Dioecy, the presence of male and female individuals, has evolved independently in multiple flowering plant lineages1,2,3. Although theoretical models for the evolution of dioecy, such as the ‘two-mutations’ model, are well established4,5, little is known about the specific genes determining sex and their evolutionary history3. Kiwifruit, a major tree crop consumed worldwide, is a dioecious species. In kiwifruit we previously identified a Y-encoded sex-determinant candidate gene acting as the suppressor of feminization (SuF), named Shy Girl (SyGI)6. Here, we identify a second Y-encoded sex-determinant that we named Friendly Boy (FrBy), which exhibits strong expression in tapetal cells. Gene-editing and complementation analyses in Arabidopsis thaliana and Nicotiana tabacum indicated that FrBy acts for the maintenance of male (M) functions, independently of SyGI, and that these functions are conserved across angiosperm species. We further characterized the genomic architecture of the small (<1 megabase pairs (Mb)) male-specific region of the Y chromosome (MSY), which harbours only two genes expressed extensively in developing gynoecia and androecia, respectively: SyGI and FrBy. Re-sequencing of the genome of a natural hermaphrodite kiwifruit revealed that this individual is genetically male but carries deletion(s) of parts of the Y chromosome, including SyGI. Additionally, expression of FrBy in female kiwifruit resulted in hermaphrodite plants. These results clearly indicate that Y-encoded SyGI and FrBy act independently as the SuF and M factors in kiwifruit, respectively, and provide insight into not only the evolutionary path leading to a two-factor sex-determination system, but also a new breeding approach for dioecious species.
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We thank L. Comai (UC Davis Department Plant Biology and Genome Center) for technical advice and bioinformatics support; Y. Kazama and K. Ishii (Riken Institute) for technical support in using the DelMapper programme; and N. Nieuwenhuizen and J. (L.) Zhang (Plant and Food Research) for vector construction. The KE population was originally provided by Kagawa Prefectural Agricultural Experiment Station. Some of this work was performed at the Vincent J. Coates Genomics Sequencing Laboratory at UC Berkeley, supported by NIH Instrumentation (grant No. S10 OD018174). This work was supported by PRESTO (grant Nos. JPMJPR15Q1 (to T.A.) and JPMJPR15Q6 (to S.S.S.)) from the Japan Science and Technology Agency (JST), by a Grant-in-Aid for Scientific Research on Innovative Areas (No. 19H04862 to T.A.) from JSPS and by the National Science Foundation (NSF) IOS award (grant No. 1457230 to I.M.H.).
The authors declare no competing interests.
Peer review information: Nature Plants thanks Roberta Bergero, Susanne Renner and Qi Zhou for their contribution to the peer review of this work.
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Akagi, T., Pilkington, S.M., Varkonyi-Gasic, E. et al. Two Y-chromosome-encoded genes determine sex in kiwifruit. Nat. Plants 5, 801–809 (2019). https://doi.org/10.1038/s41477-019-0489-6
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