Role Of Lipid Phosphate Phosphatase In Lipid Metabolism And Growth In Rice

Lipid phosphate phosphatase(LPP)catalyzes the dephosphorylation of lipid phosphate such as phosphatidic acid(PA),diacylglycerol pyrophosphate(DGPP),and lysophosphatidic acid(LPA)to produce diacylglycerol(DAG)or monoacylglycerol(MAG).Both PA and DAG are important signaling molecules and are also intermediates for lipid metabolism involved in various biological processes including growth and stress response.Most studies focus on animal cells.The knowledge of LPP is relatively limited and the role of LPP is yet to be characterized in plants.In this study,the role and molecular regulation of LPP?5 were explored.The results showed that loss of LPPa5 resulted in reduced growth,and pale yellow-green leaves,companied by defective thylakoid grana structure.The lppa5 mutant exhibited decreased chlorophyll content,reduced photo synthetic rate,less plant height,and shorter root length,as compared to wild type plants.The reduced growth and pale yellow-green leaf phenotype were rescued by the LPPa5 complementation,suggesting that LPP a5 plays important roles in plant growth and thylakoid membrane biogenesis.GUS activity drove by LPPa5 promoter showed that LPPa5 was highly expressed in green and growing actively tissues such as leaves,root tips and root hair inanition points.LPPa5 is mainly localized to endoplasmic reticulum.To further characterize the biochemical property,LPPa5 was expressed in E.coli cells and was used for the activity assay using different lipids as substrates.LPP?5 is able to catalyze the dephosphorylation of PA and DGPP to produce DAG,and to catalyze the dephosphorylation of LPA to MAG.LPPa5 activity was optimum at pH 7 and was independent of Mg2+ and other metal factors such as Ca2+?Mn2+ and Fe3+ under the micromolar concentration,but was inhibited by N-ethylmaleimide.Lipid profiling revealed that loss of LPPa5 resulted in reduced monogalactosyldiaclyglycerol(MGDG),digalactosyldiacylglycerol(DGDG),and phosphatidylethanolamine(PE)in leaves,whereas that reduced DAG in the roots of lppa5 mutant.The results suggest that LPP?5 functions distinguishable effects in different tissues;LPPa5 activation provides the DAG substrate for MGDG and DGDG biosynthesis for thylakoid membrane biogenesis in leaves,whereas it plays a role for normal DAG level to maintain root growth.In addition,the role of LPP?2 was also characterized in this study.The result showed that loss of LPP?2 led to growth retard and exhibited a slim leaf size with normal green leaf color.The LPP?2 catalyzes the dephosphorylation of PA to generate DAG,but exhibited a lower activity toward LPA,which is different from that of LPPa5.The results suggest that different LPPs exhibit heterogenetic regulation in plants.