Isolation of a MADS-box gene (ERAF17) and correlation of its expression with the induction of formation of female flowers by ethylene in cucumber plants (Cucumis sativus L.)

Ethylene regulates sex expression in cucumber (Cucumis sativus L.) plants. When the apices of monoecious cucumber seedlings (cv. Shimoshirazu-jibai) were treated with the ethylene-releasing compound, ethephon, female flowers were induced at the nodes. To clarify the action of ethylene in the regulation of sex expression, we attempted to isolate genes whose expression changed during induction of the formation of female flowers at the apices of these cucumber plants upon treatment with ethephon. Using the differential-display method, we identified 20 clones (#1 to #20) that reflected differences in the accumulation of transcripts in apices treated or not treated with ethephon. Sequence analysis of cDNA fragments revealed that the cDNA #17 had the sequence of a MADS-box gene. We isolated the full-length cDNA and showed that it included both a MAIDS box and a K box, and the corresponding gene was designated ERAF17. We examined the expression of ERAF17 in the apices of cv. Shimoshirazu-jibai and in those of a gynoecious cultivar (Rensei). In these cultivars, the timing and levels of expression of the ERAF17 transcript were correlated with the development of female flowers. Induction of the synthesis of the ERAF17 transcript by ethephon occurred within 4 h of the start of treatment and continued for 4 days at least. Expression of ERAF17 at apices was localized in the floral buds of the gynoecious cultivar, and expression was maintained in female flowers thorough their development. Our results suggest that the induction of the formation of female flowers by ethylene might be regulated by the expression of ERAF17 in floral buds at the apices of cucumber plants and that expression of this gene might also be involved in the development of female flowers.