The heterotrimeric G protein β subunit RGB1 is required for seedling formation in rice

Background: The heterotrimeric G protein beta subunit RGB1 plays an important role in plant growth and development. However, the molecular mechanisms underlying the regulation of rice growth by RGB1 remain elusive. Results: Here, the rgb1 mutants rgb1-1 (+1bp), rgb1-2 (-1bp), and rgb1-3 (-11bp) were isolated using the CRISPR/Cas9 system, and they were arrested at 1day after germination and ultimately exhibited seedling lethality. The dynamic anatomical characteristics of the embryos of the rgb1 seedlings and WT during early postgermination and according to TUNEL assays showed that the suppressed growth of the rgb1 mutants was caused by cell death. In addition to the limited shoot and root development, the development of the embryo shoot-root axis was suppressed in the rgb1 mutants. RGB1 was expressed mainly in the root epidermal and vascular tissues of the embryo. Moreover, transcript profiling analysis revealed that the expression of a large number of auxin-, cytokinin-, and brassinosteroid-inducible genes was upregulated or downregulated in the rgb1 mutant compared to the wild type during seedling development. Conclusions: Overall, the rgb1 mutants provide an ideal material for exploring the molecular mechanism underlying rice seedling formation during early postgermination development by G proteins. Significance statement The heterotrimeric G protein beta subunit RGB1 acts as a crucial factor in promoting early postgermination seedling development in rice.