Spatio-temporal development of suberized barriers in cork oak taproots

Abstract

Abstract The longevity and high activity of the cork cambium (or phellogen) from Quercus suber (cork oak) are the cornerstones for the sustainable exploitation of a unique raw material. Cork oak is a symbolic model to study cork development and cell wall suberization, yet, most genetic and molecular studies on these topics targeted other model plants. In this study we explored the potential of taproots as a model system to study phellem development and suberization in cork oak, avoiding the time constraints imposed when studying whole plants. In roots, suberin deposition is found in mature endodermis cells during primary development and in phellem cells during secondary development. By investigating the spatio-temporal characteristics of both endodermis and phellem suberization in young seedling taproots, we demonstrated that secondary growth and phellogen activity initiates very early in cork oak taproots (approx. 8 days after sowing). We further compared the transcriptomic profile of root segments undergoing primary (PD) and secondary development (SD) and identified multiple candidate genes with predicted roles in cell-wall modifications, mainly lignification and suberization, in addition to several regulatory genes, particularly transcription factor and hormone-related genes. Our results indicate that the molecular regulation of suberization and secondary development in cork oak roots is relatively conserved with other species. The provided morphological characterization creates new opportunities to allow a faster assessment of phellogen activity (as compared to studies using stem tissues), and to tackle fundamental questions regarding its regulation.