Characterization of salt-induced changes in gene expression in tomato (Lycopersicon esculentum) roots and the role played by abscisic acid

Examination of tomato (Lycopersican esculentum Mill) root mRNA profiles by differential display-polymerase chain reaction (DD-PCR) revealed that a sal t treatment induced, promoted or repressed the expression of a number of ge nes. The majority of the observed changes were indicative of a rapid and tr ansient salt-induced alteration in gene expression. Twenty partial cDNAs co rresponding primarily to salt-induced or up-regulated mRNAs were subsequent ly cloned and sequenced. The role of abscisic acid (ABA) in regulating salt -responsive gene expression in roots was explored. The DD-PCR data indicate that the majority of the salt-induced changes in the root mRNA profile occ urred in an ABA-independent manner. The expression of genes corresponding t o six cDNAs was shown unequivocally to be responsive to a salt treatment by RNA blot hybridization. Just two of these were responsive to exogenous ABA and, in salt-treated roots of the ABA-deficient mutant flacca, all were ex pressed to a level comparable to that in the wild-type. The identity of two of the salt-responsive partial cDNAs is known. The deduced amino acid sequ ence of one was similar to that of laccases that polymerize a variety of su bstrates to form resilient structures within the cell wall. One other share d amino acid sequence similarity with the C-terminus of a tobacco pathogen- induced oxygenase (PIOX). It is possible that the PIOX is involved in gener ating signaling molecules that mediate a general stress response. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.