The last step is the hardest: Lignin and suberin formation in the cell wall

Lignin and suberin are omnipresent polymers, used by humans since the dawn of civilisation. They are the defining components of wood and cork, but the occurence and importance of these two polymers is much more widespread and diverse. This is especially evident for the overall little amount of lignin and suberin deposited in the root endodermis, where absence of lignified Casparian strips or suberised secondary cell walls has a profound impact on root permeability and stress resistance. Beyond its direct physiological importance, the endodermis is therefore an interesting model system to study the cell biology of lignification and suberisation. A protracted problem in lignin and suberin research have been the crucial last steps of monomer delivery to, and polymerisation within, the cell wall. Here, I will report on high-order CRISPR/Cas9-induced mutants of suberin and lignin biosynthetic enzymes, providing strong evidence for the function of GDSL lipase and peroxidases in suberin and lignin polymerisation, respectively. I will also describe overlooked subcellular structures that are strongly associated with suberin deposition in the endodermis and could be involved in delivery of suberin precursor to the cell walls.