Functional Analysis Of Tomato SUMO E3 Ligase SlSIZ1

Plants are inevitable subjected to various abiotic stresses in the growth and development,such as strong light,draught,extreme temperature,and so on.These abiotic stresses influence the normal life process in plants.Post-translational modification is an important process in eukaryotes.The SUMOylation plays significant roles in post-translational modification.E1 activation,E2 conjugation and E3 ligation enzyme facilitate SUMOs bind to target proteins.SUMOylation is involved in regulation the response to high and low temperature,drought stress,salinity stress,development and nutrition metabolism.SIZ1,a SUMO E3 ligase,mediates the SUMOylation of target proteins.And SIZ1 also plays important roles in response to abiotic stresses,such as high and low temperature,drought stress and excess copper.Tomato,an important vegetable crop,originated from tropic.However,the thermotolerance of tomato is poor.High temperature,usually accompanied with drought stress which cause severely damage to tomato such as production decline and death.Few researches were displayed the roles of SIZ1 in response to drought and heat stresses in tomato.Meanwhile,the function of SIZ1 was also unclear in tomato.So,it showed great theoretical and practical value to explore the physiological function of tomato SlSIZ1 under drought and heat stresses.The SlSIZ1 gene was isolated from tomato.The functional analysis of SlSIZ1 was investigated using Arabidopsis,tobacco and tomato.The major results are as follow:(1)The tomato was treated by low temperature(4°C),high temperature(42°C),drought(PEG)and oxidation(MV).The SUMO conjugate levels were induced by all these stress treatments.SUMO conjugate was induced obviously under low and high temperature and drought stress.Under oxidation stress,the SUMO conjugate was induced slightly.(2)We cloned the SlSIZ1 gene(GenBank number,KP323389)from tomato leaves.The full length open reading frame(ORF)of SlSIZ1 is 2658 bp,and encoding 886 amino acids.The predicted molecular weight is 97.35 kDa,the isoelectric point is 4.92.This gene is located in the tomato chromosome 11.(3)SlSIZ1 can express in the tomato root,stem,leaf and flower,and the highest expression was observed in the leaf.The expression of SlSIZ1 was induced by heat,chiliing,drought and salinity,although it is not obvious.It suggested that the role of SIZ1 in response to abiotic stresses is associated with mediating SUMOylation of targeted proteins.The SlSIZ1 is located in nucleus.(4)Five conserved motifs were found in the sequence of SlSIZ1.Overexpression SlSIZ1 in Arabidopsis siz1-2 mutants partially complemented the phenotypes of dwarf,ABA-hypersensitivity and SUMO conjugation and exhibited the activity of SUMO E3 ligase to promote the accumulation of SUMO conjugates.(5)Under drought stress,overexpression SlSIZ1 could reduce the accumulation of ROS and MDA,increase the content of free proline,upregulate stresses-related genes and induce the SUMO conjugations in transgenic tobacco plants.Meanwhile,the germination rates and growth were higher in transgenic tobacco.So,overexpression SlSIZ1 can enhance the drought tolerance of transgenic tobacco.(6)Under heat stress,overexpression of SlSIZ1 could reduce the accumulation of ROS and induce the SUMO conjugations in tomato.SlSIZ1 mediated SUMOylation of SlHsfA1 may be benefit to enhance HsfA1's activity for up-regulating SlHsfA2,SlHsp70 and SlHsp90.Meanwhile,the degration of Hsp70 was decreased in transgenic tomato.SlHsp70 maybe also could interact with SlSIZ1 weakly.We hypothesize that the low decrease of SlHsp70 may be associated with SUMOylation,which enhanced its stability.Therefore,overexpression SlSIZ1 could enhance the thermotolerance of tomato.