The rice pathogenesis-related protein OsPR10a was scarcely expressed in OsCDPK1-silenced (Ri-1) rice, which was highly sensitive to pathogen infection. After inoculating the leaves with bacterial blight (Xanthomonas oryzae pv. oryzae; Xoo), we found that the expression of OsPR10a was up- and down-regulated in OEtr-1 (overexpression of the constitutively active truncated form of OsCDPK1) and Ri-1 rice plants, respectively. OsPR10a and OsCDPK1 showed corresponding expression patterns and were up-regulated in response to the jasmonic acid, salicylic acid and Xoo treatments, and OsPR1 and OsPR4 were significantly up-regulated in OEtr-1. These results suggest that OsCDPK1 may be an upstream regulator involved in rice innate immunity and conferred broad-spectrum of disease resistance. Following the Xoo inoculation, the OEtr-1 and Ri-1 seedlings showed enhanced and reduced disease resistance, respectively. The dihybrid rice Ri-1/OsPR10a-Ox not only bypassed the effect of OsCDPK1 silencing on the susceptibility to Xoo but also showed enhanced disease resistance and, consistent with Ri-1 phenotypes, increased plant height and grain size. Our results reveal that OsCDPK1 plays novel key roles in the cross-talk and mediation of the balance between stress response and development and provides a clue for improving grain yield and disease resistance simultaneously in rice.
Overexpression of a constitutively active truncated form of OsCDPK1 (OEtr) in rice produced smaller seeds, but a double-stranded RNA gene-silenced form of OsCDPK1 (Ri) yielded larger seeds, suggesting that OsCDPK1 plays a functional role in rice seed development. In the study presented here, we propose a model in which OsCDPK1 plays key roles in negatively controlling the grain size, amylose content, and endosperm appearance, and also affects the physicochemical properties of the starch. The dehulled transgenic OEtr grains were smaller than the dehulled wild-type grains, and the OEtr endosperm was opaque and had a low amylose content and numerous small loosely packed polyhedral starch granules. However, the OEtr grain sizes and endosperm appearances were not affected by temperature, which ranged from low (22 °C) to high (31 °C) during the grain-filling phase. In contrast, the transgenic Ri grains were larger, had higher amylose content, and had more transparent endosperms filled with tightly packed polyhedral starch granules. This demonstrates that OsCDPK1 plays a novel functional role in starch biosynthesis during seed development and affects the transparent appearance of the endosperm. These results improve our understanding of the molecular mechanisms through which the grain-filling process occurs in rice.
Overexpression of a constitutively active truncated form of OsCDPK1 (OEtr) in rice produced smaller seeds, but a double-stranded RNA gene-silenced form of OsCDPK1 (Ri) yielded large seeds, suggesting that OsCDPK1 plays a functional role in rice seed development. In the study presented here, we propose a model in which OsCDPK1 plays key roles in negatively controlling the grain size, amylose content, and endosperm appearance, and also affects the physicochemical properties of the starch. The dehulled transgenic OEtr grains were smaller than the dehulled wild-type grains, and the OEtr endosperm was opaque and had a low amylose content and numerous small loosely packed polyhedral starch granules. However, the OEtr grain sizes and endosperm appearances were not affected by the temperature being either optimal (25 °C ) or low (22 °C) or high (31 °C) during the grain-filling phase. In contrast, the transgenic Ri grains were larger, had higher amylose contents, and had more transparent endosperms filled with tightly packed polyhedral starch granules. This demonstrates that OsCDPK1 plays a novel functional role in starch biosynthesis during seed development and affects the transparent appearance of the endosperm. These results improve our understanding of the molecular mechanisms through which the grain filling process occurs in rice.
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