Shaping root architecture

Plant shape, or architecture, is a primary determinant of productivity and yield. The shape of the above-ground part of the plant determines light interception and photosynthesis, whereas the below-ground root system determines the interaction with the soil, including the uptake of water and nutrients and anchoring. As plant cells are bound by a cell wall and cannot move, shape is an outcome of the reorientation of the cell division plane and subsequent cell growth. In the model plant Arabidopsis, distribution patterns of the plant growth regulator auxin have been linked with altered cell division planes during lateral root initiation and in primary roots. The importance of orienting cell planes also becomes apparent in asymmetric cell divisions associated with the Arabidopsis root stem cell niche that are sustained by the activity of PLETHORA (PLT) proteins. These members of the AP2 transcription factor family are the main regulators of primary root meristem maintenance and the position of the meristematic boundary, regeneration, lateral root formation, and have an intimate relationship with auxin. Studying the orientation of cell division planes in higher plants is difficult due to tissue complexity while mosses like Physcomitrium patens have a simpler tissue organization and core genes are highly conserved but lack the complexity. This makes Physcomitrium patens a valuable model organism for studying the basic mechanisms of oriented cell divisions. Furthermore, besides the known players, new pathways involved in root architecture will be identified using different approaches e.g., using microbiota as tools to identify new players involved in optimizing root system architecture. Taken together, these combined efforts will continue to elucidate the molecular mechanisms that drive the key processes in root architecture.