Heterotrimeric G Protein γ Subunit Gene RGG2 Plays Key Roles In Plant Architecture And Drought Resistasnce In Rice

Heterotrimeric G proteins (G proteins) are a versatile component of transmembrane signal transduction, associated with a wide range of growth and development in plants, fungi, and animals. The classical heterotrimer consist of three different subunits:α,β,and γ. There are four G pretein y subunits in rice:RGG1, RGG2, GS3 and qPE9-1/DEP1. GS3 acts as a negative regulator in regulating grain and organ size. While qPE9-1 is a key gene in the formation of rice erect panicles, and involved in the response of nitrogen and ABA in rice. The other two G protein y subunits RGG1 and RGG2 have not been functionally characterized. In this study, we provide evidence that RGG2 plays multiple roles in rice plant architecture, grain size, ABA responses and drought-stress tolerance. The main results are as follows:1. RGG2 belongs to a type B G-protein y subunit, and interacts with RGB1 (αβ subunit of rice G protein).2. RGG2 constitutively expresses in all plant tissues, including leaf, sheath, stem, panicle, node and root. A notably higher transcript accumulation for RGG2 in both vegetative and reproductive tissues was detected, while the expression levels of RGG1, GS3 and qPE9-1 were very low. Subcellular localization indicated that RGG2 protein is localized at nucleus, cytoplasm, and plasma membrane.3. Overexpression of RGG2 leads to dwarf plant, erect panicles and leaves, short and small grains, and finally a reduced grain yield production.4. Scanning electron microscope analysis of spikelet hull and comparison of longitudinal sections of uppermost second internodes showed that RGG2 might inhibit longitudinal growth by repressing cell elongation. In addition, none of the genes involved in cell cycle in rice showed more than 2-fold change in transcript levels 5-8 cm panicles between Nipponbare and OE2, which are consistent with the cytological observations of spikelet hulls and internodes.5. The responses to ABA are highly enhanced in the transgenic lines, and RGG2 might be a negative regulator in seed germination and post-germination seedling growth in rice.6. Compared with wild-type, the RGG2 overexpression lines exhibited a lower water loss and higher survival ratio under drought treatments.Taken together, as a G protein y subunit, RGG2 not only regulates plant architecture and grain size, but also participates in ABA and drought stress responses in rice.