Increasing CK content enhances rice resistance to sheath blight caused by necrotrophic pathogen Rhizoctonia solani
作者单位：Jiangsu Key Laboratory of Crop Genetics and Physiology/Co-Innovation Center for Modern Production Technology of Grain CropsKey Laboratory of Plant Functional Genomics of the Ministry of EducationYangzhou University Institute of Agricultural Sciences in Coastal Region of Jiangsu Province
会议名称：《2016年全国植物生物学大会》
会议日期：2016年
学科分类：09[农学] 0904[农学-植物保护] 090401[农学-植物病理学] 090402[农学-农业昆虫与害虫防治]
关 键 词：rice cytokinins sheath blight stay-green disease resistance
摘 要：Sheath blight(SB),caused by necrotrophic fungus Rhizoctonia solani Kühn(R. Solani),is one of the most destructive diseases in rice worldwide. Increasing studies have showed that plant hormone cytokinins(CKs) play an important role in regulation of plant disease resistance. However,its role in enhancing rice resistance to SB remains unknown. Here,we found that exogenous application of synthetic CK kinetin(KT) reduced the severity of R. Solani-induced symptoms. Transgenic rice lines with increased endogenous CK levels by engineering CK-biosynthesis gene IPT delayed senescence or a stay-green phenotype and significantly enhanced SB resistance in both field tests and detached leaf inoculation assays. In contrast,transgenic rice lines overexpressing CKX4,encoding a CKdegradation enzyme,contain significantly lower CKs content compared to wild type and show significantly enhanced susceptibility to SB. We also found a ′stay-green′ rice mutant,which maintains high CK content due to loss of function of CK degradation,displays higher resistance to SB at the later developmental stage. We conclude from our microscopic examination that the mechanism leading to enhanced resistance by increasing CK content is due to stronger ability of the transgenic lines or the mutant plant to inhibit cell death caused by R. solani,which ultimately results in poor pathogen infection. Importantly,we found that the transgenic lines and the ′stay-green′ mutant with increased CK levels are almost the same as WT in their morphological and yield traits. Taken together,our results demonstrate that modulating CK levels is a feasible approach to the development of new rice varieties with excellent SB disease resistance,which is of great importance in rice breeding toward SB resistance.