MYB107 and MYB9 homologs regulate suberin deposition in angiosperms

Suberin, a polymer composed of both aliphatic and aromatic domains is deposited as a rough matrix upon plant surface damage. Its proper assembly is essential for effective abiotic and biotic stress response, including controlling water and ion flux and acting as a physical barrier to pathogens. Yet, most suberin is assembled during normal growth; e.g. in the root endodermis, the bark of trees, potato tubers skin and seed coats. To identify genes associated with the developmental control of suberin deposition we investigated the chemical composition and transcriptomes of suberized tomato and russet apple fruit surfaces. Consequently, a gene expression signature for suberin polymer assembly was revealed that is highly conserved in angiosperms. Seed permeability assays of knockout mutants corresponding to signature genes unrevealed regulatory proteins (i.e. AtMYB9 and AtMYB107) required for suberin assembly in the Arabidopsis seed coat. Seeds of atmyb107 and atmyb9 mutants displayed a significant reduction in suberin metabolites, increased permeability, and more rapid germination under osmotically stressful conditions. AtMYB9 and AtMYB107 appear to synchronize the transcriptional induction of aliphatic and aromatic monomers biosynthetic pathways and transport besides suberin polymerization in the seed outer integument layer. Collectively, our findings establish a regulatory system controlling developmentally deposited suberin which likely differs from the one of stress- induced polymer assembly recognized to date.