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

Abstract

Anthracnose, caused by <i>Colletotrichum gloeosporioides</i>, is one of the most damaging pepper (<i>Capsicum annum</i> 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 (<i>CaChiIII2</i>), pepper plants and Arabidopsis seeds were treated with melatonin, then <i>CaChiIII2</i> activation, hydrogen peroxide (H₂O₂) levels, and antioxidant enzymes activity during plant-pathogen interactions were investigated. Melatonin pretreatment uncoupled the knockdown of <i>CaChiIII2</i> and transiently activated its expression level in both control and <i>CaChiIII2</i>-silenced pepper plants and enhanced plant resistance. Suppression of <i>CaChiIII2</i> 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 <i>CaChiIII2</i> in transgenic Arabidopsis lines was elevated under <i>C. gloeosporioides</i> infection and exhibited resistance through decreasing H₂O₂ biosynthesis and maintaining H₂O₂ at a steady-state level. Whereas melatonin primed <i>CaChiIII2</i>-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 <i>CaChiIII2</i> knockdown and OE, we found that melatonin efficiently induced <i>CaChiIII2</i> and other pathogenesis-related genes expressions, responsible for the innate immunity response of pepper against anthracnose disease.