Enzyme activities of Arabidopsis inositol polyphosphate kinases AtIPK2α and AtIPK2ß are involved in pollen development, pollen tube guidance and embryogenesis.

ABSTRACT

Inositol polyphosphate kinase (IPK2) is a key component of inositol polyphosphate signaling. There are two highly homologous inositol polyphosphate kinases (AtIPK2α and AtIPK2ß) in Arabidopsis. Previous studies that overexpressed or reduced the expression of AtIPK2α and AtIPK2ß revealed their roles in auxiliary shoot branching, abiotic stress responses and root growth. Here, we report that AtIPK2α and AtIPK2ß act redundantly during pollen development, pollen tube guidance and embryogenesis. Single knock-out mutants of atipk2α and atipk2ß were indistinguishable from the wild type, whereas the atipk2α atipk2ß double mutant could not be obtained. Detailed genetic and cytological investigations showed that the mutation of AtIPK2α and AtIPK2ß resulted in severely reduced transmission of male gametophyte as a result of abnormal pollen development and defective pollen tube guidance. In addition, the early embryo development of the atipk2α atipk2ß double mutant was also aborted. Expressing either catalytically inactive or substrate specificity-altered variants of AtIPK2ß could not rescue the male gametophyte and embryogenesis defects of the atipk2α atipk2ß double mutant, implying that the kinase activity of AtIPK2 is required for pollen development, pollen tube guidance and embryogenesis. Taken together, our results provide genetic evidence for the requirement of inositol polyphosphate signaling in plant sexual reproduction.