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

Key message: A physical map of Aegilops geniculata chromosome 7M^g was constructed, and a novel purple coleoptile gene was localized at 7M^gS 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, U^gU^gM^gM^g), a wild relative of common wheat, possesses many favorable genes. In this study, Ae. geniculata chromosome 7M^g 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^g and localize the purple coleoptile gene, 59 molecular markers specific to 7M^g were developed, and 43 wheat-Ae. geniculata 7M^g chromosome structure aberrations were generated based on chromosome centromeric breakage-fusion and ph1b-induced homoeologous recombination. Segment sizes and breakpoint positions of each 7M^g structure aberration were further characterized using in situ hybridization and molecular marker analysis. Consequently, a physical map of chromosome 7M^g was constructed with 59 molecular markers, comprising six bins with 28 markers on 7M^gS and six bins with 31 markers on 7M^gL, and the purple coleoptile gene was mapped to an interval of FL 0.60-0.65 on 7M^gS. The newly developed wheat-Ae. geniculata 7M^g structural aberrations and the physical map of 7M^g will facilitate the transfer and utilization of desirable genes from 7M^g in the future.