| Rice (Oryza sativa L.) is one of the important food crops in the world. Sheath blight disease caused by the soilborne necrotrophic fungal pathogen Rhizoctonia solani Kiihn is one of the most destructive rice diseases in rice cultivation areas of the world, restricting rice yield and stable production. Developing sheath-blight-resistant cultivars through heredity breeding and gene improvement has reached only limited success due to the lack of resistant adapted germplasm, the limited efficiency and effectiveness of available screening methods, and the polygenic nature of the resistance.1. The inoculation and scoring system for rice sheath blight is an important basis for breeding resistant rice cultivars. In this study, the micro-chamber method for determination of rice responses to the sheath blight pathogen Rhizoctonia solani was improved by inoculation of rice seedlings with similar growth rates under controlled illumination, temperature and humidity conditions in plant growth chamber. The rice cultivars YSBR1, Teqing, Taijing394, Nipponbare and Lemont showed sheath blight resistance from high to low levels, which was consistent with the results of field inoculation with adult rice plants. Four rice genes related to disease resistance were analyzed by RT-PCR, and induced gene expression was observed in inoculated seedlings and adult plants. The disease rating methods based on the highest pulvinus and the height of straightened seedling resulted in sheath blight scores ranging from2.82to8.54and from1.20to3.39, respectively. The scoring method using the highest pulvinus led to similar disease scores for both seedlings and adult plants, and thus is more suitable for the micro-chamber inoculation system. Therefore, the improved micro-chamber method can be effectively used to distinguish between the rice cultivars with different resistance levels, to expedite the screening of resistant germplasms, and to investigate the molecular mechanisms of sheath blight resistance in rice.2. In this study, we isolated some receptor-like protein kinases which were induced by the sheath blight fungus R. solani to the adult plants of rice cultivars YSBR1and Lemont on field. Analysis of the phenotype and genetic characteristic, and inoculating the sheath blight pathogen to transgenic plants of those receptor-like protein kinases indicated that: The identification results at rice adult stage in field showed that:(1) RNAi masculine plants of the X21gene enhanced resistance to sheath blight compared with wild type Taijing394.(2) RNAi masculine plants of the X8and X11gene enhanced susceptibility to sheath blight compared with wild type Taijing394.(3) Transgenic masculine trains of X18RNAi plants revealed a highly susceptible standard to sheath blight than feminine trains. And over expression lines of the X18gene exhibited reduced root formation and elongation compared with wild-type and RNAi plants. The identification results in rice seedling stage showed that:(1) RNAi masculine plants of the X23gene was found to enhance resistance against infection with R. solani compared with feminine trains.(2) RNAi masculine plants of the X24gene was found to enhance susceptibility to sheath blight compared with feminine trains. In addition, over expression lines of the X33gene had lower fertility than wide type.3. To investigate subcellular location of receptor-like protein kinases X12, X14, X31, X33, we inserted the ORF of candidate genes into pXGJ70and transformed the recombination plasmid into rice protoplasts. Images of fusion protein were then captured with the laser scanning confocal microscope. We initially identified that receptor-like protein kinases was located to cytoplasm or cytomembrane. Such result is in agreement with the previous researches. |
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