Molecular Mechanisms On The Role Of Salicylic Acid In The Interaction Between Wheat And Fusarium Graminearum

Common wheat(Triticum aestivum)is one of the most important cereal crops,and closely related to food security.Fusarium head blight(FHB)is one of the mainly diseases of wheat,which threatens stable yield,high yield and high quality of wheat.Fusarium graminearum is the main causal agent of FHB in wheat.The effectiveness of control FHB depend on the environmental condition in the growing season and characteristics of pathogen,the complete and continuous control of FHB cannot be achieved through genetic resistance breeding,biological and chemical methods.Further study on the interaction mechanism between F.graminearum and wheat will help us to prevent and control FHB.As a major plant defense hormone,salicylic acid(SA)play an important role in inhibit F.graminearum infection.However,the interaction mechanism of SA between F.graminearum and wheat is still unclear.In this study,We identified the function of genes that predictive involve in SA transfer(FGSG?07325),metabolism(FGSG?08116)and inhibiting effect(FGSG?02668 and FGSG?11315).It will help us to explain the inhibition mechanism of SA between F.graminearum and wheat.The results were as follows:1.FgABCC9(FGSG?07325)encodes an ABC-C(ATP-binding cassette transporter family C)transporter in F.graminearum,which was highly expressed during infection in wheat and was up-regulated by the plant defense hormone salicylic acid(SA)and the fungicide tebuconazole.The predicted tertiary structure of FgABCC9 protein was consistent with the schematic of ABC exporter.Deletion of FgABCC9 resulted in decreased mycelial growth,increased sensitivity to SA and tebuconazole,reduced accumulation of deoxynivalenol(DON)and less pathogenicity towards wheat.Re-introduction of a functional FgABCC9 gene into?FgABCC9 recovered the phenotypes of wild type.FgABCC9 protein was usually distributed in the cell membrane,and enhanced when treated with SA and tebuconazole by Subcellular localization.Transgenic expression of FgABCC9 in Arabidopsis thaliana increased the accumulation of SA in its leaves without activation of SA signaling,suggesting that FgABCC9 functions as an SA exporter.Taken together,FgABCC9 protein as an exporter which may invole in pumpout excess SA and tebuconazole during F.graminearum and wheat interaction.2.We identified a salicylate hydroxylase gene(FGSG?08116;FgNah G)in F.graminearum.This gene encodes a protein that catalyzes the conversion of SA to catechol.Additionally,FgNah G was widely distributed within hyphae.Disrupting the FgNah G gene(?FgNah G)led to enhanced sensitivity to SA,increased accumulation of SA in wheat spikes during the early infection stage,and inhibited development of head blight symptoms.However,FgNah G did not affect mycotoxin production.Re-introducing a functional FgNah G gene into the?FgNah G mutant recovered the wild-type phenotype.FgNah G was widely distributed within hyphae by Subcellular localization.Moreover,the expression of FgNah G in transgenic Arabidopsis thaliana decreased the SA concentration and the resistance of leaves to F.graminearum.These results indicate that the endogenous SA in wheat influences the resistance against F.graminearum.So,the capacity to metabolize SA can help F.graminearum alleviate SA inhibit when F.graminearum infect wheat.3.Linoleic acid(LA;cis-9,cis-12 C18:2)plays an important role in wheat resistance to F.graminearum infection.We characterised a cis-12 Linoleic acid isomerase(LAI)gene of F.graminearum(FGSG?02668;FgLAI12),which was downregulated by salicylic acid(SA),a plant defence hormone.Disruption of FgLAI12 in F.graminearum resulted in decreased accumulation of cis-9,trans-11 conjugated linoleic acid(CLA),enhanced sensitivity to SA,and increased accumulation of linoleic acid(LA)and SA in wheat spikes during infection.In addition,mycelial growth,accumulation of deoxynivalenol,and pathogenicity in wheat spikes were reduced.Re-introduction of a functional FgLAI12 gene into ?FgLAI12 recovered the wild-type phenotype.Fluorescent microscopic analysis showed that FgLAI12 protein was usually expressed in the septa zone of conidia and the vacuole of hyphae,but was expressed in the cell membrane of hyphae in response to exogenous LA,which may be an element of LA metabolism during infection by F.graminearum.The cis-12 LAI enzyme encoded by FgLAI12 is critical for fungal response to mycelial growth,alleviate SA and LA inhibite,and virulence during F.graminearum and wheat interaction.The gene FgLAI12 is potentially valuable for biotechnological synthesis of cis-9,trans-11 CLA.4.Cell wall mannoprotein(CWM)plays an important role in fungi/host interactions.Here,we characterized FgCWM1(FGSG?11315),encoding a CWM in F.graminearum.FgCWM1 was highly expressed in wheat spikes by 24 h after initial inoculation,and was upregulated by SA.Compared with wild-type(WT),Disruption of FgCWM1(?FgCWM1)reduced mannose and protein accumulation in the fungal cell wall,especially under SA treatment,and resulted in defective fungal cell walls,leading to increased fungal sensitivity to SA.?FgCWM1 exhibited reduced pathogenicity towards wheat,but it produced the same amount of deoxynivalenol both in culture and in spikes.Complementation of ?FgCWM1 with FgCWM1 restored the WT phenotype.Localization analyses revealed that FgCWM1 was distributed on the cell wall,consistent with its structural role.Thus,the cell wall integrity is critical for F.graminearum response to SA inhibit and pathogenicity for interaction between F.graminearum and wheat.