Two R2R3‐MYB proteins are broad repressors of flavonoid and phenylpropanoid metabolism in poplar

Abstract

The phenylpropanoid pathway leads to the production of many important plant secondary metabolites including lignin, chlorogenic acids, flavonoids, and phenolic glycosides. Early studies have demonstrated that flavonoid biosynthesis is transcriptionally regulated, often by a MYB, bHLH, and WDR transcription factor complex. In poplar, several R2R3 MYB transcription factors are known to be involved in flavonoid biosynthesis. Previous work determined that poplar MYB134 and MYB115 are major activators of the proanthocyanidin pathway, and also induce the expression of repressor-like MYB transcription factors. Here we characterize two new repressor MYBs, poplar MYB165 and MYB194, paralogs which comprise a subgroup of R2R3-MYBs distinct from previously reported poplar repressors. Both MYB165 and MYB194 repressed the activation of flavonoid promoters by MYB134 in transient activation assays, and both interacted with a co-expressed bHLH transcription factor, bHLH131, in yeast two-hybrid assays. Overexpression of MYB165 and MYB194 in hybrid poplar resulted in greatly reduced accumulation of several phenylpropanoids including anthocyanins, proanthocyanidins, phenolic glycosides, and hydroxycinnamic acid esters. Transcriptome analysis of MYB165- and MYB194-overexpressing poplars confirmed repression of many phenylpropanoid enzyme genes. In addition, other MYB genes as well as several shikimate pathway enzyme genes were downregulated by MYB165-overexpression. By contrast, leaf aromatic amino acid concentrations were greater in MYB165-overexpressing poplars. Our findings indicate that MYB165 is a major repressor of the flavonoid and phenylpropanoid pathway in poplar, and may also affect the shikimate pathway. The coordinated action of repressor and activator MYBs could be important for the fine tuning of proanthocyanidin biosynthesis during development or following stress.

MYB transcription factor CiMYB42 regulates limonoids biosynthesis in citrus

“…Such differential regulation of the triterpenoid pathway has recently been reported in W. somnifera by the WsWRKY1 [30], in tomato by the GAME9 [46] In general, one target genes were regulated by several TFs, in the same way, one TF also involved in multiple biosynthetic step. Such result was also reported by previous observations [48,49]. The fact that CiMYB42-transgenics effectively altered limonoids accumulation give us a better understanding of the molecular mechanisms that control the citrus limonoids biosynthesis.…”

Integrative Transcriptomic and Metabolic Analyses Provide Insights into the Role of Trichomes in Tea Plant (Camellia Sinensis)

“…It has been demonstrated that the phenylpropanoid and flavonoid biosynthesis pathways are regulated by different TF classes, such as MYB, WRKY, NAC, and bHLH, through modulating the expression of the related structural genes. Among these TFs, MYB-bHLH-WD40 repeat (MBW) ternary complexes have been illustrated to be one of the most important regulatory components that are involved in phenylpropanoid and flavonoid biosynthesis [52][53][54][55][56]. To date, certain MBW component genes that regulate flavonoid biosynthesis have been identified in tea plants.…”

R2R3‐MYB transcription factor MYB6 promotes anthocyanin and proanthocyanidin biosynthesis but inhibits secondary cell wall formation in Populus tomentosa

“…In the poplar genome, 192 R2R3 MYB transcription factors have been predicted (Wilkins et al ., ), but only a small number of MYB members, including MYB134 (Mellway et al ., ), MYB182 (Yoshida et al ., ), MYB119 (Cho et al ., ), MYB57 (Wan et al ., ), MYB115 (James et al ., ; Wang et al ., ), PtrMYB012 (Kim et al ., ), and MYB165 and MYB192 (Ma et al ., ), have been found to regulate the flavonoid biosynthetic pathway. In the study reported herein, we isolated and characterized the poplar transcription factor MYB6, which shows high homology in amino acid sequences to other MYB5‐like transcription factors.…”