McMYB12 Transcription Factors Co-regulate Proanthocyanidin and Anthocyanin Biosynthesis in Malus Crabapple

Abstract

The flavonoid compounds, proanthocyanidins (PAs), protect plants from biotic stresses, contribute to the taste of many fruits, and are beneficial to human health in the form of dietary antioxidants. In this study, we functionally characterized two Malus crabapple R2R3-MYB transcription factors, McMYB12a and McMYB12b, which co-regulate PAs and anthocyanin biosynthesis. McMYB12a was shown to be mainly responsible for upregulating the expression of anthocyanin biosynthetic genes by binding to their promoters, but to be only partially responsible for regulating PAs biosynthetic genes. In contrast, McMYB12b showed preferential binding to the promoters of PAs biosynthetic genes. Overexpression of McMYB12a and McMYB12b in tobacco (Nicotiana tabacum) altered the expression of flavonoid biosynthetic genes and promoted the accumulation of PAs and anthocyanins in tobacco petals. Conversely, transient silencing their expression in crabapple plants, using a conserved gene region, resulted in reduced PAs and anthocyanin production a green leaf phenotype. Meanwhile, transient overexpression of the two genes and silenced McMYB12s in apple (Malus domestica) fruit had a similar effect as overexpression in tobacco and silenced in crabapple. This study reveals a new mechanism for the coordinated regulation of PAs and anthocyanin accumulation in crabapple leaves, which depends on an auto-regulatory balance involving McMYB12a and McMYB12b expression.

Apigenin produced by maize flavone synthase I and II protects plants against UV‐B‐induced damage

“…In flowers, leaves, and seeds of different plant species, flavones act as copigments by complexing with anthocyanins (Fossen et al, 2007;Goto & Kondo, 1991;Ishikura, 1981;Kalisz, Oszmiański, Hładyszowski, & Mitek, 2013;Shiono, Matsugaki, & Takeda, 2008;Tanaka & Brugliera, 2013;Tanaka, Sasaki, & Ohmiya, 2008). Moreover, association between anthocyanin and protoanthocyanidin accumulation has been recently reported in Malus crabapples, involving the same regulators (Tian et al, 2017). Noteworthy, anthocyanin and nonflavonoid compounds involved in defense against herbivores are controlled by the anthocyanin regulators, indicating that the same regulators can modulate different specialized metabolite pathways (Outchkourov et al, 2014).…”

Transcriptome Analysis Identifies Two Ethylene Response Factors That Regulate Proanthocyanidin Biosynthesis During Malus Crabapple Fruit Development

“…'Flame' tissue culture plants were harvested from one-yearold branches before spring bud germination, and the culturing conditions were as previously described (Tian et al, 2017).…”

“…Full-length RAP2-4 and RAV1 were cloned into a modified pBI101 vector using seamless cloning at the NdeI and KpnI sites. The PCR primers used are shown in Table S1 (Tian et al, 2016).…”

“…Recently, MdMYBPA1, a PA1-type MYB TF, was cloned from redfleshed apple; overexpressing MdMYBPA1 could promote PA accumulation in apple calli by binding the promoters of genes in the PA and anthocyanin biosynthetic pathways . In crabapple, McMYB12a and McMYB12b coordinately regulate PA biosynthesis by binding to the promoters of PA biosynthetic genes (Tian et al, 2016). Moreover, several MYB transcription factors, such as VvMYBC2-L1, VvMYBPA1, VvMYBPA2, and VvMYBPAR, have been shown to specifically regulate the PA biosynthetic pathway by significantly activating enzymes in the flavonoid pathway in grape (Vitis vinifera) (Huang et al, 2014;Koyama et al, 2014).…”

“…Crabapple (Malus) belongs to the Malus Mill family of Rosaceae and is represented by a large germplasm collection (Tian et al, 2011); its fruits produce abundant anthocyanins, flavonols, PAs, and phlorizin compounds. Procyanidin B1, procyanidin B2, epicatechin, and catechin are the main PA compounds in crabapple fruits (Tian et al, 2017;Li et al, 2019). This makes it a valuable model for studying the molecular mechanisms of PA biosynthesis.…”