Role Of Specific Phosphorylation Sites Of Brassinosteroid Inensitive1 Receptor Kinase In Plant Growth And Development

Brassinosteroid insensitive 1(BRI1), the receptor of brassinosteroids(BRs), is a serine/threonine protein kinase which initiates BR signaling and regulates plant growth and development via its protein kinase activity. Previous research has identified phosphorylation sites of BRI1 in vivo/vitro, but the significance of which on BR signaling and plant development has not been discussed comprehensively. To investigate this, we systematically characterized BRI1 mimic non-phosphorylation site-directed mutants in weak bri1-5 background. In addition, function analysis of specific phosphorylation site in SlBRI1 corresponding to critical site of BRI1 in Arabidopsis was conducted. Results below were concluded.Firstly, we demonstrated that T1039, T1042, S1044 were critical for vegetative development because mutants of eliminating phosphorylation at these sites exhibited aberrant leaf growth, while S1172, S1187 might regulate vegetative growth negatively for the mutants’ slightly inhibited leaf growth. Secondly, that mimic non-phosphorylated T1039, T1042, S1044 decreased plant height in maturity indicated the essential role of these sites in plant height regulation. Thirdly, comparison of seed yield-related traits showed that unphosphorylated S1168, S1172, S1179+T1180 mutants dramatically reduced seed yield because of the largely decreased number of branches and effective siliques, while eliminating phosphorylation at T1042 caused increased seed production due to the increase of these two indexes. It suggested that BRI1 might regulate seed yield in Arabidopsis by influencing the number of branches and effective siliques, and S1168, S1172, S1179+T1180 were the critical sites in these regulation. In addition, low seed yield of unphosphorylated S1044 mutants indicated that S1044 played important roles in the every growth stage. T1042 could be an essential site in crop breeding because of the smaller rosette width, shorter plant height and normal seed yield compared with BRI1 transgencis. Fourthly, the inhibited elongation of hypocotyls and roots, limited dephosphorylation of BES1 and lower expression of CPD of unphosphorylated T1042 and S1044 mutants under exogenous BL suggested that T1042 and S1044 were essential for BR signaling. On the contrary, the performance of unphosphorylated S1168, S1172, S1179+T1180 mutants had no difference from that of wild-type BRI1. It indicated the important role of T1042 and S1044 in BR signaling. Lastly, the cytoplasmic kinase domains of tomato SlBRI1 shares high similarity with Arabidopsis BRI1. And BRI1:S1044, which played an important role in BR signaling was conserved with SlBRI1:S1049, suggesting great potential of manipulating this phosphorylation site on agriculture application. We’ve got the wild-type SlBRI1 transgenics and transformation tomato with mimic non-phosphorylation at Ser-1049.Taken together, function differentiation of BRI1 phosphorylation sites exists and it provides new approaches to precisely regulate agriculture production through modifying specific phosphorylation sites.