CaMYB31, an R2R3-MYB transcription factor, regulates the capsaicinoid biosynthetic pathway in chili pepper fruits and is regulated by plant hormones, wounding,

The MYB transcription factor family is very large and functionally diverse in plants, however, only a few members of this family have been reported and characterized in chili pepper (Capsicum spp.). In the present study, we performed genome-wide analyses of the MYB family in Capsicum annuum, including phylogenetic relationships, conserved domain, gene structure organization, motif protein arrangement, chromosome distribution, chemical properties predictions, RNA-seq expression, and RT-qPCR expression assays. A total of 235 non-redundant MYB proteins were identified from C. annuum, including R2R3-MYB, 3R-MYB, atypical MYB, and MYB-related subclasses. The sequence analysis of CaMYBs compared with other plant MYB proteins revealed gene conservation, but also potential specialized genes. Tissue-specific expression profiles showed that CaMYB genes were differentially expressed, suggesting that they are functionally divergent. Furthermore, the integration of our data allowed us to propose strong CaMYBs candidates to be regulating phenylpropanoid, lignin, capsaicinoid, carotenoid, and vitamin C biosynthesis, providing new insights into the role of MYB transcription factors in secondary metabolism. This study adds valuable knowledge about the functions of CaMYB genes in various processes in the Capsicum genus.

Pepper ( Capsicum L.) is a major vegetable and spice crop worldwide. Global production of both fresh and dried fruit continues to increase steadily in terms of area harvested and yield. Various topics are addressed in this review, including recent additions to and clarification of Capsicum taxonomy, genetic resources of Capsicum , cytogenetic studies, the current status of our understanding of the mechanisms affecting the biosynthesis of capsaicinoids, the use of gene mutations to elucidate carotenoid biosynthetic pathways and their regulation, and recent advances in whole-genome sequencing and assembly.

The effects of AT3-gene silencing on the expression of genes involved in capsaicinoid biosynthesis was investigated in chili pepper (Capsicum annuum L.) cv. Tampiqueño 74 fruits. Seeds were germinated and seedlings were grown in a greenhouse until they produced fruits. Capsaicinoids (capsaicin and dihydrocapsaicin) content and AT3 gene expression were determined in placenta tissue from fruits at 10, 20, 30, 40, 50, and 60 days post-anthesis (DPA). Capsaicin was more abundant than dihydrocapsaicin and both exhibited a similar accumulation pattern at different developmental stages starting at 20 DPA, reaching maximum values at 30 – 40 DPA before decreasing. AT3 gene expression, as measured by quantitative RT-PCR, was positively correlated with capsaicinoid accumulation; AT3 transcripts were detected at 20 DPA, achieved a maximum at 30 – 40 DPA and then decreased. The Tampiqueño 74 seedlings were infected with Agrobacterium tumefaciens bearing a pTRV2-AT3 construct to induce virus-mediated silencing. Fruits were harvested at 40 DPA, and capsaicinoid content and AT3 gene expression were carried out in placenta tissue. A reduction of 81.1 % in AT3 expression and also in capsaicin (89.6 %) and dihydrocapsaicin (87.7 %) content was recorded in the AT3-gene silenced chili pepper plants. Furthermore, fruits from the AT3-silenced plants compared to the non-infected control plants showed a statistically significant reduction in the expression of genes involved in capsaicinoid biosynthesis [pAmt (89.4 %), BCAT (68.8 %), Kas (90.4 %) and Acl (58.6 %)]. These data indicate that AT3 silencing had a negative effect on the transcription of genes involved mainly in the branched-chain fatty acid pathway of capsaicinoid biosynthesis.

A detailed screen of the Solanum lycopersicum cv M82 × Solanum pennellii ac. LA716 introgression line (IL) population revealed ILs with altered leaf trichome de