OsPIPK1, a rice phosphatidylinositol monophosphate kinase, regulates rice heading by modifying the expression of floral induction genes

A rice gene, OsPIPK1, encoding a 792-aa putative phosphatidylinositol 4-phosphate 5-kinase (PIPK), was identified and characterized. Comparison between the cDNA and genomic sequences revealed the presence of 10 exons ( 39 - 1050 bp) and 9 introns ( 88 - 745 bp) in OsPIPK1 gene. The deduced amino acid sequence of OsPIPK1 contains a lipid kinase domain that is highly homologous to those of previously isolated PIPKs, and structural analysis revealed the intriguing presence of multiple MORN motifs at the N-terminus. The MORN motifs have also been detected in PIPKs from Arabidopsis thaliana and Oryza sativa, but not in the well-characterized PIPKs from animal and yeast cells. RT-PCR analysis indicated that OsPIPK1 was expressed almost constitutively in roots, shoots, stems, leaves and flowers, and upregulated following treatment with plant hormones or application of various stresses. An antisense transgenic strategy was used to suppress the expression of OsPIPK1, and homozygous transgenic plants showed earlier heading ( 7 - 14 days earlier) than control plants, suggesting that OsPIPK1 negatively regulates. oral initiation. This was further confirmed by morphologic observation showing earlier. oral development in antisense plants, as well as leaf emergence measurement indicating delayed leaf development under OsPIPK1 deficiency, a common phenotype observed with earlier flowering. RT-PCR analysis and cDNA chip technology were used to examine transcripts of various genes in the transgenic plants and the results showed altered transcriptions of several flowering-time or - identity related genes, suggesting that OsPIPK1 is involved in rice heading through regulation of. oral induction genes, signaling and metabolic pathways.