Inducing Intergeneric Chromosomal Tranlocations Between Wheat And Its Wild Relatives Through Pollen Irradiation

Sectionâ… Mass Production of Intergeneric Chromosomal Transiocations through Pollen Irradiation of Triticum durum-Haynaldia villosa AmphiploidHaynaldia villosa possesses a lot of important agronomic traits and has been a powerful gene resource for wheat improvement. However, only several wheat-H.villosa translocation lines have been reported so far. In this study, we attempted to develop an efficient method for inducing wheat-H.villosa chromosomal translocations. Triticum durum-Haynaldia villosa amphiploid pollen treated with 1200 rad ⁶⁰Co-γ-rays was pollinated to Triticum aestivum cv. 'Chinese Spring'. Ninety-eight intergeneric translocated chromosomes between T.durum and H.villosa were detected by genomic in situ hybridization in 44 of 61 M₁ plants, indicating a translocation occurrence frequency of 72.1ï¼…, much higher than that ever reported. There were 26, 62 and 10 translocated chromosomes involving whole arm translocations, terminal translocations, and intercarlary translocations, respectively. Of the total 108 breakage-fusion events, 79 ones involved interstitial regions and 29 ones involved centric regions. The ratio of small alien segment terminal translocations was much higher than that of large alien segment terminal translocations. All the M₁ plants were self-sterile, and their backcross progeny was all obtained with 'Chinese Spring' as pollen donors. Transmission analysis showed that most of the translocations were transmittable. This study provided a new strategy for rapid mass production of wheat-alien chromosomal translocations, especially terminal translocations that will be more significant for wheat improvement.Sectionâ…¡Efficient Detection of Structural Changes Involving Haynaldia villosa Chromosome 6V through Double-Terminal-Marker Analysis Any chromosome without structural changes maintains two original ends. At least 95ï¼…of the chromosomal translocations or deletions reported so far maintain a single original end. In this research, 6VS-₃₈₁ and 6VL-₃₅₈, two amplicon markers specific to distal regions of the short and long arms of Haynaldia villosa chromosome 6V, respectively, were developed based on wheat expressed sequence tags and used for detecting structural changes involving 6V. Seventy-four plants with putative chromosomal structural changes were screened out from 465 M₁ or M₂ plants deriving from pollen irradiation, and cytogenetically identified involving 20 structure-changed chromosomes including 12 whole arm translocations that were all T6VS·W, 4 terminal translocations, 1 6VL terminal deletion, 1 translocation deletion, and 2 intercalary translocations either of which was detected involving another T6VS·W translocation in the same plant. The powdery mildew resistance gene, Pro21, was then located into the chromosomal interval 6VS0.33-0.58 based on the chromosomal structural changes obtained in this and earlier researches. Higher efficiency in detecting of chromosomal structural changes was showed when the double-terminal-marker analysis was applied in M₂ populations than in M₁ plants. This study provided a new strategy for efficient detection of structural aberrations involving a specific alien chromosome.Sectionâ…¢Molecular Cytogenetie Analysis of a Triticum aestivum-Haynaldia villosa Reciprocal Chromosomal Translocation Induced by Pollen IrradiationThe short arm of Haynaldia villosa chromosome 6V confers Pm21 that conditions high resistance to almost all known powdery mildew races. In the middle of the 1990s, Cytogenetic Institute, Nanjing Agricultural University (CINAU) has developed the T6VS·6AL translocation line with high yield and powdery mildew resistance. However, this translocation obviously has a large amount of redundant alien genes. To develop terminal and/or intercalary translocations with as short as possible alien chromosomal segments conferring Pm21 is more important in wheat breeding. In addition, the more translocations with different breakpoint positions at the length of 6VS are, the higher resolution of physical mapping of Pm21 is. In this research, our objective is to induce new translocations involving H.villosa chromosome 6V through pollen irradiation. Pollen of Triticum aestivum-Haynaldia villosa 6V monosomic addition lines (2n=43), treated with 1000 rad ⁶⁰Co-γ-rays, was pollinated to T.aestivum cv. 'Chinese Spring'. Pollen mother cells (PMCs) of M₁ plants at meiotic metaphase I were used for GISH analysis. A trivalent formed by two T.aestivum-H.villosa translocation chromosomes and a wheat chromosome was observed in a M₁ plant, indicating that the translocation chromosomes might be resulted from a reciprocal translocation event. The translocation involving the large alien segment was called 'large alien segment translocation' (LAST) while the translocation involving the small alien segment was called 'small alien segment translocation' (SAST). Sequential C-banding and GISH technique was used to identify a homozygous M₂ plant (LAST″+SAST″, 2n=44). The results showed that the reciprocal translocation involved T.aestivum chromosome 7B and H.villosa chromosome 6V with the translocation breakpoints at about FL0.60 of 7BS and about FL0.70 of 6VS, respectively. The LAST chromosome was identified as T7BS-6VS·6VL while the SAST chromosome was identified as T6VS-7BS·7BL. Seven chromosome constitution types were observed in the M₂ population with the ratio of 3(LAST″+SAST″): 20(LAST′+SAST′): 2(LAST″+SAST″): 1(LAST′+SAST″): 1LAST: 2SAST′: 22(none alien). The LAST chromosome occurred accompanied by the SAST chromosome at most times. Resistance analysis showed that the plant with a single LAST chromosome was resistant to powdery mildew. Then, Pm21 was located at the proximal region of FL0.70 of 6VS. Meiotic analysis of M₂ plants with the genomc of 20â…¡^W+â… ^7B+â… ^{T7BS-6VS·6VL}+â… ^{T6VS-7BS·7BL} (2n=43) showed that T7BS-6VS·6VL and T6VS-7BS·7BL co-segregated at meiotic anaphaseâ… or telophaseâ… in 88.5ï¼…of PMCs. The LAST chromosome T7BS-6VS·6VL stayed late or centric-misdivided in several PMCs at anaphaseâ… . An intercalary translocation, T7BL·6VS-7BS, arising from the centric breakage-fusion of 7B and T7BS-6VS·6VL, was then detected in a progeny of a plant with the genome of 20â…¡^W+â… ^7B+â… ^{T7BS-6VS·6VL}. It provided a new strategy for inducing intercalary translocations with alien chromosomal segments conferring target genes. Homozygous T7BS-6VS·6VL and T6VS-7BS·7BL translocation lines were obtained in M₃ generation.Sectionâ…£Molecular and Cytogenetic Identification of a Reciprocal Chromosomal Tranlocation Line Involving Triticum aestivum Chromosome 7A and Roegneria Kamoji Chromosome 1Rk^#1 and its Scab Resistance AnalysisPollen of Triticum aestivum-Roegneria kamoji 1Rk^#1 (delL) disomic addition line, treated with 1000 tad ⁶⁰Co-γ-rays, was pollinated to T.aestivum cv. 'Chinese Spring'. A translocation line involving two translocated chromosomes with the arm ratios of 2:1 and 3:1, respectively, was screened out by C-banding and GISH techniques. The translocation with the arm ratio of 2:1 involved wheat 7AL and an alien segment with an very large centrimetic C-band and a sub-telomeric dark-red band in the GISH pattern that was speculated as a 45SrDNA site. Another translocation involved wheat 7AS and a short alien arm that also had a big centrimeric C-band. The 45SrDNA was used to identify the alien chromosome 1Rk^#1 arms and a 45SrDNA site was located at the telomeric region of 1Rk^#1 short arm through sequential C-banding and 45SrDNA-FISH analyses of a wheat-R.kamoji 1Rk^#1 addition line (2n=44). The two translocation chromosomes were then identified as 7AL·1Rk^#1S and 1Rk^#1delL·7AS through sequential C-banding and GISH analyses. Three chromosome constitution types were detected including typeâ… (2n=42, with a whole wheat chromosome completement); typeâ…¡(2n=43, with 2 homoeozygous translocation chromosomes and a wheat 7A), and typeâ…¢(2n=44, with 2 pairs of translocation chromosomes and no 7A chromosome). A typeâ…¡plant was backcrossed to CS with the former as female and male parents, respectively. And 20 typeâ… and 16 typeâ…¡plants were obtained by the former backcross while 18 typeâ… and 4 typeâ…¡plants were obtained by the latter backcross. It indicated that the two translocation chromosome co-segregate at meiosis, and the translocations have much higher transmission frequency through female gametes than male ones. Successive M₂, M₃, and M₄ generations were applied to scab resistance analysis. The result showed that at least one locus was on the 1Rk^#1 chromosome and the scab resistance expression differed in different years and different locations.