Identification of dominant genetic markers relevant to male sex determination in mulberry (Morus alba L.)

Morus alba (white mulberry) is a cultivated species of mulberry that exists as both dioecious and monoecious plants in nature. Although it has been cultivated for years as an essential crop for sericulture, and although various cultivars are readily available, its sex determination mechanisms are not yet clear. In the present study, we aimed to elucidate sex determination mechanisms of mulberry using both genetic and genomic approaches. Female and male cultivars of dioecious M. alba were crossed, and the segregation of sex was analyzed in the F-1 plants. In the F-1 plants, female and male plants were segregated at an almost equal ratio. By comparing the restriction site associated DNA sequencing analysis data between female- and male-bulked DNA of these F-1 plants, the male-bulk-specific RAD tags were predominantly identified. Thus, we presumed that the male M. alba is heterogametic whereas the female M. alba is homogametic. Based on the corresponding sequences of male-bulk-specific RAD tags, putative male-specific markers were developed, and these markers exhibited linkage with the male sex in individual F-1 plants. However, genotypes of these markers did not always show an association with sex in the cultivars of M. alba, M. bombycis, and M. lhou. Around half of the analyzed female cultivars showed identical marker genotypes to male, whereas all the analyzed male and monoecious cultivars showed a consistent genotype. According to these results, the DNA markers developed in this study were found to be relevant to male flower determination, and are thus expected to be helpful for elucidating the mechanisms underlying the evolutionary and sex determination systems of mulberry plants.