The Mechanism Of Gibberellins And Brassinolide In Regulation Of Resistance To Early Blight Of Postharvest Tomato Fruit

Tomato(Solanum lycopersicum)plays an important role in vegetable industry in China,while it is sensitive to numerous diseases caused by fungus.Early blight caused by Alternaria solani is one of the most common postharvest fungal diseases,which resulted in huge economic losses for tomato industry extremely.Gibberellins(GAs)and brassinolide(BR)are crucial endogenous hormones of plants,both of them contribute to regulate the response to the biotic stress in plants.Meanwhile,tomato,as a model plant,is valuable for the study about the regulation mechanism in the development of physiology and pathology of fruit and vegetables.This study is conducted to investigate the regulation mechanism of GA and BR in the response to Alternaria solani in postharvest tomato fruit,which has great theoretical value and practical significance in perfecting the signal network of resistance to disease in postharvest fruit and vegetables and reducing the loss of postharvest fruit and vegetables.Postharvest tomato fruit of the wild type(Solanum lycopersicum L.cv.Money maker)and the mutant gib-3,deficient of GA,at the mature green stage were inoculated Alternaria solani,stored at room temperature for 9 days(90%-95% relative humidity).Disease incidence and lesion area were observed during the storage.The activities of phenylalanine ammonialyase(PAL),chitinase(CHI),?-1,3-glucanase(GLU),and polyphenoloxidase(PPO)were evaluated in this study.The content of BR and the expression of ICS1 and NPR1,as well as WRKY transcription factors such as SlWRKY8,SlWRKY46,SlWRKY51,SlWRKY69 and SlWRKY80 were also compared in the two groups.In addition,the wild type pretreated with 0.5 mM BR and brassinazole(BRz),respectively.Tomato fruits harvested at the mature green stage after pretreatment were inoculated and stored with the same methods to the previous section.Similarly,disease incidence and lesion area were observed,the activities of enzymes responsible for disease resistance and the expressions of genes were also analyzed,and the sample at 0,3,5 days from control group and BR treatment group were studied by quantitative proteomics.The main results are as follows.(1)Compared to the wild-type tomato fruit,the disease incidence and lesion area of gib-3 tomato fruit declined significantly with the the increasement of the activities of PPO,PAL,CHI and GLU,and the content of BR rised.The expressions of ICS1 and NPR1 were up-regulated.Additionally,the expressions of SlWRKY8 and SlWRKY51 were up-regulated at the mature green stage,SlWRKY46 showed more high level of expression at hard-ripe stage and ripe stage,the expressions of SlWRKY69 and SlWRKY80 were up-regulated during the whole storage.The results presented that GA regulates the resistance of postharvest tomato fruit to early blight negatively.(2)Compared to the tomato fruit in control and BRz-treated group,the disease incidence and lesion area of the tomato fruit treated with BR were less than other two groups.PPO,PAL,CHI and GLU showed more high-level activities.The expressions of ICS1,NPR1 and WRKY transcription factors such as SlWRKY8,SlWRKY46,SlWRKY51,SlWRKY69 and SlWRKY80 were up-regulated.The results showed that BR improved the resistance to early blight in tomato fruit.(3)The results of quantitative proteomics were as follows: compared to the tomato fruit of control group,GO functions of the differential proteins in BR-treated group enriched in structural molecule activity,biological regulation,antioxidant activity and response to stimulus significantly.KEGG pathway enriched in phenylpropanoid biosynthesis and flavonoid biosynthesis.There were 2 proteins up-regulated and 13 proteins down-regulated screened.One of the up-regulated proteins was related to immune system process,and participated in phenylpropanoid biosynthesis.The other was located in chloroplast nucleoid,and contributed to protein processing in endoplasmic reticulum.GO functions of the down regulated proteins were concerned with macromolecular complex,supramolecular complex and structural molecule activity.The results indicated that BR induced the resistance to early blight in tomato fruit by promoting the biosynthesis of phenylpropanoid and programmed cell death at the infected organization.