Transcriptome and soluble sugar content analyses reveal the defense response of cotton leaves to Verticillium dahliae

Verticillium dahliae is a soil-borne phytopathogenic fungus causing destructive Verticillium wilt disease that greatly threats cotton production worldwide. The mechanism of cotton resistance to Verticillium wilt is very complex and requires further research. In this study, RNA-sequencing was used to investigate the defense responses of cotton leaves using varieties resistant (Zhongzhimian 2 or Z2) or susceptible (Xinluzao 7 or X7) to V. dahliae. The leaf samples were collected at 48 and 72hpi (hours post infection) from the two varieties infected by V. dahliae (strain Vd991) or treated by water. Compared to X7, Z2 had less genes responding to V. dahliae infection at 72hpi and had no DEGs found at 48hpi. Several reported disease resistance pathways were found to be up-regulated in Z2, with some of those pathways down-regulated in X7. Unexpectedly, several photosynthesis-related pathways, including photosynthesis-antenna proteins, photosynthesis, and porphyrin and chlorophyll metabolism, were significantly up-regulated in leaves of X7 infected by V. dahliae, leading to different profile of the soluble sugars, particularly the glucose content, which was significantly decreased at 72hpi and 48hpi in X7 and Z2, respectively. These results suggest that the leaves of resistant variety have a slower and different response to V. dahliae compared to that of susceptible variety, and that translocation of sugars produced by photosynthesis in cotton leaves might vary in the two varieties. Additionally, several HUB genes regulating disease response were identified, which might serve as potential candidates for breeding cotton disease resistance.

大丽轮枝菌（Verticillium dahliae）是一种土传植物病原真菌，可引发毁灭性的黄萎病，对全球棉花生产造成严重威胁。棉花抗黄萎病的机制极为复杂，仍有待深入研究。本研究采用RNA测序（RNA-sequencing）技术，分别以抗大丽轮枝菌的品种中植棉2号（Zhongzhimian 2，简称Z2）与感病品种新陆早7号（Xinluzao 7，简称X7）为材料，探究二者叶片的防御响应。研究于接种大丽轮枝菌菌株Vd991或清水处理后的48小时（hours post infection，简称hpi）与72小时，采集两个品种的叶片样本。与X7相比，Z2在72hpi时响应大丽轮枝菌侵染的基因数量更少，且在48hpi时未检测到差异表达基因（Differentially Expressed Genes，DEGs）。多个已报道的抗病通路在Z2中显著上调，而其中部分通路在X7中呈下调趋势。出乎意料的是，接种大丽轮枝菌的X7叶片中，包括光合天线蛋白、光合作用以及卟啉与叶绿素代谢在内的多个光合作用相关通路均显著上调，这导致可溶性糖的谱型发生改变，其中葡萄糖含量变化尤为显著：X7在72hpi、Z2在48hpi时葡萄糖含量均出现明显下降。本研究结果表明，与感病品种相比，抗病品种的叶片对大丽轮枝菌侵染的响应更为缓慢且模式不同，且两个品种棉花叶片光合产物糖的转运过程可能存在差异。此外，本研究还鉴定出多个调控病害响应的枢纽基因（HUB genes），这些基因可作为棉花抗病育种的潜在候选靶点。