Identification of candidate genes associated with sex differentiation and determination of gender diphasic plant Lilium apertum (Liliaceae)

Gender diphasy is a very rare sexual strategy in flowering plant, in which each individual can reproduce as either male or female phase plants over years according to circumstances. However, the limited genetic information related to the molecular basis of sex determination remains largely unknown. Here, comparative transcriptome analysis on hermaphroditic and male flowers at a critical sex divergence stage was performed to identify sex-biased differentially expressed genes (DEGs) in a gender diphasic lily species Lilium apertum. A total of 2,338 unigenes were identified as DEGs of which the top match specie is oil palm whose gender affected by environmental conditions, such as water deficit. Among seven pathways enriched in KEGG enrichment analysis, many DEGs involved in photosynthesis, protein processing in endoplasmic reticulum, and zeatin biosynthesis were up-regulated in hermaphroditic flower. While many DEGs involved in phenylpropanoid biosynthesis, plant-pathogen interaction, cutin, suberine and wax biosynthesis, and starch and sucrose metabolism were up-regulated in male flower. Moreover, the significant higher level of zeatin (ZT) in hermaphroditic flower and available nitrogen (N) that is kind of necessary synthetic substrate of cytokinin (CK) in hermaphroditic plants may be attributed to, at least in part, sex differentiation of L. apertum. Additionally, the significant sex-biased expression of two important drought-associated proteins, late embryogenesis abundant (LEA) proteins and heat-shock proteins (HSPs), could be considered as marker to distinguish the hermaphroditic and male flower at earlier developmental stage. We hypothesize that N deficiency or/and water loss signaling induced apoptosis and arrested the pistil development, in turn, affected the sex divergence of L. apertum. Our results demonstrated, for the first time in well-documented gender diphasic plants, that genes related to many pathways might regulate sex changes triggered by environmental conditions.