Fig. 1

Pathogenesis-related signal sensing and transduction in Fusarium graminearum. During infection, GPCRs (Giv1-Giv3, FGRRES_16221, and FgSte2) and other cell membrane receptors (FgSho1, FgSln1, and FgMsb2) in F. graminearum sense various environmental and plant cues to activate intracellular G-protein, MAPK, cAMP-PKA signal pathways, and downstream transcription factors for regulating the differentiation of infection structures and hyphae, the secretion of pathogenicity factors such as cell wall- degrading enzyme and effector, and DON production. Three MAPK and cAMP-PKA signal pathways are required for DON production and full virulence of F. graminearum. FgSte50 is an adaptor protein in both Gpmk1 invasive growth (IG) and Mgv1 cell wall integrity (CWI) MAPK pathways. The FgSte11-FgSte7-Gpmk1 kinase cascade is responsible for signal transduction in the F. graminearum IG pathway. Transcription factors FgSte12, FgMcm1, and FgSfl1 are the downstream targets of Gpmk1. FgBck1-FgMkk1-FgMgv1 kinase cascade is responsible for signal transduction in the F. graminearum CWI MAPK pathway. The transcription factors Fgp1, FgRlm1, and FgSwi6 are potential downstream targets of FgMgv1. F. graminearum Hog1 is the MAPK that functions in the high-osmolarity glycerol (HOG) MAPK pathway, in which the response regulator protein FgRrg-1 is involved in wheat infection, and FgSsk2 and FgPbs2 act as the MEKK and MEK, respectively. ATF/CREB transcription factor FgAtf1 is the downstream target of FgHog1. The downstream transcription factors of MAPK pathway are involved in pathogenicity by regulating the expression of pathogenicity genes, including TRI genes, cell wall-degrading enzyme genes, and effector genes. The cAMP-PKA signaling pathway also plays an important role in the pathogenicity of F. graminearum. CPK1 and CPK2 (two catalytic subunits of PKA), PKR (the regulatory subunit of PKA), Fac1 (the adenylate cyclase), and FgCap1 (protein associated with the adenylate cyclase) are key components in the cAMP-PKA signaling pathway. FgSfl1 is one of the downstream transcription factors of PKA. FgAreA, a global regulator of nitrogen metabolism, interacts with Tri10 for the transcriptional regulation of TRI genes. F. graminearum-induced putrescine stimulates FgAreA to enter the nucleus. FgAreA binds to the promoter regions of TRI genes to rearrange the nucleosome array. The exposure of nucleosome-free regions subsequently facilitates the deposition of histone H2B monoubiquitination (H2B ub1) and histone 3 lysine 4 di- and trimethylations (H3K4 me2/3) on TRI genes, which further activates the expression of TRI genes and promotes DON biosynthesis and F. graminearum infection