Photoprotective Mechanism Of Tomato Cyclic Electron Transport And Synergistic Effect Of NaCl And Melatonin Under Low Night Temperature

The phenomenon of low night temperature is common during the winter production of solar greenhouse in north China.Low night temperature leads to photoinhibition,which directly decrease photosynthetic efficiency of leaves.PSI cyclic electron transfer?CEF?mediated by the Proton Gradient Regulation 5?PGR5?and PGR5 Like 1?PGRL1?pathway is very important for photoprotection,and some metabolic substances such as melatonin can also alleviate stress injury and enhance photosynthetic efficiency of plants.Therefore,the regulation of PGR5/PGRL1 complex and melatonin on photosynthesis of tomato under low night temperature is worth exploring.This study first analyzed the function of PGR5/PGRL1 and its photoprotection regulation of tomato leaves under low night temperature,then studied the role of CEF in the adaptability of salt-low temperature cross stress,and finally studied the regulation of melatonin on photosynthesis of tomato under low night temperature.The main results are as follows:1.The role of PGR5/PGRL1 dependent CEF in regulating photoprotectionCRISPR/Cas9 technology was used to knock out tomato PGR5 and PGRL1 genes,and PGR5/PGRL1 overexpression and RNAi silencing T1 generation materials were also obtained.PGR5/PGRL1 functional defective plants grow all showed very weak,photosynthesis assimilation rates have dropped dramatically,PS?and PS?still severely photoinhibition even in a suitable environment,and the effect on PS?is more apparent,the CEF of PGR5/PGRL1functional defective plants at extremely low levels,the Y?ND?showed almost completely inhibit,plants can also remain higher NPQ at PS?under strong light intensity,indicated the photoprotection role of PGR5/PGRL1 on PS?and PS?are difference.2.Photoprotective effect of PGR5/PGRL1 complex dependent CEF on tomato leaves at low night temperatureAfter treatment with low night temperature,Pn,E and GH₂O of WT were significantly lower than PGR5-OE and PGRL1-OE.Transmission electron microscopy?TEM?results of chloroplast showed that PGR5/PGRL1 dependent CEF could alleviate the damage of low night temperature to chloroplast quality.PGR5-OE and PGRL1-OE significantly improves the PSI and PS?activity of tomato leaves under low night temperature,as well as the ETR?I?,ETR?II?and CEF,low temperature photoinhibition was alleviated by enhancing Y?ND?and Y?NPQ?.The results showed that the overexpression of PGR5 and PGRL1 could alleviate the photoinhibition of low night temperature on the photosynthetic performance of tomato leaves.3.The PGR5/PGRL1 pathway induces transcriptome and proteome remodeling in tomato in response to low night temperatureUnder normal temperature,in comparison with PGR5-RNAi,PGR5-OE Up-regulated 890genes expression,down-regulated 301 gene expression,the degree of enrichment of systemic acquired resistance and light-harvesting antenna of PSI items are the highest,a lot of differences protein concentration in photosynthesis and chloroplast relevant entries,the most enrichment of KEGG metabolic pathways is photosynthesis.Compared with WT at low night temperature,differentially expressed genes induced by PGR5-OE were mainly enriched in nucleus,chloroplast,protein kinase activity and defense response.Thylakoids were the most enriched proteins in cell components,and ascorbic acid and other secondary metabolisms were the most enriched by KEGG.It was suggested that PGR5/PGRL1 dependent CEF could induce a large number of genes and proteins related to photosynthesis and chloroplast quality and stress response in response to low night temperature stress4.Regulatory role of CEF in photosynthetic acclimation of tomato leaves under salt-low temperature cross stressSalt-low temperature cross stress results show that the Na Cl pretreatment significantly reduced CO₂ assimilation rate and photochemical reaction efficiency,and induced non-photochemical quenching at PS?and PS?,however,Na Cl pretreatment could significantly enhance the photosynthetic capacity of tomato leaves,and improve the PS?II?and PS?I?activities,Y?I?and Y?II?,and linear and PSI cyclic electron transfer rates of tomato plants suffer subsequent low temperature stress.In this process,CEF is an important photoprotection mechanism,when Na Cl pretreatment plants experience low temperature stress,higher CEF plays an important role in regulating the distribution of light energy among photosystems,balancing photoprotection and photochemical reaction.5.Effects of low night temperature on photosynthetic performance of tomatoes pretreated with melatoninExogenous melatonin treatment significantly reduced MDA content and increased POD activity in tomato leaves at low night temperature,while photosynthetic gas exchange rate,photosystem activity and electron transfer were significantly increased.A large number of photosynthetic and chloroplast mass related genes and proteins were induced by melatonin pretreatment,among which 423 genes were up-regulated and 115 genes were down-regulated,which were mainly concentrated in stress response and metabolism of carbohydrates,terpenes and polyketones,and biosynthesis of brassinosteroids.77 proteins were up-regulated and 49were down-regulated,which were mainly related to the biosynthesis of flavonoids,chloroplast envelope,chloroplast endopeptidase Clp complex,carbohydrate,amino acid,flavonoid and vitamin metabolism.We obtained the T1 generation material of tomato melatonin decomposase enzyme gene M3H overexpression T1 generation materials,Fv/Fm and Pm of M3H overexpression plants in room temperature and under low night temperature were significantly lower than that of WT,and low night temperature after processing the MDA content and SOD activity increased dramatically,M3H overexpression of photosynthetic pigment content decreased significantly,and Y?I?,Y???,ETR?I?,ETR???and CEF were significantly lower,show that overexpression of M3H reduces the tomato photochemical reaction efficiency.6.PGR5/PGRL1 mediates the effect of melatonin on photosynthesis in tomato leaves at low night temperatureMelatonin pretreatment significantly improved Y?I?,Y???and ETR?I?,ETR?II?and PSI cyclic electron transfer of the PGR5,PGRL1 RNAi silence plant,among which the ETR?I?affect the most obvious;Melatonin pretreatment significantly reduced PGR5 and PGRL1 RNAi silence plant Y?NA?and Y?NO?,and significantly improves the Y?ND?and Y?NPQ?,these results showed that PGR5/PGRL1 pathway mediated melatonin through adjusting the donor side and receptor side of PS?and improve NPQ alleviate the inhibition of low night temperature on photosynthetic apparatus of tomato.In conclusion,PGR5/PGRL1 is the main CEF pathway in tomatoes,which can alleviate the photosynthetic inhibition of low night temperature on tomato leaves by PSI donor side and accept side regulation as well as NPQ.CEF plays an important regulatory role in plant resistance to salt-low temperature cross stress.Melatonin can improve tomato resistance to low night temperature by regulating photosynthetic efficiency.