BrLETM2 Protein Modulates Anthocyanin Accumulation by Promoting ROS Production in Turnip (Brassica rapa subsp. rapa).

Hyon Dok Song,Yuhua Li,Nam Hyok Mun,Pyol Kim,Saneyuki Kawabata,Jianfei Yang,Yunzhu Chen,Bowei Chen,Yu Wang

doi:10.3390/ijms22073538

Abstract

In ‘Tsuda’ turnip, the swollen root peel accumulates anthocyanin pigments in a light-dependent manner, but the mechanism is unclear. Here, mutant g120w which accumulated extremely low levels of anthocyanin after light exposure was identified. Segregation analysis showed that the anthocyanin-deficient phenotype was controlled by a single recessive gene. By using bulked-segregant analysis sequencing and CAPS marker-based genetic mapping analyses, a 21.6-kb region on chromosome A07 was mapped, in which a calcium-binding EF hand family protein named BrLETM2 was identified as the causal gene. RNA sequencing analysis showed that differentially expressed genes (DEGs) between wild type and g120w in light-exposed swollen root peels were enriched in anthocyanin biosynthetic process and reactive oxygen species (ROS) biosynthetic process GO term. Furthermore, nitroblue tetrazolium (NBT) staining showed that the ROS level decreased in g120w mutant. Anthocyanins induced by UV-A were abolished by the pre-treatment of seedlings with DPI (an inhibitor of nicotinamide adenine nucleoside phosphorylase (NADPH) oxidase) and decreased in g120w mutant. These results indicate that BrLETM2 modulates ROS signaling to promote anthocyanin accumulation in turnip under UV-A and provides new insight into the mechanism of how ROS and light regulate anthocyanin production.

Highlights

Anthocyanins are polyphenolic secondary metabolites that are ubiquitous in the plant kingdom
In this study, starting from the genetic analysis of the turnip mutant with anthocyanin-deficiency phenotype, we identified an LETM protein that controls the anthocyanin pigmentation of turnip swollen root peel and elucidated the mechanism of its action after UV-A exposure
We demonstrated that BrLETM2 is a positive regulator of anthocyanin pigmentation, which can be induced by UV-A and promote the reactive oxygen species (ROS) production

Summary

Introduction

Anthocyanins are polyphenolic secondary metabolites that are ubiquitous in the plant kingdom. They play a role in reproduction, by attracting pollinators and seed dispersers, and in protection against various abiotic and biotic stresses [1]. Anthocyanin-enriched fruits and vegetables are considered to be healthy and delectable, which are important target traits in horticulture plants breeding programs. Anthocyanins are produced from a well-characterized pathway that contains key structural genes: CHALCONE SYNTHASE (CHS), CHALCONE ISOMERASE (CHI), FLAVANONE. The regulation of anthocyanin biosynthesis pathway is mediated by the regulatory. MBW complex, in which R2R3-MYB, basic helix-loop-helix (bHLH), and WD40-repeat (WDR) transcription factors (TFs) are involved [2]. In Arabidopsis, the key components of the complex—R2R3-MYB protein PRODUCTION OF ANTHOCYANIN PIGMENT1

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