Project description:Marine phytoplankton are a diverse group of photoautotrophic organisms and key mediators in the global carbon cycle. Phytoplankton physiology and biomass accumulation are closely tied to mixed layer depth, but the intracellular metabolic pathways activated in response to changing mixed layer depths remain unexplored. Here, metatranscriptomics was used to characterize the phytoplankton community response to a mixed layer shallowing from 233 meters to 5 meters over the course of two days during the late spring in the Northwest Atlantic. Most phytoplankton genera downregulated core photosynthesis, carbon storage, and carbon fixation genes as the system transitioned from a deep to a shallow mixed layer and shifted towards catabolism of stored carbon ic pathways supportive of rapid cell growth. In contrast, phytoplankton genera exhibited divergent transcriptional strategies for photosystem light harvesting complex genes during this transition. Active infection, taken as the ratio of virus to host transcripts, increased in the Bacillariophyta (diatom) phylum and decreased in the Chlorophyta (green algae) phylum upon mixed layer shallowing. A conceptual model is proposed to provide ecophysiological context for our findings, in which light limitation during deep mixing induces populations into a transcriptional state which maximizes interrupts the oscillating levels of transcripts related to photosynthesis, carbon storage, and carbon fixation found in shallow mixed layers with relatively higher growth rates. We propose that upon sensing high light levels during mixed layer shallowing, phytoplankton resume diel oscillation of core sets of genes enabling photoprotection, biosynthesis and cell replication. Our findings highlight the shared and unique transcriptional response strategies within phytoplankton communities acclimating to the dynamic light environment associated with transient deep mixing and shallowing events during the annual North Atlantic bloom.

Project description:In the surface ocean, carbon is fixed by phytoplankton and respired by the entire marine community at an astonishingly high rate. At any point in time, the difference between these two processes yields a carbon pool in surface particles that is a combination of both freshly fixed and partially degraded material. On a molecular level, we have a limited knowledge of the small molecules, or metabolites, within this pool. Specific metabolites have been shown to be responsible for fueling respiration, maintaining organismal interactions, and transferring energy throughout the microbial community. Metabolomics, or the direct observation and quantification of the small molecules that are the result of cellular activity, provides an important lens through which we can begin to assess the standing stocks of small compounds that likely fuel a great deal of heterotrophic activity in the surface ocean. Here we describe community metabolomes of particulate material into the North Pacific Ocean and compare the metabolomes to a variety of phytoplankton grown in the lab. Using both targeted and untargeted metabolomics, we identify metabolites in the particulate carbon pool and explore their latitudinal and phylogenetic distributions. This analysis reveals several compounds that have not been previously recognized as abundant components of the marine organic carbon pool. We found that the community metabolome showed distinct differences between the regimes that likely reflects the phytoplankton community present. The community metabolome in surface waters of the subtropical domain was remarkably consistent even when sampled weeks apart, while the northern regions showed a patichier and less reproducible community metabolome. Some individual compounds showed distinct patterns between oceanographic regimes, including homarine, an abundant molecule that can contribute up to 4\% of the total particulate carbon pool in marine surface waters. Glutamic acid and glutamine showed opposite patterns in the oceanographic regimes, suggesting differences in community-level nitrogen assimilation in these different regimes. Overall, this study offers a new perspective into particulate carbon composition in oceanographic research, reveals important carbon pools that may fuel the microbial loop, and suggests an altered community-level nitrogen assimilation capacity over the North Pacific transition zone.

Project description:In the surface ocean, carbon is fixed by phytoplankton and respired by the entire marine community at an astonishingly high rate. At any point in time, the difference between these two processes yields a carbon pool in surface particles that is a combination of both freshly fixed and partially degraded material. On a molecular level, we have a limited knowledge of the small molecules, or metabolites, within this pool. Specific metabolites have been shown to be responsible for fueling respiration, maintaining organismal interactions, and transferring energy throughout the microbial community. Metabolomics, or the direct observation and quantification of the small molecules that are the result of cellular activity, provides an important lens through which we can begin to assess the standing stocks of small compounds that likely fuel a great deal of heterotrophic activity in the surface ocean. Here we describe community metabolomes of particulate material into the North Pacific Ocean and compare the metabolomes to a variety of phytoplankton grown in the lab. Using both targeted and untargeted metabolomics, we identify metabolites in the particulate carbon pool and explore their latitudinal and phylogenetic distributions. This analysis reveals several compounds that have not been previously recognized as abundant components of the marine organic carbon pool. We found that the community metabolome showed distinct differences between the regimes that likely reflects the phytoplankton community present. The community metabolome in surface waters of the subtropical domain was remarkably consistent even when sampled weeks apart, while the northern regions showed a patchier and less reproducible community metabolome. Some individual compounds showed distinct patterns between oceanographic regimes, including homarine, an abundant molecule that can contribute up to 4% of the total particulate carbon pool in marine surface waters. Glutamic acid and glutamine showed opposite patterns in the oceanographic regimes, suggesting differences in community-level nitrogen assimilation in these different regimes. Overall, this study offers a new perspective into particulate carbon composition in oceanographic research, reveals important carbon pools that may fuel the microbial loop, and suggests an altered community-level nitrogen assimilation capacity over the North Pacific transition zone.

Project description:Water soluble carbohydrates (WSC, composed of mainly fructans, sucrose, glucose and fructose) deposited in wheat stems are important carbon sources for grain filling. Variation in stem WSC concentrations among wheat genotypes is one of the genetic factors influencing grain weight and yield under water-limited environments. Here, we describe the molecular dissection of carbohydrate metabolism in stems, at the WSC accumulation phase, of recombinant inbred SB (Seri/Babax) lines of Triticum aestivum differing in stem WSC concentrations. Affymetrix GeneChip analysis of carbohydrate metabolic enzymes revealed that the mRNA levels of two fructan synthetic enzyme families (sucrose:sucrose 1-fructosyltransferase and sucrose:fructan 6-fructosyltransferase) in the stem were positively correlated with stem WSC and fructan concentrations, while the mRNA levels of enzyme families involved in sucrose hydrolysis (sucrose synthase and soluble acid invertase) were inversely correlated with WSC concentrations. Differential regulation of the mRNA levels of these sucrose hydrolytic enzymes in SB lines resulted in genotypic differences in these enzyme activities. Down-regulation of sucrose synthase and soluble acid invertase in high WSC lines was accompanied by significant decreases in the mRNA levels of enzyme families related to sugar catabolic pathways (fructokinase and mitochondrion pyruvate dehydrogenase complex) and enzyme families involved in diverting UDP-glucose to cell wall synthesis (UDP-glucose 6-dehydrogenase, UDP-glucuronate decarboxylase and cellulose synthase), resulting in a reduction in cell wall polysaccharide contents (mainly hemicellulose) in the stem of high WSC lines. These data suggest that differential carbon partitioning in the wheat stem is one mechanism that contributes to genotypic variation in WSC accumulation. We used Affymetrix GeneChip to dissect genotypic variation in carbohydrate metabolism related to water soluble carbohydrate accumulation in stems of wheat. Experiment Overall Design: 8 genotypes of recombinant inbred lines Seri M82 x Babax with 2 biological replicates per genotype. Grown in the field under rain-fed conditions

Project description:Water soluble carbohydrates (WSC, composed of mainly fructans, sucrose, glucose and fructose) deposited in wheat stems are important carbon sources for grain filling. Variation in stem WSC concentrations among wheat genotypes is one of the genetic factors influencing grain weight and yield under water-limited environments. Here, we describe the molecular dissection of carbohydrate metabolism in stems, at the WSC accumulation phase, of recombinant inbred SB (Seri/Babax) lines of Triticum aestivum differing in stem WSC concentrations. Affymetrix GeneChip analysis of carbohydrate metabolic enzymes revealed that the mRNA levels of two fructan synthetic enzyme families (sucrose:sucrose 1-fructosyltransferase and sucrose:fructan 6-fructosyltransferase) in the stem were positively correlated with stem WSC and fructan concentrations, while the mRNA levels of enzyme families involved in sucrose hydrolysis (sucrose synthase and soluble acid invertase) were inversely correlated with WSC concentrations. Differential regulation of the mRNA levels of these sucrose hydrolytic enzymes in SB lines resulted in genotypic differences in these enzyme activities. Down-regulation of sucrose synthase and soluble acid invertase in high WSC lines was accompanied by significant decreases in the mRNA levels of enzyme families related to sugar catabolic pathways (fructokinase and mitochondrion pyruvate dehydrogenase complex) and enzyme families involved in diverting UDP-glucose to cell wall synthesis (UDP-glucose 6-dehydrogenase, UDP-glucuronate decarboxylase and cellulose synthase), resulting in a reduction in cell wall polysaccharide contents (mainly hemicellulose) in the stem of high WSC lines. These data suggest that differential carbon partitioning in the wheat stem is one mechanism that contributes to genotypic variation in WSC accumulation. We used Affymetrix GeneChip to dissect genotypic variation in carbohydrate metabolism related to water soluble carbohydrate accumulation in stems of wheat. Keywords: Genotypic differences in water soluble carbohydrate metabolism in stem

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Kīlauea lava fuels phytoplankton bloom in the North Pacific Ocean - study of particulate metabolites

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