Enzyme activities of Arabidopsis inositol polyphosphate kinases AtIPK2α and AtIPK2β are involved in pollen development, pollen tube guidance and embryogenesis

Abstract

SUMMARYInositol polyphosphate kinase (IPK2) is a key component of inositol polyphosphate signaling. There are two highly homologous inositol polyphosphate kinases (AtIPK2a and AtIPK2b) in Arabidopsis. Previous studies that overexpressed or reduced the expression of AtIPK2a and AtIPK2b revealed their roles in auxiliary shoot branching, abiotic stress responses and root growth. Here, we report that AtIPK2a and AtIPK2b act redundantly during pollen development, pollen tube guidance and embryogenesis. Single knock-out mutants of atipk2a and atipk2b were indistinguishable from the wild type, whereas the atipk2a atipk2b double mutant could not be obtained. Detailed genetic and cytological investigations showed that the mutation of AtIPK2a and AtIPK2b 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 atipk2a atipk2b double mutant was also aborted. Expressing either catalytically inactive or substrate specificity-altered variants of AtIPK2b could not rescue the male gametophyte and embryogenesis defects of the atipk2a atipk2b 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.

Arabidopsis inositol polyphosphate multikinase delays flowering time through mediating transcriptional activation of FLOWERING LOCUS C

“…All the plants used in this study were Arabidopsis thaliana Columbia type (Col-0) background. The atipk2β-1 (SALK_025091) and atipk2β-2 (SALK_104995) mutant lines were described previously by Zhang et al (2007) and Zhan et al (2015) . The flc-6 null mutant, obtained from the Arabidopsis Biological Resource Center, was originally described by Bouveret et al (2006) .…”

“…The complementary lines of the atipk2β mutant were generated by introducing a construct encoding an AtIPK2β-Green Fluorescent Protein (GFP) fusion protein under the control of the native promoter into atipk2β-2 , as described by Zhan et al (2015) . For overexpression transgenic lines, the AtIPK2β or FVE coding sequence was inserted into the pCAMBIA1302 vector after the CaMV 35S promoter region and followed by the coding sequence of GFP.…”

“…AtIPK2β, an IPMK identified in Arabidopsis, exhibits conserved 6-/3-kinase activity and is homologous to yeast IPK2, as expressing AtIPK2β in the IPK2 deletion yeast partially compensates its growth defects ( Stevenson-Paulik et al , 2002 ; Xia et al , 2003 ; Bosch and Saiardi, 2012 ). A recent study showed that the kinase activity of AtIPK2β is essential for its function in plant sexual reproduction, including in pollen development, pollen tube guidance, and embryogenesis ( Zhan et al , 2015 ). Several investigations have also suggested a potential role of AtIPK2β in transcriptional regulation.…”

Gametophytic Pollen Tube Guidance: Attractant Peptides, Gametic Controls, and Receptors

“…The relationships between CNGC18 and MDIS1-MIK/PRK6 are of interest. Other pollen tube molecules for ovular guidance include glycosylphosphatidylinositol anchor and its biosynthesis proteins Dai et al, 2014), mitogen-activated protein kinases (Guan et al, 2014), AGC kinases for eukaryotic polarized cell growth (Zhang et al, 2009), endoplasmic reticulum-localized K + channel (Lu et al, 2011) and luminal proteins (Li et al, 2011), small secreted peptide phytosulfokine (Stührwohldt et al, 2015), and inositol polyphosphate kinases (Zhan et al, 2015). It remains to be elucidated whether these molecules are involved in sensing and competency control for LURE or other gametophytic attractant pathways .…”

ZmSTK1 and ZmSTK2, encoding receptor‐like cytoplasmic kinase, are involved in maize pollen development with additive effect

“…LIP1 and LIP2, belonging to the receptor-like cytoplasmic kinase (RLCK) VII subfamily, also show functional redundancy to attraction towards the female attractant AtLURE1 in Arabidopsis (Liu et al, 2013). Highly homologous inositol polyphosphate kinases AtIPK2a and AtIPK2b in Arabidopsis act redundantly during pollen development, pollen tube guidance and embryogenesis (Zhan et al, 2015). Also in Arabidopsis, PIP5K1 and PIP5K2, belonging to the phosphatidylinositol 4-phosphate 5kinase (PIP5 K) family, are functionally redundant as homozygous double mutants do not render viable pollen grains (Ugalde et al, 2016).…”