Tore Brembu | Norwegian University of Science and Technology (original) (raw)

Papers by Tore Brembu

Algal growth is strongly affected by nitrogen (N) availability. Diatoms, an ecologically importan... more Algal growth is strongly affected by nitrogen (N) availability. Diatoms, an ecologically important group of unicellular algae, have evolved several acclimation mechanisms to cope with N deprivation. In this study, we integrated physiological data with transcriptional and metabolite data to reveal molecular and metabolic modifications in N-deprived conditions in the marine diatom Phaeodactylum tricornutum. Physiological and metabolite measurements indicated that the photosynthetic capacity and chlorophyll content of the cells decreased, while neutral lipids increased in N-deprived cultures. Global gene expression analysis showed that P. tricornutum responded to N deprivation through an increase in N transport, assimilation, and utilization of organic N resources. Following N deprivation, reduced biosynthesis and increased recycling of N compounds like amino acids, proteins, and nucleic acids was observed at the transcript level. The majority of the genes associated with photosynthesis and chlorophyll biosynthesis were also repressed. Carbon metabolism was restructured through downregulation of the Calvin cycle and chrysolaminarin bio-synthesis, and coordinated upregulation of glycolysis, the tricarboxylic acid cycle, and pyruvate metabolism, leading to funnelling of carbon sources to lipid metabolism. Finally, reallocation of membrane lipids and induction of de novo triacylglycerol biosynthesis directed cells to accumulation of neutral lipids.

Peptide ligands play crucial roles in the life cycle of plants by modulating the innate immunity ... more Peptide ligands play crucial roles in the life cycle of plants by modulating the innate immunity against pathogens and regulating growth and developmental processes. One well-studied example is INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), which controls floral organ abscission and lateral root emergence in Arabidopsis thaliana. IDA belongs to a family of five additional IDA-LIKE (IDL) members that have all been suggested to be involved in regulation of Arabidopsis development. Here we present three novel members of the IDL subfamily and show that two of them are strongly and rapidly induced by different biotic and abiotic stresses. Furthermore, we provide data that the recently identified PAMP-INDUCED SECRETED PEPTIDE (PIP) and PIP-LIKE (PIPL) peptides, which show similarity to the IDL and C-TERMINALLY ENCODED PEPTIDE (CEP) peptides, are not only involved in innate immune response in Arabidopsis but are also induced by abiotic stress. Expression patterns of the IDA/IDL and PIP/PIPL genes were analysed using in silico data, qRT-PCR and GUS promoter lines. Transcriptomic responses to PIPL3 peptide treatment suggested a role in regulation of biotic stress responses and cell wall modification.

PLoS ONE, 2013

Photosynthetic diatoms that live suspended throughout the water column will constantly be swept u... more Photosynthetic diatoms that live suspended throughout the water column will constantly be swept up and down by vertical mixing. When returned to the photic zone after experiencing longer periods in darkness, mechanisms exist that enable the diatoms both to survive sudden light exposure and immediately utilize the available energy in photosynthesis and growth. We have investigated both the response to prolonged darkness and the re-acclimation to moderate intensity white irradiance (E = 100 mmol m 22 s 21 ) in the diatom Phaeodactylum tricornutum, using an integrated approach involving global transcriptional profiling, pigment analyses, imaging and photo-physiological measurements. The responses were studied during continuous white light, after 48 h of dark treatment and after 0.5 h, 6 h, and 24 h of re-exposure to the initial irradiance. The analyses resulted in several intriguing findings. Dark treatment of the cells led to 1) significantly decreased nuclear transcriptional activity, 2) distinct intracellular changes, 3) fixed ratios of the light-harvesting pigments despite a decrease in the total cell pigment pool, and 4) only a minor drop in photosynthetic efficiency (W PSII_max ). Re-introduction of the cells to the initial light conditions revealed 5) distinct expression profiles for nuclear genes involved in photosynthesis and those involved in photoprotection, 6) rapid rise in photosynthetic parameters (a and rETR max ) within 0.5 h of reexposure to light despite a very modest de novo synthesis of photosynthetic compounds, and 7) increasingly efficient resonance energy transfer from fucoxanthin chlorophyll a/c-binding protein complexes to photosystem II reaction centers during the first 0.5 h, supporting the observations stated in 6). In summary, the results show that despite extensive transcriptional, metabolic and intracellular changes, the ability of cells to perform photosynthesis was kept intact during the length of the experiment. We conclude that P. tricornutum maintains a functional photosynthetic apparatus during dark periods that enables prompt recovery upon re-illumination. Citation: Nymark M, Valle KC, Hancke K, Winge P, Andresen K, et al. (2013) Molecular and Photosynthetic Responses to Prolonged Darkness and Subsequent Acclimation to Re-Illumination in the Diatom Phaeodactylum tricornutum. PLoS ONE 8(3): e58722.

Marine Genomics, 2013

The chloroplast genome of the diatom Seminavis robusta: New features 2 introduced through multipl... more The chloroplast genome of the diatom Seminavis robusta: New features 2 introduced through multiple mechanisms of horizontal gene transfer ☆ 3 Tore Q1

Photosynthetic diatoms are exposed to rapid and unpredictable changes in irradiance and spectral ... more Photosynthetic diatoms are exposed to rapid and unpredictable changes in irradiance and spectral quality, and must be able to acclimate their light harvesting systems to varying light conditions. Molecular mechanisms behind light acclimation in diatoms are largely unknown. We set out to investigate the mechanisms of high light acclimation in Phaeodactylum tricornutum using an integrated approach involving global transcriptional profiling, metabolite profiling and variable fluorescence technique. Algae cultures were acclimated to low light (LL), after which the cultures were transferred to high light (HL). Molecular, metabolic and physiological responses were studied at time points 0.5 h, 3 h, 6 h, 12 h, 24 h and 48 h after transfer to HL conditions. The integrated results indicate that the acclimation mechanisms in diatoms can be divided into an initial response phase (0-0.5 h), an intermediate acclimation phase (3-12 h) and a late acclimation phase (12-48 h). The initial phase is recognized by strong and rapid regulation of genes encoding proteins involved in photosynthesis, pigment metabolism and reactive oxygen species (ROS) scavenging systems. A significant increase in light protecting metabolites occur together with the induction of transcriptional processes involved in protection of cellular structures at this early phase. During the following phases, the metabolite profiling display a pronounced decrease in light harvesting pigments, whereas the variable fluorescence measurements show that the photosynthetic capacity increases strongly during the late acclimation phase. We show that P. tricornutum is capable of swift and efficient execution of photoprotective mechanisms, followed by changes in the composition of the photosynthetic machinery that enable the diatoms to utilize the excess energy available in HL. Central molecular players in light protection and acclimation to high irradiance have been identified.

PLoS ONE, 2014

Due to the selective attenuation of solar light and the absorption properties of seawater and sea... more Due to the selective attenuation of solar light and the absorption properties of seawater and seawater constituents, free-floating photosynthetic organisms have to cope with rapid and unpredictable changes in both intensity and spectral quality. We have studied the transcriptional, metabolic and photo-physiological responses to light of different spectral quality in the marine diatom Phaeodactylum tricornutum through time-series studies of cultures exposed to equal doses of photosynthetically usable radiation of blue, green and red light. The experiments showed that short-term differences in gene expression and profiles are mainly light quality-dependent. Transcription of photosynthesis-associated nuclear genes was activated mainly through a light quality-independent mechanism likely to rely on chloroplast-to-nucleus signaling. In contrast, genes encoding proteins important for photoprotection and PSII repair were highly dependent on a blue light receptor-mediated signal. Changes in energy transfer efficiency by light-harvesting pigments were spectrally dependent; furthermore, a declining trend in photosynthetic efficiency was observed in red light. The combined results suggest that diatoms possess a light quality-dependent ability to activate photoprotection and efficient repair of photodamaged PSII. In spite of approximately equal numbers of PSII-absorbed quanta in blue, green and red light, the spectral quality of light is important for diatom responses to ambient light conditions.

PloS one, Jan 1, 2011

MIRO GTPases have evolved to regulate mitochondrial trafficking and morphology in eukaryotic orga... more MIRO GTPases have evolved to regulate mitochondrial trafficking and morphology in eukaryotic organisms. A previous study showed that T-DNA insertion in the Arabidopsis MIRO1 gene is lethal during embryogenesis and affects pollen tube growth and mitochondrial morphology in pollen, whereas T-DNA insertion in MIRO2 does not affect plant development visibly. Phylogenetic analysis of MIRO from plants revealed that MIRO 1 and 2 orthologs in dicots cluster in two separate groups due to a gene/genome duplication event, suggesting that functional redundancy may exists between the two MIRO genes. To investigate this possibility, we generated miro1 (+/2) /miro2-2 (2/2) plants. Compared to miro1 (+/2) plants, the miro1 (+/2) /miro2-2 (2/2) plants showed increased segregation distortion. miro1 (+/2) /miro2-2 (2/2) siliques contained less aborted seeds, but more than 3 times the number of undeveloped ovules. In addition, reciprocal crosses showed that cotransmission through the male gametes was nearly absent, whereas co-transmission through the female gametes was severely reduced in miro1 (+/2) /miro2-2 (2/2) plants. Further investigations revealed that loss of MIRO2 (miro2 (2/2) ) function in the miro1 (+/2) background enhanced pollen tube growth defects. In developing miro1 (+/2) /miro2 (2/2) embryo sacs, fusion of polar nuclei was further delayed or impaired compared to miro1 plants. This phenotype has not been reported previously for miro1 plants and coincides with studies showing that defects in some mitochondria-targeted genes results in the same phenotype. Our observations show that loss of function in MIRO2 in a miro1 (+/2) background enhances the miro1 (+/2) phenotype significantly, even though miro2 (2/2) plants alone does not display any phenotypes. Based on these findings, we conclude that MIRO1 and MIRO2 are unequally redundant and that a proportion of the miro1 (+/2) /miro2 (2/2) plants haploid gametes displays the complete null phenotype of MIRO GTPase function at key developmental stages.

… science & technology, Jan 1, 2011

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Small GTP-binding proteins are molecular switches that serve as important regulators of numerous ... more Small GTP-binding proteins are molecular switches that serve as important regulators of numerous cellular processes. In animal and plant cells, the Rho family of small GTPases participate in eg organisation of the actin cytoskeleton, production of reactive oxygen species through the ...

Journal of Plant Growth Regulation, Jan 1, 2005

PLoS One, Jan 1, 2009

Phytochemistry, Jan 1, 2006

Journal of experimental …, Jan 1, 2005

The RAC/ROP family of small GTPases are central regulators of important cellular processes in pla... more The RAC/ROP family of small GTPases are central regulators of important cellular processes in plants. AtRAC2/ROP7 is an ancient member of the RAC/ROP gene family in Arabidopsis thaliana whose functions are generally unknown. In order to study the spatial expression pattern of the AtRAC2/ROP7 gene, transgenic plants expressing GUS or GFP under the control of the AtRAC2/ROP7 promoter were analysed. Functional analysis of AtRAC2/ROP7 was done using transgenic plants overexpressing wild-type and constitutively activated AtRAC2/ROP7 (Val15Gly), and an AtRAC2/ROP7 T-DNA insertion mutant. The AtRAC2/ROP7 promoter directs a highly specific xylem-specific expression in the root, hypocotyl, stem, and leaves. The expression is developmentally limited to the late stages of xylem differentiation, and coincides with the formation of secondary cell walls. Leaf epidermal cells of transgenic plants overexpressing constitutively active AtRAC2/ ROP7 exhibited highly impaired lobe formation, suggesting that AtRAC2/ROP7 is able to regulate polar cell expansion. Finally, GFP-AtRAC2/ROP7 fusion proteins were localized to the plasma membrane. The results indicate a role for AtRAC2/ROP7 in the development of secondary cell walls of xylem vessels.

Trends in Plant …, Jan 1, 2009

A novel candidate ligand-receptor system, INFLORES-CENCE DEFICIENT IN ABSCISSION (IDA) and the re... more A novel candidate ligand-receptor system, INFLORES-CENCE DEFICIENT IN ABSCISSION (IDA) and the related receptor-like kinases (RLKs) HAESA (HAE) and HAESA-LIKE (HSL)2, has been shown to control floral abscission in Arabidopsis thaliana. Furthermore, several IDA-LIKE (IDL) proteins, which contain a conserved C-terminal domain resembling that of the CLAVATA (CLV)3-ENDO-SPERM SURROUNDING REGION (ESR)-RELATED (CLE) protein family, have been shown to be partially redundant with IDA. Here, we use the genetic similarities between the IDA and CLV3 signalling systems to hypothesize that closely related peptide ligands are likely to interact with families of closely related RLKs. Guided by this hypothesis and with the aid of genetics and novel methods, ligand-receptor systems can be identified to improve our understanding of developmental processes in plants.

Cell Research, Jan 1, 2006

Rho GTPases are molecular switches that act as key regulators of a many cellular processes, inclu... more Rho GTPases are molecular switches that act as key regulators of a many cellular processes, including cell movement, morphogenesis, host defense, cell division and gene expression. Rho GTPases are found in all eukaryotic kingdoms. Plants lack clear homologs to conventional Rho GTPases found in yeast and animals; instead, they have over time developed a unique subfamily, ROPs, also known as RAC. The origin of ROP-like proteins appears to precede the appearance of land plants. This review aims to discuss the evolution of ROP/RAC and to compare plant ROP and animal Rho GTPases, focusing on similarities and differences in regulation of the GTPases and their downstream effectors. Abbreviations: CRIB (Cdc42/Rac-interactive binding); DH (Dbl homology); FH (formin homology); GAP (GTPase-activating protein); GDI (GDP dissociation inhibitor); GEF (GDP exchange factor); PH (Pleckstrin homology); PRONE (plant-specific Rop nucleotide exchanger); Rboh (Respiratory burst oxidase homolog); RIC (ROP-interactive CRIB-containing protein); RLK (Receptor-like kinase); ROP (Rho-related GTPase from plants); ROS (reactive oxygen species) Cell Research | www.cell-research.com Rho GTPases in animals and plants 436 npg of GTPase activity and downstream pathways.

The Plant Cell Online, Jan 1, 2004

Genetics, Jan 1, 2000

Rho GTPases regulate a number of important cellular functions in eukaryotes, such as organization... more Rho GTPases regulate a number of important cellular functions in eukaryotes, such as organization of the cytoskeleton, stress-induced signal transduction, cell death, cell growth, and differentiation. We have conducted an extensive screening, characterization, and analysis of genes belonging to the Ras superfamily of GTPases in land plants (embryophyta) and found that the Rho family is composed mainly of proteins with homology to RAC-like proteins in terrestrial plants. Here we present the genomic and cDNA sequences of the RAC gene family from the plant Arabidopsis thaliana. On the basis of amino acid alignments and genomic structure comparison of the corresponding genes, the 11 encoded AtRAC proteins can be divided into two distinct groups of which one group apparently has evolved only in vascular plants. Our phylogenetic analysis suggests that the plant RAC genes underwent a rapid evolution and diversification prior to the emergence of the embryophyta, creating a group that is distinct from rac/cdc42 genes in other eukaryotes. In embryophyta, RAC genes have later undergone an expansion through numerous large gene duplications. Five of these RAC duplications in Arabidopsis thaliana are reported here. We also present an hypothesis suggesting that the characteristic RAC proteins in higher plants have evolved to compensate the loss of RAS proteins.

Plant molecular biology, Jan 1, 1997

The Rho family of GTPases are in higher eukaryotes divided into 3 major subfamilies; the Rho, Rac... more The Rho family of GTPases are in higher eukaryotes divided into 3 major subfamilies; the Rho, Rac and Cdc42 proteins. In plants, however, the Rho family is restricted to one large family of Rac-like proteins. From work with mammalian phagocytes the Rac proteins are known to activate a multicomponent NADPH-dependent oxidase which results in accumulation of H 2 O 2 , a process termed oxidative burst. In plants a similar oxidative burst is observed and plays an important role in its defence against pathogen infections, suggesting a similar role for the plant Rac-like proteins. The Rho family of GTPases proteins are also involved in control of cell morphology, and are also thought to mediate signals from cell membrane receptors.