Primary Research On MAPKKKX Involved In The Primary Root Growth Modulated By ABA In Arabidopsis

Plants have developed various signal transduction pathways in order to modulate diverse cellularresponses for adaptation to changing environment conditions. Among these machineries, mitogen-activatedprotein kinase (MAPK) cascades are fundamental signal pathways conserved in eukaryotes.Mitogen-activated protein kinase cascades consist of three signal transducing components, MAPKKKs,MAPKKs and MAPKs. In response to stimuli, MAPKKK can activate MAPKK by phosphorylation, whichin turn activates MAPK by phosphorylation. The Arabidopsis (Arabidopsis thaliana) genome encodes60-80predicted MAPKKKs,10MAPKKs and20MAPKs. It has been reported that MAPK cascades havean important role in ABA signal transduction, however, it is not clear whether MAPK cascades involved inthe primary root growth modulated by ABA in Arabidopsis.We identified T-DNA insertion homozygous mutant mapkkkx of MAPKKK family in Arabidopsis. Wetherefore used it to analyze the function of MAPKKKX in primary root growth modulated by ABA inArabidopsis. By phenotype analysis, in the absence of ABA, primary root growth was indistinguishablebetween mapkkkx and WT. However, the primary roots of mapkkkx were more than twice as long as theprimary roots of WT on the50μM ABA plate. We concluded that mapkkkx showed insensitive to ABA inprimary root length in contrast to WT. However, other phytohormones and stress could not provide thedifference. RT-PCR revealed ABA repressed the transcription of MAPKKKX, and MAPKKKX regulatedthe expression of marker genes responding to ABA. In order to verify that MAPKKKX brought thephenotype of the mutant, we constructed the MAPKKKX complementary vector and overexpression vector.Fluorescence localization result of MAPKKKX::GFP showed MAPKKKX localized in cytoplasm. Theresults of the yeast two-hybrid revealed that MAPKKKX interacted MKK1-MKK10. In order to verify thevalidity of the yeast two-hybrid, we constructed the vectors of BiFC.These results suggested that MAPKKK involved in the primary root growth modulated by ABA inArabidopsis.