AcWRKY75 and AcMYB108 mediated ABA-GA antagonism in the regulation of pineapple internal browning.

Gibberellic acid (GA) and abscisic acid (ABA) antagonistically regulate various biological processes, but whether they antagonistically regulate tissue browning remains unclear. Here, we showed that ABA reduced pineapple internal browning (IB) by inhibiting phenolic biosynthesis via downregulating AcWRKY75 and AcMYB108, while GA3 had the opposite effects. Biochemical evidences showed AcWRKY75 and AcMYB108 directly bound to and activated the phenolic biosynthetic gene Ac4CL5. Interestingly, AcMYB108 directly bound to AcWRKY75 promoter and activated its transcription, indicating that AcMYB108 functions upstream of AcWRKY75. Arabidopsis overexpressing AcWRKY75, AcMYB108 or Ac4CL5 displayed promoted phenolic biosynthesis. AcWRKY75 transient overexpression in pineapple reduced, while its transient silencing enhanced IB and phenolic accumulation. Transcriptomic profiling of pineapples transiently overexpressing and silencing AcWRKY75 revealed that plant hormone signal transduction and phenylpropanoid biosynthesis were among the most significantly enriched KEGG pathways, suggesting the role of AcWRKY75 in regulating phenolic biosynthesis involves plant hormones. ABA suppressed and GA3 enhanced enzyme activity of GUS transiently expressed in tobacco driven by promoter of AcWRKY75, AcMYB108 or Ac4CL5. This work suggests that WRKY75 and MYB108 are involved in antagonism between ABA and GA in regulating IB, and may shed novel insight into the role of ABA and GA in regulating plant tissue browning.