Part One. A Role Of Arabidopsis Inositol Polyphosphate Kinase, AtIPK2α, In Pollen Germination And Root Growth Part Two. Molecular Genetic Study Of Zygote Activation In Arabidopsis

Phosphatidylinositol (PI) signaling pathway is critical during plant growth /development, especially cell responses to environmental stimuli. An Arabidopsisthaliana cDNA encoding inositol polyphosphate kinase (AtIPK2α) was isolated andtransformed into Escherichia coli to express recombinant AtIPK2α protein. Enzymaticassays of recombinant protein in vitro indicated that AtIPK2α phosphorylates Ins(1,4,5)P3 successively at the D-6, D-3 positions, and Ins (1,3,4,5)P4 at D-6, resulting inthe generation of Ins (1,3,4,5,6)P5. Promoter-β-glucuronidase (GUS) reporter genestudies revealed AtIPK2α transcriptional activity in various tissues, including roots androot hairs, pollen grains, the flower stigma, and siliques. Antisense lines, in which theAtIPK2α coding region was fused in reverse orientation to its own promoter, wereobtained. AtIPK2α transcript level was strongly reduced in several independenttransformants, as shown by reverse transcriptase - polymerase chain reaction (RT-PCR).Both pollen germination and pollen tube growth were enhanced in the antisense lineswhen compared to that of the wild-type, especially at non-optimal Ca2+ concentrationpresent in the culture medium. Root growth and root hair development was alsostimulated in the antisense lines, both in the presence of elevated external Ca2+concentration and upon the addition of EGTA. These observations suggest a general andimportant role of AtIPK2α, and hence inositol polyphosphate metabolism, in theregulation of plant growth.