Plant nuclear lipid signaling

Abstract

Our goal is to characterize the nuclear PI pathway in plants and understand the role of phosphatidylinositol 4,5 bisphosphate (PtdIns(4,5)P2) in regulating nuclear signaling. Because PtdIns(4,5)P2 is so low in plants, our approach was to generate a plant cell line with increased nuclear PtdInsP kinase activity. We expressed the human phosphatidylinositol 4‐phosphate 5 kinase 1α (HsPIP5K1) in Nicotiana tabacum cells, isolated nuclei from the transformed and non‐transformed cells and compared the effect of expressing HsPIP5K1 on nuclear lipids. Lipid kinase activity was assayed. The PIPK specific activity was 20‐fold higher in HsPIP5K1–expressing cell nuclei. Transformed nuclei contained an average of 32.4 pmoles of PtdInsP(4,5)P2 per mg protein while the PtdInsP(4,5)P2 in WT nuclei was not detectable. Nuclear lipids in HsPIP5K1‐expressing cells showed a decrease in total LysoPC and LysoPE; however, the percentage of unsaturated fatty acids increased in several phospholipids e.g. 18:1 in LysoPC and LysoPE. In spite of the increase in nuclear PtdInsP(4,5)P2, the HsPIP5K1 cells continue to divide and grow although the rate of DNA synthesis is less. We are currently assessing the status of the posttranslational modifications of histones in anticipation that these will be affected by the high levels of PtdInsP(4,5)P2. Funded in part by grant from NSF (WFB) and NIH training grant (CBD).