Riboflavin Primes Pepper Resistance to Ralstonia solanacearum Through Coordinated Antioxidant Responses and Lignin Deposition

Abstract

Reactive oxygen species (ROS) are pivotal regulators of plant–pathogen interactions. Comparative transcriptomic analysis of a bacterial wilt-susceptible pepper cultivar (HS03) and a resistant cultivar (HR01) revealed impaired riboflavin biosynthesis in HS03. Exogenous riboflavin application compensated for this deficiency and conferred significant protection against Ralstonia solanacearum. Physiological and transcriptomic analyses further demonstrated that riboflavin functions as both an inducer of ROS signaling and a modulator of defense-associated metabolism. Riboflavin treatment elicited a biphasic defense response characterized by an early H2O2 burst accompanied by dynamic changes in antioxidant enzyme activities. In particular, the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) increased markedly at 6 h after riboflavin application compared with control. Following R. solanacearum inoculation, riboflavin-pretreated plants exhibited higher POD, ascorbate peroxidase (APX), and CAT activities at 6 h post-inoculation compared with control. This early antioxidant response induced by riboflavin was followed by increased lignin accumulation and the transcriptional activation of genes associated with cutin, suberin, and wax biosynthesis, galactose metabolism, and tyrosine metabolism at 12 h post-inoculation. Riboflavin pretreatment also enhanced the expression of genes encoding nonexpressor of pathogenesis-related genes 1 (NPR1) and calmodulin (CALM), implicating hormone signaling and calcium-mediated pathogen recognition in riboflavin-induced resistance. Collectively, these results suggest that riboflavin primes pepper defense against R. solanacearum by coordinating early ROS-associated antioxidant responses and subsequent cell-wall reinforcement. Riboflavin may therefore represent a promising environmentally compatible agent for the sustainable management of bacterial wilt in pepper.