The ethylene-regulated expression of CS-ETR2 and CS-ERS genes in cucumber plants and their possible involvement with sex expression in flowers

It has been reported that ethylene production by cucumber plants is strongly related to the sex expression of their flowers. It has also been shown that both CS-ACS2 gene expression and ethylene evolution are much greater in gynoecious cucumber plants than monoecious ones. To investigate the action mechanism of ethylene in the induction of femaleness of cucumber flowers, we isolated three ethylene-receptor-related genes, CS-ETR1, CS-ETR2 and CS-ERS, from cucumber (Cucumis sativus L.) plants. Of these three genes, CS-ETR2 and CS-ERS mRNA accumulated more substantially in the shoot apices of the gynoecious cucumber than those of the monoecious one. Their expression patterns correlated with the expression of the CS-A CS2 gene and with ethylene evolution in the shoot apices of the two types of cucumber plants. Accumulation of CS-ETR2 and CS-ERS mRNA was significantly elevated by the application of Ethrel, an ethylene-releasing agent, to the shoot apices of monoecious cucumber plants. In contrast, the accumulation of their transcripts was lowered when aminoethoxyvinyl glycine (AVG), an inhibitor of ethylene biosynthesis, was applied to the shoot apices of gynoecious cucumber plants. Thus, the expression of CS-ETR2 and CS-ERS is, at least in part, regulated by ethylene. The greater accumulation of CS-ETR2 and CS-ERS mRNA in gynoecious cucumber plants may be due to the higher level of endogenous ethylene, which plays a role in the development of female flowers.