Phenylacetate Hydroxylase <scp>SsPhacA</scp> Modulates <i>p</i> ‐Coumaric Acid Accumulation to Regulate the Mating/Filamentation of <i>Sporisorium scitamineum</i>

Sugarcane smut, caused by Sporisorium scitamineum, is one of the most severe sugarcane diseases. A key pathogenic step is dikaryotic mycelium formation via sexual reproduction, but its regulatory mechanism is unclear. In this study, we identified a phenylacetate hydroxylase gene, SsPHACA, that is highly expressed during the sexual mating/filamentation of S. scitamineum and enriched within the phenylalanine metabolic pathway. SsPHACA deletion mutants presented significantly reduced sexual mating/filamentation and pathogenicity. Additionally, deletion of SsPHACA resulted in marked downregulation of the pheromone-responsive transcription factor gene SsPRF1, a critical regulator of sexual mating/filamentation in S. scitamineum, as well as its downstream genes at the a- and b-locus genes. Constitutive expression of SsPRF1 restored the sexual mating/filamentation of the SsPHACA deletion mutant. Metabolomic analyses revealed that SsPhacA mediates phenylalanine metabolism in S. scitamineum and modulates the accumulation of p-coumaric acid, an intermediate in phenylalanine metabolism. Exogenous supplementation with p-coumaric acid increased the transcriptional level of SsPRF1 and partially restored sexual mating/filamentation in SsPHACA deletion mutants. In summary, our results demonstrate that SsPhacA mediates the phenylalanine metabolic pathway to modulate p-coumaric acid accumulation, which increases the transcriptional level of SsPRF1, thereby regulating sexual reproduction in S. scitamineum. These findings not only identify a new regulatory factor involved in the sexual mating/filamentation of S. scitamineum, but also provide a new theoretical foundation for the development of disease control strategies targeting metabolic pathways.