The effect of structural variation of the long arm of rye 6R on its meiotic behavior and the location of a segment with powdery mildew resistance

To investigate the effect of structural variation of rye 6RL arms on their meiotic behavior and to locate powdery mildew resistance gene(s), we developed a wheat–rye T6BS.6RL^Ar translocation chromosome and its deleted translocations, T6BS.6RL^Ar-2 and T6BS.6RL^Ar-4. Some 6RL-specific markers were used to determine that the segments from 733.91 to 849.52 Mb and from 832.72 Mb to the telomere of 6RL^Ar arms were deleted from T6BS.6RL^Ar-2 and T6BS.6RL^Ar-4, respectively. Translocations T6BS.6RL^Ar and T6BS.6RL^Ar-4 were resistant to powdery mildew and T6BS.6RL^Ar-2 was susceptible. The segment of 6RL^Ar with powdery mildew resistance was about 100 Mb. Deletion of the 6RL^Ar telomeric region inhibited the pairing and recombination of T6BS.6RL^Ar-4. Compared with T6BS.6RL^Ar and T6BS.6RL^Ar-4, T6BS.6RL^Ar-2 showed a normal meiotic behavior. Immunolocalization using anti-ZYP1, anti-DMC1 and anti-MLH1 proteins indicated that more DSBs (DNA double-strand breaks) and crossovers formed on the 6RL^Ar arm in T6BS.6RL^Ar, and this might be related to the formation of anaphase I bridges of 6RL^Ar. Although the 6RL^Ar deletions were used to physically locate powdery mildew resistance gene(s), more accurate location through meiotic recombination was needed. The results in this study indicated that altering the structure of the 6RL^Ar arm promoted normal meiotic behavior, and this might facilitate the localization of resistance genes through meiotic homologous recombination.