Comparative Mapping to Develop Markers in the Aegilops sharonensis Gametocidal Introgression

In the process of recurrent backcrossing to produce alien chromosome addition lines in wheat, some wild species’ chromosomes were found to transmit preferentially to the offspring. These chromosomes have been termed cuckoo chromosomes (or gametocidal chromosomes). The gametocidal genes in species such as Aegilops sharonensis are exclusively transmitted to the next generation through both the male and female gametes when introduced into wheat. Thus, those traits linked with gametocidal genes, are found in all offspring without the requirement for selection. The mechanism for the transmission of the gametocidal genes appear to occur by the induction of extensive chromosome damage in gametes lacking the gametocidal chromosomes and these aberrations are also observed in the endosperm. Previous studies indicate that at least two-linked genes are involved in the mechanism responsible for preferential transmission. The first, the ‘breaker’, induces chromosome breakage while the second, the ‘inhibitor’, prevents chromosome breakage. Here, we show the development of more than 70 markers in the chromosomal introgression region, T4D-4Ssh^L (IL B8/2 and IL B8/9), and 9 in the smaller region, T4B-4Ssh^L (Friebe et al., 2003), from Ae. sharonensis carrying the gametocidal genes. The former were obtained through genome synteny with rice and Brachypodium while the later were developed through the chromosome survey sequence for Triticum aestivum cv. Chinese Spring generated by the IWGSC. The order of the markers on the introgression is the best fit predication according to available data. Deletion mutant introgression lines where the breaker gene is deleted, showing 100% spike fertility, or where the inhibitor gene is deleted, showing 100% spike sterility, are being analysed with the developed markers with the aim of fine mapping the locations of the gametocidal genes.