A MYB/bHLH complex regulates tissue‐specific anthocyanin biosynthesis in the inner pericarp of red‐centered kiwifruit Actinidia chinensis cv. Hongyang

Abstract

These authors contributed equally to this work. SUMMARYMany Actinidia cultivars are characterized by anthocyanin accumulation, specifically in the inner pericarp, but the underlying regulatory mechanism remains elusive. Here we report two interacting transcription factors, AcMYB123 and AcbHLH42, that regulate tissue-specific anthocyanin biosynthesis in the inner pericarp of Actinidia chinensis cv. Hongyang. Through transcriptome profiling analysis we identified five MYB and three bHLH transcription factors that were upregulated in the inner pericarp. We show that the combinatorial action of two of them, AcMYB123 and AcbHLH42, is required for activating promoters of AcANS and AcF3GT1 that encode the dedicated enzymes for anthocyanin biosynthesis. The presence of anthocyanin in the inner pericarp appears to be tightly associated with elevated expression of AcMYB123 and AcbHLH42. RNA interference repression of AcMYB123, AcbHLH42, AcF3GT1 and AcANS in 'Hongyang' fruits resulted in significantly reduced anthocyanin biosynthesis. Using both transient assays in Nicotiana tabacum leaves or Actinidia arguta fruits and stable transformation in Arabidopsis, we demonstrate that co-expression of AcMYB123 and AcbHLH42 is a prerequisite for anthocyanin production by activating transcription of AcF3GT1 and AcANS or the homologous genes. Phylogenetic analysis suggests that AcMYB123 or AcbHLH42 are closely related to TT2 or TT8, respectively, which determines proanthocyanidin biosynthesis in Arabidopsis, and to anthocyanin regulators in monocots rather than regulators in dicots. All these experimental results suggest that AcMYB123 and AcbHLH42 are the components involved in spatiotemporal regulation of anthocyanin biosynthesis specifically in the inner pericarp of kiwifruit.

Annotation of genes involved in high level of dihydromyricetin production in vine tea (Ampelopsis grossedentata) by transcriptome analysis

“…In addition, it has been demonstrated that many transcription factors (TFs), including MYBs, NACs, basic helix-loop-helix (bHLH), WD40s, and WRKYs, are involved in the regulation of metabolic biosynthesis in plants and the regulatory pattern of these transcription factors is usually tissue-specific [43][44][45][46][47]. MYBs play a critical role in fruit and flower color formation via the regulation of structural genes in the flavonoid or anthocyanin biosynthetic pathway [43][44][45][48][49][50][51].…”

“…Additionally, GmMYB58 and GmMYB205 were demonstrated to be seed-specific activators for isoflavonoid biosynthesis in Glycine max [45]. Numerous reports have indicated that transcription factors from MYB, bHLH, and WD-repeat (WDR) families generally form a ternary complex (MBW complex), which coordinately activates or represses multiple genes in the regulatory network to influence metabolic biosynthesis [46,47,53,54]. Our study has identified a number of transcription factors including MYB, bHLH, and bZIP genes from vine tea (Additional file 11: Table S5).…”

Systematic analysis of the basic/helix-loop-helix (bHLH) transcription factor family in pummelo (Citrus grandis) and identification of the key members involved in the response to iron deficiency

“…As an essential superfamily of TFs, bHLH proteins participate in regulating of a series of biological and developmental processes, such as flowering [19], root development [20], seed germination [21], anthocyanin or flavonoid metabolism [22][23][24], hormonal signaling regulation [25,26], as well as biotic and abiotic stresses responses [14,[27][28][29]. Under Fe deficiency stress, bHLHs have been shown to play a predominant regulatory role.…”

Metabolomics Study of Flavonoids and Anthocyanin-Related Gene Analysis in Kiwifruit (Actinidia chinensis) and Kiwiberry (Actinidia arguta)

“…The genetic mechanisms underlying anthocyanin accumulation have been repeatedly studied in many horticultural crops via transcriptome analysis (El-Sharkawy et al 2015;Cao et al 2018;Lin et al 2018;Bai et al 2017). Although transcriptomic studies were conducted on kiwifruit and kiwiberry, and some candidate genes were screened out (Li et al 2018a;Li et al 2018b;Li et al 2015b;Wang et al 2019;Peng et al 2019), these results were mainly based on limited numbers of anthocyanidin-related metabolites. Furthermore, pigmented kiwifruit and kiwiberry also showed distinct pigmentation patterns.…”