Mutation of the matrix metalloproteinase At2-MMP inhibits growth and causes late flowering and early senescence in Arabidopsis

This study characterizes the expression and functional significance of the member of the matrix metalloproteinase (MMP) family At2-MMP from Arabidopsis. By transcript analysis, expression of At2-MMP was found in leaves and roots of juvenile Arabidopsis and leaves, roots, and inflorescences of mature flowering plants showing strong increase of transcript abundance with aging. Cell specificity of expression of At2-MMP was studied by in situ hybridizations in leaves and flowers of Arabidopsis. In leaves, the gene was expressed in the phloem, in developing xylem elements, epidermal cells, and neighboring mesophyll cell layers. In flowers, Signals were localized in pistils, ovules, and receptacles. In an Arabidopsis mutant (at2-mmp-1) carrying a tDNA insertion in At2-MMP, neither germination nor development of plants was modified in comparison to the wild type in the juvenile rosette stage. Starting with the on-set of shoots, growth of roots, leaves, and shoots was inhibited compared with the wild type, and the plants were characterized by late flowering. Besides the flowering, at2-mmp-1 plants showed fast degradation of chlorophyll in leaves and early senescence. These results demonstrate the involvement of At2-MMP in plant growth, morphogenesis, and development with particular relevance for flowering and senescence.