Mechanism Of Rice G Protein RGB1 Regulating Rice Grain Filling

Heterotrimeric G protein(G protein)-mediated signal transduction pathway is a conserved signaling pathway in eukaryotes and plays an important role in the regulation of eukaryotic growth and development.G protein is composed of three subunits-?,? and ?,and each subunit participates in multiple signal response processes in living organism activities.The research on rice G protein in grain regulation mainly focuses on ? subunits,but we know little about the function of ? subunit.In this study,was used the monocotyledonous plant rice as a material to study the role and mechanism of rice G protein ? subunit RGB1 in regulating grain development The results are as follows:1.Compared with wide-type Wuyujing 8(WYJ8),grains of RGB1 RNA-interfered transgenic is short round.The 1000-grain weight and the number of grains per panicle is significantly reduced.Furthermore,the development of grains of RGB1 RNA-interfered transgenic rice was significant delayed in the grain filling stage.The total starch content was significantly lower in grains of RGB1 RNA-interfered transgenic rice than that of the wild type.2.We analyzed the expression pattern of rice tissues using the data from the Ricexpro website and found that the subunits of rice G protein were expressed in roots,stems,leaves,sheaths and ears.However,unlike other subunits,the ? subunit RGB1 is highly expressed in embryos and endosperm.The results of wester blot show that high levels of RGB 1 expression accumulate during grain development,indicating that RGB1 have function during whole grain development stages.3.To evaluate the effect of RGB1 on grain filling,we measured the expressional profiles of genes under the regulation of RGB1 in the grains of WYJ8 and RGB1 RNA-interfered transgenic rice at the early stage of grain filling,using the RNA-seq assay.The Kyoto Encyclopedia of Genes and Genomes(KEGG)pathway enrichment analysis showed that the differently expressed genes(DEGs)were significantly enriched for "starch and sucrose metabolism" and "plant hormone transduction",suggesting that RGB1 may regulate grain starch synthesis through manipulating hormone homeostasis and/or hormone-mediated signaling.4.We analyzed the expression pattern of twelve starch synthesis genes in grains of WYJ8 and RGB1 RNA-interfered lines during the grain filling period using real-time quantitative PCR.The results showed that the expression levels of these genes were lower than the wild type at 5-10 days.In addition,we also examined eight selected transcription factors related to grain development,and the expression levels of these transcription factors were all delayed in RGB1 RNA-interfered lines.The co-expression analysis showed that RGB1 can affect the expression of transcription factors related to grain development,thereby regulating the expression of starch synthesis genes.5.The content of free IAA in grains of RGB1 RNA-interfered lines was constantly lower than that of WYJ8 during filling.Furthermore,regression analysis revealed significant and positive correlations between OsYUC11 expression and auxin content,suggesting that RGB1 stimulates the accumulation of IAA mainly by OsYUC11.Altogether,we found that G protein ? subunit RGB1 positively regulates starch accumulation largely through transcription factors and IAA,which enhance the expression of genes encoding starch biosynthesis during the early stage of grain filling.