Unveiling the resistance risk and molecular mechanism of Xanthomonas oryzae pv. oryzicola to zhongshengmycin.

Zhongshengmycin, an N-aminoglycoside agricultural antibiotic, has been widely used to control bacterial leaf streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) in China. However, the resistance risk and its underlying molecular mechanisms remain poorly understood. In this study, we determined the sensitivity of 101 Xoc isolates collected from major rice-growing regions in China, with a mean EC50 value of 0.7005 ± 0.2407 μg/mL; no naturally occurring resistant strains were detected. Five resistant mutants were obtained through laboratory adaptation, and these mutants exhibited significantly reduced growth rate, motility, biofilm formation, and pathogenicity, indicating substantial fitness costs. No cross-resistance was detected between zhongshengmycin and kasugamycin, zinc thiazole, tetramycin, or xinjunan acetate. Whole-genome resequencing combined with genetic transformation verified that the I162S mutation in the ribosomal protein S3 (rpsC) conferred low-level resistance to zhongshengmycin. Transcriptome analysis revealed significantly upregulated amino acid biosynthesis pathways and two GNAT family acetyltransferase genes in resistant mutants. Collectively, these findings suggest that zhongshengmycin resistance in Xoc may be co-mediated by the rpsC mutation, upregulation of key amino acid biosynthesis pathways, and overexpression of GNAT family acetyltransferases. This work provides a scientific basis for field monitoring of resistance to zhongshengmycin and sustainable management strategies against BLS.