Lesion mimic mutants constitute a valuable genetic resource for unraveling the signaling pathways and molecular mechanisms governing the programmed cell death and defense responses of plants. Here, we identified a lesion mimic mutant, spl-D, from T-DNA insertion rice lines. The mutant exhibited higher accumulation of H2O2, spontaneous cell death, decreased chlorophyll content, up-regulation of defense-related genes, and enhanced disease resistance. The causative gene, OsGRDP1, encodes a cytosol- and membrane-associated glycine-rich domain protein. OsGRDP1 was expressed constitutively in all of the organs of the wild-type plant, but was up-regulated throughout plant development in the spl-D mutant. Both the overexpression and knockdown (RNAi) of OsGRDP1 resulted in the lesion mimic phenotype. Moreover, the intact-protein level of OsGRDP1 was reduced in the spotted leaves from both overexpression and RNAi plants, suggesting that the disruption of intact OsGRDP1 is responsible for lesion formation. OsGRDP1 interacted with an aspartic proteinase, OsAP25. In the spl-D and overexpression plants, proteinase activity was elevated, and lesion formation was partially suppressed by an aspartic proteinase inhibitor. Taken together, our results reveal that OsGRDP1 is a critical feedback regulator, thus contributing to the elucidation of the mechanism underlying cell death and disease resistance.

中文翻译：

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一种新的富含甘氨酸的结构域蛋白 GRDP1，作为控制水稻细胞死亡和抗病性的关键反馈调节因子

病变模拟突变体构成了一种有价值的遗传资源，用于解开控制程序性细胞死亡和植物防御反应的信号通路和分子机制。在这里，我们从 T-DNA 插入水稻品系中鉴定了一个病变模拟突变体spl-D 。该突变体表现出更高的 H2O2 积累、自发性细胞死亡、叶绿素含量降低、防御相关基因上调和抗病性增强。致病基因OsGRDP1编码胞质溶胶和膜相关的富含甘氨酸的结构域蛋白。OsGRDP1在野生型植物的所有器官中组成型表达，但在spl-D的整个植物发育过程中上调突变体。OsGRDP1的过表达和敲低 (RNAi)均导致病变模拟表型。此外，过表达植物和 RNAi 植物的斑点叶片中 OsGRDP1 的完整蛋白水平降低，这表明完整 OsGRDP1 的破坏是损伤形成的原因。OsGRDP1 与天冬氨酸蛋白酶 OsAP25 相互作用。在spl-D和过表达植物中，蛋白酶活性升高，而病灶形成被天冬氨酸蛋白酶抑制剂部分抑制。总之，我们的结果表明 OsGRDP1 是一个关键的反馈调节因子，从而有助于阐明细胞死亡和抗病性的机制。