Zhang Baojun, Liu Xu, Sun Yurong, Xu Lin, Ren Zhixian, Zhao Yaofei, Han Yuanhuai
College of Plant Protection, Shanxi Agricultural University, Taiyuan, China.
Shanxi Key Laboratory of Minor Crop Germplasm Innovation and Molecular Breeding, Taiyuan, China.
Front Plant Sci. 2022 Jul 12;13:928040. doi: 10.3389/fpls.2022.928040. eCollection 2022.
Downy mildew of foxtail millet is an important oomycete disease caused by , affecting the yield and quality of the crop. Foxtail millet infected with exhibit symptoms of leaf yellowing and leaf cracking. To uncover the pathogenic mechanism of this disease, we explored the effects on chlorophyll synthesis and photosynthesis of foxtail millet leaves infected by . An elite foxtail millet variety, JG21, susceptible to , was used as for this study. inhibited chlorophyll synthesis and caused loose mesophyll cell arrangement. In addition, some cells were severely vacuolated in -infected foxtail millet leaves at the early stages of infection. could invade the mesophyll cells through haustoria which destroyed the chloroplast structure at the middle stages of infection causing significant accumulation of osmiophilic particles (OPs) and disintegrated chloroplast grana lamellae. Furthermore, foxtail millet leaves split longitudinally at the later stages of infection. Chlorophyll and carotenoid contents in infected leaves decreased significantly compared with those in the control. Net photosynthetic rate (Pn) of leaves and stomatal conductance showed a downward trend, and intercellular carbon dioxide concentrations increased significantly following the infection with . A total of 1,618 differentially expressed genes (DEGs) were detected between the control group and the treatment groups using RNA sequencing (RNA-Seq) among S1-S5 stages. DEGs associated with "photosynthesis" and "light reaction" were enriched. Gene expression patterns showed that 91.3% of 23 genes related to chlorophyll synthesis and photosynthesis, were significantly down-regulated than the control during S1-S5 stages. Based on the gene expression dataset, weighed gene co-expression network analysis (WGCNA) with 19 gene co-expression modules related to photosynthesis revealed six hub genes related to chlorophyll synthesis, which were suppressed during infection. The results suggest that infection of led to weak chlorophyll synthesis and rapid chloroplasts disappearance in foxtail millet. The defense responses and resistance of foxtail millet to were inhibited because chloroplast structure and function were destroyed in leaves, and the sexual reproduction in could be completed rapidly.
谷子霜霉病是由[病原菌名称缺失]引起的一种重要卵菌病害，影响作物产量和品质。感染[病原菌名称缺失]的谷子表现出叶片发黄和叶片开裂症状。为揭示该病害的致病机制，我们探究了[病原菌名称缺失]对感染谷子叶片叶绿素合成和光合作用的影响。选用对[病原菌名称缺失]敏感的优良谷子品种JG21进行本研究。[病原菌名称缺失]抑制叶绿素合成并导致叶肉细胞排列疏松。此外，在感染初期，感染[病原菌名称缺失]的谷子叶片中一些细胞出现严重液泡化。[病原菌名称缺失]可通过吸器侵入叶肉细胞，在感染中期破坏叶绿体结构，导致嗜锇颗粒（OPs）大量积累和叶绿体基粒片层解体。此外，在感染后期谷子叶片纵向开裂。与对照相比，感染叶片中的叶绿素和类胡萝卜素含量显著降低。叶片净光合速率（Pn）和气孔导度呈下降趋势，感染[病原菌名称缺失]后细胞间二氧化碳浓度显著增加。在S1 - S5阶段，通过RNA测序（RNA - Seq）在对照组和处理组之间共检测到1618个差异表达基因（DEG）。与“光合作用”和“光反应”相关的DEG被富集。基因表达模式显示，在S1 - S5阶段，与叶绿素合成和光合作用相关的23个基因中有91.3%显著下调。基于基因表达数据集，对与光合作用相关的19个基因共表达模块进行加权基因共表达网络分析（WGCNA），发现6个与叶绿素合成相关的枢纽基因在感染期间受到抑制。结果表明，[病原菌名称缺失]感染导致谷子叶绿素合成减弱和叶绿体快速消失。由于叶片中叶绿体结构和功能被破坏，谷子对[病原菌名称缺失]的防御反应和抗性受到抑制，且[病原菌名称缺失]的有性繁殖可迅速完成。
