CitUNE1 inhibits (+)-valencene synthesis by regulating CsTPS1 in 'Newhall' sweet orange

(+)-Valencene is the characteristic volatile compound in 'Newhall' sweet orange, and CsTPS1 is the gene that codes for the (+)-valencene synthase. Here, four transcription factors, including CitUNE1, CitUNE3, CitSCL1, and CitSCL13, were screened as candidate proteins by yeast one-hybrid (Y1H) library screening with CsTPS1 promoter as the bait. Among them, CitUNE1 bound to the G-box on the promoter of CsTPS1 and suppressed CsTPS1 expression, confirmed by Y1H, dual-luciferase assay, point-mutation experiment and EMSA. The expression pattern of CitUNE1 showed a negative correlation with both the content of (+)-valencene and CsTPS1 transcripts level, both during fruit development and after ethylene treatment. Furthermore, the role of CitUNE1 in (+)-valencene synthesis was confirmed using the transient over-expression and silencing in 'Newhall' sweet orange. Transient over-expression of CitUNE1 inhibited CsTPS1 expression and reduced the accumulation of (+)-valencene, while silencing of CitUNE1 induced CsTPS1 expression and triggered (+)-valencene synthesis in 'Newhall' sweet orange.