Na~+-dependent GhBASS5 Regulates The Salt Tolerance Of Upland Cotton

Soil salinization is one of prime abiotic stresses that limits agricultural production.Salt stress can cause osmotic stress and ion toxicity to plants.In order to adapt to the high-salt environment,plants have formed a variety of physiological and biochemical mechanisms to cope with salt stress,reducing the transport of sodium ions into the cell,increasing the transport of sodium ions out of the cell,and storing sodium ions in the vacuole.These processes require the participation of sodium ion transporter.The identification of sodium ion transporters is very important to mitigate salt stress.The BASS family is a type of transporter of sodium metabolism.GhBASS5 participates in the transport of Na~+in plants and down-regulation in salt stress.Overexpression of GhBASS5 reduces the salt tolerance of Arabidopsis.This study focuses on the salt-tolerant regulatory mechanism of GhBASS5 in upland cotton under salt stress.It was found that the expression level of GhBASS5 in the salt-sensitive variety ZG5(Zhong G5)of upland cotton was higher than that of the salt-tolerant variety Z07(Zhong 07),and the expression level of GhBASS5 of both varieties was down-regulated after salt stress through the analysis of cotton transcriptome data in this study.The expression level of GhBASS5 of seven cotton varieties with different salt tolerance was measured by real-time quantitative PCR,and it was found that the expression level of GhBASS5 was negatively correlated with salt tolerance of cotton.Through the determination of sodium ion content in plant tissues and xylem sap,it is found that the expression of GhBASS5 is related to the accumulation of Na~+.The absorption of sodium ions in plant cells was measured by sodium ion probe,which proved that GhBASS5was involved in Na~+transfer into cells.The net sodium flux was measured by Non-invasive Micro-test Technology,and it was found that GhBASS5 affected the Na~+efflux of plant roots.Promoter experiments found that the expression of GhBASS5 is regulated by transcription factors GhMYB39 while the expression of GhMYB39 is affected by IAA.It was found that the silencing of GHMYB39 by VIGS(virus induced gene silencing)technology will lead to the the down-regulation of GHBASS5,and the physiological index characteristics such as sodium ion content,proline content,soluble sugar content and antioxidant enzyme activity of plants are affected.In combination with the down-regulation of GhMYB39 expression under salt stress,a salt-tolerance mechanism of GhBASS5 is proposed.Under normal conditions,GhBASS5 makes plants sensitive to salt by participating in the transport of sodium ions from root to shoot.Salt stress reduces the content of IAA and down-regulates GhMYB39,and GhMYB39 positively regulates the expression of GhBASS5.Therefore,the down-regulation of GhBASS5expression under salt stress reduces the transport of sodium ions in plants and enhances plant salt tolerance.By the full-genome transcriptome sequencing analysis of the Arabidopsis wild-type(WT),At BASS5 gene knockout mutant(atbass5)and atbass5 mutant complementary GhBASS5 plant(co-atbass5),and measuring the content of glucosinolates and the accumulation of sodium ions,it was found that GhBASS5 could complement atbass5’s defects of glucosinolate synthesis and sodium ion transport.Compared with WT,the glucosinolate synthesis pathway genes expression of atbass5mutant were up-regulated but the glucosinolate content was reduced,and compared with atbass5,the glucosinolate synthesis pathway genes expression of co-atbass5 were down-regulated but the glucosinolate content was increased.Compared with wild-type,most genes related to salt stress,osmotic stress and water deprivation were down-regulated in atbass5 mutants and the accumulation of sodium ions in a saline environment was reduced.Compared with atbass5,most genes related to salt stress,osmotic stress and water deprivation were up-regulated in co-atbass5 and the accumulation of sodium ions in the salt environment was increased.In this study,the analysis of transcriptome data combined with the measurement of plant tissue,xylem sap and protoplast sodium ions proved that GhBASS5 is involved in the absorption and transport of sodium ions.Through promoter experiments and gene silencing techniques,it was found that GhBASS5 is regulated by the transcription factor GhMYB39,and the expression of GhMYB39 is affected by IAA.Therefore,a salt-tolerance mechanism of GhBASS5 was proposed,which provided a new idea for the research on the salt tolerance regulation mechanism of cotton.