Molecular characterization of At5PTase1, an inositol phosphatase capable of terminating inositol trisphosphate signaling

The inositol triyhosphate (IP3)-signaling pathway has been associated with several developmental and physiological processes in plants, but we current ly know little about the regulation of this pathway. Inositol 5 ' phosphata ses (5PTases) are enzymes that remove a 5 ' phosphate from several potentia l second messengers, including IP3. In catalyzing the removal of a 5 ' phos yhate from second messenger substrates, 5PTases can act to terminate signal transduction events. We describe the molecular analysis of At5PTasel, a 5P Tase gene from Arabidopsis. When expressed transiently in Arabidopsis leaf tissue or ectopically in transgenic plants, At5PTasel allowed for the incre ased hydrolysis of I(1,4,5)P-3 and I(1,3,4,5)P-4 substrates. At5PTase1 did not hydrolyze I(1)P, I(1,4)P-2, or PI(4,5)P-2 substrates. This substrate sp ecificity was similar to that of the human Type I 5PTase. We identified 14 other potential At5PTase genes and constructed an unrooted phylogenetic tre e containing putative Arabidopsis, human, and yeast 5PTase proteins. This a nalysis indicated that the Arabidopsis 5PTases were grouped in two separate branches of the tree. The multiplicity of At5PTases indicates that these e nzymes may have different substrate specificities and play different roles in signal termination in Arabidopsis.