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The fungal plant pathogen, <i>Fusarium graminearum</i>, contains two genes, <i>FgCPK1</i> and <i>FgCPK2</i>, encoding the catalytic subunits of cAMP-dependent protein kinase A. <i>FgCPK1</i> and <i>FgCPK2</i> are responsible for most of the PKA activities and have overlapping functions in various cellular processes in <i>F. graminearum</i>. The <i>cpk1 cpk2</i> double mutant was significantly reduced in growth, rarely produced conidia, and was non-pathogenic. In this study, we found that the <i>cpk1 cpk2</i> double mutant was unstable and produced fast-growing spontaneous sectors that were defective in plant infection. All spontaneous suppressor strains had mutations in <i>FgSFL1</i>, a transcription factor gene orthologous to <i>SFL1</i> 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 <i>SFL1</i> deletion mutant and found that it produced less than 2% of conidia than that of the wild-type strain PH-1. The <i>sfl1</i> 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 <i>sfl1</i> mutant perithecia. The infection ability of the <i>sfl1</i> deletion mutant was also obviously defective. Furthermore, we found that in addition to the S223 and S559 phosphorylation sites, <i>FgSFL1</i> 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 <i>FgSFL1</i> and its conserved PKA phosphorylation sites are important for vegetative growth, conidiation, sexual reproduction, and pathogenesis in <i>F. graminearum</i>.