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 phospholipase C (PI-PLC) in the higher plant Arabidopsis thaliana was cloned by use of the polymerase chain reaction. The cDNA, designated cAtPLC1, encodes a putative polypeptide of 561 aa with a calculated molecular mass of 54 RDa. The putative product includes so-called X and Y domains found in all PI-PLCs identified to date. In mammalian cells, there are three types of PI- PLC, PLC-β, -γ, and -δ. The overall structure of the putative AtPLC1 protein is most similar to that of PLC-δ, although the AtPLC1 protein is much smaller than PLCs from other organisms. The recombinant AtPLC1 protein synthesized in Escherichia coli was able to hydrolyze phosphatidylinositol 4,5-bisphosphate and 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 that the AtPLC1 gene is expressed at very low levels in the plant under normal conditions but is induced to a significant extent under various environmental stresses, such as dehydration, salinity, and low temperature. These observations suggest that AtPLC1 might be involved in the signal- transduction pathways of environmental stresses and that an increase in the level of AtPLC1 might amplify the signal, in a manner that contributes to the adaptation of the plant to these stresses.