Regulatory Mechanism Of FvNPR1 Protein On Disease Resistance In Post-harvest Strawberry Fruits

Strawberry fruit is sweet and sour,juicy,nutritious and delicious,deeply loved by the public.However,it is easily subjected to mechanical damage and pathogenic microorganism infection and decay,which makes strawberry serious loss in the process of storage and transportation.In order to reduce the loss caused by disease and improve the quality,chemical fungicides are widely used,but due to the resistance problem of chemical fungicides,and pesticide residues may cause a series of food safety problems,so the use of chemical fungicides is limited to some extent.Therefore,how to inhibit the infection of pathogens after the strawberry fruit harvest has become an urgent problem to be solved.The main line is the regulation of TGA and NPR1 protein,FvFLS2/FvBAK1/FvBIK1 receptor complex and the interaction mechanism in the disease resistance response of postharvest strawberry fruit induced by elicitors(BTH and BR).To study the regulatory role of NPR1 protein and FvBAK1 transcription factor in strawberry fruit disease resistance network,the results are as follows:(1)Identification of strawberry TGA family and interaction analysis with NPR1 protein were studied.The results showed that 17 strawberry TGA family members were retrieved in the genome database of tetraploid forest strawberry(Fragaria vesca),which were uneven distributed on 7 chromosomes.Most genes ranged between 6 ～ 7.96 kb,coding protein length of 147 ～ 545 aa,molecular weight of 17.04 ～ 60.29 kD,isoelectric point of 5.77 ～ 8.92,instability coefficient of 39.05 ～ 67.1,and fat index of 50.44 ～ 96.28.Most of these encoded proteins are unstable hydrophilic proteins,do not contain transmembrane domains and are all nuclear localized proteins.According to the phylogenetic tree of strawberry,it can be divided into five subgroups.Strawberry TGA family members are mainly clustered in subgroups I,IV and V,and a few are clustered in subgroups Ⅲ.The cis-acting elements of the promoters of strawberry TGA family members are similar,including stress response elements and plant hormone response elements.The FaNPR1 protein contains a BTB domain and three ANK repeats on the genetically conserved domain,and a nuclear localization signal and seven disulfide bonds in the amino acid sequence BTH treatment of strawberry fruit can induce SAR response and improve cell reduction potential,and then FaNPR1 protein from cytoplasm to nucleus to interact with strawberry TGA transcription factor,initiate the expression of downstream PRs genes,activate the priming defense response and enhance the resistance of strawberry fruit against pathogen invasion.(2)The effect of BR treatment on strawberry fruit decay and quality after harvest was studied.The results showed that BR elicers from 5 μM to 50 μM could inhibit the decay of strawberry fruit,especially BR at a concentration of 10 μM could significantly limit the development of B.cinerea.Natural rot increased sharply in the late storage period,and B.cinerea had strong infection of strawberry fruit.BR treatment could significantly reduce the incidence and spot diameter of strawberry fruit,while reducing the infection rate of gray mold B.cinerea infection seriously affected the storage quality of strawberry fruit,BR treatment can control TA,TSS,hardness and the corresponding sensory quality decline,at the same time promote the accumulation of total anthocyanins,phenol and other antioxidant content,accelerate the rise of DPPH radical clearance,effectively improve the antioxidant capacity of strawberry fruit,improve the overall quality of fruit.These results indicate that BR treatment has some effects on the decay and quality of harvested strawberry fruit,and BR can induce the disease resistance of strawberry fruit,thus reducing the occurrence of gray mold.It is very important to choose the appropriate concentration of BR for the preservation of strawberries,because different fruits and vegetables and tissues have slightly different requirements on the concentration and mode of BR treatment.Therefore,exploring the treatment method of appropriate concentration and treatment in the application of green elicitor BR will make them have a better development prospect in the field of preservation.(3)The involvement of the receptor-like kinase complex of FvFLS2 and FvBAK1 in brassinoloid-induced postharvest immunity in strawberry fruits was investigated.The results showed that FvFLS2,FvBAK1 and FvBIK1 are three plasma membrane-localized kinases involved in the process of BR induced strawberry fruit resistance,and in yeast cells FvBAK1 physically interacts with FvFLS2,FvBIK1 and FvRBOHD according to the yeast two-hybrid assay.The induction of NPR1,PR1,PR1,PR2 and PR5 genes and ROS increased in strawberry fruit.The ROS burst and SA-dependent defense responses were enhanced in BR-treated strawberry fruits during B.cinerea infection.Overexpression of BAK1 promotes ROS accumulation and BR-induced defense responses,whereas mutants with loss-of-function of BAK1 impair BR-induced SA signaling and immunity against necrotizing fungal pathogens.BAK1,SA signaling,and BR-induced disease resistance to B.cinerea were positively correlated.These results illustrate that FvBAK1 further forms a receptor complex with the downstream substrate BIK1 and induces RBOHD transcription according to the PTI response induced by B.cinerea.The interaction between FvBIK1 and FvRBOHD contributes to the FvRBOHD-dependent burst of ROS,a ROS that enhances SA signaling during the PTI response of postpicked strawberry fruits exposed to necrotizing fungi.We illustrate the importance of FvBAK1 as an upstream regulator of FvBIK1 and a FvFLS2 coreceptor in the establishment of post-harvest PTI signaling in strawberry fruit.