Effects Of Over-expression Of SlSUT4 On Growth And Drought Tolerance Of Tomato

SUT4 is a subfamily of SUT(sucrose transporter)family.It plays important roles in the growth and development of plants,photosynthate allocation,sugar signal and stress tolerance.SUT4 has different subcellular locolizations in different plant species,suggesting that it has different roles in different plants.Solanum lycopersicum SUT4(SlSUT4)is mainly located on vacuolar membrane and it transports sucrose from the vacuole to the cytosol.Up to date,the studies on SlSUT4 have mainly focused on its structure,subcellular localization and its role in sugar transport,while littile is known about its role in plant growth and stress tolerance.Based on this,we constructed 35S::SlSUT4 over-expression vector and obtained transgenic tomato plants.The effects of SlSUT4 over-expression on tomato growth and drought tolerance were investigated by using T1 generation of the transgenic plants.The study will build a baisis for exploring the relationship between sugar signal and plant hormones.The main findings are as follows:1.35S::SlSUT4 over-expression vector was constructed and SlSUT4 over-expression tomato plants were obtained by Agrobacterium tumefaciens-mediated genetic transformation.2.In well watering conditions,compared with the wild type plants,the SlSUT4-over-expressed plants had higher leaf net photosynthetic rate,total chlorophyll content,shoot dry weight and plant height.The contents of sucrose,glucose,fructose and starch in the leaves of transgenic plantswere increased significantly;the sucrose and starch contents in the roots were slightlyincreased,the content of fructose did not change significantly,and the glucose content were decreased significantly.Compared with the wild type plants,although the root biomass of the transgenic plants was not changed,the root volume,surface area and total length were decreased,and the.average diameter of roots was increased.The concentrations of abscisic acid and gibberellin in roots were lower in the transgenic plants than the wild type,while the concentration of cytokinin showed an opposite trend.The auxin concentration showed no difference between these two plants.In well watering conditions,SlSUT4 over-expression enhanced the growth of tomato shoot.Compared with the wild type,SlSUT4 over-expression-mediated changes in root morphologymay be associated with the concentration changes of gibberelin and cytokinin,and it may also be associated with glucose-mediated signaling.3.In drought conditions,the decrease extent of plant height in SlSUT4 overexpressed plants was higher than that of the wild type;the transgenic plants wilted earlier,and the concentration of malondialdehyde-the product of membrane lipid peroxidation,in the leaves of the transgenic plants was also significantly higher than that of the wild-type plants.Under drought conditions,the contents of sucrose,starch,glucose and fructose in the roots and leaves of wild plants were significantly increased;in the transgenic plants,the contents of sucrose and starch were increased while the contents of glucose and fructose were decreased significantly in the leaves.There was no significant change in glucose,sucrose,fructose and starch contents in the roots between the wild type and transgenic plants.Under normal water supply,the expressions of HXK1/2/3/4,NCED1-the key enzyme gene in ABA synthesis,as well as the content of ABA were higher in the leaves of SlSUT4over-expressed plants than those in the wild type,while the expressions of these genes and ABA content in the root showed opposite results.Compared with the wild type,the change of glucose level in the transgenic plants may regulate the synthesis of ABA as a sugar signal.Under drought conditions,the expressions of NCED1 and HXK2/3 in the leaves of wild and transgenic plants were all increased,and the expressions of HXK1/4 were decreased.In the roots,the expressions of NCED1 and HXK1/2/3/4 were induced by drought,except that HXK3 expression was down-regulated in the wild type plants.The adaptive response of HXKs expression under drought stress needs further investigations.The results suggest that SlSUT4 may play an important role in growth and drought response in tomato.