Dauda Wadzani Palnam, Singh Rana Virendra, Solanke Amolkumar U, Krishnan Gopala, Bashya Bishnu Maya, Aggarwal Rashmi, Shanmugam Veerubommu
ICAR-Indian Agricultural Research Institute, New Delhi, India.
Crop Science Unit, Department of Agronomy, Federal University, Gashua, Yobe State, Nigeria.
J Appl Microbiol. 2022 Nov;133(5):3215-3227. doi: 10.1111/jam.15776. Epub 2022 Aug 23.
To understand the mechanism of necrosis incited by a host-selective phytotoxin designated as Rhizoctonia solani toxin (RST) identified to be a potential pathogenic factor of R. solani AG1 IA, causing sheath blight (ShB) of rice.
The metabolomic changes induced by the phytotoxic metabolite in a ShB susceptible rice cultivar were elucidated by gas chromatography-mass spectrometry analysis and compared with that of the pathogen to identify rice metabolites targeted by the phytotoxin. The profiles of about 29 metabolites with various physiological roles in rice plants have been identified worldwide. Unsupervised and supervised multivariate chemometrics (principal component analysis and partial least squares-discriminant analysis) and cluster (Heat maps) analyses were used to compare the metabolites obtained from chemical profiles of the treatments with sterile distilled water (SDW) control. The results indicated that the rice plant expressed more metabolites in response to the pathogen than the phytotoxin and was lowest in SDW control. The key metabolites expressed in rice in response to the treatments were investigated by the variable importance in projection (VIP) analysis using p < 0.05 VIP >15. The analysis identified 7 and 11 upregulating metabolites in the phytotoxin and the pathogen treatments, respectively, compared to the untreated control. Among the phytotoxin-treated and the pathogen inoculated samples, the phytotoxin-treated sample recorded upregulation of six metabolites, whereas nine metabolites were upregulated in the pathogen-inoculated samples. These upregulating metabolites are speculated for the necrotic symptoms characteristic to both the phytotoxin and pathogen. In this analysis, hexadecanoic acid and dotriacontane were highly expressed metabolites specific to the phytotoxin and pathogen-treated samples, respectively. Besides upregulation, the metabolites also have a VIP score of >1.5 and hence fulfilled the criteria of classifying them as reliable potential biomarkers. In the pathway analysis, hexadecanoic acid and dotriacontane were identified to be involved in several important biosynthetic pathways of rice, such as the biosynthesis of saturated fatty acid and unsaturated fatty acids cutin, suberin and wax.
The study concludes that though certain metabolites induced by the phytotoxin in the susceptible variety during necrosis shares with that of the pathogen, the identification of metabolites specific to the phytotoxin in comparison to the pathogenic and SDW controls indicated that the phytotoxin modulates the host metabolism differently and hence can be a potential pathogenicity factor of the ShB fungus.
Due to lack of knowledge on the pathway genes of RST and in the absence of an ShB-resistant variety, understanding differentially expressed metabolic changes induced in the susceptible variety by the phytotoxin in comparison to that of the pathogenic and uninoculated controls enables us to identify the key metabolite changes during the ShB infection. Such metabolomic changes can further be used to infer gene functions for exploitation in ShB control.
了解一种被称为立枯丝核菌毒素（RST）的寄主选择性植物毒素引发坏死的机制，该毒素被确定为引起水稻纹枯病的立枯丝核菌AG1 IA的潜在致病因子。
通过气相色谱 - 质谱分析阐明了这种植物毒性代谢物在一个对纹枯病敏感的水稻品种中诱导的代谢组变化，并与病原菌诱导的变化进行比较，以鉴定该植物毒素作用的水稻代谢物。全世界已鉴定出约29种在水稻植株中具有各种生理作用的代谢物谱。使用无监督和有监督的多元化学计量学（主成分分析和偏最小二乘判别分析）以及聚类（热图）分析来比较用无菌蒸馏水（SDW）对照处理的化学谱中获得的代谢物。结果表明，与植物毒素相比，水稻植株对病原菌产生更多的代谢物响应，而在SDW对照中最低。使用p < 0.05且VIP > 15的变量重要性投影（VIP）分析研究了水稻中对处理产生响应的关键代谢物。分析确定，与未处理对照相比，在植物毒素处理和病原菌处理中分别有7种和11种上调代谢物。在植物毒素处理和病原菌接种的样品中，植物毒素处理的样品记录到6种代谢物上调，而病原菌接种的样品中有9种代谢物上调。推测这些上调的代谢物与植物毒素和病原菌特有的坏死症状有关。在此分析中，十六烷酸和三十二烷分别是植物毒素处理和病原菌处理样品中高度表达的特异性代谢物。除了上调外，这些代谢物的VIP评分也> 1.5，因此符合将它们分类为可靠潜在生物标志物的标准。在途径分析中，十六烷酸和三十二烷被确定参与水稻的几个重要生物合成途径，如饱和脂肪酸和不饱和脂肪酸角质、木栓质和蜡质的生物合成。
该研究得出结论，虽然在坏死过程中植物毒素在易感品种中诱导的某些代谢物与病原菌诱导的代谢物相同，但与病原菌和SDW对照相比，鉴定出植物毒素特有的代谢物表明植物毒素对寄主代谢的调节不同，因此可能是纹枯病菌的潜在致病因子。
由于缺乏关于RST途径基因的知识，且没有抗纹枯病品种，了解植物毒素在易感品种中诱导的差异表达代谢变化与病原菌和未接种对照相比，使我们能够识别纹枯病感染期间关键的代谢物变化。这种代谢组变化可进一步用于推断基因功能，以用于纹枯病防治。
