Effects Of A Gene Essential For Riboflavin Biosyntheie On Disease Resistance In Arabidopsis

Riboflavin (vitamin 82) is required for microbes, plants, human and other animals.The vitamin plays an important role in plant disease resistance and may regulate plant growth as well. Riboflavin is an activator of a novel signaling pathway leading to systemic resistance , which requires protein kinases and the NIM1/NPR1 protein, but does not require accumulation of SA. On the other hand, lumizine synthase (LS) catalyses the penultimate step of riboflavin biosynthesis. Whether the expression of the gene LS is induced by elicitors that induce disease resistance is unclear. In this study, the author determined two approaches are used to determine contents of riboflavin and LS expression after plants were treated with different elicitors including salicylic acid, jasmonic acid and ethylene, which mediate basal plant defense pathways. In addition, it was planned to determine effects of LS overexpressing on disease resistance in transgenic Arabidopsis plants.Previous studies have shown that treatment of Arabidopsis plants with riboflavin induces resistance to Pseudomonas syringae pv. tomato. The process is similar to that induced by the multiple-functional elicitors harpin and elicitin. The author determined harpin and elicitin, together with SA, methyl jasmonate (MeJA), and the ethylene precursor ACC, for effects on the bacterial growth in plants. Results showed that bacterial population in plants treated with these materials was markedly lower than that in control plants treated with water. Therefore, determining effects of these elicitors on riboflavin biosynthesis could indicate whether riboflavin affects basal defense pathways.Effects of the five elicitors on LS gene expression was investigated. Although the gene had a low level of constitutive expression, based on assays of control plants, its expression pattern and extents were affected differently by treatment with elicitors. Treatment with SA caused an increase in LS transcripts in 24 hours. MeJA treatment increased the gene expression after 12 hours of treatment. The gene transcription increased in 6 hours after the application of harpinEa- However, treatment with ACC orelicitin decreased levels of gene expression in 6 and 12 hours, respectively. Thereafter, LS gene expressed in plants treated with ACC or elicitin similarly as did in control plants.The author determined whether treatment with the five elicitors affects production of free riboflavin in plants consistently with expression of the LSgene. Riboflavin increased levels in plants treated SA or MeJA after 24 hours of treatment. In contrast, treatment with elicitin caused decrease in riboflavin concentration after 6 hours. Interestingly, treatment with ACC or harphiEa decreased riboflavin levels in 6 hours but an evident increase thereafter. Clearly, changes of endogenous riboflavin levels are consistent with changes of the LS gene expression in plants treated with different elicitors.Finally, the LS gene was cloned the transformation vector containing the 35S promoter, and introduced into Arabidopsis plants. A LS -transgenic Arabidopsis line had been generated; more lines are being screened. Transgenic plants that overexpress the LS gene will be investigated to determine whether genetic modulation of riboflavin biosynthesis affects pathogen defense and relevant processes.In conclusion, treatment of Arabidopsis plants with SA, JA and ethylene stimulates the LS gene expression. This process is coincident with increase in riboflavin levels in the plants. Therefore modulation of endogenous riboflavin levels is associated with the basal defense pathways mediated differentially by SA, JA and ethylene.