Unveiling phenylpropanoid regulation: the role of DzMYB activator and repressor in durian (Durio zibethinus) fruit

Abstract

The durian fruit has high nutritional value attributed to enriched bioactive compounds, including phenolics, carotenoids, and vitamins. While various transcription factors (TFs) govern phenylpropanoid biosynthesis, MYB TFs emerge as pivotal players in regulating key genes within this pathway. This study delves into the identification of additional candidate MYB TFs from the transcriptome database of the Monthong cultivar at five developmental/postharvest ripening stages. Candidate transcriptional activators were discerned among MYBs upregulated during the ripe stage, based on the positive correlation observed between flavonoid biosynthetic genes and flavonoid contents in ripe durian pulps. Conversely, MYBs downregulated during the ripe stage were considered candidate repressors. The study focused on a candidate MYB activator (DzMYB2) and a candidate MYB repressor (DzMYB3) for functional characterization. LC–MS/MS analysis in Nicotiana benthamiana leaves transiently expressing DzMYB2 revealed increased phenolic compound contents compared to those expressing green fluorescence protein controls, while transiently expressed DzMYB3 led to a decrease in phenolic compounds. Furthermore, it was demonstrated that DzMYB2 controls phenylpropanoid biosynthesis in durian by regulating the promoters of various biosynthetic genes, including phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR). Simultaneously, DzMYB3 regulates the promoters of PAL, 4-coumaroyl-CoA ligase (4CL), CHS, and CHI, resulting in the activation and repression of gene expression, respectively. Additionally, it was discovered that DzMYB2 and DzMYB3 could bind to another TF, DzbHLH1, in the regulation of flavonoid biosynthesis. These findings enhance our understanding of the pivotal role of MYB proteins in regulating the phenylpropanoid pathway in durian pulps.