Rice Phosphatidylinositol Signal Transduction Pathway Of Phosphatidylinositol Kinase (ospipk1) Molecular Genetic Analysis Of A Phosphoric Acid

Phosphatidylinositol (PI) signaling pathway plays an important role in plantgrowth and development. Till now the studies on PI signaling pathway in highplants are mainly focused on the isolation of relevant genes and functionalanalysis of key enzymes ofthe pathway. PI phosphate kinases (PIPKs) catalyze the PI phosphate (PIP) to generatethe PI bisphosphate (PIP2), indicating that PIPKs are important enzyme tosynthesize the lipid signaling molecules in eucaryotic cells. A rice expressedsequence tag (EST) encoding putative rice PIPK (Accession number D48536)was identified by searching the dbEST database using cDNA of AtPIP5K1 asbait. The identity or positive in the conserved lipid kinase domain between thepeptide encoded by rice EST and AtPIP5K1 is 42% or 66%, respectively.Primers were designed according to the EST sequence and used for the screeningof a rice cDNA library through a PCR-based screening method. A 2460 bpcDNA, named OsPIPK1, encoding a 792 amino acids peptide, was isolated andused for further analysis. OsPIPK1 has high homology with all kind of PIPKsisoforms. RT-PCR analysis showed that OsPIPK1 was expressed throughout theOryza stiva tissues at a low level, except in the spike and the young seedlingwhere it is expressed at a relatively higher level. Transgenic approaches with antisense strategy were performed to study thephysiological roles of OsPIPK1. The antisense chain of OsPIPK1, driven byconstitutive CaMV35S promoter, was subcloned into the p1301 vector toconstruct the antisense expression plasmid. Transgenic rice plants were obtainedvia Agrobacterium tumefaciens mediated transformation. Homozygoustransgenic plants showed weak growth and earlier heading (7-14 days earlier)comparing to control plants. Further detailed analysis of transcriptionof chosenfloral induction and homeotic genes indicated altered expression offlowering-time or identity related genes, suggesting that OsPIPK1 involved in 3rice heading through regulation of flowering related genes. Genes with alteredtranscriptions under OsPIPK1 deficiency were further studied via cDNA chiptechnology, and relevant metabolism was discussed. RT-PCR analysis indicated that OsPIPK1 mRNA was induced by somestress treatments such as ABA and NaCl. Phenotype observation showed thatantisense transgenic plants showed hypersensitive responses to ABA and NaClstresses. We found that the distribution pattern of actin cytoskeleton in the lateralroots of antisense transgenic seedlings have great difference with that ofwild-type seedlings after stress treatments. These results cast a light in the waythat OsPIPK1 involves in the rice response to stresses. With the help of a modified yeast SMET system, we demonstrate thatOsPIPK1, as well as AtPI4K?and OsPI4K2, are membrane-binding proteins.The specific domains responsible for the membrane binding were under furtheranalyzed to reveal its mechanism.