STRESS SIGNALING THROUGH CA2+ CALMODULIN-DEPENDENT PROTEIN PHOSPHATASE CALCINEURIN MEDIATES SALT ADAPTATION IN PLANTS/

Calcineurin (CaN) is a Ca2+- and calmodulin-dependent protein phosphat ase (PP2B) that, in yeast, is an integral intermediate of a salt-stres s signal transduction pathway that effects NaCl tolerance through the regulation of Na+ influx and efflux, A truncated form of the catalytic subunit and the regulatory subunit of yeast CaN were coexpressed in t ransgenic tobacco plants to reconstitute a constitutively activated ph osphatase in vivo, Several different transgenic lines that expressed a ctivated CaN also exhibited substantial NaCl tolerance, and this trait was linked to the genetic inheritance of the CaN transgene, Enhanced capacity of plants expressing CaN to survive NaCl shock was similar wh en evaluation was conducted on seedlings in tissue culture raft vessel s or plants in hydroponic culture that were transpiring actively, Root growth was less perturbed than shoot growth by NaCl in plants express ing CaN, Also, NaCl stress survival of control shoots was enhanced sub stantially when grafted onto roots of plants expressing CaN, further i mplicating a significant function of the phosphatase in the preservati on of root integrity during salt shock. Together, these results indica te that in plants, like in yeast, a Ca2+- and calmodulin-dependent CaN signal pathway regulates determinants of salt tolerance required for stress adaptation, Furthermore, modulation of this pathway by expressi on of an activated regulatory intermediate substantially enhanced salt tolerance.