A putative R3 MYB repressor is the candidate gene underlying atroviolacium, a locus for anthocyanin pigmentation in tomato fruit.

Xue Cao,Jianchang Gao,Guoping Wang,Xiaoxuan Wang,Xiaolin Liu,Xiaotian Wang,Tong Van Giang,Zejun Huang,Jing Wang,Yongchen Du,Zhengkun Qiu,Yanmei Guo

doi:10.1093/jxb/erx382

Abstract

Anthocyanins are potential health-promoting compounds in the human diet. The atv (atroviolacium) locus, derived from the wild tomato species Solanum cheesmaniae, has been shown to enhance anthocyanin pigmentation in tomato fruit when it co-exists with either the Aft (Anthocyanin fruit) or the Abg (Aubergine) locus. In the present study, the atv locus was fine-mapped to an approximately 5.0-kb interval on chromosome 7. A putative R3 MYB repressor was identified in this interval and is hereby designated as SlMYBATV. The allele of SlMYBATV underlying the atv locus harbored a 4-bp insertion in its coding region, which is predicted to result in a frame-shift and premature protein truncation. The other candidate R3 MYB and R2R3 MYB repressors of anthocyanin biosynthesis were also identified in tomato via a genome-wide search. Transcriptional analysis showed that most of the structural genes and several regulatory genes of anthocyanin biosynthesis were up-regulated in the tomato SlMYBATV mutant lines. These findings may facilitate the elucidation of the molecular mechanisms underlying anthocyanin pigmentation in tomato fruit and help in the marker-assisted selection of anthocyanin-enriched tomato cultivars.

Highlights

Anthocyanins belong to the bioactive family of compounds known as flavonoids
Anthocyanins are potential health-promoting compounds in the human diet (He and Giusti, 2010; Li et al, 2017), but none are present in cultivated tomato fruit (Gonzali et al, 2009)
The atv, Anthocyanin fruit (Aft), and Abg loci from wild tomato species can promote anthocyanin pigmentation in fruit, and the atv locus can dramatically increase the amount of anthocyanins in cultivated tomato fruit when it is combined with either the Aft or Abg locus (Mes et al, 2008)

Summary

Introduction

Anthocyanins belong to the bioactive family of compounds known as flavonoids. These play important biological roles in plants such as attracting pollinators and seed distributors, and providing protection against various stresses caused by pathogens, ultraviolet (UV), high-intensity light, wounding, cold temperature, and drought (Gould, 2004; Albert et al, 2009; Olsen et al, 2009; Zhang et al, 2013). Transcriptional regulation of anthocyanin biosynthesis is controlled by several classes of transcription factors (TFs), including MYB TFs, basic helix-loop-helix (bHLH) TFs, and WD-repeat (WDR) proteins. These TFs form a protein complex (MBW complex) that positively regulates the expression of structural genes (Bulgakov et al, 2017; Xu et al, 2015). In addition to the proteins that activate anthocyanin biosynthesis, two distinct groups of MYB TFs decrease anthocyanin production, namely R3-MYB and R2R3-MYB repressors, which respectively contain one or two repeats of the MYB domain region (Aharoni et al, 2001; Dubos et al, 2008; Matsui et al, 2008; Zhu et al, 2009; Paolocci et al, 2011; Albert et al, 2014)

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Conclusion