Plant Transport and Signalling Laboratory, ARC Centre of Excellence in Plant Energy Biology, Waite Research Institute, University of Adelaide, Glen Osmond, SA, 5064, Australia
The molecular mechanisms involved in chloride (Cl–) nutrition in plants are not well defined. Although chloride is a micronutrient it often accumulates to macronutrient levels and under saline conditions to toxic levels. Salinity tolerance has been correlated with shoot Cl– exclusion in several crop species (e.g. grapevine, citrus, soybean and barley). This process has been shown to be a multigenic trait. Several plasma membrane-localised anion channels of the root vasculature that have their activity down-regulated by ABA and salt stress are hypothesized to confer the major regulatory step in root-to-shoot transfer of Cl–. Researchers in the Plant Transport and Signalling Lab have recently identified 5 transport proteins involved in this process in a variety of crops (soybean, grapevine and Arabidopsis) in collaboration with a number of groups (Australian Centre for Plant Functional Genomics, Chinese Academy of Agricultural Sciences and CSIRO). Two of these proteins have been localised to endomembranes, CCC and CHX20, and are hypothesised to have a role in pH control of the compartments which influences vesicle trafficking – which is emerging as an important process in salinity tolerance. Whilst three proteins, NPF2.4, NPF2.5 and SLAH1, directly transport Cl– across the plasma membrane; NPF2.4 and SLAH1 are associated with the root vasculature and knockdown of their expression results in a reduction in shoot Cl– and an improvement in growth under saline conditions. NPF2.5 is expressed in the root cortex and is likely to efflux Cl– from the root. This presentation will describe new data that shows how the co-ordinated activity of these transporters affects shoot chloride concentration and salinity tolerance.