The MADS-box transcription factor CmFYF promotes the production of male flowers and inhibits the fruit development in melon (Cucumis melo L.).

The FOREVER YOUNG FLOWER (FYF/AGL42) gene plays an important role in regulating the flower development especially the flowering time, and senescence and abscission of floral organs. Melon is an important horticultural crop, and the flower development has an important influence on pollination, fertilization and final fruit yield. However, the function of FYF homolog is still unknown in melon. In this study, the characteristic of melon CmFYF was analyzed combining with molecular biology, developmental biology and biochemical tools. CmFYF was present in all detected tissues of melon, but its expression level was significantly higher in shoot apex of lateral branches and male flowers than that in other tissues. Subcellular localization revealed that CmFYF was located in the nucleus. CmFYF was able to respond to multiple hormone and environmental signals including GA3, SA, MeJA, cold and drought. Ectopic expression of CmFYF in Arabidopsis resulted in the early flowering phenotype and increased plant height, but had no effect on the flower organs or fruits development. In melon, overexpression of CmFYF increased the number of male flowers, but inhibited the size of fruit. These results suggested that CmFYF of melon was partially equivalent to AtFYF of Arabidopsis. Further biochemical analyses indicated that CmFYF directly interacted with CmAGb (a homolog of Arabidopsis AGAMOUS), CmKNAT7 (KNOTTED-LIKE HOMEOBOX OF ARABIDOPSIS THALIANA 7) and itself at the protein level. Therefore, this study enriched the function of FYF homologs and revealed a preliminary molecular mechanism underlying the male flower production and fruit development in melon.