| Fusarium head blight of wheat caused by Fusarium graminearum is a major fungal disease affecting grain production and food safety in China.In addition to reducing wheat yield,deoxynivalenol(DON)and other mycotoxins produced by F.graminarum can also contaminate wheat and its products,causing a serious threat to human and animal health.Effective prevention and control of Fusarium head blight and reducing toxin pollution in cereals are important agricultural production problems that need to be solved urgently,and are important guarantees for food security and food safety in China.Exploring the key metabolic pathways in F.graminearum interaction,screening natural products and their analogues with multiple functions such as antifungal,growth regulation,induced resistance,and weed control,and revealing their molecular mechanisms are of great guiding significance for molecular breeding of F.graminearum resistance,development of environmentally friendly multi-effect agricultural agents,and formulation of new strategies for F.graminearum control.In this study,the combined transcriptome and metabolome analysis was used to delineate the metabolic profile of wheat spikes at the early stage(24 h)of F.graminearum infection.A total of 659 compounds were detected,including 28 types of organic acids,amino acids,lipids,nucleotides,sugars,alkaloids,phenols and hormones.Among them,45 metabolites were significantly increased(FC>2,p<0.05)and 46 metabolites were significantly decreased(FC<0.5,p<0.05).PCA analysis showed that the proportion of PC1 was 71.5%,PC2 was 20.1%,and the sum of PC1 and PC2 was 91.6%,indicating that F.graminearum infection caused significant changes in metabolite components in wheat spikes.The results showed that only 0-13.0% sugars,vitamins,choline,alkaloids and terpenoids in wheat spikes significantly increased or decreased at the early stage of F.graminearum infection,while up to 20.0% of hormone compounds changed significantly,suggesting that plant hormones played an important role in the interaction between wheat and F.graminearum.Therefore,we focused on the four hormone-related pathways JA,SA,ET and IAA in wheat spikes at the early stage of F.graminearum infection,and conducted metabolomics and transcriptome correlation analysis,and the results were as follows:(1)The content of α-linolenic acid,the upstream precursor of JA synthesis pathway,was significantly decreased,while JA and its derivatives Me JA and JA-Ile were significantly increased.JA-Ile can promote the binding of receptor COI1 to the negative regulator JAZ protein,result in the degradation of JAZ by 26 S proteasome,relieve the inhibitory effect of JAZ on the transcription factor MYC2,and thus initiate the transcription of JA-responsive genes.Therefore,the increase of JA-Ile content in wheat spikes at the early stage of infection indicated that JA signaling pathway might be activated.(2)The precursors of SA biosynthesis,L-phenylalanine and cinnamic acid,were significantly increased in wheat spikes,while the intermediate chorismic acid(CA)and the final product SA were significantly decreased.The genes related to SA synthesis were significantly down-regulated,indicating that SA signaling pathway was inhibited in wheat spikes at the early stage of infection.(3)The content of methionine,the starting compound of ET synthesis pathway,was significantly decreased,while the S-adenosylmethionine synthase(SAMs)and 1-aminocyclopropane-1-carboxylate synthase(ACCs)in the ET synthesis pathway were up-regulated,indicating that the ET signaling pathway might be activated in wheat spike at the early stage of F.graminearum infection.(4)The content of indole,the precursor compound of IAA synthesis,was significantly decreased,while the content of IAA did not change significantly,but its derivatives methyl indole acetate(Me-IAA)and5-hydroxyindole acetic acid(5-HIAA)increased 2.2 and 3.9 times,respectively.Transcriptome analysis showed that almost all the genes involved in the three IAA synthesis pathways were up-regulated.These results indicated that IAA signaling pathway was activated in wheat spikes at early stage of F.graminearum infection.In summary,up to20.0% of the hormonal compounds in wheat spikes were significantly changed during the early stage of F.graminearum infection,in which JA,IAA,and ET signaling pathways were activated while SA signaling pathway was inhibited.Previous studies have shown that endogenous plant hormones play an important role in the interaction between F.graminearum and wheat.At present,exogenous application of some plant hormones and their analogues is often used to regulate plant growth,disease resistance,drought resistance,and cold resistance in agricultural production.However,whether phytohormones and their analogues have direct antagonistic effects on pathogenic fungi is rarely reported.In this study,the antagonistic activities of plant hormones such as JA,SA,IAA,2,4-D(auxin analogue),NAA(naphthalene acetic acid),KT(kinetin)and GA(gibberellin)and their analogues against F.graminogastrium were detected by exogenous addition,and the hormone compounds with direct antagonistic effects on the growth and pathogenicity of pathogenic fungi were screened.It was found that both IAA and 2,4-D significantly inhibited the colony growth of F.graminearum,and 2,4-D was more effective at the same concentration.2,4-D is a synthetic auxin with similar physiological effects and more stable properties as IAA.In this study,the inhibitory effects of 2,4-D on the growth and development,DON toxin synthesis and pathogenicity of F.graminearum were systematically examined,and the molecular mechanism of the inhibitory effects of 2,4-D on F.graminearum was further revealed.The results showed that 2,4-D inhibited the colony growth,conidial formation,spore germination and germ tube elongation of F.graminearum,but had no effect on sexual reproduction.In addition,2,4-D significantly inhibited the pathogenicity of F.graminearum.Further studies showed that 2,4-D inhibited the formation of infection structures,the expansion of infected hyphae and the biosynthesis of DON toxins,and caused a large accumulation of ROS in the hyphae of F.graminearum.The combined metabolomics and transcriptome analysis showed that 2,4-D treatment led to the significant accumulation of glycerol and arabitol in F.graminearum.The expression of genes related to glycerol and arabitol synthesis,such as glycerol-3-phosphate dehydrogenase(GPD3)and ribulokinase(RBK),was up-regulated by more than 2 folds.We also found that 2,4-D treatment did not induce the accumulation of glycerol and arabitol in the Fg Hog1 mutant,while the Fghog1-mediated hyperosmotic glycerol signaling pathway activation also increased the accumulation of glycerol and arabitol,suggesting that the Fg Hog1 signaling pathway may be the target of 2,4-D.Western blot results also showed that 2,4-D treatment significantly increased the phosphorylation level of Fg Hog1,which may be the main reason for 2,4-D inhibiting the growth of F.graminearum.In addition,we found that 2,4-D treatment significantly reduced the phosphorylation of Gpmk1 in Fus3/Kss1 pathway,but not Mgv1 in the cell wall integrity pathway.In conclusion,the inhibition of the growth of F.gramiearum colony by IAA analogue 2,4-D may be partially dependent on overactivation of Fg Hog1 signaling pathway,and the inhibition of pathogenicity may be realized by inhibiting the Gpmk1 signaling pathway. |
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