The Xanthomonas axonopodis pv. glycines Cellulase EngXCA Governs Dual Roles in Virulence and Innate Immunity in Soybean.

The Xanthomonas axonopodis pv. glycines (Xag) cellulase EngXCA exhibits a dual functionality in the soybean pathosystem. Deletion of engXCA significantly attenuated bacterial growth and symptom severity, a phenotype that was fully restored by genetic complementation. Plants infected with ΔengXCA exhibited attenuated defense responses, including reduced H2O2 accumulation, callose deposition, and PCD, indicating that EngXCA acts as an immunity elicitor. Soybeans infected with ΔengXCAΔhrcC elicited weaker immune responses than those infected with ΔhrcC alone, confirming that EngXCA functions independently of the T3SS. Hormonal profiling revealed that EngXCA modulates phytohormone crosstalk by reducing ABA and ACC levels while concurrently elevating JA. Transcriptomics analysis further demonstrated that EngXCA differentially modulates multiple immune signaling pathways, with the upregulation of MAPK genes and the concurrent downregulation of PR and ERF genes. Collectively, these findings identify EngXCA as both a virulence determinant and an immunity modulator that orchestrates hormonal and transcriptional reprogramming in the Xag-soybean pathosystem.