Riboflavin induces disease resistance in plants by activating a novel signal transduction pathway

The role of riboflavin as an elicitor of systemic resistance and an activat or of a novel signaling process in plants was demonstrated. Following treat ment with riboflavin, Arabidopsis thaliana developed systemic resistance to Peronospora parasitica and Pseudomonas syringae pv. Tomato, and tobacco de veloped systemic resistance to Tobacco mosaic virus (TMV) and Alternaria al ternata. Riboflavin, at concentrations necessary for resistance induction, did not cause cell death in plants or directly affect growth of the cultura ble pathogens. Riboflavin induced expression of pathogenesis-related (PR) g enes in the plants, suggesting its ability to trigger a signal transduction pathway that leads to systemic resistance. Both the protein kinase inhibit or K252a and mutation in the NIM1/NPR1 gene which controls transcription of defense genes, impaired responsiveness to riboflavin. In contrast, ribofla vin induced resistance and PR gene expression in NahG plants, which fail to accumulate salicylic acid (SA). Thus, riboflavin-induced resistance requir es protein kinase signaling mechanisms and a functional NIM1/NPR1 gene, but not accumulation of SA. Riboflavin is an elicitor of systemic resistance, and it triggers resistance signal transduction in a distinct manner.