Abstract
Manipulating grain size is an effective strategy for increasing cereal yields. Here we identify a pathway composed of five subunits of the heterotrimeric G proteins that regulate grain length in rice. The Gβ protein is essential for plant survival and growth. Gα provides a foundation for grain size expansion. Three Gγ proteins, DEP1, GGC2 and GS3, antagonistically regulate grain size. DEP1 and GGC2, individually or in combination, increase grain length when in complex with Gβ. GS3, having no effect on grain size by itself, reduces grain length by competitively interacting with Gβ. By combining different G-protein variants, we can decrease grain length by up to 35% or increase it by up to 19%, which leads to over 40% decreasing to 28% increasing of grain weight. The wide existence of such a conserved system among angiosperms suggests a possible general predictable approach to manipulating grain/organ sizes.
Highlights
Manipulating grain size is an effective strategy for increasing cereal yields
Recent advances in rice functional genomics facilitated the cloning of a series of loci controlling grain size, including genes for grain length such as GS31, GL3.12,3, An-14, GLW75 and GS26,7; genes for grain width such as GW28, GW59,10, GS511, GW812 and GW713,14; and genes for grain weight such as GIF115, GE16, TGW617, GW6a18, BG119 and XIAO20
G protein signaling is initiated by G-protein coupled receptors (GPCRs), such that the Gα subunit is activated through the exchange of a GDP for GTP, which causes its dissociation with the Gβγ dimer
Summary
We identify a pathway composed of five subunits of the heterotrimeric G proteins that regulate grain length in rice. Rice encodes one each of Gα and Gβ, and five Gγ proteins[25,26] Both Gα and Gβ proteins are positive regulators of cell proliferation and grain size growth[27,28,29,30]. GS3, encoding a Gγ subunit (Group III) of the heterotrimeric G proteins, is a major QTL for grain size[1,38]. We identify a pathway made up of five subunits of the heterotrimeric G proteins that regulates grain size in rice. We show that manipulating the three Gγ proteins, DEP1, GGC2 and GS3, can achieve designed grain size, demonstrating a predictable approach to improve grain yield and quality
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