SnRK1 acts upstream ofPRODUCTION OF ANTHOCYANIN PIGMENT1, contributing to fine-tuning flavonoid biosynthesis during acclimation

Abstract

AbstractIn land plants, one of the processes vital to cope with environmental changes is the accumulation of photoprotective flavonoids such as flavonols and anthocyanins. The inactivation of SUCROSE NON-FERMENTING1 RELATED PROTEIN KINASE1 (SnRK1), which acts in a chloroplast-derived sugar signalling pathway, permits the activation of flavonoid biosynthesis in high-light. The present study provides genetic evidence that SnRK1 acts upstream ofPRODUCTION OF ANTHOCYANIN PIGMENT1 (PAP1), encoding a crucial transcription factor that activates the anthocyanin branch of flavonoid biosynthesis during high-light acclimation. A time-resolved expression analysis indicates a two-step suppression of MYB LIKE2 (MYBL2), a repressor of anthocyanin production, involving SnRK1 inactivation for stable anthocyanin accumulation during prolonged high-light exposure. Furthermore, overexpression ofPAP1resulted in the marked suppression ofMYB11, MYB12andMYB111andFLAVONOL SYNTHASE1, initiating the flavonol branch of the pathway. Analysis of a flavonoid-deficientCHALCONE SYNTHASEmutant overexpressingPAP1suggests that regulation of flavonoid biosynthesis is independent of flavonoid intermediates and end products but PAP1-dependent. It is proposed that PAP1 suppresses the flavonol branch by an as yet unknown mechanism, thereby promoting the consumption of carbon building blocks for anthocyanin production to permit the fine-tuning of the pathway.