The Roles Of BSK1,BSK3 And BSK5 In The Regulation Of Water Stress Responses In Arabidopsis

Water stress,which caused by drought and high salinity,is one of the major abiotic stresses that adversely affect plant growth and crop yield.Plants have evolved a series of complex mechanisms to transduce stress signals and regulate the expression of various genes in response to the water stress.Growing evidence has shown that BRs enhance the plant water stress tolerance by enhancing the antioxidant defense.Several components of the BR signaling pathway,like BRI1,BSK,BIN2,BES1 and so on,have been identified.However,it is not clear that whether these components are involved in response to water stress.BSKs have 12 members in Arabidopsis.It was reported that loss-of-function mutation of bsk3-1 reduces BR sensitivity.When overexpressed in the BR-insensitive bril-5 mutant or BR-deficient det2-1 mutant background,BSK1,BSK3,and BSK5 obviously suppress the dwarfism of the mutants.The phenotypes correlated with altered expression of the BZR1-targeted gene DWF4,indicating that overexpression of the BSKs activates downstream BR signaling.Moreover,the bsk1-1 mutation suppresses the powdery mildew resistance and ethylene-induced senescence in edr2.In addition,BSK1 is physically associated with FLS2,and the flg22-induced ROS burst is relieved in the bskl-1 mutant,indicating that BSK1 is a positive regulator in plant immunity-defense responses.All these studies imply that BSKs may be involved in many aspects of plant development and stress responses.To gain a better understanding of BSKs in response to water stress,we obtained T-DNA insertion mutants of BSKs.The preliminary results showed that bskl and bsk3 have stronger tolerance to water stress,while bsk5 is more sensitive to water stress.Then,we successfully obtained BSK1-and BSK3-overexpressing lines by agrobacterium-mediated genetic transformation.We investigated the roles of BSK1,BSK3 and BSK5 in the regulation of water stress responses in Arabidopsis.The results are listed as follows:The differences in drought and salt tolerance were observed between mutants and wild type.Under the treatments of soil drought and NaCl,bsk1 and bsk3 showed strong tolerance,bsk5 appeared sensitive to stress.Then we analyzed the germination rate and seedling growth of mutants under water stress.The germination rate and seedling growth of bskl and bsk3 were better than those of wild type.However,bsk5 mutation was worse compared to wild type.The results also showed bskl and bsk3 have strong tolerance,while bsk5 is sensitive to water stress.To further study the mechanism of BSK1,BSK3 and BSK5 in response to water stress,4-week-old plants were treated with 200 mM NaCl and 15%PEG to analyze the physiological traits.The bskl and bsk3 mutants showed higher relative water content,proline content and the activities of APX,CAT,SOD than those of wide type,which effectively enhanced the water stress tolerance in Arabidopsis.Furthermore,electrolyte leakage and MDA content were lower in bskl and bsk3 than those of wide type,indicating that loss-of-fuction of BSK1 or BSK3 reduced the stress-induced oxidative damage.However,overexpression lines displayed small differences with wide type,and bsk5 was opposite to bskl and bsk3.In summary,our results suggest that BSK1,BSK3 and BSK5 play an important role in water stress responses in Arabidopsis.