High Temperature Induced Anthocyanin Inhibition and Active Degradation in Malus profusion.

Bachir Daoura Goudia,Fangwang Ma,Rana Naveed Ur Rehman,Pengmin Li,Yaohua You,Lei Zhang,Abdul Rehman Khan

doi:10.3389/fpls.2017.01401

Abstract

The red fleshed fruits of Malus profusion represent gradual color loss during high temperature in summer, potentially due to active degradation of anthocyanin. The objective of this study was to examine both physiological and molecular evidence of anthocyanin degradation. Malus crabapple fruits were exposed to either room temperature (RT = 18 ± 2°C: 25 ± 2°C) or high temperature (HT = 33 ± 2°C: 25 ± 2°C) regimens (12 h: 12 h) under hypoxic (2%) or normoxic (21%) oxygen levels. The results showed that the concentration of cyanidin 3-galactoside (cy-3-gal) was dramatically reduced following HT treatments due to a significant down-regulation of anthocyanin biosynthetic genes (MpCHS, MpDFR, MpLDOX, MpUFGT, and MpMYB10). Among other repressor MYBs, MpMYB15 expression was high following HT treatment of the fruit. HT led to the generation of a substantial concentration of H2O2 due to enhanced activities of superoxide dismutase (SOD), methane dicarboxylic aldehyde (MDA) content and cell sap pH value. Similarly, transcript levels of MpVHA-B1 and MpVHA-B2 were reduced which are involved in the vacuolar transportation of anthocyanin. The enzymatic degradation of anthocyanin was eventually enhanced coupled with the oxidative activities of peroxidase (POD) and H2O2. Conversely, the RT treatments potentially enhanced anthocyanin content by stabilizing physiological attributes (such as MDA, H2O2, and pH, among others) and sustaining sufficient biosynthetic gene expression levels. Quantitative real-time PCR analysis indicated that the transcription of MpPOD1, MpPOD8 and MpPOD9 genes in fruit tissues was up-regulated due to HT treatment and that hypoxic conditions seems more compatible with the responsible POD isoenzymes involved in active anthocyanin degradation. The results of the current study could be useful for understanding as well as elucidating the physiological phenomenon and molecular signaling cascade underlying active anthocyanin degradation in Malus crops.

Highlights

Anthocyanins are colored pigments that are ubiquitous in plants and often transitorily accumulated in the peripheral layer of mesophyll tissues (Steyn et al, 2002)
The biosynthesis of anthocyanin occurs via an intricate phenylpropanoid pathway which is predominantly controlled by a plethora of structural genes [such as chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR), leucoanthocyanidin oxygenase (LDOX), and UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT), among others] and a ternary complex of transcription factors (TFs) known as MYB-bHLH-WD40 (MBW) (Feng et al, 2013; Albert et al, 2014)
Regarding the RT treatments, anthocyanin accumulation was significantly enhanced, while the transcript levels of biosynthetic genes were not significant at 0 day (Figures 3B,D,E). This phenomenon might be due to improved pigment stability at room temperature, since in orchards, fruits are exposed to abbreviated heat stress at noon and a net anthocyanin at day 0 counterbalance by simultaneous biosynthesis and active degradation

Summary

Introduction

Anthocyanins are colored pigments that are ubiquitous in plants and often transitorily accumulated in the peripheral layer of mesophyll tissues (Steyn et al, 2002) Their presence is mainly pertinent to a wide range of functions at the cellular level, like the beautiful coloration of the flower/fruit parts for pollinator recruitment or seed dispersal, photo-protection, thermo-tolerance, High Temperature Induced Anthocyanin Degradation and aposematic defense warnings against herbivores (Hughes et al, 2013). Such pigments are considered potential sources of nutraceuticals due to their pronounced scavenging capacity of reactive oxygen species (ROS) (Agati et al, 2012). MYB TFs are induced by light and cold temperature, and their constitutive expression results in the persistent ability to bind to their own promoter in an auto-regulatory loop due to the presence of an extra five tandem repeats, resulting in increased red coloration (Espley et al, 2009; Albert et al, 2014)

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