H₂O₂-mediated Regulation Of Plant Heat Stress Response

Heat stress is defined as increased temperature sufficient to cause irreversible damage to plant growth and development.Generally,the ambient temperature of 10-15?above the optimum growth temperature will cause heat stress to plants.It was predicted that the global temperature will increase by about 1-2?by 2050,and 3-5°C by 2100.High temperature will damage plasma membrane stability,protein function,RNA cleavage,cytoskeletal structure,etc.,leading to disorders of plant cell function,restraining the growth,and even causing plant death.It was predicted that the production of major crops including wheat,corn,rice,will drop by 50%,if global average temperature increases by3?.Heat stress also produces excess amount of reactive oxygen species(ROS),causing oxidative stress in plants.However,how ROS function in the process remains to be elucidated.Here,we report that heat stress-mediated increase of H₂O₂ reduces photosynthesis and inhibits plant growth through sulfenylating PGLP1 at Cys86 and thus repressing its enzymatic activity.Further,we obtained transgenic plants with higher thermal tolerance by expressing catalase2(CAT2)with chloroplast targeting peptide and thus reducing heat-mediated H₂O₂ accumulation.The main results are as follows:1.Plants accumulate H₂O₂ under heat stress and show the sensitivity to heat stress in terms of reduced chlorophll content,inhibited photosynthesis,less fresh weight and decresed survival rate.2.We found PGLP1,an important metabolic enzyme of photorespiration to degradate toxic 2PG,can be sulfenylated,and thus this PGLP1 sulfenylation inhibited its enzymy activity.3.By mutating each of the five cysteines of PGLP1 and detecting the sensitivity of these mutated enzymes to H₂O₂,we found that the Cys86 site is responsible for H₂O₂sulfenylation.Further,we demonstrated that the Cys86 of PGLP1 was also sulfenylated in vivo for lower enzyme activity.4.We showed that the overexpression of PGLP1 but not PGLP1-C86S can promote chlorophll synthesis,photosynthesis,plant growth and thermal tolerance compared with the wild type.Consistentaly,PGLP1-RNAi plants exbited opposite phynotype.5.We also demonstrated that expressing CAT2 with chloroplast targeting peptide can reduce heat-mediated H₂O₂ accumulation,thus decrease PGLP1 sulfenylation,conferring plant thermal tolerance in terms of higher chlorophyll content,photosynthesis,fresh weight and survival rate compared with the wild type.In summary,we found that heat-mediated plant H₂O₂ accumulation decresed chlorophyll content,photosynthesis,fresh weight and survival rate by sulfenylating PGLP1 at Cys86,and thus inhibiting its enzyme activity.Introduction of CAT2 into chloroplasts can effectively reduce the heat-mediated accumulation of H₂O₂ and decrease PGLP1 sulfenylation,thus enhancing plant thermal tolerance.