RESUMO
Target of rapamycin (TOR) kinase is a sensor and a central integrator of internal and external metabolic cues. However, in algae and in higher plants, the components of TOR kinase signaling are yet to be characterized. Here, we establish an assay system to study TOR kinase activity in Chlamydomonas reinhardtii using the phosphorylation status of its putative downstream target, CrS6K. Using this assay, we probe the modulation of cellular TOR kinase activity under various physiological states such as photoautotrophy, heterotrophy, mixotrophy, and nitrogen (N) starvation. Importantly, we uncover that excess acetate in the medium leads to high cellular reactive oxygen species levels, triggering autophagy and a concomitant drop in TOR kinase activity in a dose-dependent manner, thus leading to a N-starvation-like cellular phenotype, even when nitrogen is present.
Assuntos
Chlamydomonas reinhardtii/enzimologia , Chlamydomonas reinhardtii/metabolismo , Estresse Fisiológico , Serina-Treonina Quinases TOR/metabolismo , Acetatos/metabolismo , Atrazina/farmacologia , Atrazina/efeitos da radiação , Autofagia/efeitos dos fármacos , Autofagia/efeitos da radiação , Chlamydomonas reinhardtii/efeitos dos fármacos , Chlamydomonas reinhardtii/efeitos da radiação , Processos Heterotróficos/efeitos dos fármacos , Processos Heterotróficos/efeitos da radiação , Luz , Modelos Biológicos , Mutagênese Insercional/genética , Processos Fototróficos/efeitos dos fármacos , Processos Fototróficos/efeitos da radiação , Espécies Reativas de Oxigênio/metabolismo , Reprodutibilidade dos Testes , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/efeitos da radiação , Estresse Fisiológico/efeitos dos fármacos , Estresse Fisiológico/efeitos da radiaçãoRESUMO
While the role of TOR kinase in the chloroplast biogenesis and transcriptional regulation of photosynthesis is well documented in Arabidopsis, the functional relevance of this metabolic sensor kinase in chloroplast-mitochondria cross talk is unknown. Using Chlamydomonas reinhardtii as the model system, we demonstrate the role of TOR kinase in the regulation of chloroplast and mitochondrial functions: We show that TOR kinase inhibition impairs the maintenance of high ETR associated with PSII and low NPQ and inhibits efficient state transitions between PSII and PSI. While compromised photosynthetic functions are observed in TOR kinase inhibited cells, same conditions lead to augmentation in mitochondrial basal respiration rate by twofold and concomitantly a rise in ATP production. Interestingly, such upregulated mitochondrial functions in TOR-inhibited cells are mediated by fragmented mitochondria via upregulating COXIIb and downregulating Hxk1 and AOX1 protein levels. We propose that TOR kinase may act as a sensor that counter-regulates chloroplast versus mitochondrial functions in a normal C. reinhardtii cell.
