Reduced expression of glycolate oxidase leads to enhanced disease resistance in rice

Epitranscriptome profiles reveal participation of the RNA methyltransferase gene OsMTA1 in rice seed germination and salt stress response

BACKGROUND

RNA m6A methylation installed by RNA methyltransferases plays a crucial role in regulating plant growth and development and environmental stress responses. However, the underlying molecular mechanisms of m6A methylation involved in seed germination and stress responses are largely unknown. In the present study, we surveyed global m6A methylation in rice seed germination under salt stress and the control (no stress) using an osmta1 mutant and its wild type.

RESULTS

The knockout of OsMTA1 resulted in a decreased level of m6A methylation and delayed seed germination, together with increased oxidative damage in the osmta1-1 mutant, especially under salt stress, indicating that OsMTA1 performs a crucial function in rice seed germination and salt stress response. Comparative analysis of m6A profiling using methylated RNA immunoprecipitation sequencing revealed that a unique set of genes that functioned in seed germination, cell growth, and development, including OsbZIP78 and OsA8, were hypomethylated in osmta1-1 embryos and germinating seeds. Numerous genes involved in plant growth and stress response were hypomethylated in the osmta1-1 mutant during seed germination under salt stress. Further combined analysis of the m6A methylome and transcriptome revealed that the loss of function of OsMTA1 had a more complex impact on gene expression in osmta1-1. Several hypomethylated genes with a negative role in growth and development, such as OsHsfA7 and OsHDAC3, were highly up-regulated in the osmta1-1 mutant under the control condition. In contrast, several hypomethylated genes positively associated with stress response were down-regulated, whereas a different set of hypomethylated genes that functioned as negative regulators of growth and stress response were up-regulated in the osmta1-1 mutant under salt stress. These results further demonstrated that OsMTA1-mediated m6A methylation modulated rice seed germination and salt stress response by regulating transcription of a unique set of genes with diverse functions.

CONCLUSION

Our results reveal a crucial role for the m6A methyltransferase gene OsMTA1 in regulating rice seed germination and salt stress response, and provide candidate genes to assist in breeding new stress-tolerant rice varieties.

Glycolate oxidase gene family identification and functional analyses in cotton resistance to Verticillium wilt

Glycolate oxidase (GOX) plays an important role in the regulation of photorespiration and photosynthesis in plants. However, as one of the main enzymes to produce the second messenger hydrogen peroxide (H2O2), its functions in response to pathogens are still poorly understood. In this study, we carried out genome-wide identification, and 14 GOX genes were identified in Gossypium hirsutum. These GOX genes are located on 10 chromosomes and divided into hydroxyacid-oxidases (HAOX) and GOX groups. After infection with Verticillium dahliae Kleb., six GOX gene expression levels were changed. Moreover, H2O2, salicylic acid (SA), and the content and activity of GOX increased in cotton. GhHAOX2-D-silenced plants showed more wilting than control plants after infection with V. dahliae. Additionally, H2O2 accumulation and SA content were reduced in GhHAOX2-D-silenced plants. The expression levels of GhPAL, GhPAD4, and GhPR1 and the lignin content of the silenced plants were significantly lower than those of the control plants. These results indicate that GhHAOX2-D is a positive regulator of Verticillium wilt tolerance in cotton and may promote H2O2 accumulation via the synergistic effects of GOX genes and SA. Collectively, GOX genes play an important role in cotton resistance to Verticillium wilt.

Identification and characterization of Glycolate oxidase gene family in garden lettuce (Lactuca sativa cv. 'Salinas') and its response under various biotic, abiotic, and developmental stresses

Glycolate oxidase (GLO) is an FMN-containing enzyme localized in peroxisomes and performs in various molecular and biochemical mechanisms. It is a key player in plant glycolate and glyoxylate accumulation pathways. The role of GLO in disease and stress resistance is well-documented in various plant species. Although studies have been conducted regarding the role of GLO genes from spinach on a microbial level, the direct response of GLO genes to various stresses in short-season and leafy plants like lettuce has not been published yet. The genome of Lactuca sativa cultivar 'Salinas' (v8) was used to identify GLO gene members in lettuce by performing various computational analysis. Dual synteny, protein-protein interactions, and targeted miRNA analyses were conducted to understand the function of GLO genes. The identified GLO genes showed further clustering into two groups i.e., glycolate oxidase (GOX) and hydroxyacid oxidase (HAOX). Genes were observed to be distributed unevenly on three chromosomes, and syntenic analysis revealed that segmental duplication was prevalent. Thus, it might be the main reason for GLO gene diversity in lettuce. Almost all LsGLO genes showed syntenic blocks in respective plant genomes under study. Protein-protein interactions of LsGLO genes revealed various functional enrichments, mainly photorespiration, and lactate oxidation, and among biological processes oxidative photosynthetic carbon pathway was highly significant. Results of in-depth analyses disclosed the interaction of GLO genes with other members of the glycolate pathway and the activity of GLO genes in various organs and developmental stages in lettuce. The extensive genome evaluation of GLO gene family in garden lettuce is believed to be a reference for cloning and studying functional analyses of GLO genes and characterizing other members of glycolate/glyoxylate biosynthesis pathway in various plant species.

The role of photorespiration in plant immunity

To defend themselves in the face of biotic stresses, plants employ a sophisticated immune system that requires the coordination of other biological and metabolic pathways. Photorespiration, a byproduct pathway of oxygenic photosynthesis that spans multiple cellular compartments and links primary metabolisms, plays important roles in defense responses. Hydrogen peroxide, whose homeostasis is strongly impacted by photorespiration, is a crucial signaling molecule in plant immunity. Photorespiratory metabolites, interaction between photorespiration and defense hormone biosynthesis, and other mechanisms, are also implicated. An improved understanding of the relationship between plant immunity and photorespiration may provide a much-needed knowledge basis for crop engineering to maximize photosynthesis without negative tradeoffs in plant immunity, especially because the photorespiratory pathway has become a major target for genetic engineering with the goal to increase photosynthetic efficiency.

The steroid-inducible pOp6/LhGR gene expression system is fast, sensitive and does not cause plant growth defects in rice (Oryza sativa)

Inducible systems for transgene expression activated by a chemical inducer or an inducer of non-plant origin are desirable tools for both basic plant research and biotechnology. Although, the technology has been widely exploited in dicotyledonous model plants such as Arabidopsis, it has not been optimised for use with the monocotyledonous model species, namely rice. We have adapted the dexamethasone-inducible pOp6/LhGR system for rice and the results indicated that it is fast, sensitive and tightly regulated, with high levels of induction that remain stable over several generations. Most importantly, we have shown that the system does not cause negative growth defects in vitro or in soil grown plants. Interestingly in the process of testing, we found that another steroid, triamcinolone acetonide, is a more potent inducer in rice than dexamethasone. We present serious considerations for the construct design to avoid undesirable effects caused by the system in plants, leakiness and possible silencing, as well as simple steps to maximize translation efficiency of a gene of interest. Finally, we compare the performance of the pOp6/LhGR system with other chemically inducible systems tested in rice in terms of the properties of an ideal inducible system.

Two VOZ transcription factors link an E3 ligase and an NLR immune receptor to modulate immunity in rice

Nucleotide-binding leucine-rich repeat (NLR) proteins play critical roles in plant immunity. However, how NLRs are regulated and activate defense signaling is not fully understood. The rice (Oryza sativa) NLR receptor Piz-t confers broad-spectrum resistance to the fungal pathogen Magnaporthe oryzae and the RING-type E3 ligase AVRPIZ-T INTERACTING PROTEIN 10 (APIP10) negatively regulates Piz-t accumulation. In this study, we found that APIP10 interacts with two rice transcription factors, VASCULAR PLANT ONE-ZINC FINGER 1 (OsVOZ1) and OsVOZ2, and promotes their degradation through the 26S proteasome pathway. OsVOZ1 displays transcriptional repression activity while OsVOZ2 confers transcriptional activation activity in planta. The osvoz1 and osvoz2 single mutants display modest but opposite M. oryzae resistance in the non-Piz-t background. However, the osvoz1 osvoz2 double mutant exhibits strong dwarfism and cell death, and silencing of both genes via RNA interference also leads to dwarfism, mild cell death, and enhanced resistance to M. oryzae in the non-Piz-t background. Both OsVOZ1 and OsVOZ2 interact with Piz-t. Double silencing of OsVOZ1 and OsVOZ2 in the Piz-t background decreases Piz-t protein accumulation and transcription, reactive oxygen species-dependent cell death, and resistance to M. oryzae containing AvrPiz-t. Taken together, these results indicate that OsVOZ1 and OsVOZ2 negatively regulate basal defense but contribute positively to Piz-t-mediated immunity.

Responses of Marine Diatom Skeletonema marinoi to Nutrient Deficiency: Programmed Cell Death

Diatoms are important phytoplankton and contribute greatly to the primary productivity of marine ecosystems. Despite the ecological significance of diatoms and the importance of programmed cell death (PCD) in the fluctuation of diatom populations, little is known about the molecular mechanisms of PCD triggered by different nutrient stresses. Here we describe the physiological, morphological, biochemical, and molecular changes in response to low levels of nutrients in the ubiquitous diatom Skeletonema marinoi The levels of gene expression involved in oxidation resistance and PCD strongly increased upon nitrogen (N) or phosphorus (P) starvation. The enzymatic activity of caspase 3-like protein also increased. Differences in mRNA levels and protein activities were observed between the low-N and low-P treatments, suggesting that PCD could have a differential response to different nutrient stresses. When cultures were replete with N or P, the growth inhibition stopped. Meanwhile, the enzymatic activity of caspase 3-like protein and the number of cells with damaged membranes decreased. These results suggest that PCD is an important cell fate decision mechanism in the marine diatom S. marinoi Our results provide important insight into how diatoms adjust phenotypic and genotypic features of their cell-regulated death programs when stressed by nutrient limitations. Overall, this study could allow us to better understand the molecular mechanism behind the formation and termination of diatom blooms in the marine environment.IMPORTANCE Our study showed how the ubiquitous diatom S. marinoi responded to different nutrient limitations with PCD in terms of physiological, morphological, biochemical, and molecular characteristics. Some PCD-related genes (PDCD4, GOX, and HSP90) induced by N deficiency were relatively upregulated compared to those induced by P deficiency. In contrast, the expression of the TSG101 gene in S. marinoi showed a clear and constant increase during P limitation compared to N limitation. These findings suggest that PCD is a complex mechanism involving several different proteins. The systematic mRNA level investigations provide new insight into understanding the oxidative stress- and cell death-related functional genes of diatoms involved in the response to nutrient fluctuations (N or P stress) in the marine environment.

Enzymatic Properties of Recombinant Phospho-Mimetic Photorespiratory Glycolate Oxidases from Arabidopsis thaliana and Zea mays

In photosynthetic organisms, the photorespiratory cycle is an essential pathway leading to the recycling of 2-phosphoglycolate, produced by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, to 3-phosphoglycerate. Although photorespiration is a widely studied process, its regulation remains poorly understood. In this context, phosphoproteomics studies have detected six phosphorylation sites associated with photorespiratory glycolate oxidases from Arabidopsis thaliana (AtGOX1 and AtGOX2). Phosphorylation sites at T4, T158, S212 and T265 were selected and studied using Arabidopsis and maize recombinant glycolate oxidase (GOX) proteins mutated to produce either phospho-dead or phospho-mimetic enzymes in order to compare their kinetic parameters. Phospho-mimetic mutations (T4D, T158D and T265D) led to a severe inhibition of GOX activity without altering the K_M glycolate. In two cases (T4D and T158D), this was associated with the loss of the cofactor, flavin mononucleotide. Phospho-dead versions exhibited different modifications according to the phospho-site and/or the GOX mutated. Indeed, all T4V and T265A enzymes had kinetic parameters similar to wild-type GOX and all T158V proteins showed low activities while S212A and S212D mutations had no effect on AtGOX1 activity and AtGOX2/ZmGO1 activities were 50% reduced. Taken together, our results suggest that GOX phosphorylation has the potential to modulate GOX activity.

Development of efficient protocol for rice transformation overexpressing MAP kinase and their effect on root phenotypic traits

Exhaustive studies on mitogen-activated protein kinase (MAPK) have reported the importance in regulating a variety of responses during plant growth and development. In particular, the potential MAPK genes, MPK3 and MPK6, seem to regulate a plethora of responses, conferring tolerance to varied abiotic, biotic, and developmental stimuli. This makes both MPK3 and MPK6 potential targets for further studies. It would be an important concern to overexpress and knock out these pivotal proteins and then, in turn, to monitor the plant response which is expected to correlate action of a gene to a trait in cellular and organismal contexts. However, overexpression of MAPK genes has remained a puzzle in plants. In the present study, we report the generation of stable transgenic lines overexpressing OsMPK3 in indica and japonica cultivars and OsMPK6 in japonica cultivar under the control of an inducible promoter. We also establish the crucial steps and troubleshooting for each of the indicated rice transformation medium components. Later, we study the potential role of these MAPKs in high-throughput analysis of root system architectural (RSA) traits. It was observed that OsMPK6 overexpression lines had a more robust and spread out root architectural system while OsMPK3 overexpression lines had a typical bushy phenotype.

Genomic variations in the 3'-termini of Rice stripe virus in the rotation between vector insect and host plant

A large number of plant RNA viruses circulate between plants and insects. For RNA viruses, host alternations may impose a differential selective pressure on viral populations and induce variations in viral genomes. Here, we report the variations in the 3'-terminal regions of the multiple-segment RNA virus Rice stripe virus (RSV) that were discovered through de novo assembly of the genome using RNA sequencing data from infected host plants and vector insects. The newly assembled RSV genome contained 16- and 15-nt extensions at the 3'-termini of two genome segments compared with the published reference RSV genome. Our study demonstrated that these extensional sequences were consistently observed in two RSV isolates belonging to distinct genetic subtypes in RSV-infected rice, wheat and tobacco. Moreover, the de novo assembled genome of Southern rice black-streaked dwarf virus also contained 3'-terminal extensions in five RNA segments compared with the reference genome. Time course experiments confirmed that the 3'-terminal extensions of RSV were enriched in the vector insects, were gradually eliminated in the host plant and potentially affected viral replication. These findings indicate that variations in the 3'-termini of viral genomes may be different adaptive strategies for plant RNA viruses in insects and plants.

Glycolate oxidase gene family in Nicotiana benthamiana: genome-wide identification and functional analyses in disease resistance

Glycolate oxidase (GOX)-dependent production of H2O2 in response to pathogens and its function in disease resistance are still poorly understood. In this study, we performed genome-wide identification of GOX gene family in Nicotiana benthamiana and analyzed their function in various types of disease resistance. Sixteen GOX genes were identified in N. benthamiana genome. They consisted of GOX and HAOX groups. All but two NbGOX proteins contained an alpha_hydroxyacid_oxid_FMN domain with extra 43-52 amino acids compared to that of FMN-dependent alpha-hydroxyacid oxidizing enzymes (NCBI-CDD cd02809). Silencing of three NbGOX family genes NbHAOX8, NbGOX1 and NbGOX4 differently affected resistance to various pathogens including Tobacco rattle virus, Xanthomonas oryzae pv. oryzae (Xoo) and Sclerotinia sclerotiorum. Effect of these genes on resistance to Xoo is well correlated with that on Xoo-responsive H2O2 accumulation. Additionally, silencing of these genes enhanced PAMP-triggered immunity as shown by increased flg22-elicited H2O2 accumulation in NbGOX-silenced plants. These NbGOX family genes were distinguishable in altering expression of defense genes. Analysis of mutual effect on gene expression indicated that NbGOX4 might function through repressing NbHAOX8 and NbGOX1. Collectively, our results reveal the important roles and functional complexity of GOX genes in disease resistance in N. benthamiana.

Tomato photorespiratory glycolate-oxidase-derived H2 O2 production contributes to basal defence against Pseudomonas syringae

Despite being essential for C₃ plants, photorespiration is believed to cause a significant crop yield loss even under future climates. However, how photorespiration affects plant basal defence still remains largely unknown. Here, we studied the involvement of photorespiration in tomato-Pseudomonas syringae pv. tomato DC3000 interaction focusing on three photorespiratory genes. Inoculation with P. syringae increased photorespiration rate (Pr) and expression of glycolate oxidase (GOX2), serine glyoxylate aminotransferase (SGT) and serine hydroxyl methyltransferase (SHMT1); however, inhibition of photorespiration by isonicotinic acid hydrazide decreased tomato basal defence against P. syringae. Furthermore, silencing of GOX2, SGT or SHMT1 genes in tomato decreased Pr but increased susceptibility to P. syringae, whereas transient overexpression of GOX2, SGT or SHMT1 in tobacco increased basal defence. Further study revealed that salicylic acid (SA) signalling is involved in GOX2-mediated, SGT-mediated and SHMT1-mediated defence. Moreover, H₂ O₂ pretreatment remarkably alleviated the GOX2 silencing-induced depression in basal defence and SA signalling, whereas it had no effect on that of SGT-silenced and SHMT1-silenced plants. Taken together, these results suggest that H₂ O₂ is critical for GOX2-modulated but not SGT-modulated or SHMT1-modulated SA signalling and subsequent basal defence against P. syringae. This work deepens the understanding of photorespiration-involved defence responses to bacterial attack in plants.

Moving nitrogen to the centre of plant defence against pathogens

BACKGROUND

Plants require nitrogen (N) for growth, development and defence against abiotic and biotic stresses. The extensive use of artificial N fertilizers has played an important role in the Green Revolution. N assimilation can involve a reductase series ( NO3- → NO2- → NH4+ ) followed by transamination to form amino acids. Given its widespread use, the agricultural impact of N nutrition on disease development has been extensively examined.

SCOPE

When a pathogen first comes into contact with a host, it is usually nutrient starved such that rapid assimilation of host nutrients is essential for successful pathogenesis. Equally, the host may reallocate its nutrients to defence responses or away from the site of attempted infection. Exogenous application of N fertilizer can, therefore, shift the balance in favour of the host or pathogen. In line with this, increasing N has been reported either to increase or to decrease plant resistance to pathogens, which reflects differences in the infection strategies of discrete pathogens. Beyond considering only N content, the use of NO3- or NH4+ fertilizers affects the outcome of plant-pathogen interactions. NO3- feeding augments hypersensitive response- (HR) mediated resistance, while ammonium nutrition can compromise defence. Metabolically, NO3- enhances production of polyamines such as spermine and spermidine, which are established defence signals, with NH4+ nutrition leading to increased γ-aminobutyric acid (GABA) levels which may be a nutrient source for the pathogen. Within the defensive N economy, the roles of nitric oxide must also be considered. This is mostly generated from NO2- by nitrate reductase and is elicited by both pathogen-associated microbial patterns and gene-for-gene-mediated defences. Nitric oxide (NO) production and associated defences are therefore NO3- dependent and are compromised by NH4+ .

CONCLUSION

This review demonstrates how N content and form plays an essential role in defensive primary and secondary metabolism and NO-mediated events.

A Genetic Screen Identifies a Requirement for Cysteine-Rich-Receptor-Like Kinases in Rice NH1 (OsNPR1)-Mediated Immunity

Systemic acquired resistance, mediated by the Arabidopsis NPR1 gene and the rice NH1 gene, confers broad-spectrum immunity to diverse pathogens. NPR1 and NH1 interact with TGA transcription factors to activate downstream defense genes. Despite the importance of this defense response, the signaling components downstream of NPR1/NH1 and TGA proteins are poorly defined. Here we report the identification of a rice mutant, snim1, which suppresses NH1-mediated immunity and demonstrate that two genes encoding previously uncharacterized cysteine-rich-receptor-like kinases (CRK6 and CRK10), complement the snim1 mutant phenotype. Silencing of CRK6 and CRK10 genes individually in the parental genetic background recreates the snim1 phenotype. We identified a rice mutant in the Kitaake genetic background with a frameshift mutation in crk10; this mutant also displays a compromised immune response highlighting the important role of crk10. We also show that elevated levels of NH1 expression lead to enhanced CRK10 expression and that the rice TGA2.1 protein binds to the CRK10 promoter. These experiments demonstrate a requirement for CRKs in NH1-mediated immunity and establish a molecular link between NH1 and induction of CRK10 expression.

To survive, plants and animals must resist microbial infection. Plants employ an immune response called systemic acquired resistance that confers long-lasting resistance to a broad-spectrum of pathogens. Researchers have previously identified two key proteins (NPR1/NH1 and TGA) that control this immune response. Despite these advances, there remain many gaps in our knowledge and understanding of this important immune response. We have identified a new gene (CRK10) required for this immune response; without it, plants are more susceptible to infection. These findings advance basic knowledge of systemic acquired resistance and open the door to a new avenue of research on this exciting and important resistance mechanism.

Photorespiratory glycolate-glyoxylate metabolism

Photorespiration is one of the major carbon metabolism pathways in oxygen-producing photosynthetic organisms. This pathway recycles 2-phosphoglycolate (2-PG), a toxic metabolite, to 3-phosphoglycerate when ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) uses oxygen instead of carbon dioxide. The photorespiratory cycle is in competition with photosynthetic CO2 fixation and it is accompanied by carbon, nitrogen and energy losses. Thus, photorespiration has become a target to improve crop yields. Moreover, during the photorespiratory cycle intermediate metabolites that are toxic to Calvin-Benson cycle and RuBisCO activities, such as 2-PG, glycolate and glyoxylate, are produced. Thus, the presence of an efficient 2-PG/glycolate/glyoxylate 'detoxification' pathway is required to ensure normal development of photosynthetic organisms. Here we review our current knowledge concerning the enzymes that carry out the glycolate-glyoxylate metabolic steps of photorespiration from glycolate production in the chloroplasts to the synthesis of glycine in the peroxisomes. We describe the properties of the proteins involved in glycolate-glyoxylate metabolism in Archaeplastida and the phenotypes observed when knocking down/out these specific photorespiratory players. Advances in our understanding of the regulation of glycolate-glyoxylate metabolism are highlighted.

Perspectives for a better understanding of the metabolic integration of photorespiration within a complex plant primary metabolism network

Photorespiration is an essential high flux metabolic pathway that is found in all oxygen-producing photosynthetic organisms. It is often viewed as a closed metabolic repair pathway that serves to detoxify 2-phosphoglycolic acid and to recycle carbon to fuel the Calvin-Benson cycle. However, this view is too simplistic since the photorespiratory cycle is known to interact with several primary metabolic pathways, including photosynthesis, nitrate assimilation, amino acid metabolism, C1 metabolism and the Krebs (TCA) cycle. Here we will review recent advances in photorespiration research and discuss future priorities to better understand (i) the metabolic integration of the photorespiratory cycle within the complex network of plant primary metabolism and (ii) the importance of photorespiration in response to abiotic and biotic stresses.

Application of an Integrated Omics Approach for Identifying Host Proteins That Interact With Odontoglossum ringspot virus Capsid Protein

The glutamic acid at position 100 (E(100)) in the capsid protein (CP) of Odontoglossum ringspot virus (ORSV) plays an important role in long-distance viral movement in Nicotiana benthamiana. The ORSV(E100A) mutant, which has a glutamic acid to alanine substitution, shows a loss of systemic infectivity in N. benthamiana. Transmission electron microscopy and size-exclusion chromatography assays showed that E(100) is essential for CP-CP interaction and viral particle assembly. To identify the ORSV triggering or response genes and CP-interacting proteins (CP-IP), an integrated omics approach based on next-generation sequencing and proteomics profiling was used in this study. The whole-transcriptomes of healthy and ORSV-infected leaves of N. benthamiana were analyzed, and the gene information was used to create a N. benthamiana protein database that was used for protein identification following mass spectrometry analysis. The integrated omics approach identified several putative host proteins that interact with ORSV CP(WT) and were categorized as photosystem subunits, defense-associated proteins, and cell division components. The expression pattern and CP interaction of these CP-IP were examined by semiquantitative reverse transcription polymerase chain reaction and an in vitro binding assay, respectively, to verify the in silico data. Among these proteins, a proteinase inhibitor of N. benthamiana (NbPI2) was highly associated with CP(E100A) as compared with CP(WT), and NbPI1 and NbPI2 were highly induced in ORSV-infected plants. NbPI1- and NbPI2-silenced plants (via a Tobacco rattle virus-induced gene-silencing system) did not exhibit a difference in ORSV infection. Thus, whether NbPI1 and NbPI2 play a role in plant immunity requires further investigation. In summary, the integrated omics approach provides massive and valuable information to identify the ORSV CP-IP and these CP-IP will help us to understand the movement of this virus and plant-virus interaction.

Key genes as stress indicators in the ubiquitous diatom Skeletonema marinoi

BACKGROUND

The dense phytoplankton blooms that characterize productive regions and seasons in the oceans are dominated, from high to low latitudes and from coast line to open ocean, by comparatively few, often cosmopolitan species of diatoms. These key dominant species may undergo dramatic changes due to global climate change.

RESULTS

In order to identify molecular stress-indicators for the ubiquitous diatom species Skeletonema marinoi, we tested stress-related genes in different environmental conditions (i.e. nutrient starvation/depletion, CO2-enrichment and combined effects of these stressors) using RT-qPCR. The data show that these stressors impact algal growth rate, inducing early aging and profound changes in expression levels of the genes of interest.

CONCLUSIONS

Most analyzed genes (e.g. antioxidant-related and aldehyde dehydrogenases) were strongly down-regulated which may indicate a strategy to avoid unnecessary over-investment in their respective proteins. By contrast, key genes were activated (e.g. HSPs, GOX) which may allow the diatom species to better cope with adverse conditions. We propose the use of this panel of genes as early bio-indicators of environmental stress factors in a changing ocean.