Discussion On The Mechanism Of CmPIFs In Response To Powdery Mildew Stress Induced By Red Light In Melon(Cucumis Melo L.)

Oriental melon(Cucumis melo var.makuwa Makino),commonly known as "muskmelon",is widely cultivated in most areas of China due to its strong adaptability and considerable economic benefits,especially in Northeast and North China.Powdery mildew is the most common fungal disease in the protected cultivation of melon,which can seriously harm the plant health and lead to poor fruit quality and substantial yield reduction.Phytochrome interacting factors(PIFs)can integrate environmental signals such as light and temperature as well as various hormone signals in plants,regulate plant growth and development,and mediate plants to resist adversity stress.In this study,the members of the melon PIFs gene family were identified from the whole genome level,and the classification,gene structure,conserved domains and molecular characteristics of the family members which were analyzed by using bioinformatics technology.Quantitative real-time PCR(q PT-PCR)was used to determine the expression patterns of CmPIFs under the red light(RL),powdery mildew(PM),and inoculation powdery mildew after red light induction(RL+PM).Through VIGS(Virus-induced gene silencing)technology,its function in response to powdery mildew stress has been analyzed.The main findings are as follows:1.By using the method of homology comparison,four PIFs family members were identified from the whole genome of muskmelon,named CmPIF1,CmPIF3,CmPIF4 and CmPIF8.Chromosome location analysis inferred that the four members were located on chromosomes 4,5,7 and 11 respectively.The difference of gene sequence length between members is 3903 bp ～ 11550 bp;protein molecular weight is 52.5 ～ 74.6 k Da,and the isoelectric point of protein is 5.96 ～ 6.84.2.Red light induction significantly reduced the number of dead cells and the content of O2·-in infected leaves,reduced the area of powdery mildew spots on leaves,and finally significantly reduced the incidence of disease.Enzyme-linked immunoassay(ELISA)was used to measure the Jasmonic acid(JA)content in the infected leaves.It was found that JA accumulated rapidly in the body after the plant was infected by powdery mildew bacteria,and reached the highest level on the 5th day after treatment.But the JA content in the infected leaves under RL+PM treatment was significantly higher than that under PM treatment.Therefore,the red light may promote the accumulation of JA in plants,thereby enhancing the resistance of melon to powdery mildew.3.The members of the CmPIFs family of melons all responded to the red light.Among them,CmPIF1 and CmPIF3 were significantly up-regulated,and CmPIF8 was significantly down-regulated.CmPIF1,CmPIF3,and CmPIF4 were significantly up-regulated,while the expression levels of CmPIF8 were significantly down-regulated in infected leaves after PM treatment,and reached the maximum on the 5th and 7th day after PM treatment(when there are obvious white spots on the leaves).The change trend of relative gene expression after RL PM treatment was similar to that of PM treatment,but the gene expression level was lower than that of PM treatment,and the difference of CmPIF3 and CmPIF8 was the most obvious.4.RL+PM treatment of transient silent plants(TRV: CmPIFs)and non-transgenic plants(TRV: 00)of oriental melon,found TRV: CmPIF3 the smallest area of powdery mildew on the leaves,disease level,disease index,number of dead cells and O2·-content was the lowest,and the JA hormone level in infected leaves was significantly higher than that in control.Hence,it is inferred that CmPIF3 silencing can effectively reduce the sensitivity of plants to powdery mildew,reduce the occurrence of powdery mildew,and play an important role in the powdery mildew resistance pathway of melon.Moreover,the yeast one-hybrid test confirmed that CmPIF3 and CmLOX13 may interact with each other,indicating that CmPIF3 may regulate the transcription level of CmLOX13 through the interaction with the plant,thus affecting the content of JA in plants and mediating the response of oriental melon to powdery mildew stress.To sum up,four gene family members of CmPIF1,CmPIF3,CmPIF4 and CmPIF8 were identified in melon genome.The red light induction can improve the resistance of oriental melon to powdery mildew,CmPIF3 play a negative regulatory role in this pathway,and may interact with CmLOX13 to affect the JA level in plants,mediate oriental melon against powdery mildew stress.