Unraveling mechanisms of cell expansion linking solute transport, metabolism, plasmodesmtal gating and cell wall dynamics

Cell expansion is a major component of plant cell development and plays a key role in organ growth, hence realization of crop productivity. Thus, unraveling mechanisms controlling plant cell expansion is essential not only for understanding fundamental plant biology but also for designing innovative approaches to increase crop yield and quality. The multicellular plant tissues, however, impose enormous technique challenges to assess the contribution of molecular or cellular events to the expansion of given cell types as they often deeply embedded within the tissues, thus are not readily accessible for sampling or measurement. In this context, cotton fibers, singlecelled hairs developed from the seed coat epidermis represent an ideal system for studying regulation of cell expansion, owing to their rapid and synchronized elongation (up to 3~5 cm long) and high accessibility for experimentation. Recently, we demonstrated the essential role of vacuolar invertase (VIN) in early fiber elongation. Remarkably, we discovered that VIN controls cotton fiber and Arabidopsis root elongating through osmotic dependent and independent pathways, respectively. This shows mechanistic complexity of cell expansion. Here, we evaluate the coordinated actions of multiple pathways in regulating cotton fiber elongation linking solute transport and metabolism with plasmodesmatal gating, water flow and cell wall dynamics and we outline future directions for deepening our understanding of plant cell expansion.