Regulation of ion homeostasis in plants and fungi

摘要

Calcineurin is a Ca~(2+) - and calmodulin-dependent protein phosphatase that, in the yeast Saccharomyces cerevisiae, is an intermediate of a signal transduction pathway that permits NaCl tolerance through the regulation of Na~+ influx and efflux transport proteins. A recombinant, activated form of yeast calcineurin increased the salt tolerance of yeast cells and of transgenic tobacco plants. Enhanced capacity of plants expressing calcineurin to survive NaCl shock was linked to root function and to preservation of root integrity during salt shock. AtNHX1, a approx60-kDa protein with significant sequence and Topological similarities to NHE-type Na~+/H~+ antiporters has been identified in Arabidopsis thaliana. AtNHX1 is a functional ortholog of ScNHX1, a Na~+/H~+ antiporter involved in intracellular Na~+ sequestration in S. cerevisiae. AtNHX1 conveyed NaCl tolerance to yeast cells that correlated with higher cellular ion content and increased ion uptake into an intracellular pool that was energetically dependent on the vacuolar (H~+) ATPase. The activity of AtNHX1 required a functional calcineurin. Together, these results suggest that in plants, like in yeast, a calcineurin-dependent signal pathway regulates ion transporters that are determinants of salt tolerance.