Melatonin Mitigates the Infection of Colletotrichum gloeosporioides via Modulation of the Chitinase Gene and Antioxidant Activity in Capsicum annuum L.

Muhammad Ali,Saeed Ul Haq,Izhar Muhammad,Zhen-Hui Gong,Anthony Tumbeh Lamin-Samu,Ibadullah Jan,Gang Lu,Mohamed Farghal,Abid Khan,Abdul Mateen Khattak

doi:10.3390/antiox10010007

Abstract

Anthracnose, caused by Colletotrichum gloeosporioides, is one of the most damaging pepper (Capsicum annum L.) disease. Melatonin induces transcription of defense-related genes that enhance resistance to pathogens and mediate physiological activities in plants. To study whether the melatonin-mediated pathogen resistance is associated with chitinase gene (CaChiIII2), pepper plants and Arabidopsis seeds were treated with melatonin, then CaChiIII2 activation, hydrogen peroxide (H2O2) levels, and antioxidant enzymes activity during plant–pathogen interactions were investigated. Melatonin pretreatment uncoupled the knockdown of CaChiIII2 and transiently activated its expression level in both control and CaChiIII2-silenced pepper plants and enhanced plant resistance. Suppression of CaChiIII2 in pepper plants showed a significant decreased in the induction of defense-related genes and resistance to pathogens compared with control plants. Moreover, melatonin efficiently enabled plants to maintain intracellular H2O2 concentrations at steady-state levels and enhanced the activities of antioxidant enzymes, which possibly improved disease resistance. The activation of the chitinase gene CaChiIII2 in transgenic Arabidopsis lines was elevated under C. gloeosporioides infection and exhibited resistance through decreasing H2O2 biosynthesis and maintaining H2O2 at a steady-state level. Whereas melatonin primed CaChiIII2-overexpressed (OE) and wild-type (WT) Arabidopsis seedlings displayed a remarkable increase in root-length compared to the unprimed WT plants. Using an array of CaChiIII2 knockdown and OE, we found that melatonin efficiently induced CaChiIII2 and other pathogenesis-related genes expressions, responsible for the innate immunity response of pepper against anthracnose disease.

Highlights

The genus Colletotrichum includes several important plant pathogens that affect several herbaceous and woody species
In the in-vitro study, we examined the antifungal effect of exogenous application of melatonin at concentrations of 0, 50, 100, and 500 μM
At 50 μM concentration, the antifungal activity of melatonin was not obvious on P. capsici strains compared to Colletotrichum species

Summary

Introduction

The genus Colletotrichum includes several important plant pathogens that affect several herbaceous and woody species. Colletotrichum is the eighth most important genus of fungi that causes plant diseases worldwide [1]. This fungus causes disease symptoms that are generally known as anthracnose in a wide range of vegetables, fruits, and other crops, including pepper [2,3,4]. The appearance of necrotic lesions on plant parts, including leaves, stems, flowers, and fruits, is the main symptom of this disease. It may cause seedling blight, stem-rot and crown, etc. The most destructive sub-species are Colletotrichum acutatum and Colletotrichum gloeosporioides [8,9,10]

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