Panicle size is one of the yield determining traits in rice (Oryza sativa L.). In the current study, a rice mutant named cytokinin oxidase/dehydrogenase (Osckx2-2) was developed from the indica cultivar 9311 by ethyl methanesulfonate (EMS) mutagenesis. A comparison of agronomic traits showed that the panicle of the Osckx2-2 mutant was longer with dense branching pattern and higher seed setting rate compared to the wild-type (WT). In addition, the grains in the Osckx2-2 mutant were markedly longer, wider, and heavier compared to the WT. Histological analysis revealed that a higher number of the spikelet cells with bigger size resulted in larger grains in the Osckx2-2 mutant. By map-based cloning, SNP was detected in the 3′-UTR of the OsCKX2-2 gene which encodes cytokinin dehydrogenase and the cleaved amplified polymorphic sequence (CAPS) marker was developed based on the detected SNP. The RT-qPCR analysis displayed a decreased OsCKX2-2 expression in the Osckx2-2 mutant panicles. Meanwhile, the enzymatic activity assay showed the reduced cytokinin dehydrogenase enzyme activity, whereas the enzyme-linked immunosorbent assay (ELISA) revealed remarkably higher endogenous cytokinin content in the Osckx2-2 mutant in contrast to WT. The analysis of grain quality parameters showed that the degree of chalkiness and gel consistency decreased, while the amylose content and alkaline spreading value increased in the Osckx2-2 mutant. The OsCKX2-2 gene and Osckx2-2 mutant would be beneficial in marker-assisted backcrossing to improve yield in rice.

中文翻译：

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水稻基因 OsCKX2-2 通过增加内源细胞分裂素含量来调节花序和籽粒大小

穗大小是水稻 (Oryza sativa L.) 的产量决定性状之一。在目前的研究中，通过甲磺酸乙酯 (EMS) 诱变从籼稻品种 9311 中开发出一种名为细胞分裂素氧化酶/脱氢酶 (Osckx2-2) 的水稻突变体。农艺性状的比较表明，与野生型（WT）相比，Osckx2-2 突变体的穗更长，分枝密集，结实率更高。此外，与 WT 相比，Osckx2-2 突变体中的谷物明显更长、更宽、更重。组织学分析表明，在 Osckx2-2 突变体中，更大数量的具有更大尺寸的小穗细胞导致更大的籽粒。通过基于地图的克隆，在编码细胞分裂素脱氢酶的 OsCKX2-2 基因的 3'-UTR 中检测到 SNP，并基于检测到的 SNP 开发了切割的扩增多态性序列 (CAPS) 标记。RT-qPCR 分析显示 Osckx2-2 突变体穗中 OsCKX2-2 表达降低。同时，酶活性测定显示细胞分裂素脱氢酶活性降低，而酶联免疫吸附测定 (ELISA) 显示与 WT 相比，Osckx2-2 突变体中的内源性细胞分裂素含量显着更高。籽粒品质参数分析表明，Osckx2-2突变体的垩白度和凝胶稠度降低，而直链淀粉含量和碱性铺展值增加。OsCKX2-2 基因和 Osckx2-2 突变体将有利于标记辅助回交以提高水稻产量。