The role of NADPH oxidases (NOXs) in pathogenesis and development in the Curvularia leaf spot agent Curvularia lunata remains poorly understood. In this study, we identified C. lunata ClNOX2, which localized to the plasma membrane and was responsible for reactive oxygen species (ROS) generation. Scavenging the ROS production inhibited the conidial germination and appressorial formation. The ClNOX2 and ClBRN1 deletion mutants were defective in 1,8-dihydroxynaphthalene (DHN) melanin accumulation, appressorial formation, and cellulase synthesis and exhibited lower virulence. However, disruption of the ClNOX2 and ClBRN1 genes facilitated hyphal growth, enhanced stress adaptation to cell-wall-disrupting agents, and promoted developmental processes such as conidiation, conidial germination, and pseudothecium and ascus formation. Interestingly, loss of ClM1, the cell wall integrity (CWI) mitogen-activated protein kinase gene in C. lunata, led to morphology and pathogenicity phenotypes similar to ClNOX2 and ClBRN1 deletion mutants such as abnormal conidia, fewer appressoria, less melanin, increased hyphal growth, and enhanced tolerance to Congo red (CR). These results indicated that the ClNOX2 gene plays an important role in C. lunata development and virulence via regulating intracellular DHN melanin biosynthesis. Quantitative reverse-transcription PCR revealed that the ClNOX2-related ROS signaling pathway and ClM1-mediated CWI signaling pathway are cross-linked in regulating DHN melanin biosynthesis. Our findings provide new insights into how ClNOX2 participates in pathogenesis and development in hemibiotrophic plant fungal pathogens.

Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

NADPH氧化酶（NOXs）的发病机理和发展，在弯孢菌叶斑病剂的作用，弯孢菌仍然知之甚少。在这项研究中，我们确定Ç。lunata ClNOX2，其定位在质膜上，并负责产生活性氧（ROS）。清除ROS的产生抑制了分生孢子的萌发和附生器官的形成。的ClNOX2和ClBRN1缺失突变体在1,8-二羟基萘（DHN）黑色素聚集，附着胞的形成，和纤维素酶的合成缺陷的，表现出较低的毒性。但是，ClNOX2和ClBRN1的破坏这些基因促进了菌丝的生长，增强了对细胞壁破坏剂的适应性，并促进了分生孢子，分生孢子萌发，假the和天疱疮的形成。有趣的是，损失CLM1，在细胞壁完整性（CWI）促分裂原活化蛋白激酶基因Ç。lunata导致类似于ClNOX2和ClBRN1缺失突变体的形态和致病性表型，例如异常分生孢子，较少的压感，较少的黑色素，增加的菌丝生长和增强的对刚果红（CR）的耐受性。这些结果表明ClNOX2基因在月球梭菌中起重要作用。通过调节细胞内DHN黑色素的生物合成来开发和毒力。定量逆转录PCR显示，ClNOX2相关的ROS信号通路和ClM1介导的CWI信号通路在调节DHN黑色素生物合成中是交联的。我们的发现为ClNOX2如何参与半营养植物真菌病原体的发病机理和发育提供了新的见解。

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