The Mechanism Of AtBASS5 Relying On Na~+ To Regulate Drought Tolerance In Arabidopsis

Plant roots are the parts that sense drought and send out stomata regulation.Closing stomata to avoid existing water loss is an important strategy for plants to adapt to drought,which requires efficient communication between roots and leaf stomata.Drought stress causes the accumulation of salt in the soil,and Na⁺is the most abundant in soil salt.Na⁺dependent bile acid transporter(BASS5)is located in the vascular tissue,absorbs Na⁺in the soil and transports it to the ground.BASS5 is also involved in the synthesis of glucosinolates(GLS).GLS is degraded by myrosinase(TGGs)in guard cells to produce isothiocyanates(ITCs).ITCs then activate the guard cell reactive oxygen species(ROS)signaling pathway to trigger stomata closure.Therefore,it is particularly important to study how to recognize roots drought in plants that causes leaves stomata to close in response to drought stress through AtBASS5 gene.For this experiment,the following materials were utilized:wide-type Arabidopsis thaliana(WT),over expression of AtBASS5 transgenic Arabidopsis(OE),T-DNA insertion in AtBASS5 mutant Arabidopsis(atbass5).The following results were obtained by the detection of physiological and biochemical experiment,such as gene localization,ion concentration and glucosinolates concentration analysis,by simulating drought stress with 10%(w/v)PEG:1.Drought stress caused an increase in AtBASS5 expression by real-time fluorescence quantitative PCR analysis.Under 10%(w/v)PEG simulated drought stress conditions,the relative water content,water deficit rate and osmotic regulators of the three genotypes of WT,OE,atbass5 Arabidopsis were determined,and three genotypes of Arabidopsis were found to be drought resistant.The ability from high to low is OE,WT,atbass5.suggesting that AtBASS5 is regulating the drought resistance of plants.2.By measuring the GLS content,it was found that the aliphatic glucosinolates content of OE plants was increased under the condition of PEG simulated drought treatment,while there was no effect on the aliphatic glucosinolates content in the atbass5.External application of aliphatic glucosinolates restored drought tolerance and stomatal closure in atbass5.It is shown that AtBASS5 responds to stomatal closure by regulating aliphatic glucosinolates.3.AtBASS5 was found to be constitutive expressed,with higher expression in roots than in leaves,and concentrated in microtubule tissue expression in roots as indicated by quantitative real-time PCR,in situ PCR,and histochemical staining of Pro _AtBASS5::GUS transgenic plants for analysis.Through Non-invasive Micro-test Technology and ion content measurement in different tissues of Arabidopsis,it was found that OE accumulated more Na⁺in leaves,and atbass5 accumulated more Na⁺roots.This gene is involved in the absorption and transport of Na⁺in Arabidopsis.4.WT,OE,and atbass5,were treated with simulated drought stress using a mixture of PEG with different cations(Na⁺,K⁺,and Li⁺).By counting the stomata with the observation that only solutions containing Na⁺could close WT and OE stomata,while other ions could not be recognized by the plants and responded to drought stress.Changing the concentration of Na⁺in the solution at constant osmotic potential revealed that the stomata decreased with increasing Na⁺concentration.Thus the function of AtBASS5 in regulating stomata is Na⁺dose-dependent.5.Grafting experiments by overexpression of AtBASS5 with tgg2-1,ghr1,aba2-1mutants showed that AtBASS5 was independent of the ABA signaling pathway in response to drought stress and was dependent on the GLS-TGGs system.In conclusion,this study revealed a long-distance signal pathway that plants transcode the Na⁺concentration in soil water into GLS signals in plants that cause stomata to close through degradation of GLS.The drought response pathway from root perception of drought to leaf stomatal regulation in plants was demonstrated for the first time.It provides theoretical guidance for the further study of AtBASS5,and also provides ideas to improve the tolerance mechanism of plants to drought stress.