow regular meiotic behaviour. The ph-induced recombinant was less regular in meiosis. A probe, pEleAcc2, originally isolated from Th. elongatum and that hybridizes to dispersed repeated DNA sequences, was utilised to detect Th. intermedium chromatin, which confers resistance to BYDV, in wheat backgrounds. Quantification of these hybridization signals indicated that the translocations involved a portion of alien chromatin that was smaller than the complete long arm of 7Ai-1. Restriction fragment length polymorphism analysis confirmed the loss of the short arm of 7Ai-1 and indicated the retention of segments of the long arm of 7Ai-1. Two 7Ai-1L DNA markers always assorted with the BYDV resistance. A third 7Ai-IL DNA marker was also present in seven of eight recombinants. In all recombinants except TC7, the 7Ai-1L markers replaced the 7DL markers. None of the wheat group 7 markers was missing from TC7. It is concluded that all the resistant lines are the result of recombination with wheat chromosome 7D, except line TC7, which is the result of recombination with an unidentified nongroup 7 chromosome.     

Structural organization of an alien Thinopyrum intermedium group 7 chromosome in U.S. soft red winter wheat (Triticum aestivum L.).

Barley yellow dwarf virus (BYDV) resistance in soft red winter wheat (SRWW) cultivars has been achieved by substituting a group 7 chromosome from Thinopyrum intermedium for chromosome 7D. To localize BYDV resistance, a detailed molecular genetic analysis was done on the alien group 7 Th. intermedium chromosome to determine its structural organization. Triticeae group 7 RFLP markers and rye specific repetitive sequences used in the analysis showed that the alien chromosome in the P29 substitution line has distinguishing features. The 350-480 bp rye telomeric sequence family was present on the long arm as determined by Southern and fluorescence in situ hybridization. However, further analysis using a rye dispersed repetitive sequence indicated that this alien chromosome does not contain introgressed segments from the rye genome. The alien chromosome is homoeologous to wheat chromosomes 7A and 7D as determined by RFLP analysis. Presence of the waxy gene on chromosomes 7A, 7B, and 7D but its absence on the alien chromosome in P29 suggests some internal structural differences on the short arm between Th. intermedium and wheat group 7 chromosomes. The identification of rye telomeric sequences on the alien Thinopyrum chromosome and the homoeology to wheat chromosomes 7A and 7D provide the necessary information and tools to analyze smaller segments of the Thinopyrum chromosome and to localize BYDV resistance in SRWW cultivars.     

Screening and analysis of differentially expressed genes from an alien addition line of wheat Thinopyrum intermedium induced by barley yellow dwarf virus infection.

The alien addition line TAI-27 contains a pair of chromosomes of Thinopyrum intermedium that carry resistance against barley yellow dwarf virus (BYDV). A subtractive library was constructed using the leaves of TAI-27, which were infected by Schizaphis graminum carrying the GAV strain of BYDV, and the control at the three-leaf stage. Nine differentially expressed genes were identified from 100 randomly picked clones and sequenced. Two of the nine clones were highly homologous with known genes. Of the remaining seven cDNA clones, five clones matched with known expressed sequence tag (EST) sequences from wheat and (or) barley whereas the other two clones were unknown. Five of the nine differentially expressed sequences (WTJ9, WTJ11, WTJ15, WTJ19, and WTJ32) were highly homologous (identities >94%) with ESTs from wheat or barley challenged with pathogens. These five sequences and another one (WTJ18) were also highly homologous (identities >86%) with abiotic stress induced ESTs in wheat or barley. Reverse Northern hybridization showed that seven of the nine differentially expressed cDNA sequences hybridized with cDNA of T. intermedium infected by BYDV. Three of these also hybridized with cDNA of line 3B-2 (a parent of TAI-27) infected by BYDV. The alien chromosome in TAI-27 was microdissected. The second round linker adaptor mediated PCR products of the alien chromosomal DNA were labeled with digoxygenin and used as the probe to hybridize with the nine differentially expressed genes. The analysis showed that seven differentially expressed genes were homologous with the alien chromosome of TAI-27. These seven differentially expressed sequences could be used as ESTs of the alien chromosome of TAI-27. This research laid the foundation for screening and cloning of new specific functional genes conferring resistance to BYDV and probably other pathogens.     

Trigenomic chromosomes by recombination of <Emphasis Type="Italic">Thinopyrum intermedium </Emphasis>and <Emphasis Type="Italic">Th. ponticum </Emphasis>translocations in wheat

Rusts and barley yellow dwarf virus (BYDV) are among the main diseases affecting wheat production world wide for which wild relatives have been the source of a number of translocations carrying resistance genes. Nevertheless, along with desirable traits, alien translocations often carry deleterious genes. We have generated recombinants in a bread wheat background between two alien translocations: TC5, ex-Thinopyrum (Th) intermedium, carrying BYDV resistance gene Bdv2; and T4m, ex-Th. ponticum, carrying rust resistance genes Lr19 and Sr25. Because both these translocations are on the wheat chromosome arm 7DL, homoeologous recombination was attempted in the double hemizygote (TC5/T4m) in a background homozygous for the ph1b mutation. The identification of recombinants was facilitated by the use of newly developed molecular markers for each of the alien genomes represented in the two translocations and by studying derived F₂, F₃ and doubled haploid populations. The occurrence of recombination was confirmed with molecular markers and bioassays on families of testcrosses between putative recombinants and bread wheat, and in F₂ populations derived from the testcrosses. As a consequence it has been possible to derive a genetic map of markers and resistance genes on these previously fixed alien linkage blocks. We have obtained fertile progeny carrying new tri-genomic recombinant chromosomes. Furthermore we have demonstrated that some of the recombinants carried resistance genes Lr19 and Bdv2 yet lacked the self-elimination trait associated with shortened T4 segments. We have also shown that the recombinant translocations are fixed and stable once removed from the influence of the ph1b. The molecular markers developed in this study will facilitate selection of individuals carrying recombinant Th. intermedium–Th. ponticum translocations (Pontin series) in breeding programs. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Development of novel PCR markers linked to the BYDV resistance gene <Emphasis Type="Italic">Bdv2</Emphasis> useful in wheat for marker-assisted selection

The distal segment of the long arm of the Thinopyrum intermedium chromosome 7Ai1 carries the barley yellow dwarf virus (BYDV) resistance gene Bdv2. This segment was transferred to the distal region of the long arm of wheat chromosome 7D in the Yw series of translocation lines by using the ph1b mutant to induce homoeologous pairing. To transfer Bdv2 to commercial varieties, we developed two resistance gene-analog polymorphism (RGAP) markers, Tgp-1₃₅₀ and Tgp-2₂₁₀, and one randomly amplified polymorphic DNA (RAPD) marker, OPD04₁₃₀₀. The diagnostic fragments of the RGAP marker Tgp-1₃₅₀ and the RAPD marker OPD04₁₃₀₀ were cloned, sequenced and converted into sequence-characterized amplified region (SCAR) markers, named SC-gp1 and SC-D04, respectively. SC-gp1 and SC-D04 were validated based on available translocation lines and segregating F₂ individuals. Our results indicated that the SCAR markers co-segregated with the BYDV resistance associated with Bdv2. Therefore, they can be used as a low-cost, high-throughput alternative to conventional phenotypic screening in wheat-breeding programs exploiting Bdv2. The marker-assisted selection for BYDV resistance was successfully performed in a wheat-breeding program.Electronic Supplementary Material Supplementary material is available for this article at     

Molecular characterization of a Thinopyrum intermedium group 2 chromosome (2Ai-2) conferring resistance to barley yellow dwarf virus.

The wheat--Thinopyrum intermedium addition lines Z1 and Z2 carry 21 pairs of wheat chromosomes and one pair of Th. intermedium chromosomes (2Ai-2) conferring resistance to barley yellow dwarf virus (BYDV). GISH results using the genomic DNA of Pseudoroegneria strigosa (S genome) as the probe indicated that the 2Ai-2 chromosome in Z1 and Z2 is an S-J intercalary translocation. Most of the 2Ai-2 chromosome belongs to the S genome, except for about one third in the middle region of the long arm that belongs to the J genome. The results of detailed RFLP analyses confirmed that the 2Ai-2 chromosome is extensively homoeologous to wheat group 2 chromosomes. Some new RFLP markers specific to the 2Ai-2 chromosome were identified. A RAPD marker, OP-R16(340), specific to the 2Ai-2 chromosome, was screened. We converted the RAPD marker into a sequence-characterized amplified region (SCAR) marker (designated SC-R16). The study establishes the basis for selecting translocation lines with small segments of the 2Ai-2 chromosome and localizing the BYDV resistance gene when introgressed into a wheat background.     

携带抗黄矮病基因的中间偃麦草染色体2Ai_2特异的分子标记

The wheat-Thinopyrum intermedium addition lines Z1,Z2 contain a pair of Th. intermedium chromosomes 2Ai-2 carrying the gene with resistance to barley yellow dwarf virus (BYDV). Genomic in situ hybridization (GISH) was used to analyze the chromosome constitution of Z1,Z2 by using genomic DNA probes from Th. intermedium and Pseudoroegneria strigosa. The results showed that the chromosome constitution of either Z1 or Z2 composes of 42 wheat chromosomes and two Th. intermedium chromosomes (2Ai-2). The 2Ai-2 chromosome is St-E intercalary translocation, in which the E genomic chromosome segment translocated into the middle region of the long arm of chromosome belonging to St genome. With the genomic DNA probe of Ps. strigosa, the GISH pattern specific to the 2Ai-2 chromosome may be used as a molecular cytogenetic marker. A detailed RFLP analysis on Z1, Z2 and their parents was carried out by using 12 probes on the wheat group 2 chromosomes. Twenty RFLP markers specific to the 2Ai-2 chromosome were identified. Two RAPD markers of OPR16 –350 and OPH09 -1580, specific to the 2Ai-2 chromosome, were identified from 280 RAPD primers. These molecular markers could be used to assisted-select translocation lines with small segment of the 2Ai-2 chromosome and provide tools to localize the BYDV resistance.     

Resistance to eyespot of wheat, caused by Tapesia yallundae, derived from Thinopyrum intermedium homoeologous group 4 chromosome

Thinopyrum intermedium was identified previously as resistant to Tapesia yallundae, cause of eyespot of wheat. Using GUS-transformed isolates of T. yallundae as inoculum, we determined that wheat lines carrying Th. intermedium chromosome 4Ai#2 or the short arm of chromosome 4Ai#2 were as resistant to the pathogen as the eyespot-resistant wheat- Th. ponticum chromosome substitution line SS767 (PI 611939) and winter wheat cultivar Madsen, which carries gene Pch1 for eyespot resistance. Chromosome 4E from Th. elongatum and chromosome 4J from Th. bessarabicum did not confer resistance to T. yallundae. Genome-specific PCR primers confirmed the presence of Thinopyrum chromatin in these wheat- Thinopyrum lines. Genomic in situ hybridization using an St genomic probe from Pseudoroegneria strigosa demonstrated that chromosome 4Ai#2 belongs to the J^s genome of Thinopyrum. The eyespot resistance in the wheat- Th. intermedium lines is thus controlled by the short arm of this J^s chromosome. This is the first report of resistance to T. yallundae controlled by a J^s genome chromosome of Th. intermedium.     

携带抗黄矮病基因的中间偃麦草染色体2Ai—2特异的分子标记

小麦－中间偃麦草二体异附加系Ｚ１、Ｚ２具有一对携带抗黄矮病基因的中间偃麦草染色体２Ａｉ－２。利用中间偃麦草（Ｔｈｉｎｏｐｙｒｕｍ ｉｎｔｅｒｍｅｄｉｕｍ （Ｈｏｓｔ） Ｂａｋｗｏｔｈ ａｎｄ Ｄｅｗｅｙ）和拟鹅冠草（Ｐｓｅｕｄｏｒｏｅｇｎｅｉａ ｓｔｒｉｇｏｓａ）基因组ＤＮＡ作探针,对Ｚ１、Ｚ２进行基因组原位杂交分析。结果表明,Ｚ１、Ｚ２附加的一对中间偃麦草染色体２Ａｉ－２为Ｓｔ－Ｅ染色体,Ｅ组染     

A single wheatgrass chromosome reduces the concentration of barley yellow dwarf virus in wheat

Seedlings of a series of addition or substitution lines of wheat containing different Thinopyrum intermedium chromosomes were inoculated with the PAV and RPV serotypes of barley yellow dwarf virus (BYDV). Reduced virus titres in infected plants were ascribed to a single pair of homoeologous group 7 chromosomes from Th. intermedium in the disomic addition lines L1 and TAF 2. The group 7 chromosome is associated with red pigmentation of coleoptiles, which was also observed in two lines ditelosomic for the α arm of the chromosome. However, when infected with the PAV serotype of BYDV, the ditelosomic lines had normal virus titres and it is concluded that potential determinants of BYDV resistance are located on the β arm of the Group 7 chromosome.     

抗黄矮病小麦新品系YW443的分子细胞遗传学鉴定

以小麦－中间偃麦草二体附加系Ｌ１衍生抗病系ＰＰ９－１为抗源,与小麦推广品种陕７８５９．丰抗８号杂交并自交,在Ｆ６代中选到农艺性状优良的高抗黄矮病小麦新品系ＹＷ４４３。对ＹＷ４４３及其亲本进行抗病性鉴定。结果表明：ＹＷ４４３高抗大麦黄矮病毒ＧＰＶ、ＧＡＶ株系。利用基因组原位杂交,ＲＦＬＰ分析和ＲＡＰＤ分析,研究诉遗传构成及其抗病基因染色体归属。结果表明：ＹＷ４４３（２ｎ＝４３）的遗传构成了４０条（２     

Development and characterization of wheat- Leymus racemosus translocation lines with resistance to Fusarium Head Blight

Wheat scab (Fusarium Head Blight, FHB) is a destructive disease in the warm and humid wheat-growing areas of the world. Finding diverse sources of FHB resistance is critical for genetic diversity of resistance for wheat breeding programs. Leymus racemosus is a wild perennial relative of wheat and is highly resistant to FHB. Three wheat- L. racemosus disomic addition (DA) lines DA5Lr#1, DA7Lr#1 and DALr.7 resistant to FHB were used to develop wheat- L.racemosus translocation lines through irradiation and gametocidal gene-induced chromosome breakage. A total of nine wheat-alien translocation lines with wheat scab resistance were identified by chromosome C-banding, GISH, telosomic pairing and RFLP analyses. In line NAU614, the long arm of 5Lr#1 was translocated to wheat chromosome 6B. Four lines, NAU601, NAU615, NAU617, and NAU635, had a part of the short arm of 7Lr#1 transferred to different wheat chromosomes. Four other lines, NAU611, NAU634, NAU633, and NAU618, contained translocations involving Leymus chromosome Lr.7 and different wheat chromosomes. The resistance level of the translocation lines with a single alien chromosome segment was higher than the susceptible wheat parent Chinese Spring but lower than the alien resistant parent L. racemosus. At least three resistance genes in L. racemosus were identified. One was located on chromosome Lr.7, and two could be assigned to the long arm of 5Lr#1 and the short arm of 7Lr#1.     

Molecular cytogenetic characterization of alien introgressions with gene Fhb3 for resistance to Fusarium head blight disease of wheat

Fusarium head blight (FHB) resistance was identified in the alien species Leymus racemosus, and wheat-Leymus introgression lines with FHB resistance were reported previously. Detailed molecular cytogenetic analysis of alien introgressions T01, T09, and T14 and the mapping of Fhb3, a new gene for FHB resistance, are reported here. The introgression line T09 had an unknown wheat-Leymus translocation chromosome. A total of 36 RFLP markers selected from the seven homoeologous groups of wheat were used to characterize T09 and determine the homoeologous relationship of the introgressed Leymus chromosome with wheat. Only short arm markers for group 7 detected Leymus-specific fragments in T09, whereas 7AS-specific RFLP fragments were missing. C-banding and genomic in situ hybridization results indicated that T09 has a compensating Robertsonian translocation T7AL·7Lr#1S involving the long arm of wheat chromosome 7A and the short arm of Leymus chromosome 7Lr#1 substituting for chromosome arm 7AS of wheat. Introgression lines T01 (2n = 44) and T14 (2n = 44) each had two pairs of independent translocation chromosomes. T01 had T4BS·4BL-7Lr#1S + T4BL-7Lr#1S·5Lr#1S. T14 had T6BS·6BL-7Lr#1S + T6BL·5Lr#1S. These translocations were recovered in the progeny of the irradiated line Lr#1 (T5Lr#1S·7Lr#1S). The three translocation lines, T01, T09, and T14, and the disomic addition 7Lr#1 were consistently resistant to FHB in greenhouse point-inoculation experiments, whereas the disomic addition 5Lr#1 was susceptible. The data indicated that at least one novel FHB resistance gene from Leymus, designated Fhb3, resides in the distal region of the short arm of chromosome 7Lr#1, because the resistant translocation lines share a common distal segment of 7Lr#1S. Three PCR-based markers, BE586744-STS, BE404728-STS, and BE586111-STS, specific for 7Lr#1S were developed to expedite marker-assisted selection in breeding programs.     

Introgression and characterization of barley yellow dwarf virus resistance from Thinopyrum intermedium into wheat.

Wheatgrasses (species of Agropyron complex) have previously been reported to be resistant to barley yellow dwarf virus (BYDV). To introgress this resistance into wheat, Triticum aestivum x Thinopyrum (Agropyron) intermedium hybrids were advanced through a backcrossing program and reaction to BYDV, as determined by enzyme-linked immunosorbent assay (ELISA), is reported for the first time in backcross populations of wide hybrids between wheat and wheatgrasses. ELISA values revealed highly resistant to highly susceptible segregants in backcrosses. BYDV resistance was expressed in some backcross derivatives. Continued selection, based on cytology and ELISA in each generation, eliminated most of the unwanted wheatgrass chromosomes and produced self-fertile BYDV resistant wheat lines. The BYDV resistant lines with 2n = 42 had normal chromosome pairing similar to wheat, and their F1 hybrids with wheat had two univalents. DNA analyses showed that the source of alien chromatin in these BYDV resistant wheat lines is distinguishable from that in other Th. intermedium derived BYDV resistant wheat lines. Chromosome pairing and restriction fragment length polymorphism analyses indicated that the 42 chromosome resistant Purdue wheat lines are substitution lines in which chromosome 7D was replaced by a chromosome from Th. intermedium that was carrying gene(s) for BYDV resistance.     

<Emphasis Type="Italic">Pm37</Emphasis>, a new broadly effective powdery mildew resistance gene from <Emphasis Type="Italic">Triticum </Emphasis><Emphasis Type="Italic">timopheevii</Emphasis>

Powdery mildew is an important foliar disease in wheat, especially in areas with a cool or maritime climate. A dominant powdery mildew resistance gene transferred to the hexaploid germplasm line NC99BGTAG11 from T. timopheevii subsp. armeniacum was mapped distally on the long arm of chromosome 7A. Differential reactions were observed between the resistance gene in NC99BGTAG11 and the alleles of the Pm1 locus that is also located on chromosome arm 7AL. Observed segregation in F_2:3 lines from the cross NC99BGTAG11 × Axminster (Pm1a) demonstrate that germplasm line NC99BGTAG11 carries a novel powdery mildew resistance gene, which is now designated as Pm37. This new gene is highly effective against all powdery mildew isolates tested so far. Analyses of the population with molecular markers indicate that Pm37 is located 16 cM proximal to the Pm1 complex. Simple sequence repeat (SSR) markers Xgwm332 and Xwmc790 were located 0.5 cM proximal and distal, respectively, to Pm37. In order to identify new markers in the region, wheat expressed sequence tags (ESTs) located in the distal 10% of 7AL that were orthologous to sequences from chromosome 6 of rice were targeted. The two new EST-derived STS markers were located distal to Pm37 and one marker was closely linked to the Pm1a region. These new markers can be used in marker-assisted selection schemes to develop wheat cultivars with pyramids of powdery mildew resistance genes, including combinations of Pm37 in coupling linkage with alleles of the Pm1 locus.     

Molecular cytogenetic characterization of Thinopyrum intermedium-derived wheat germplasm specifying resistance to wheat streak mosaic virus

Thinopyrum intermedium is a promising source of resistance to wheat streak mosaic virus (WSMV), a devastating disease of wheat. Three wheat germplasm lines possessing resistance to WSMV, derived from Triticum aestivum×Th. intermedium crosses, are analyzed by C-banding and genomic in situ hybridization (GISH) to determine the amount and location of alien chromatin in the transfer lines. Line CI15092 was confirmed as a disomic substitution line in which wheat chromosome 4A was replaced by Th. intermedium chromosome 4Ai?2. The other two lines, CI17766 and A29-13-3, carry an identical Robertsonian translocation chromosome in which the complete short arm of chromosome 4Ai?2 was transferred to the long arm of wheat chromosome 4A. Fluorescence in situ hybridization (FISH) using ABD genomic DNA from wheat as a probe and S genomic DNA from Pseudoroegneria stipifolia as the blocker, and vice versa, revealed that the entire short arm of the translocation was derived from the short arm of chromosome 4Ai?2 and the breakpoint was located at the centromere. Chromosomal arm ratios (L/S) of 2.12 in CI17766 and 2.15 in A29-13-3 showed that the translocated chromosome is submetacentric. This translocated chromosome is designated as T4AL?? 4Ai?2S as suggested by Friebe et al. (1991).     

Dissecting of the FHB resistance QTL on the short arm of wheat chromosome 2D using a comparative genomic approach: from QTL to candidate gene

Colinearity in gene content and order between rice and closely related cereal crops has been a powerful tool for gene identification. Using a comparative genomic approach, we have identified the rice genomic region syntenous to the region of the short arm of wheat chromosome 2D, on which quantitative trait loci (QTLs) for Fusarium head blight (FHB) resistance and for controlling accumulation of the mycotoxin deoxynivalenol (DON) are closely located. Utilizing markers known to reside near the FHB resistance QTL and data from several wheat genetic maps, we have limited the syntenous region to 6.8 Mb of the short arm of rice chromosome 4. From the 6.8-Mb sequence of rice chromosome 4, we found three putative rice genes that could have a role in detoxification of mycotoxins. DNA sequences of these putative rice genes were used in BLAST searches to identify wheat expressed sequence tags (ESTs) exhibiting significant similarity. Combined data from expression analysis and gene mapping of wheat homologues and results of analysis of DON accumulation using doubled haploid populations revealed that a putative gene for multidrug resistance-associated protein (MRP) is a possible candidate for the FHB resistance and/or DON accumulation controlling QTLs on wheat chromosome 2DS and can be used as a molecular marker to eliminate the susceptible allele when the Chinese wheat variety Sumai 3 is used as a resistance source. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Comparative mapping of wheat chromosome 1AS which contains the tiller inhibition gene (<Emphasis Type="Italic">tin</Emphasis>) with rice chromosome 5S

The capacity to tiller is a key factor that determines plant architecture. Using molecular markers, a single major gene reducing tiller number, formally named the tiller inhibition gene (tin), was mapped to the short arm of chromosome 1A in wheat. We identified a tightly linked microsatellite marker (Xgwm136) that may be useful in future marker-assisted selection. The tin gene was mapped to the distal deletion bin of chromosome 1AS (FLM value 0.86) and wheat ESTs which were previously mapped to the same deletion bin were used to identify 18 closely related sequences in the syntenic region of rice chromosome 5. For a subset of wheat ESTs that detected flanking markers for tin, we identified closely related sequences within the most distal 300 kb of rice chromosome 5S. The synteny between the distal chromosome ends of wheat 1AS and rice 5S appeared to be disrupted at the hairy glume locus and seed storage protein loci. We compared map position of tin with other reduced tillering mutants characterised in other cereals to identify possible orthologous genes.