Transcriptional and Post-transcriptional Regulation of Ethylene Biosynthesis by Salicyclic Acid in Kiwifruit

Levels of ethylene, implicated in a diverse array of plants for inducing fruit ripening, is influenced by genetic and environmental factors, such as the other plant hormones. Among these, salicylic acid (SA) has been demonstrated to inhibit ethylene biosynthesis in fruit, yet the underlying regulatory mechanisms remains elusive. Here, we showed that treatment with exogenous ASA (acetylsalicylic acid) dramatically reduced ethylene production, as well as activities of ACC synthase (ACS) and ACC oxidase (ACO), in kiwifruit tissues. Comparative transcriptome analysis indicated the differential expression of ethylene biosynthetic genes (AdACS1/2 and AdACO5). A screen of transcription factors indicated that AdERF105L and AdWRKY29 were ASA-responsive regulators of AdACS1/2 and AdACO5, respectively. In addition to these genes, AdACS3 and AdACO3 were abundantly expressed in both ASA-treated and control tissues. AdACS3 protein was phosphorylated and stabilized by AdMPK16, a mitogen-activated protein kinase; while AdACO3 activity was enhanced by AdAP, an aspartic peptidase. Exogenous ASA down-regulated AdMPK16 and AdAP, thereby influencing ethylene biosynthesis at a post-transcriptional level. These findings propose a multidimensional system for SA-inhibition on ethylene biosynthesis, inducing differential expression of some ethylene biosynthesis genes, as well as differential effects on protein activity on other targets. SummaryInvolvement of transcription factors, protein kinase and aspartic peptidase in synergistically regulating salicylic acid-induced ethylene decrease in kiwifruit flesh