Chloroplast damage induced by the inhibition of fatty acid synthesis triggers autophagy in chlamydomonas

Fatty acids are synthesized in the stroma of plant and algal chloroplasts by the fatty acid synthase complex. Newly synthesized fatty acids are then used to generate plastidial lipids that are essential for chloroplast structure and function. Here, we show that inhibition of fatty acid synthesis in the model alga Chlamydomonas reinhardtii activates autophagy, a highly conserved catabolic process by which cells degrade intracellular material under adverse conditions to maintain cell homeostasis. Treatment of Chlamydomonas cells with cerulenin, a specific fatty acid synthase inhibitor, stimulated lipidation of the autophagosome protein ATG8 and enhanced autophagic flux. We found that inhibition of fatty acid synthesis decreased monogalactosyldiacylglycerol abundance, increased lutein content, down-regulated photosynthesis, and increased the production of reactive oxygen species. Electron microscopy revealed a high degree of thylakoid membrane stacking in cerulenin-treated cells. Moreover, global transcriptomic analysis of these cells showed an up-regulation of genes encoding chloroplast proteins involved in protein folding and oxidative stress and the induction of major catabolic processes, including autophagy and proteasome pathways. Thus, our results uncovered a link between lipid metabolism, chloroplast integrity, and autophagy through a mechanism that involves the activation of a chloroplast quality control system.Ministerio de Economía y Competitividad BFU2015-68216-PJunta de Andalucía CVI-7336, BIO2015-74432-JI

Activation of Autophagy by Metals in Chlamydomonas reinhardtii

Autophagy is an intracellular self-degradation pathway by which eukaryotic cells recycle their own material in response to specific stress conditions. Exposure to high concentrations of metals causes cell damage, although the effect of metal stress on autophagy has not been explored in photosynthetic organisms. In this study, we investigated the effect of metal excess on autophagy in the model unicellular green alga Chlamydomonas reinhardtii. We show in cells treated with nickel an upregulation of ATG8 that is independent of CRR1, a global regulator of copper signaling in Chlamydomonas. A similar effect on ATG8 was observed with copper and cobalt but not with cadmium or mercury ions. Transcriptome sequencing data revealed an increase in the abundance of the protein degradation machinery, including that responsible for autophagy, and a substantial overlap of that increased abundance with the hydrogen peroxide response in cells treated with nickel ions. Thus, our results indicate that metal stress triggers autophagy in Chlamydomonas and suggest that excess nickel may cause oxidative damage, which in turn activates degradative pathways, including autophagy, to clear impaired components and recover cellular homeostasisMinisterio de Economía y Competitividad BFU2012-35913Junta de Andalucía CVI-7336National Institutes of Health GM42143, R24 GM09247

Estudio de la conexión de la autofagia con el metabolismo de lípidos en el alga verde unicelular Chlamydomonas reinhardtii

[EN] Autophagy is a conserved catabolic process in eukaryotic organisms by which cells degrade or recycle internal constituents under stress or optimal conditions to produce new macromolecules or energy. Chamydomonas reinhardtii, in which autophagy process is conserved, is a unicellular green alga commonly used as a model organism for photosynthesis research. Recently, its importance has grown up commercially and biotechnologically because of its application in biofuel production, as this organism is able to synthetize triacylglycerols (TAGs). Due to its high potential, a number of recent studies have been reported to understand the parameters involved in lipids synthesis. In this context, it is known that the starch-deficient mutant strain, sta6, accumulates more lipids than wild type cells. Furthermore, lipid levels increase when cells are grown under nitrogen deficiency. The lack of nitrogen generates stress which in turn triggers autophagy. The relationship between autophagy, starch and lipid metabolism is analyzed in this work. Here, we report that starch deficiency in cells growing with or without nitrogen does not induce autophagy. However, when cells were treated with cerulenin, a fatty acids synthase inhibitor, autophagy is induced because of fatty acids profile modification and especially because of the decrease of the glucolipid MGDG, which is part of thylakoid membranes and photosystems. The relationship between autophagy and MGDG fall has never been described before.[ES] La autofagia es un proceso catabólico de degradación y reciclado de componentes celulares internos conservado en eucariotas que se produce ante un estrés o condiciones óptimas de crecimiento para generar nuevas macromoléculas o energía. Chlamydomonas reinhardtii es una microalga verde unicelular muy utilizada en el laboratorio como organismo modelo para estudios fotosintéticos y en la que está conservado este proceso. Recientemente, ha cobrado interés a nivel biotecnológico y comercial debido a su aplicación en biocombustibles, ya que son capaces de producir Triacilgliceroles (TAGs). Desde que se demostró el gran potencial de estas microalgas, se han realizado diversos estudios para concretar los parámetros que afectan a su síntesis. En este contexto, se conoce que la estirpe mutante en la síntesis de almidón, sta6, acumula más lípidos que la estirpe silvestre y que este contenido aumenta en medio en deficiencia de nitrógeno, condición de estrés que activa la autofagia. En este trabajo se ha investigado la relación de la autofagia con la producción de almidón y la acumulación de lípidos. Nuestros resultados indican que la ausencia de almidón en medio con y sin nitrógeno no induce la autofagia. Sin embargo, al tratar con cerulenina, compuesto inhibidor de la ácido graso sintasa, la autofagia se induce debido a la modificación del perfil de ácido grasos de la célula y, sobre todo, debido a la reducción del glucolípido MGDG, lípido presente en la membrana tilacoidal y en los fotosistemas. Esta relación entre la inducción de la autofagia y la disminución en los niveles de MGDG no ha sido descrita hasta el momento en ningún sistema.Andrés Garrido, A. (2014). Estudio de la conexión de la autofagia con el metabolismo de lípidos en el alga verde unicelular Chlamydomonas reinhardtii. http://hdl.handle.net/10251/47387Archivo delegad

Activation of Autophagy by Metals in Chlamydomonas reinhardtii

Autophagy is an intracellular self-degradation pathway by which eukaryotic cells recycle their own material in response to specific stress conditions. Exposure to high concentrations of metals causes cell damage, although the effect of metal stress on autophagy has not been explored in photosynthetic organisms. In this study, we investigated the effect of metal excess on autophagy in the model unicellular green alga Chlamydomonas reinhardtii. We show in cells treated with nickel an upregulation of ATG8 that is independent of CRR1, a global regulator of copper signaling in Chlamydomonas. A similar effect on ATG8 was observed with copper and cobalt but not with cadmium or mercury ions. Transcriptome sequencing data revealed an increase in the abundance of the protein degradation machinery, including that responsible for autophagy, and a substantial overlap of that increased abundance with the hydrogen peroxide response in cells treated with nickel ions. Thus, our results indicate that metal stress triggers autophagy in Chlamydomonas and suggest that excess nickel may cause oxidative damage, which in turn activates degradative pathways, including autophagy, to clear impaired components and recover cellular homeostasisPeer reviewe