β-Xylosidase Overexpression Alters Pectin and Cellulose Distribution and Modulates Blast Disease Resistance in Rice

Plant cell walls provide structural integrity and defense against biotic and abiotic stresses. In rice (Oryza sativa), xylan is the major hemicellulose, and β-xylosidase hydrolyzes xylan by removing xylose residues from non-reducing ends. We analyzed a transgenic rice line (OsXylGH3-1-FOX) that constitutively overexpresses a GH3-family β-xylosidase (Os03g0749100) under the maize ubiquitin promoter. Following inoculation with M. oryzae, OsXylGH3-1-FOX leaves exhibited increased lesion numbers and disease indices, indicating reduced resistance, whereas leaf sheaths showed fewer fungal penetrations, suggesting enhanced resistance. To investigate these organ-specific responses, we quantified cell wall components. In leaves, xylose and arabinose decreased by ~33%, and galacturonic acid (pectin) by ~50%. In leaf sheaths, xylose and arabinose were unchanged, while galacturonic acid and cellulose increased by ~50% and ~70%, respectively. Histochemical staining confirmed reduced pectin in leaves and stronger, organized cellulose and pectin in leaf sheaths. These findings suggest that decreased pectin weakens cell adhesion, facilitating pathogen ingress in leaves, whereas increased pectin and cellulose reinforce wall integrity in leaf sheaths. Thus, pectin and cellulose abundance strongly correlate with organ-specific blast resistance, while hemicellulose plays a secondary role.