Construction of a physical map for Aegilops geniculata chromosome 7M and localization of its novel purple coleoptile gene.

A physical map of Aegilops geniculata chromosome 7M was constructed, and a novel purple coleoptile gene was localized at 7MS bin FL 0.60-0.65 by development of wheat-Ae. geniculata structural aberrations. The development of wheat-wild relative chromosomal structure aberrations not only provides novel germplasm resources for wheat improvement, but also aids in mapping desirable genes to specific chromosomal regions. Aegilops geniculata (2n = 4x = 28, UUMM), a wild relative of common wheat, possesses many favorable genes. In this study, Ae. geniculata chromosome 7M was identified as harboring a purple coleoptile gene by phenotypic evaluation of Chinese Spring (CS)-Ae. geniculata addition and substitution lines. To construct a physical map of chromosome 7M and localize the purple coleoptile gene, 59 molecular markers specific to 7M were developed, and 43 wheat-Ae. geniculata 7M chromosome structure aberrations were generated based on chromosome centromeric breakage-fusion and ph1b-induced homoeologous recombination. Segment sizes and breakpoint positions of each 7M structure aberration were further characterized using in situ hybridization and molecular marker analysis. Consequently, a physical map of chromosome 7M was constructed with 59 molecular markers, comprising six bins with 28 markers on 7MS and six bins with 31 markers on 7ML, and the purple coleoptile gene was mapped to an interval of FL 0.60-0.65 on 7MS. The newly developed wheat-Ae. geniculata 7M structural aberrations and the physical map of 7M will facilitate the transfer and utilization of desirable genes from 7M in the future.