Biological function of a methyl jasmonate-inducible gene MJI3 in arabidopsis (arabidopsis thaliana)

Abstract

Methyl jasmonate (MeJA) is a volatile plant cellular regulator that modulates expression of various genes involved in diverse developmental and defensive processes. In a previous experiment performed in our laboratory with Arabidopsis DNA microarray chips, numerous MeJA-inducible genes including those with unidentified biological functions were screened out. Among them, MJI3 (At1g75830) gene was selected for further studies to identify their biological roles in MeJA-responsive cellular metabolism. In this work, structural characteristics of the gene were explored by computer-based sequence analysis. Tissue-specificity of the gene expression and activation by MeJA treatment were examined through Northern blot analyses. MJI3 expression was induced by MeJA and ethylene treatments, exhibiting synergistic effect between the two phytohormones. In addition, the MJI3 gene was fused with CaMV 35S promoter and transformed into Arabidopsis to generate transgenic plants that overexpress the MJI3 gene. Transgenic lines integrated with single copy of the insert were selected on antibiotics-medium and by genomic Southern blot analysis. Northern blot analyses revealed that the transgenic plants constitutively express the jasmonate-inducible genes PDF1.2 and JR2, but not salicylate-inducible gene PR1. Moreover, the transgenic Arabidopsis plants exhibited enhanced resistance to fungal pathogens, Alternaria brassicicola, which is known to be relied on jasmonate-dependent defense responses. In this study, therefore, it has been demonstrated that MJI3 encodes a plant defensin, functioning as a MeJA-responsive defenserelated gene.