| Strawberry powdery mildew is considered as the most common of fungal diseases,and affects the development of the strawberry industry and causes serious economic losses.It is common that chemical supplements are useful for prevention of powdery mildew,leading to consumer health and food safety threat,therefore,it is of great practical significance to carry out efficient and harmless control of strawberry fungal diseases.Understanding the molecular regulatory mechanism of strawberry resistance to powdery mildew is the basis for the control of strawberry powdery mildew,and it is also one of the foundations for the cultivation and genetic improvement of strawberry varieties.A lots of studies have shown that salicylic acid(SA)and jasmonic acid(JA),plant growth regulators,play important regulatory roles in plant disease resistance.In this thesis,octoploid strawberry(Fragria x ananassa cv.'Benihoppe')is used as material.Strawberry is divided into a double-distilled water treatment group(control group)and an SA induction group.Podosphaera aphanis inoculation under artificially controlled conditions,the comparative transcriptomics technology was used to screen the differential expression genes(DEGs)of strawberry before and after resistance to powdery mildew,and to determine the resistance of strawberry to white powder by analyzing the expression of different genes related to the salicylic acid pathway,jasmonic acid pathway and phenylpropane metabolic pathway The regulation network node of bacteria aims to clarify the molecular regulation mechanism of strawberry powdery mildew from the perspective of signal pathways regulated by plant growth regulators,and provide a theoretical basis for improving the efficiency of strawberry powdery mildew control.The main findings are as follows:1.The physiological and biochemical characteristics of SA-primed strawberry resistance to powdery mildew was clarified.After powdery mildew infection,the activity of enzymes related to the disease-resistant active oxygen metabolism system in strawberries increased,such as SOD,POD,CAT,PAL,and PPO in strawberry leaves increased,while the five enzyme activities from SA group was higher than that in the control group.At the same time,the fluorescence parameter indicators(Fv/Fm,?NO,and ?PSII)related to photosynthesis decreased significantly after powdery mildew infection,but the reduction of these parameters in SA group was smaller than that in the control group.In addition,the germination rate of powdery mildew spores in the SA-induced group was significantly lower than that in the control group.These results showed that SA could not only improve the resistance of strawberry to powdery mildew,but also inhibit the germination rate of powdery mildew spores.2.The RNA-seq results showed that the unigenes of strawberry responded to powdery mildew infection in the double-distilled water treatment group were 48,020,while the unigenes of strawberry response to powdery mildew infection in the SA induction group was 45,896.The control group had 4,198 DEGs,while the SA group had 3,754 DEGs.In addition,PCA analysis also confirmed that DEGs are stable.KEGG pathway enrichment analysis found that phenylpropane and flavonoid biosynthetic pathways are the main enrichment pathways of strawberry in response to powdery mildew infection.Phylogenetic analysis and conserved domain analysis indicate that Fa MYB9/11,Fab HLH3,and Fa TTG1 are involved in regulating anthocyanin biosynthesis in leaves,leading to the accumulation of the secondary metabolite proanthocyanidins.Our further research also proved that the total flavonoids(TFC)and proanthocyanidins(PAs)content of strawberry in SA group was higher than those in control group.The results show that SA can increase the content of TFC and PAs in strawberry.3.This study proves that the two key enzymes in SA biosynthesis in strawberry are phenylalanine ammonia lyase(PAL)and isobranched acid synthase(ICS),which is consistent with other species.Two key genes for salicylic acid synthesis(Fa ICS1 and Fa PAL2),the expression of Fa ICS1 did not change significantly during the infection of powdery mildew in the control group,and the expression of Fa PAL2 showed a significant upward trend,while the expression of Fa ICS1 and Fa PAL2 in the SA induction group was in the early stage of induction Significantly increased,indicating that the response of red-faced strawberry to powdery mildew may be based on the PAL pathway,while the ICS pathway may be suppressed in the early stage of powdery mildew infection.In the early stage of powdery mildew infection of strawberry leaves(from 0 to 3 dpi),the SA-induced PR1 gene expression was significantly up-regulated without Fa NPR1;while Fa NPR3 may be an inhibitor of the SA signaling pathway,strawberries need to quickly balance the negative effects caused by excessive SA effect.Genes related to the JA signaling pathway at the beginning of SA induction,Fa LOX?Fa AOS?Fa JAR?Fa JAZ?Fa WKRY33 and Fa MYC2 were significantly increased,suggesting that the SA pathway and the JA pathway have a synergistic effect,and SA may promote JA organisms to a certain extent.Synthesis,JA and SA have a synergistic effect in the process of strawberry against powdery mildew.In addition,the expression levels of genes encoding disease-related proteins PRs(PR1,PR2,PR3,and PR5)in strawberries in the two groups of treatments showed a continuous upward trend throughout the course of the disease,indicating that they play an important role in strawberry resistance to powdery mildew.To sum up,SA induction can promote the biosynthesis of JA,which leads to the accumulation of PAs and the significant up-regulation of genes related to the downstream disease course.Both of them participate in the defense against P.aphanis.4.The molecular regulation mechanism of strawberry resistance to powdery mildew is also achieved through multiple ways.Key homologous genes in the immune response(PTI)pathway and effector protein-evoked immune response(ETI)pathway triggered by strawberry pathogen-associated molecular patterns were identified.Both of these pathways are involved in the SA signaling pathway,and they jointly participate in the molecular regulatory network of strawberry against powdery mildew.Comprehensive phylogenetic analysis,conserved domain analysis,and DEGs expression analysis during the course of disease,put forward a more comprehensive map of the molecular regulation network of strawberry against powdery mildew.In summary,SA can enhance the resistance to powdery mildew by participating in regulating the activity of active oxygen metabolism system enzymes related to disease resistance in strawberry and the content of certain secondary metabolites.In addition,SA can cooperate with JA in the early stage of induction Activating the expression of multiple defense genes not only enables strawberry to acquire systemic acquired resistance,but also inhibits powdery mildew at the infection site together with proanthocyanidins.This article preliminarily constructed the molecular regulation network of strawberry resistance to powdery mildew,and laid the foundation for the research innovation and development of strawberry disease resistance regulation technology. |
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