Mechanism Of Transcription Factor HY5 Systemically Regulating High Light Stress Tolerance In Tomato

Light is one of the basic conditions for maintaining plant survival.Plants convert energy from sunlight into chemical energy to provide matter and energy for growth and development.However,when the light intensity exceeds the threshold required by plants,it will turn into high light stress for plants,resulting in photooxidative cellular damage and photoinhibition,which greatly limiting the growth and development of plants.In the midsummer or high-altitude areas with sufficient sunlight energy,high light stress is one of the common abiotic stresses for the production of tomato(Solanum lycopersicum)and other vegetable crops.However,the stress signal transduction pathway mediated by transcription factors is one of the important adaptation mechanisms for plants to cope with abiotic stresses.Therefore,Analyzing the response mechanism of vegetable crops to high light stress through the transcriptional regulatory network,and using gene editing,physiological,biochemical,environmental regulation and other means to improve the acclimation of vegetable crops to high-light environment,is meaningful for improving the quality and yield of vegetable crops.Based on this,this paper uses tomato as the model plant for research,using photobiology,plant physiology,molecular biology,bioinformatics,and genetics to explore the systemic responses of tomato to high light stress and examine the systemic signaling pathway of tomato to response high light stress.In addition,we further determined the mechanism of transcription factor LONG HYPOCOTYL 5(HY5)and C2H2 zinc finger protein(ZFP17)in improving the high light stress tolerance of tomato.The main research results obtained are as follows:1.The systemic responses of tomato to high light stress were explored.Setting partial shading treatment to exposed the plant’s local leaves to high light stress.The results show that applying high light stress to local leaves can effectively improve the ability of the distal unstressed(systemic)leaves to resist high light stress,and through further analysis of the parameters about photoprotection,it is found that the high light stress on local leaves can activate the xanthophyll cycle of the distal(systemic)leaves and enhance the NPQ-dependent photoprotection,and then when the distal(systemic)leaves are subjected to high light stress subsequently,the reaction time of responding to the high light stress is greatly shortened,thereby enhancing the high light stress resistance.2.The systemic signal that mediating the systemic responses of tomato to highlight stress is clarified.Using HY5-related mutant plants as the upper leaves for grafting with the lower leaves of wild-type plants.Immunoblot analysis of the proteins extracted from the lower leaves showed that when only the upper leaves were irradiated with high light,HY5 could move from the upper leaves to the shading lower leaves under the induction of high light stress.Furthermore,by comparing the systemic responses of different grafted plants to high light stress,the results showed that the HY5 protein in the upper leaves played a key role in inducing the systemic responses of tomato to high light stress.3.The mechanism of transcription factor HY5 in activating the xanthophyll cycle was analyzed.Through the analysis of gene expression and protein content,it is found that high light stress can significantly induce the expression of Sl HY5 and the accumulation of HY5 protein.At the same time,the violaxanthin de-epoxidase(VDE)and the proton gradient regulatory protein 5(PGR5)as important regulators of the xanthophyll cycle,their synthetic genes are also significantly up-regulated under the induction of high light stress.The content of VDE and the PSII subunit S(Psb S)protein which acts as proton receptor also increases significantly,and the trend of their time dynamic changes is consistent with HY5 under high light stress.Further analysis using EMSA,yeast one-hybrid system,Ch IP,and dual luciferase reporter gene system showed that HY5 can directly bind to the promoters to activate the expression of SlPGR5 and SlVDE.4.Clarifying the systemic signaling pathway that SlPGR5 and SlVDE mediating HY5 to regulate the systemic responses of tomato to high light stress.The pgr5 mutant plants and the vde gene-silencing plants were used as the lower leaves to graft with the upper leaves of wild-type plants,and the upper leaves were treated with high light stress,and then the parameters about photoprotection of the shading lower leaves were analyzed.The results showed that no matter either the SlPGR5 or the SlVDE was lacking in lower leaves,the systemic signal HY5 would lose the downstream target genes,leading to the failure of the xanthophyll cycle activation in lower leaves.As the result,the tomato plants weakened the systemic responses to high light stress.These results prove that SlPGR5 and SlVDE act as signal receptors downstream of the systemic signal,mediating HY5 to regulate the systemic responses to high light stress.5.Exploring the mechanism of the C2H2 zinc finger protein ZFP17 and HY5 jointly regulating the resistance of tomato to high light stress.According to the results of protein structure and gene expression analysis,screening out the C2H2 zinc finger protein ZFP17,which was significantly induced by high light stress.Then,through the construction of ZFP17 transgenic plants,the verification of protein interaction relationship and the VIGS experiment,we found that ZFP17 could physically interact with HY5,and then enhancing the effect of HY5 in up-regulating the resistance to high light stress of tomato by NPQ-dependent pathway.