A GENE ENCODING A PHOSPHATIDYLINOSITOL-SPECIFIC PHOSPHOLIPASE-C IS INDUCED BY DEHYDRATION AND SALT STRESS IN ARABIDOPSIS-THALIANA

A cDNA corresponding to a putative phosphatidylinositol-specific phosp holipase C (PI-PLC) in the higher plant Arabidopsis thaliana was clone d by use of the polymerase chain reaction, The cDNA, designated cAtPLC 1, encodes a putative polypeptide of 561 aa with a calculated molecula r mass of 64 kDa. The putative product includes so-called X and Y doma ins found in all PI-PLCs identified to date. In mammalian cells, there are three types of PI-PLC, PLC-beta, -gamma, and -delta. The overall structure of the putative AtPLC1 protein is most similar to that of PL C-delta, although the AtPLC1 protein is much smaller than PLCs from ot her organisms. The recombinant AtPLC1 protein synthesized in Escherich ia coli was able to hydrolyze phosphatidylinositol 4,5-bisphosphate an d this activity was completely dependent on Ca2+, as observed also for mammalian PI-PLCs. These results suggest that the AtPLC1 gene encodes a genuine PI-PLC of a higher plant. Northern blot analysis showed tha t the AtPLC1 gene is expressed at very low levels in the plant under n ormal conditions but is induced to a significant extent under various environmental stresses, such as dehydration, salinity, and low tempera ture, These observations suggest that AtPLC1 might be involved in the signal-transduction pathways of environmental stresses and that an inc rease in the level of AtPLC1 might amplify the signal, in a manner tha t contributes to the adaptation of the plant to these stresses.