Study On Role Of Priming In Induced Resistance By β-aminobutyric Acid In Harvested Mango Fruit

Mango(Mangifera indica Linn.)is a very important economic crop in the tropics and subtropical regions.However,mango is extremely susceptible to decay and deterioration due to the infection of pathogenic microorganisms during postharvest storage and transportation,leading to severe quality deterioration and huge economic losses.Anthracnose caused by Colletotrichum gloeosporioides is well known as one of the most destructive postharvest diseases in mango fruit.It has become a research hotspot on controlling postharvest disease based on induced disease resistance in fruit and vegetable by applying physical,chemical and biological elicitors.Upon treatment with some chemical elicitors,the defense reaction in plants can be set to an alarmed state,in which the stronger defense responses will be activated once the plants are infected by pathogens.This type of interaction between host and pathogen is referred to as ’priming’.Priming of defense has played an important role in induced resistance on harvested fruit,but cell mechanisms of defense priming are poorly understood.Using mango fruit and C.gleosporioides as the interaction system,in this study,the mango fruit were treated with β-aminobutyric acid(BABA),followed by the inoculation with pathogens.The mode of the defense-related metabolisms and signal molecules contents in fruit was analyzed,which would be conducive to ascertain the function of priming and resistance-related signal pathway regulated by priming.The results are as follows:(1)50 mM BABA treatment effectively suppressed the expansion of lesion in mango fruit inoculated with C.gloeosporioides and significantly reduced the natural incidence and index of harvested mango during storage.During the whole storage period,the average diameter of BABA treated fruit was 21.8%lower than that of the control fruit.During storage period,the natural incidence and index of BABA treated fruit were 75.2%and 75.9%lower than those of the control fruit,respectively.(2)The activities of phenylalanine ammonia enzyme(PAL),chitinase(CHT)andβ-1,3-glucanase(GLU),total phenol and flavonoids content in BABA + inoculated fruit is the highest,followed by water + inoculated,BABA,control(water).The results indicated that the resistance reaction induced by BABA might involve the priming process.(3)In this study,11 differentially expressed genes were screened using the non-reference-based transcriptome sequencing technology,and the quantitative real-time PCR(qRT-PCR)results were consistent with the transcriptome data(r=0.78).(4)The expression level of defense genes such as peroxidase gene(POD),CHT,cinnamyl-alcohol dehydrogenase gene(CAD),cysteamine dioxygenase gene(CDO),none expressor of pathogenesis-related genes(NPR1),TGA transcription factor gene(TGA)induced by BABA increased slightly at the early stage of priming to make preparation for defense.In addition,these genes expression level gradually increased after the inoculation of C.gloeosporioides to enhance the disease response.(5)BABA treatment significantly induced an increase of the salicylic acid(SA)content but did not promote a significant change in jasmonic acid(JA)content.It indicated that the priming response in induced resistance by β-aminobutyric acid in harvested mango fruit was dependent on SA signaling pathway rather than JA signaling pathway.(6)The MPK20 gene was slightly up-regulated by BABA in the early priming stage.Once attacked by pathogens,expression level of MPK20 rapidly enhanced,indicating that it might involve in the priming reaction of BABA-induced resistance against mango anthracnose.(7)The expression level of defense genes such as WRKY75,WRKY47,WRKY23 induced by BABA increased slightly at the early stage of priming,and the defense reaction was enhanced once the pathogen was inoculated.The WRKY11 gene played a negative role in priming process of BABA-induced resistance against anthracnose in harvested mango fruit.