MYB24 Negatively Regulates the Biosynthesis of Lignin and Capsaicin by Affecting the Expression of Key Genes in the Phenylpropanoid Metabolism Pathway in Capsicum chinense

Abstract

The wide application of pepper is mostly related to the content of capsaicin, and phenylpropanoid metabolism and its branch pathways may play an important role in the biosynthesis of capsaicin. The expression level of MYB24, a transcription factor screened from the transcriptome data of the pepper fruit development stage, was closely related to the spicy taste. In this experiment, CcMYB24 was cloned from Hainan Huangdenglong pepper, a hot aromatic pepper variety popular in the world for processing, and its function was confirmed by tissue expression characteristics, heterologous transformation in Arabidopsis thaliana, and VIGS technology. The results showed that the relative expression level of CcMYB24 was stable in the early stage of pepper fruit development, and increased significantly from 30 to 50 days after flowering. Heterologous expression led to a significant increase in the expression of CcMYB24 and decrease in lignin content in transgenic Arabidopsis thaliana plants. CcMYB24 silencing led to a significant increase in the expression of phenylpropanoid metabolism pathway genes PAL, 4CL, and pAMT; lignin branch CCR1 and CAD; and capsaicin pathway CS, AT3, and COMT genes in the placenta of pepper, with capsaicin content increased by more than 31.72% and lignin content increased by 20.78%. However, the expression of PAL, pAMT, AT3, COMT, etc., in the corresponding pericarps did not change significantly. Although CS, CCR1, and CAD increased significantly, the relative expression amount was smaller than that in placental tissue, and the lignin content did not change significantly. As indicated above, CcMYB24 may negatively regulate the formation of capsaicin and lignin by regulating the expression of genes from phenylpropanoid metabolism and its branch pathways.

Genetic characterization of a locus responsible for low pungency using EMS-induced mutants in Capsicum annuum L.

“…Phenylpropanoid metabolism might be connected to various secondary metabolite pathways, including the shikimate, quinate, flavonoid, and lignin pathways (Fraser and Chapple 2011 ). MYB24, a negative co-regulator of capsaicin and lignin biosynthesis, might play a role behind this connection of pathways (Yu et al 2023 ). Fatty acid biosynthesis is, however, thought to be more complex.…”

“…Similarly, several structural genes have been identified from the branched fatty acid pathway, including those encoding acyl carrier protein (ACL), acyl-ACP thioesterase (FatA), ketoacyl-ACP synthase (KAS), branched-chain amino acid aminotransferase (BCAT), and ketoacyl-ACP reductase (CaKR1) (Aluru et al 2003 ; Koeda et al 2019 ; Mazourek et al 2009 ). Furthermore, genes regulating capsaicinoid biosynthesis, such as transcription factor genes from the R2R3-MYB (Han et al 2019 ; Liu et al 2022 ; Sun et al 2019 ; Yu et al 2023 ; Zhu et al 2019 ) and WRKY families (Zhang et al 2023 ; Zhu et al 2019 ) participate in the regulatory mechanisms behind these two biosynthetic branches. Nonetheless, the functions of only a few genes in the pathway, such as Pun1 (also known as C ), pAMT , Pun3 (also known as CaMYB31 ), and CaKR1 , have been confirmed using natural loss-of-function variants.…”