Cell wall modification and lignin biosynthesis involved in disease resistance against Diaporthe citri in harvested pummelo fruit elicited by carvacrol

Abstract

BACKGROUND Phomopsis stem‐end rot caused by Diaporthe citri, causes significant commercial postharvest losses of pummelo fruit during storage. Carvacrol (CVR) is a known generally recognized as safe and has the ability to prolong the preservation of harvested fruits. In the present study, the inhibitory effects of CVR treatment at the appropriate concentration on Phomopsis stem‐end rot development of harvested pummelo fruit inoculated with D. citri were evaluated by the amounts of cell wall components, the activities and gene expressions of related enzymes involved in cell wall modification and lignin biosynthesis. RESULTS Results indicated that CVR completely inhibited D. citri growth in vitro at 200 mg L−1 and significantly controlled Phomopsis stem‐end rot development in harvested pummelo. The CVR treatment delayed peel softening and browning, and retarded electrolyte leakage, superoxide radical (O2•−) production, and malondialdehyde content. The CVR‐treated fruit maintained higher amounts of cell wall material, protopectin, hemicelluloses, and cellulose, but exhibited lower water‐soluble pectin amount. Moreover, in D. citri‐inoculated fruit, CVR treatment suppressed the activities and gene expressions of cell wall disassembling‐enzymes, including pectin methylesterase, polygalacturonase, cellulase, and β‐galactosidase, while the development of cell wall degradation was reduced. Meanwhile, the CVR treatment enhanced the lignin biosynthesis by increasing the activities and up‐regulating the gene expressions of phenylalanine ammonialyase, cinnamic alcohol dehydrogenase, and peroxidase accompanied with elevated level of lignin in pummelo fruit. CONCLUSION The disease resistance to D. citri in pummelo fruit elicited by CVR treatment is related to delaying cell wall degradation and enhancing lignin biosynthesis. © 2021 Society of Chemical Industry.

Lignin Biosynthesis Pathway and Redox Balance Act Synergistically in Conferring Resistance against Penicillium italicum Infection in 7-Demethoxytylophorine-Treated Navel Orange

“…The potential of PAAs to induce H 2 O 2 production raises the question of whether they can also regulate the phenylpropanoid pathway, as part of horticultural fruit response to fungal postharvest infection. The lignin biosynthesis pathway is part of the phenylpropanoid metabolism and plays an important role in conferring resistance against pathogen invasion. , PAL is the first rate-limiting enzyme of the pathway. It cleaves off the amino group from l -phenylalanine to generate cinnamic acid.…”

“…The diameter of water-soaked lesion on P. italicum-infected orange fruit was adopted as one of the direct indices of CBM development and recorded in millimeters (mm) at the initial stage of infection progress …”

“…As the end product in membrane lipid peroxidation, malondialdehyde (MDA) content was determined according to the thiobarbituric acid (TBA) method . Frozen pericarp tissue (2.0 g) was homogenized with 8 mL of 50 mmol L –1 phosphate buffer [pH 7.8, 1 mmol L –1 EDTA, and 2% (w/v) polyvinylpyrrolidone (PVP)].…”

“…Seven genes related to lignin biosynthesis [ PAL1 (Cs8g16290), C4H1 (Cs4g04530), 4CL2 (Cs5g24900), COMT1 (Cs5g13580), CCR2 (Cs3g13090), CAD6 (Cs3g26570), and POD3 (Cs5g32270)] and six key ROS-scavenging genes [ APX6 (Cs3g19810), GR2 (orange1.1t03206), MDHAR4 (Cs2g27950), DHAR2 (Cs7g28340), GPX8 (Cs5g04030), and GST3 (Cs1g08610)] differentially expressed at 48 h between the control and DEM-treated groups were selected from our preliminary RNA-seq data. Total RNA was extracted from 1.0 g of frozen pericarp tissue from the control and DEM-treated orange fruit, as described by Chen et al , RNA quality was evaluated by 1.0% agarose gel electrophoresis and spectroscopy at 260 nm. First-strand cDNA synthesis and RT-qPCR were orderly performed as described elsewhere .…”

“…In addition, lignin synthesis and accumulation are closely associated with induced antifungal resistance in harvested fruits. The lignin biosynthesis pathway is an important branch of the phenylpropanoid pathway, with phenylalanine ammonia lyase (PAL), 4-coumarate-CoA ligase (4CL), cinnamate 4-hydroxylase (C4H), cinnamoyl-CoA reductase (CCR), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD) serving as critical enzymes. ,, Lignin deposition reinforces the plant cell wall and the maintenance of the host’s physical barrier against biotic stress or fungal infection, which enhances the disease resistance in horticultural crops after harvest.…”