Characterisation of a plant 3‐phosphoinositide‐dependent protein kinase‐1 homologue which contains a pleckstrin homology domain

Abstract

A plant homologue of mammalian 3‐phosphoinositide‐dependent protein kinase‐1 (PDK1) has been identified in Arabidopsis and rice which displays 40% overall identity with human 3‐phosphoinositide‐dependent protein kinase‐1. Like the mammalian 3‐phosphoinositide‐dependent protein kinase‐1, Arabidopsis 3‐phosphoinositide‐dependent protein kinase‐1 and rice 3‐phosphoinositide‐dependent protein kinase‐1 possess a kinase domain at N‐termini and a pleckstrin homology domain at their C‐termini. Arabidopsis 3‐phosphoinositide‐dependent protein kinase‐1 can rescue lethality in Saccharomyces cerevisiae caused by disruption of the genes encoding yeast 3‐phosphoinositide‐dependent protein kinase‐1 homologues. Arabidopsis 3‐phosphoinositide‐dependent protein kinase‐1 interacts via its pleckstrin homology domain with phosphatidic acid, PtdIns3P, PtdIns(3,4,5)P₃ and PtdIns(3,4)P₂ and to a lesser extent with PtdIns(4,5)P₂ and PtdIns4P. Arabidopsis 3‐phosphoinositide‐dependent protein kinase‐1 is able to activate human protein kinase Bα (PKB/AKT) in the presence of PtdIns(3,4,5)P₃. Arabidopsis 3‐phosphoinositide‐dependent protein kinase‐1 is only the second plant protein reported to possess a pleckstrin homology domain and the first plant protein shown to bind 3‐phosphoinositides.