Salt regulation of O-acetylserine(thiol)lyase in Arabidopsis thaliana and increased tolerance in yeast

The cytosolic isoform of O-acetylserine(thiol)lyase (OASTL, EC 4.2.99.8), the enzyme that catalyses cysteine biosynthesis, is induced in leaves of Arabidopsis thaliana exposed to salt stress. The protein level increases after 1 d sodium chloride treatment, and progressively for up to 5 d. The overexpression in yeast of the Atcys-3A gene coding for this OASTL isoform can support the growth of the yeast cells at high concentrations of sodium chloride, suggesting that the plant protein is able to confer salt tolerance in yeast. Besides, the O-acetylserine(thiol)lyase enzyme activity is not inhibited in vitro by cations such as Li+ or Na+. Our results suggest that the plant is responding to the salt stress by inducing cysteine biosynthesis as a protection against high ion concentrations. (C) 2001 Editions scientifiques et medicales Elsevier SAS.