A project undertaken at the School of Biosciences, University of Melbourne and supervised by Staffan Persson
Salinity is major causative factor for global yield losses (1). This is in particular true for Australia, where over 3 million hectares currently are classified as salt affected, and roughly one third of all arable land are predicted to be salt contaminated by 2050 (2). It is therefore of great importance to prevent further soil salinization, but also to understand how plants can tolerate salt better and to engineer them for such characteristics. Plant growth is sustained by their ability to produce cell walls; a carbohydrate-based extracellular matrix that provides stature to the plant, protects the plant against external stress and that provides the bulk of a plant’s biomass. Cellulose is the main constituent of plant cell walls, and is synthesized at the plasma membrane by a large protein complex, referred to as the cellulose synthase (CESA) complex (3).
Figure 1. An Arabidopsis plant immersed in salt. Salinity impacts negatively on plant growth. We hope to improve the biomass producing capacity of plants when grown on salty soil. This is particularly important to Australian agriculture as large arable land areas are, or will become, affected by salt.
We identified a protein family, which we call Companions of CESAs (CCs), that protect the CESA activity during salt stress in the mustard plant Arabidopsis (4). With the funds from the Hermon Slade foundation we have been able to show the molecular mechanism by which these CC proteins operate. We could show that the engage with hydrophobic pockets on the cytoskeletal component microtubules that steer cellulose production in plant cells. The CC proteins can here link neighbouring microtubules together, which stabilize them and allow them to re-assemble after salt exposure. We targeted the CC proteins in the important crop plant rice and showed that they are important for cellulose synthesis also here and that they are likely to be regulated by phosphorylation by two different classes of kinases. The microtubule-binding mechanism of the CC proteins is remarkably similar to that of Tau, a key microtubule-regulating protein in neuropathology. Our work has dramatically extended our understanding for how cellulose synthesis is regulated during stress, revealed molecular insights into how the CC proteins function and revealed an evolutionary convergence principle in microtubule-associated proteins from plants and neurons.
Munns and Tester (2008) Annu Rev Plant Biol. 59: 651
Salinity and water quality fact sheet, Australian Department of Sustainability, Environment, Water, Population and Communities, 2012
Lampugnani et al. (2018) J Cell Sci. 131 (doi:10.1242/jcs.207373)
Endler et al. (2015) Cell. 162: 1353