Background

Grain size is a key agronomic trait that is directly associated with grain yield in rice. Although several genes related to grain size in rice have been identified, our understanding of the mechanism of grain development is still limited.

Results

In this study, we reported the characterization of a novel seed size mutant mini seed 2 (mis2), in which the grain showed reduced length, width and thickness along with wrinkled surface. Microscopic analysis revealed that the spikelet epidermal cell size was reduced but the cell number was increased in the mis2 mutant, suggesting that MIS2 controls grain size by coordinately regulating epidermal cell size and cell number. Map-based cloning revealed that MIS2 encodes a receptor-like kinase CRINKLY4 (CR4) which showed the highest expression in developing panicles. The MIS2 protein is localized primarily on the plasma membrane along with the endosome. However, the Arg258Gln mutation located in extracellular domain in the mis2 mutant disturbed its subcellular localization. Additionally, three major haplotypes of MIS2 were identified in the japonica, indica and aus rice cultivars. The 18-bp InDel (insertion and deletion) in the 5′-UTR (untranslated region) caused different expression level of MIS2 in haplotypes.

Conclusions

We reported a key role of OsCR4 in controlling grain size and shape by coordinately regulating epidermal cell size and cell number. The Arg258 in the extracellular seven-repeat domain is essential for the correct subcellular behavior and function of the OsCR4 protein.

中文翻译：

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MINI SEED 2（MIS2）编码一种受体样激酶，可控制水稻的粒大小和形状

背景

籽粒大小是关键的农艺性状，与水稻的籽粒产量直接相关。尽管已经鉴定出几种与水稻籽粒大小有关的基因，但我们对谷物发育机理的理解仍然有限。

结果

在这项研究中，我们报道了一种新型种子大小突变体迷你种子2（mis2）的特征，其中粒粒显示出减少的长度，宽度和厚度以及起皱的表面。显微镜分析显示，mis2突变体中小穗表皮细胞的大小减少了，但细胞数却增加了，这表明MIS2通过协调调节表皮细胞的大小和细胞数来控制晶粒大小。基于图的克隆表明MIS2编码受体样激酶CRINKLY4（CR4），该激酶在发育中的穗中表达最高。MIS2蛋白主要与内体一起定位在质膜上。但是，位于mis2突变体中胞外域的Arg258Gln突变干扰了其亚细胞定位。此外，三大单倍型MIS2在被认定粳稻，籼稻和AUS水稻品种。5'-UTR（非翻译区）中的18bp InDel（插入和缺失）在单倍型中引起MIS2的不同表达水平。

结论

我们报道了OsCR4在通过协调调节表皮细胞大小和细胞数量来控制晶粒大小和形状中的关键作用。细胞外七重复域中的Arg258对于OsCR4蛋白的正确亚细胞行为和功能至关重要。