Abstract
ACC synthase (ACS) is the rate-limiting enzyme of the ethylene biosynthesis pathway. We reported that LeACS2, a wound-inducible ACS in tomato, is phosphorylated in vivo, and suggested the possibility that phosphorylation regulates protein stability. In this presentation, we demonstrate phosphorylation/dephosphorylation of LeACS2 regulates its stability. Pulse-chase experiments coupled with treatment with protein kinase/phosphatase inhibitors demonstrated LeACS2 is stabilized by phosphorylation and immediately degraded after dephosphorylation. LeACS2 amount affected by the protein kinase/phosphatase inhibitors significantly influenced cellular ACS activity, ACC content, and ethylene production levels in fruit, suggesting that post-translational regulation by phosphorylation plays an important role in the control of ethylene production as well as in transcriptional regulation. Furthermore, we isolated LeCDPK2 as the protein kinase that phosphorylates LeACS2 at Ser-460. LeACS2 was immediately phosphorylated after translation by CDPK and MAP kinase at different sites in response to wound signaling and almost all functional LeACS2 molecules are in their phosphorylated form in the cell.
