An Ethylene-inhibited NF-YC Transcription Factor RhNF-YC9 Regulates Petal Expansion in Rose

The speed of flower opening is closely related to their ornamental period. Ethylene functions as a negative regulator involved in the regulation of the petal expansion process. In this study, we isolated a NF-YC transcription factor gene, RhNF-YC9, from rose petals. RhNF-YC9 expression was induced at the early stages of flower opening but was inhibited by ethylene treatment. Silencing RhNF-YC9 decreased the speed of petal expansion from stage 2 to stage 5. The expressions of 11 cell expansion-related genes involved in cell wall loosening, cell turgor modulation, and cytoskeleton remodeling were significantly down-regulated in RhNF-YC9-silenced petals. We also found that silencing RhNF-YC9 decreased the expression of gibberellin acid (GA) biosynthetic gene RhGA20ox while significantly increasing the transcripts of GA catabolic gene RhGA2ox, reducing the accumulation of GA₄ and GA₇. The influence of ethylene treatment on the expression of RhGA20ox and RhGA2ox showed the same trend. These results together suggested that RhNF-YC9 positively regulated the speed of petal expansion and mediated the crosstalk between ethylene and GA. Our findings revealed a new insight into the function of NF-YC transcription factors involved in ethylene-regulated petal expansion.