RESUMO
The use of algal biomass for biofuel production requires improvements in both biomass productivity and its energy density. Green microalgae store starch and oil as two major forms of carbon reserves. Current strategies to increase the amount of carbon reserves often compromise algal growth. To better understand the cellular mechanisms connecting cell division to carbon storage, we examined starch and oil accumulation in two Chlamydomonas mutants deficient in a gene encoding a homolog of the Arabidopsis Cell Division Cycle 5 (CDC5), a MYB DNA binding protein known to be involved in cell cycle in higher plants. The two crcdc5 mutants (crcdc5-1 and crcdc5-2) were found to accumulate significantly higher amount of starch and oil than their corresponding parental lines. Flow cytometry analysis on synchronized cultures cultivated in a diurnal light/dark cycle revealed an abnormal division of the two mutants, characterized by a prolonged S/M phase, therefore demonstrating its implication in cell cycle in Chlamydomonas. Taken together, these results suggest that the energy saved by a slowdown in cell division is used for the synthesis of reserve compounds. This work highlights the importance in understanding the interplay between cell cycle and starch/oil homeostasis, which should have a critical impact on improving lipid/starch productivity.
Assuntos
Proteínas de Algas/genética , Chlamydomonas reinhardtii/genética , Redes e Vias Metabólicas/genética , Mutação , Amido/biossíntese , Proteínas de Algas/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Biocombustíveis , Biomassa , Carbono/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Divisão Celular , Chlamydomonas reinhardtii/metabolismo , Expressão Gênica , Óleos de Plantas , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Pontos de Checagem da Fase S do Ciclo Celular/genética , Amido/genéticaRESUMO
Despite a strong interest in microalgal oil production, our understanding of the biosynthetic pathways that produce algal lipids and the genes involved in the biosynthetic processes remains incomplete. Here, we report that Chlamydomonas reinhardtii Cre09.g398289 encodes a plastid-targeted 2-lysophosphatidic acid acyltransferase (CrLPAAT1) that acylates the sn-2 position of a 2-lysophosphatidic acid to form phosphatidic acid, the first common precursor of membrane and storage lipids. In vitro enzyme assays showed that CrLPAAT1 prefers 16:0-CoA to 18:1-CoA as an acyl donor. Fluorescent protein-tagged CrLPAAT1 was localized to the plastid membrane in C. reinhardtii cells. Furthermore, expression of CrLPAAT1 in plastids led to a > 20% increase in oil content under nitrogen-deficient conditions. Taken together, these results demonstrate that CrLPAAT1 is an authentic plastid-targeted LPAAT in C. reinhardtii, and that it may be used as a molecular tool to genetically increase oil content in microalgae.