Characterization of Two Isogenic Chromosome Arm Translocations from Rye into Wheat That Show Differential Drought Resistance

Wheat is an important food staple, estimated to account for approximately 20% of all human food calories and protein consumed worldwide. Increases in wheat yields are required to accommodate increasing food demand caused by the rapidly growing human population. One potential source for that improvement is introgression of alien chromatin. Translocation of the short arm of rye (Secale cereal L.) chromosome 1 (1RS) to common wheat (Triticum aestivum L.) chromosome 1B (1RS.1BL) is used in wheat breeding programs worldwide, initially due to an array of pest and disease resistance genes, but it has also been shown to increase yield, particularly under abiotic stress conditions. To identify genetic elements responsible for drought resistance conferred by the 1RS.1BL translocation we sequenced and assembled two flow-sorted ditelosomic 1RS chromosome arms from hexaploid wheat. One chromosome arm was a complete 1RS arm from the 1RS.1BL translocation and the other was a recombinant 1BS-1RS with a small segment of wheat chromatin, which when present greatly reduces yield under drought conditions. We have identified a suite of wheat sequences that have been introduced into the recombinant 1RS chromosome arm but without a corresponding reciprocal loss of rye sequence. This suggests that the event that produced the recombinant 1BS-1RS arm might have been an out-of-register unequal crossover.  While this does not offer much assistance in the identification of the elements responsible for drought tolerance, it may provide insight about crossovers in the absence of the Ph1 locus in wheat. We are using this new sequence information to screen a large population of deletion mutants to further delimit the region responsible for different drought resistance. Apart from being useful for identifying the gene(s) responsible, this resource will provide breeders and scientists with a comprehensive draft sequence of the most widely spread 1RS.1BL translocation than is currently available for use in marker assisted breeding and mapping projects.