异源三聚体GTP结合蛋白(G蛋白)和细胞分裂素在调节植物生长发育中起着重要作用。然而，人们对它们协调调节水稻籽粒大小的机制知之甚少。
本研究对一个编码A、G、γ亚基的基因Rgg1进行了功能鉴定。在幼穗和小穗中检测到较强的GUS染色，表明该基因在调节穗部相关性状发育中起作用。Rgg1在日本晴(Nip)和武云粳30(WYJ30)中过表达，通过调节细胞分裂，显著降低了株高、穗长和粒长。然而，CRISPR/Cas9系统产生的Rgg1突变体没有明显的表型差异，这可能是由于该基因在体内的表达水平极低所致。
RGG1编码a型Gγ亚基
对NIP幼穗、NIP-Rgg1-2突变体和NIP-OE2过表达系的转录本进行了测序，结果表明许多差异表达基因(Deg)与细胞分裂素生物合成途径相关。我们通过测定内源细胞分裂素水平证实了这一结果，并发现在过表达的品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6-苄氨基嘌呤(6-BA)的敏感性。
我们的结果揭示了一个新的控制水稻籽粒大小的G蛋白-细胞分裂素模块，这将有助于理解G蛋白调节籽粒大小和植株发育的机制。
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.
Yajun Tao, Jun Miao, Jun Wang, et al. RGG1 , Involved in the Cytokinin Regulatory Pathway, Controls Grain Size in Rice. Rice, 2020
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