The Effects Of Brassinosteroids Receptor SlBRI1 Overexpression On Salt Tolerance In Tomato

Salt stress is one of the major stresses that affects plant growth and development and reduces the yield of plants.In recent years,due to climate conditions and improper human activities,the area of saline alkali land in our country is increasing year by year,especially the problem of soil salinization in facilities is becoming increasingly serious,which has become a major problem restricting the development of agriculture in our country.Tomato is the largest vegetable variety in protected cultivation area in our country,so high quality and efficient production of tomato are very important for our agricultural development.Brassinosteroids（BRs）are important plant hormone.Many studies have shown that exogenous BRs can alleviate the damage caused by salt stress,but the effect of endogenous BR signal on salt tolerance of tomato is rarely reported.In this study,tomato moneymaker（MM）,SlBRI1 overexpression lines with MM as background material and SlBRI1 weak mutant cu3^-abs1 were used as experimental materials,and MM was used as wild type（WT）.All lines were treated with NaCl stress,the physiological indexes of tomato plants from seed germination stage,seedling growth stage to field adult stage were detected to clarify the effect of SlBRI1 overexpression on salt tolerance of tomato.Furthermore,the relationship between BR signal intensity and salt tolerance of tomato was also revealed.The main results are as follows:1.Under NaCl stress,the tomato germination rate,germination energy,germination index and germination vigor index of SlBRI1 overexpression lines were significantly higher than those of WT,and WT was higher than those of cu3^-abs1.The results showed that SlBRI1overexpression could enhance the salt tolerance of tomato seeds.2.Under NaCl stress,the growth of tomato plants was inhibited to different degrees.Based on the plant height,stem diameter,dry and fresh weight of aboveground and underground parts,root shoot ratio and other indexes,SlBRI1 overexpression line was the least inhibited,followed by WT,and cu3^-abs1 was the most inhibited.It was suggested that SlBRI1 overexpression could enhance the salt tolerance of tomato seedlings.3.Under NaCl stress,overexpression of SlBRI1 could increase the content of proline in tomato seedlings,enhance the activities of antioxidant enzymes SOD,CAT,POD and APX,improve the expression level of antioxidant enzyme genes,and reduce the production of MDA and H₂O₂,so as to alleviate the damage of osmotic stress and oxidative stress on tomato seedlings and improve the salt tolerance of tomato.4.Under NaCl stress,overexpression of SlBRI1 could reduce the decomposition rate of photosynthetic pigments in tomato leaves,improve the stability of chloroplast structure,further improve the photosynthetic efficiency of tomato,and make tomato seedlings better photosynthesis under salt stress.5.Under NaCl stress,overexpression of SlBRI1 can increase the expression level of genes involved in ion transport,reduce the accumulation of Na⁺ions in tomato seedlings,improve the accumulation of K⁺ions in tomato seedlings,and increase the ratio of K⁺/Na⁺.So as to maintain the ions balance in tomato,reduce the ions toxicity caused by salt stress,and enhance salt tolerance of tomato seedlings.6.NaCl stress can induce the expression of SlBRI1,increase the intensity of BR signal in a short time,but inhibit BR signal in a long time.Moreover,the SlBRI1 overexpression line had higher SlBRI1 expression level and stronger BR signal intensity,both indicated that the SlBRI1 positively regulated salt tolerance of tomato.7.The field experiment showed that the yield,fruit firmness and soluble solids of each tomato line changed in varying degrees under salt stress.The fruit firmness,soluble solid content,fruit number per plant,and singal fruit weight of SlBRI1 overexpression lines were all significantly higher than those of WT and cu3^-abs1.Furthermore,the increase rates of fruit firmness and soluble solids were higher in SlBRI1 overexpression lines,which indicated that overexpression of SlBRI1 could increase the accumulation of aboveground assimilates to improve the quality of tomato under salt stress,and promote the fruit number to improve tomato yield under salt stress.