SUMMARYTarget of Rapamycin (TOR) is a positive regulator of growth and development in all eukaryotes, which positively regulates anabolic processes like protein synthesis, while repressing catabolic processes, including autophagy. To better understand TOR function we decided to analyze its role in seed development and germination. We therefore performed a detailed phenotypic analysis using mutants of the REGULATORY-ASSOCIATED PROTEIN OF TOR 1B (RAPTOR1B), a conserved TOR interactor, acting as a scaffold protein, which recruits substrates for the TOR kinase. Our results show that raptor1b plants produced seeds that were delayed in germination and less resistant to stresses, leading to decreased viability. These physiological phenotypes were accompanied by morphological changes including decreased seed-coat pigmentation and reduced production of seed-coat mucilage. A detailed molecular analysis revealed that many of these morphological changes were associated with significant changes of the metabolic content of raptor1b seeds, including elevated levels of free amino acids, as well as reduced levels of protective secondary metabolites and storage proteins. Most of these observed changes were accompanied by significantly altered phytohormone levels in the raptor1b seeds, with increases in abscisic acid, auxin and jasmonic acid, which are known to inhibit germination. Delayed germination and seedling growth, observed in the raptor1b seeds, could be partially restored by the exogenous supply of gibberellic acid, indicating that TOR is at the center of a regulatory hub controlling seed metabolism, maturation and germination.

SUMMARYSeveral metabolic processes tightly regulate growth and biomass accumulation. A highly conserved protein complex containing the target of rapamycin (TOR) kinase is known to integrate intra-and extracellular stimuli controlling nutrient allocation and hence cellular growth. Although several functions of TOR have been described in various heterotrophic eukaryotes, our understanding lags far behind in photosynthetic organisms. In the present investigation, we used the model alga Chlamydomonas reinhardtii to conduct a time-resolved analysis of molecular and physiological features throughout the diurnal cycle after TOR inhibition. Detailed examination of the cell cycle phases revealed that growth is not only repressed by 50%, but also that significant, non-linear delays in the progression can be observed. By using metabolomics analysis, we elucidated that the growth repression was mainly driven by differential carbon partitioning between anabolic and catabolic processes. Accordingly, the time-resolved analysis illustrated that metabolic processes including amino acid-, starch-and triacylglycerol synthesis, as well RNA degradation, were redirected within minutes of TOR inhibition. Here especially the high accumulation of nitrogen-containing compounds indicated that an active TOR kinase controls the carbon to nitrogen balance of the cell, which is responsible for biomass accumulation, growth and cell cycle progression.

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Indole-3-butyric acid (IBA) and 2,4-dichlorophenoxybutyric acid (2,4-DB) are metabolised by peroxisomal beta-oxidation to active auxins that inhibit root growth. We screened Arabidopsis mutants for resistance to IBA and 2,4-DB and identified two new 2,4-DB resistant mutants. The mutant genes encode a putative oxidoreductase (SDRa) and a putative acyl-activating enzyme (AAE18). Both proteins are localised to peroxisomes. SDRa is coexpressed with core beta-oxidation genes, but germination, seedling growth and the fatty acid profile of sdra seedlings are indistinguishable from wild type. The sdra mutant is also resistant to IBA, but aae18 is not. AAE18 is the first example of a gene required for response to 2,4-DB but not IBA. The closest relative of AAE18 is AAE17. AAE17 is predicted to be peroxisomal, but an aae17 aae18 double mutant responded similarly to aae18 for all assays. We propose that AAE18 is capable of activating 2,4-DB but IBA activating enzymes remain to be discovered. We present an updated model for peroxisomal pro-auxin metabolism in Arabidopsis that includes SDRa and AAE18.