The role of a Raf-related kinase gene from mustard (Brassica juncea) in glutathione-related signaling pathway

The mitogen-activated protein kinase (MAPK) cascades are the major components that mediate the transmission and amplification of extracellular stimuli. The signal in the cascades is initiated by mitogen-activated protein kinase kinase kinases (MAPKKKs), which phosphorylate MAPKKs that, in turn, activate MAPKs. In this study, a mustard MAPKKK gene that shared extensive sequence similarity to CTR1, designated as CTR1-like kinase (CLK), was isolated and characterized. Southern analysis indicated that CLK was present as a single copy gene in the mustard genome. In RT-PCR analysis, CLK was shown to express at lower levels in mustard roots than in aerial plant parts. In leaves, CLK expression could be upregulated by exogenous applications of methyl jasmonate but downregulated by glutathione (GSH). Results of a comparative study showed that the level of AtGSTF2 transcript was considerably lower in roots of CLK overexpressor than that of wild type plants. In root elongation inhibition assay, root growth of CLK overexpressor was less sensitive to GSH and more sensitive to GSH synthesis inhibitor l-buthionine-(S,R)-sulfoximine. These results suggest that CLK may play a role in the signaling pathway related to GSH.