Format: ORAL

Pan-Pan Bai1, Kai-Jie Gu1, Jun-Jie Wu1, Yue Sun1, Juan Xu1, He Zhang2, Guangyi Fan2, Xuanmin Guang3, Huan Liu3, Yun-Peng Zhao1

1 College of Life Sciences, Zhejiang University, China 2 BGI-Qingdao, BGI-Shenzhen, Qingdao, China 3 State Key Laboratory of Agricultural Genomics, BGI Research, Shenzhen, China

Sex determination genes of dioecy, which refers to male and female reproductive organs present in separate individuals, have been uncovered in a few angiosperms, while there is a contrasting gap in gymnosperms. Ginkgo biloba L., representing one of the five extant gymnosperm lineages, is a well-known dioecious tree species in which sex determination genes remain unknown. Here, anatomical observation, transcriptomic analyses, and evolutionary analyses strongly support that two B-class MADS-box genes at the non-recombination region of the Y chromosome acted as the sex determination genes of ginkgo. Functional transgenic analysis in Arabidopsis thaliana indicated that they were related to the male reproductive organ identity specification. Moreover, the spatial enhanced resolution omics sequencing (Stereo-seq) revealed that the highest expression level of the two sex determination genes were present in the male reproductive primordium, i.e., microsporophyll primordium, of male strobilus buds at the sex determination stage. Collectively, these results not only systematically verified the hypothesis that B-class MADS-box genes determine the sex of dioecy in gymnosperms for the first time, but also pioneered the construction of the spatial transcriptome atlas of male strobilus buds in ginkgo. In light of the present discovery, we discussed the repeated evolution of dioecy and sex chromosomes in gymnosperm as well as its time course in seed plants.