Induced Pib Expression and Resistance to Magnaporthe grisea are Compromised by Cytosine Demethylation at Critical Promoter Regions in Rice
Induced Pib Expression and Resistance to Magnaporthe grisea are Compromised by Cytosine Demethylation at Critical Promoter Regions in Rice
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DOI：
10.1111/j.1744-7909.2011.01070.x
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发表时间：
2011-10-01
影响因子：
11.4
通讯作者：
Liu, Bao
中科院分区：
文献类型：
--
作者：
Li, Yuan;Xia, Qiong;Liu, Bao
PIB是一个属于核苷酸结合位点(NBS)和富含亮氨酸重复序列(LRR)超家族的水稻抗稻瘟病基因。在非激发条件下，PIB的表达水平较低，但受到稻瘟病菌的强烈诱导，从而增强了对该病原菌的抗性。一般认为，启动子区域的胞嘧啶甲基化通常在调节相关基因的表达方面起着抑制作用。我们在此报告了PIB启动子的两个关键区在两个所研究的品种中都被严重的CG胞嘧啶甲基化。令人惊讶的是，稻瘟病菌感染诱导的PIB表达并不需要其启动子去甲基化，而5-氮杂胞苷处理的部分去甲基化实际上降低了相对于野生型植物的PIB表达。与野生型相比，5‘-azaC处理的植株对稻瘟病的抗性有所降低。相反，5‘-azaC处理不影响另外两个不含PIB基因的水稻品种的感病能力，排除了其他R基因的影响和药物处理的非特异性遗传毒性效应是造成PIB条件抗稻瘟病的原因之一。综上所述，我们的结果表明，启动子DNA甲基化在调节稻瘟病菌侵染时期PIB基因的高水平诱导表达及其对病原菌的抗性方面发挥了新的增强作用。
Pib is a well-characterized rice blast-resistance gene belonging to the nucleotide binding site (NBS) and leucine-rich repeat (LRR) superfamily. Expression of Pib was low under non-challenged conditions, but strongly induced by the blast-causing fungal pathogen Magnaporthe grisea, thereby conferring resistance to the pathogen. It is generally established that cytosine methylation of the promoter-region often plays a repressive role in modulating expression of the gene in question. We report here that two critical regions of the Pib promoter were heavily CG cytosine-methylated in both cultivars studied. Surprisingly, induced expression of Pib by M. grisea infection did not entail its promoter demethylation, and partial demethylation by 5-azacytidine-treatment actually reduced Pib expression relative to wildtype plants. Accordingly, the blast disease-resistance was compromised in the 5'-azaC-treated plants relative to wild-type. In contrast, the disease susceptibility was not affected by the 5'-azaC treatment in another two rice cultivars that did not contain the Pib gene, ruling out effects of other R genes and non-specific genotoxic effects by the drug-treatment as a cause for the compromised Pib-conditioned blast-resistance. Taken together, our results suggest that promoter DNA methylation plays a novel enhancing role in conditioning high-level of induced expression of the Pib gene in times of M. grisea infection, and its conferred resistance to the pathogen.