Key Laboratory of Molecular Epigenetics of MOE and The Institute of Genetics & Cytology, Northeast Normal University, Changchun 130024, ChinaDepartment of Agronomy, Jilin Agricultural University, Changchun 130118, ChinaCenter of Agribiotechnology, Jilin Academy of Agricultural Sciences, Changchun 130033, China.
J Integr Plant Biol. 2011 Oct;53(10):814-23. doi: 10.1111/j.1744-7909.2011.01070.x. Epub 2011 Sep 15.
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 wild-type 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.
PiB 是一个特征良好的水稻稻瘟病抗性基因，属于核苷酸结合位点（NBS）和富含亮氨酸重复（LRR）超家族。在未受挑战的条件下，PiB 的表达水平较低，但强烈地被致病真菌稻瘟病菌诱导，从而赋予了对病原体的抗性。通常认为启动子区域的胞嘧啶甲基化在调节基因表达中起着抑制作用。我们在这里报告，在两个研究的品种中，PiB 启动子的两个关键区域被高度 CG 胞嘧啶甲基化。令人惊讶的是，由 M. grisea 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 PiB 相对于野生型植物的表达。因此，5-氮杂胞苷处理的植物相对于野生型植物的稻瘟病抗性受损。相比之下，在另两个不含 PiB 基因的水稻品种中，5-氮杂胞苷处理并不影响其对稻瘟病的易感性，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导致 PiB 条件下的稻瘟病抗性受损的原因。总之，我们的结果表明，启动子 DNA 甲基化在 M. grisea 感染时高水平诱导 PiB 基因表达及其赋予对病原体的抗性方面发挥了新的增强作用。
