The Mechanism of the Development and Maintenance of Sexual Dimorphism in the Dioecious Mulberry Plant (Morus alba)

Intersexual differentiation is crucial for the speciation and maintenance of dioecious plants, but the underlying mechanisms, including the genes involved, are still poorly understood. Here, we focused on a typical dioicous plant Morus alba, to explore the molecular footprints relevant to sex evolution by revealing the differentially expressed genes (DEGs) between two sexes and the testing signals of selection for these DEGs. From the results, we found a total of 1543 DEGs. Interestingly, 333 and 66 genes expression were detected only in male and female inflorescences, respectively. Using comparative transcriptomics, the expression of 841 genes were found to be significantly higher in male than in female inflorescences and were mainly enriched in defense-related pathways including the biosynthesis of phenylpropanoids, cutin, suberine and waxes. Meanwhile, the expression of 702 genes was female-biased and largely enriched in pathways related to growth and development, such as carbohydrate metabolism, auxin signaling and cellular responses. In addition, 16.7% and 17.6% signals of selection were significantly detected in female- and male-biased genes, respectively, suggesting their non-negligible role in evolution. Our findings expanded the understanding of the molecular basis of intersexual differentiation and contribute to further research on sex evolution in dioecious plants.