Arabidopsis G-proteins ? Subunit AGB1 Interacts With BES1 To Regulate Brassinosteroid Signaling And Cell Elongation

In plant,brassinosteroid(BR)are major growth-promoting steroid hormones,which regulate the cell elongation and division,flowering,drought resistance,and light morphogenesis.Previous studies have shown that BR signals integrate with the G-proteins signals and corporately modulate cell division and elongation.However,the mechanisms between BR and G-proteins remain elusive.Here,we elucidated the direct interaction between G-proteins ? subunit AGB1 and BR transcription factor BES1.First,the assay of yeast two hybrid,Pull-down and Co-IP indicated that AGB1 interacts with BES1 in vitro and in vivo.Moreover,an AGB1-null mutant,agb1-2,was used to examine its effects on the BR hyposensitivity and the BRZ hypersensitivity,suggestting AGB1 is involved in BR signaling.Further,biochemical and genetic studies indicated that the interaction between AGB1 and BES1 alters the phosphorylation status of BES1 and increases the ratio of the dephosphorylated to the phosphorylated of BES1,which lead to the dephosphorylated BES1 accumulate in the nucleus.AGB1 also promotes BES1 to bind to the target genes of BR,and stimulates the transcription activity of BES1,which leads to the enhancement of BR response.Taken together,the interaction of AGB1 and BES1 co-regulates cell elongation by affecting the phosphorylation status and transcription level of BES1.