Tulip transcription factor TgWRKY75 activates salicylic acid and abscisic acid biosynthesis to synergistically promote petal senescence

WRKY transcription factors (TFs) play a central role in controlling plant organ senescence. However, it is unclear whether and how WRKY TFs regulate petal senescence in tulip, a widely used ornamental plant. In the present study, we report that TgWRKY75 promoted petal senescence by enhancing abscisic acid (ABA) as well as salicylic acid (SA) synthesis in tulip and in Arabidopsis. The expression level of TgWRKY75 was up-regulated in senescent petals and exogenous ABA or SA treatment induced its expression. The endogenous contents of ABA and SA significantly increased during petal senescence or depended upon TgWRKY75 overexpression. Interestingly, two SA synthesis-related genes TgICS1 and TgPAL1 were identified as direct targets of TgWRKY75 through binding to their promoters. In parallel, TgWRKY75 activated the expression of ABA biosynthesis-related gene TgNCED3 via directly binding to its promoter region. Site mutation of the W-box core motif located on the promoters of TgICS1, TgPAL1 and TgNCED3 eliminated their interactions with TgWRKY75. In summary, this study demonstrated a dual regulation of ABA and SA biosynthesis by TgWRKY75, which unveiled a synergistic process of tulip petal senescence through a feedback regulation between TgWRKY75 and ABA/SA accumulation.