The Capsicum MYB31 regulates capsaicinoid biosynthesis in the pepper pericarp

Pepper (Capsicum) are consumed worldwide as vegetables and food additives due to their pungent taste. Capsaicinoids are the bioactive compounds that confer the desired pungency to pepper fruits. Capsaicinoid biosynthesis was thought to occur exclusively in fruit placenta. Recently, biosynthesis in the pericarp of extremely pungent varieties was discovered, however, the mechanism of capsaicinoid biosynthesis regulation in the pericarp remains largely unknown. Here, the capsaicinoid contents of placenta and pericarp were analyzed. The results indicated that the Capsicum chinense pericarp accumulated a vast amount of capsaicinoids. Expression of the master regulator MYB31 and capsaicinoid biosynthesis genes (CBGs) were significantly upregulated in the pericarp in C. chinense accessions compared to accessions in other tested species. Moreover, in fruit of extremely-pungent 'Trinidad Moruga Scorpion' (C. chinense) and low-pungent '59' inbred line (C. annuum), the capsaicinoid accumulation patterns in the pericarp were consistent with expression levels of CBGs and MYB31. Silencing MYB31 in 'Trinidad Moruga Scorpion' pericarp leads to a significantly decreased CBGs transcription level and capsaicinoids content. Taken together, our results provide insights into the molecular mechanism arising from the expression of MYB31 in the pericarp that results in exceedingly hot peppers.