Heterotrimeric GTP binding proteins (G proteins) and cytokinin play important roles in regulating plant growth and development. However, little is known about the mechanism by which they coordinate the regulation of grain size in rice. We functionally characterized one gene, RGG1, encoding a type-A Gγ subunit. Strong GUS staining was detected in young panicles and spikelets, suggesting a role for this gene in modulating panicle-related trait development. Overexpression of RGG1 in Nipponbare (NIP) and Wuyunjing 30 (WYJ30) significantly decreased plant height, panicle length and grain length by regulating cell division. However, rgg1 mutants generated by the CRISPR/Cas9 system exhibited no obvious phenotypic differences, which may be due to the extremely low expression level of this gene in vivo. The transcriptomes of young panicles of NIP, the NIP-rgg1–2 mutant and the NIP-OE2 overexpression line were sequenced, and the results showed that many differentially expressed genes (DEGs) were associated with the cytokinin biosynthetic pathway. We confirmed this result by measuring the endogenous cytokinin levels and found that cytokinin content was lower in the overexpression lines. Additionally, increased expression of RGG1 decreased sensitivity to low concentrations of 6-benzylaminopurine (6-BA). Our results reveal a novel G protein—cytokinin module controlling grain size in rice and will be beneficial for understanding the mechanisms by which G proteins regulate grain size and plant development.

异三聚体GTP结合蛋白（G蛋白）和细胞分裂素在调节植物生长和发育中起重要作用。但是，关于它们协调水稻粒大小调节的机理知之甚少。我们功能上表征一个基因，RGG1，编码A型Gγ亚基。在年轻的穗和小穗中检测到强GUS染色，表明该基因在调节与穗相关的性状发育中的作用。RGG1在日本晴（NIP）和五云粳30（WYJ30）中的过表达通过调节细胞分裂而显着降低了株高，穗长和籽粒长度。但是，rgg1CRISPR / Cas9系统产生的突变体没有表现出明显的表型差异，这可能是由于该基因在体内的表达水平极低。对NIP幼穗，NIP - rgg1-2突变体和NIP-OE2过表达系的转录组进行了测序，结果表明，许多差异表达基因（DEG）与细胞分裂素的生物合成途径有关。我们通过测量内源性细胞分裂素水平证实了这一结果，发现在过度表达细胞系中细胞分裂素含量较低。此外，RGG1的表达增加降低了对低浓度的6-苄氨基嘌呤（6-BA）的敏感性。我们的结果揭示了一种新颖的G蛋白-细胞分裂素模块，可控制水稻的籽粒大小，并将有助于理解G蛋白调节籽粒大小和植物发育的机制。