A NACL-REGULATED PLANT GENE ENCODING A BRAIN PROTEIN HOMOLOG THAT ACTIVATES ADP RIBOSYLTRANSFERASE AND INHIBITS PROTEIN-KINASE-C

A cDNA clone pCZ1, with a 1.1 kb insert, was isolated from a NaCl-adap ted tobacco cell cDNA library that encodes an apparently full-length 2 9 kDa protein (251 amino acids) with a calculated pl of 5.7. The encod ed peptide had a high amino acid sequence identity with bovine 14-3-3 protein which was originally found as an abundant protein in the anima l central nervous system. Recently, proteins with sequence identity to 14-3-3 protein have also been found in plants, insects and yeast, and appear to have diverse physiological functions. Similar to the bovine brain 14-3-3 protein, the recombinant pCZ1 protein stimulated ADP-rib osylation of protein substrate by ADP-ribosyltransferase from the plan t and animal pathogenic bacterium Pseudomonas aeruginosa. This recombi nant protein also inhibited protein kinase C activity in vitro. Southe rn blot analyses indicated that most likely five genes encoding 14-3-3 -like proteins are present in tobacco. The pCZ1 cDNA insert hybridized to a single mRNA of 1.1 kb from cultured tobacco cells. The level of this mRNA transcript in tobacco cells was downregulated upon adaptatio n to NaCl but was unaffected by short-term treatment with NaCl, ABA or ethylene. In tobacco plants, expression of transcript that hybridized to pCZ1 was tissue specific, and was most abundant in roots and flowe r parts. Monoclonal antibody raised against GF14 protein, a maize prot ein with substantial sequence identity with 14-3-3 protein detected tw o bands on SDS-PAGE of total proteins from unadapted tobacco cells and only a single band from cells adapted to NaCl. The GF14 antibody was also used to illustrate that the G-box element of a salt-induced gene is associated with a 14-3-3-type protein.