FgSfl1 and Its Conserved PKA Phosphorylation Sites Are Important for Conidiation, Sexual Reproduction, and Pathogenesis in Fusarium graminearum

Abstract

The fungal plant pathogen, Fusarium graminearum, contains two genes, FgCPK1 and FgCPK2, encoding the catalytic subunits of cAMP-dependent protein kinase A. FgCPK1 and FgCPK2 are responsible for most of the PKA activities and have overlapping functions in various cellular processes in F. graminearum. The cpk1 cpk2 double mutant was significantly reduced in growth, rarely produced conidia, and was non-pathogenic. In this study, we found that the cpk1 cpk2 double mutant was unstable and produced fast-growing spontaneous sectors that were defective in plant infection. All spontaneous suppressor strains had mutations in FgSFL1, a transcription factor gene orthologous to SFL1 in yeast. Thirteen suppressor strains had non-sense mutations at Q501, three suppressor strains had frameshift mutations at W198, and five suppressor strains had mutations in the HSF binding domain of FgSfl1. Only one suppressor strain had both a non-synonymous mutation at H225 and a non-sense mutation at R490. We generated the SFL1 deletion mutant and found that it produced less than 2% of conidia than that of the wild-type strain PH-1. The sfl1 mutant was significantly reduced in the number of perithecia on carrot agar plates at 7 days post-fertilization (dpf). When incubated for more than 12 days, ascospore cirrhi were observed on the sfl1 mutant perithecia. The infection ability of the sfl1 deletion mutant was also obviously defective. Furthermore, we found that in addition to the S223 and S559 phosphorylation sites, FgSFL1 had another predicted phosphorylation site: T452. Interestingly, the S223 phosphorylation site was responsible for sexual reproduction, and the T452 phosphorylation site was responsible for growth and sexual reproduction. Only the S559 phosphorylation site was found to play an important role in conidiation, sexual reproduction, and infection. Overall, our results indicate that FgSFL1 and its conserved PKA phosphorylation sites are important for vegetative growth, conidiation, sexual reproduction, and pathogenesis in F. graminearum.

Combatting Fusarium head blight: advances in molecular interactions between Fusarium graminearum and wheat

“…In addition, the adenylate cyclase Fac1 and its associated protein FgCap1 were shown to be important for modulating the intracellular cAMP level and regulating vegetative and invasive growth of F. graminearum (Hu et al 2014;Yin et al 2018). In a recent study, FgSfl1 was characterized as a downstream transcription factor of PKA (Gong et al 2021). Three PKA phosphorylation sites S223, T452, and S559 of FgSfl1 have distinct functions in fungal development and plant infection (Gong et al 2021).…”

“…In a recent study, FgSfl1 was characterized as a downstream transcription factor of PKA (Gong et al 2021). Three PKA phosphorylation sites S223, T452, and S559 of FgSfl1 have distinct functions in fungal development and plant infection (Gong et al 2021).…”

FgSnt1 of the Set3 HDAC complex plays a key role in mediating the regulation of histone acetylation by the cAMP-PKA pathway in Fusarium graminearum

“…Like the pkr mutant, the cpk1 cpk2 mutant also often produces spontaneous suppressors with fast growth rate [ 26 , 27 ]. However, unlike 11 suppressors of pkr with mutations in CPK1 , none of the 30 suppressors of cpk1 cpk2 sequenced have mutations in PKR .…”

“…Interestingly, both the cpk1 cpk2 double and pkr deletion mutants of F. graminearum were unstable and produced spontaneous suppressor strains that had faster growth rate. All but one of the 30 spontaneous suppressor strains of the cpk1 cpk2 mutant had null mutations in FgSFL1 [26,27]. In the budding yeast Saccharomyces cerevisiae, Sfl1 is a transcription factor that functions downstream from cAMP signaling and interacts with the Cyc8-Tup1 co-repressor complex for regulating gene expression [28,29].…”

Advances in Understanding Fusarium graminearum: Genes Involved in the Regulation of Sexual Development, Pathogenesis, and Deoxynivalenol Biosynthesis

“…FgSFL1 and FgATF1 were identified as downstream effectors of the PKA signaling pathway and the HOG1 signaling pathway, respectively. Deletion mutants of fgsfl1 exhibited a decrease in the quantity of perithecia formed, while mutants of fgatf1 exhibited delayed perithecium development [51,52]. MES1 is a gene involved in cell-surface organization, and mes1 mutants consistently produced fewer perithecia in F. graminearum.…”