Isolation of an ethylene-responsive gene (ERAF16) for a putative methyltransferase and correlation of ERAF16 gene expression with female flower formation in cucumber plants (Cucumis sativus)

Ethylene regulates sex expression in cucumber plants (Cucumis sativus L.). To clarify ethylene-mediated regulation of sex expression, we previously used differential display technology to identify 20 ethylene-responsive genes in the apices of cucumber plants. In this study, we report the analysis of the full-length cDNA from clone #16 and its corresponding gene (designated as ERAF16 ), which encodes a methyltransferase. This type of methyltransferase has recently been identified, and some of them methylate signalling molecules in plants, which include salicylic acid and jasmonic acid. However, the substrate of the ERAF16 protein has not been revealed. We examined the ERAF16 expression pattern using RNA gel blot analysis of total RNA preparations from the apices of a monoecious cucumber (cv. Shimoshirazu-jibai) and a gynoecious cultivar (Rensei). The levels of ERAF16 expression in these cultivars were correlated with the development of female flowers. The induction of ERAF16 transcription by ethephon occurred within 4 h of the start of treatment. The expression of ERAF16 in immature floral buds of the gynoecious cultivar was stronger than in those of the monoecious cultivar. These results suggest that ERAF16 is included in the ethylene-induced formation of female flowers. However, ERAF16 was expressed in opened flowers and vegetative tissues. Therefore, we speculate that the role of ERAF16 protein varies, depending on the tissue and developmental stage.