Abstract
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.
Highlights
The quality of rice (Oryza sativa L.) grain is defined in terms of several main factors, including (i) eating and cooking qualities, and (ii) milling qualities and appearance [1]
The OsCDPK1::GUS expression timing in the developing rice seeds was similar to that found in a study by Ohdan et al [36], in which 27 different genes involved in starch biosynthesis were examined during rice-seed development
These results suggest that the expression of some starch-biosynthesis-related genes in the endosperm cells may be affected by OsCDPK1, followed by changing the amylose content and resulting in the opaque endosperm in the OEtr-1 grains
Summary
The quality of rice (Oryza sativa L.) grain is defined in terms of several main factors, including (i) eating and cooking qualities, and (ii) milling qualities and appearance [1]. The filling and accumulation of starch granules in developing rice endosperms can accelerate at high temperatures, causing the starch in the endosperm cells to be packed loosely and the kernel to be chalky Such grains crack during milling, yielding poor eating and cooking qualities [4,5,6]. Map-based cloning demonstrated that flo was an insertion mutation in the unknown function gene Os03g0686900 [21] and that flo was a deletion mutation in the unknown function gene Os10g0463800 [22], suggesting that these genes may play vital roles in starch biosynthesis and granule formation in the endosperm during the grain-filling process
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