Molecular insights into the structure and function of plant K(+) transport mechanisms.
Our understanding of plant potassium transport has increased in the past decade through the application of molecular biological techniques. In this review, recent work on inward and outward rectifying K(+) channels as well as high affinity K(+) transporters is described. Through the work on inward rectifying K(+) channels, we now have precise details on how the structure of these proteins determines functional characteristics such as ion conduction, pH sensitivity, selectivity and voltage sensing. The physiological function of inward rectifying K(+) channels in plants has been clarified through the analysis of expression patterns and mutational analysis. Two classes of outward rectifying K(+) channels have now been cloned from plants and their initial characterisation is reviewed. The physiological role of one class of outward rectifying K(+) channel has been demonstrated to be involved in long distance transport of K(+) from roots to shoots. The molecular structure and function of two classes of energised K(+) transporters are also reviewed. The first class is energised by Na(+) and shares structural similarities with K(+) transport mechanisms in bacteria and fungi. Structure-function studies suggest that it should be possible to increase the K(+) and Na(+) selectivity of these transporters, which will enhance the salt tolerance of higher plants. The second class of K(+) transporter is comprised of a large gene family and appears to have a dual affinity for K(+). A suite of molecular techniques, including gene cloning, oocyte expression, RNA localisation and gene inactivation, is now being used to fully characterise the biophysical and physiological function of plants K(+) transport mechanisms.
Schachtman
D P
DP
CSIRO Plant Industry, Horticulture Unit, GPO Box 350, Glen Osmond, Australia. daniel.schachtman@pi.csiro.au
D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D024683:Potassium Channels, Tandem Pore Domain; D016415:Sequence Alignment; D027981:Symporters
D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; C490286:HKT1 protein, Arabidopsis; C088864:HKT1 protein, plant; C501210:KAT1 protein, Arabidopsis; C503455:KCO1 protein, Arabidopsis; C108935:KT1 protein, Arabidopsis; D008565:Membrane Proteins; D010940:Plant Proteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D024683:Potassium Channels, Tandem Pore Domain; D027981:Symporters