The Arabidopsis gene RGO mediates cytokinin responses and increases seed yield

A novel gene, At1g77960, from Arabidopsis thaliana was characterized. At1g77960 transcripts accumulate to very high levels in plants ectopically overexpressing the Golden2-like1 (GLK1) transcription factor and is designated as a Response to GLK1 Overexpression (RGO) gene. RGO encodes a protein with domains of tandem QH and QN repeats. Transcripts and promoter GUS reporter analyses indicated that RGO is expressed in roots, leaves, stems, floral and siliques tissues but not in seeds. Expression of the RGO:YFP fusion protein demonstrated that RGO is localized to the endoplasmic reticulum. MicroRNA mediated silencing of RGO resulted in severe reductions in vegetative and root growth, delayed flowering and reduced seed yield and viability, suggesting that RGO is essential for plant development. Conversely, ectopic overexpression of RGO resulted in enhanced vegetative growth including increased axillary bud formation and a 20% higher seed yield. Stable overexpression of RGO in Brassica napus also produced a similar increase in seed yield. Cytokinin (CK) response assays including root growth, green calli formation from excised hypocotyls and chlorophyll retention during dark-induced senescence suggest that one role of RGO is to mediate CK responses in plant development. These results suggest that RGO could be a target gene for increasing crop seed yields.