Poly(phenolic) deposition is a prerequisite to poly(aliphatic) deposition for functional potato suberin

Suberin deposition in specialized cells is a critical aspect of plant protection, providing both water retention and pathogen protection functions. Tissue specific suberization during plant development is mirrored by its wound induction in cells that do not normally suberize and provides a robust experimental system to investigate the process. Suberized cells are characterized by a cell wall-associated lignin-like poly(phenolic) domain, and an ester-linked poly(aliphatic) domain, with the latter often laid down in distinct lamellar bands between the cell wall and plasma membrane. Previous work provides evidence that poly(phenolic) deposition precedes, and is necessary for, poly(aliphatic) deposition. To test this further, we generated RNAi knockdown lines of three wound-induced peroxidase genes, PRX19, PRX55, and PRX105, in potato (Solanum tuberosum), the tubers of which produce an abundance of suberin upon wounding. Peroxidases catalyze the oxidative free radical coupling of phenolic monomers to form the suberin poly(phenolic) domain. The wound-induced suberin of PRX19-RNAi tubers had severely reduced poly(phenolics), reduced poly(aliphatics), and no apparent lamella. Functionally, wound-induced PRX19-RNAi tubers were more permeable to water loss and susceptible to bacterial soft rot. Overall, our data support the hypothesis that poly(phenolic) domain assembly is a strict requirement for subsequent deposition of aliphatic lamella within wound-induced suberin.