Effects Of Glycinebetaine On D1 Protein Turnover In Tomato Under High Temperature Stress

Heat stress is one of the main environmental factors that limits the growth and productivity of crop plants.Photosynthesis is most sensitive to heat stress among various processes.Photosystem II(PSⅡ)is highly sensitive to the detrimental impact of heat and other stress.The turnover of D1 protein is essential to maintain the structure and function of the PSⅡ.Under stress conditions,plants have evolved a variety of mechanisms to adapt to abiotic stress,such as the accumulation of glycinebetaine(GB)and other compatible substances.GB as one of compatible substances can improve resistance of plants.Therefore,it is significant to study the effects of glycinebetaine on D1 protein turnover under high temperature stress to improve the thermotolerance of plants.In this study,the effects of glycinebetaine on the turnover of D1 protein were studied by using wild type and the codA transgenic tomato plants as experimental materials.The main results are as follows:(1)Under high temperature stress,compared with wild type plants,the codA transgenic plants maintained higher photosynthetic rate(Pn)and the maximal photochemical efficiency of PSⅡ(Fv/Fm).(2)Under high temperature stress,the expression of genes involved in the D1 protein de novo synthesis(psbA,hcf173 and hcf244)and D1 protein degradation(Fts H2,Deg5 and Deg8)were at a higher level in codA transgenic plants,so as to maintain faster repair cycle of D1 protein.In addition,GB can alleviate the damage of D1 protein at high temperature and maintain a lower phosphorylated D1 protein content.(3)Under high temperature stress,in comparison with wild type plants,the transgenic plants maintained the higher relatively antioxidant enzyme activities and expression of antioxidant enzyme-related genes.Hence,the accumulation of reactive oxygen species(ROS)and the inhibition of ROS to the de novo synthesis of D1 protein were alleviated and a higher D1 protein content was maintained in transgenic plants.(4)Under high temperature stress,compared with wild type tomato plants,the transgenic plants increase thermotolerance by maintaining higher level of HSP70.(5)Under high temperature stress,the transgenic plants maintained more stability of PSⅡ complex than those of wild type plants.Our results indicated that GB could protect D1 protein from high temperature and maintain the stability of D1 protein.In terms of the degradation of D1 protein,GB can maintain the higher expression of FtsH and Deg to degrade the damaged D1 protein in time during high temperature stress.As for the de novo synthesis of D1 protein,GB can maintain higher expression of psbA.Besides,GB can reduce the accumulation of ROS to alleviate the inhibition of ROS on D1 protein translation process,thus accelerating the de novo synthesis of D1 protein.