Finding a partner in the ocean: molecular and evolutionary bases of the response to sexual cues in a planktonic diatom

Microalgae play a major role as primary producers in aquatic ecosystems. Cell signalling regulates their interactions with the environment and other organisms, yet this process in phytoplankton is poorly defined. Using the marine planktonic diatom Pseudo-nitzschia multistriata, we investigated the cell response to cues released during sexual reproduction, an event that demands strong regulatory mechanisms and impacts on population dynamics. We sequenced the genome of P. multistriata and performed phylogenomic and transcriptomic analyses, which allowed the definition of gene gains and losses, horizontal gene transfers, conservation and evolutionary rate of sex-related genes. We also identified a small number of conserved noncoding elements. Sexual reproduction impacted on cell cycle progression and induced an asymmetric response of the opposite mating types. G protein-coupled receptors and cyclic guanosine monophosphate (cGMP) are implicated in the response to sexual cues, which overall entails a modulation of cell cycle, meiosis-related and nutrient transporter genes, suggesting a fine control of nutrient uptake even under nutrient-replete conditions. The controllable life cycle and the genome sequence of P. multistriata allow the reconstruction of changes occurring in diatoms in a key phase of their life cycle, providing hints on the evolution and putative function of their genes and empowering studies on sexual reproduction

Finding a partner in the ocean: molecular and evolutionary bases of the response to sexual cues in a planktonic diatom

Microalgae play a major role as primary producers in aquatic ecosystems. Cell signalling regulates their interactions with the environment and other organisms, yet this process in phytoplankton is poorly defined. Using the marine planktonic diatom Pseudo-nitzschia multistriata, we investigated the cell response to cues released during sexual reproduction, an event that demands strong regulatory mechanisms and impacts on population dynamics. We sequenced the genome of P. multistriata and performed phylogenomic and transcriptomic analyses, which allowed the definition of gene gains and losses, horizontal gene transfers, conservation and evolutionary rate of sex-related genes. We also identified a small number of conserved noncoding elements. Sexual reproduction impacted on cell cycle progression and induced an asymmetric response of the opposite mating types. G protein-coupled receptors and cyclic guanosine monophosphate (cGMP) are implicated in the response to sexual cues, which overall entails a modulation of cell cycle, meiosis-related and nutrient transporter genes, suggesting a fine control of nutrient uptake even under nutrient-replete conditions. The controllable life cycle and the genome sequence of P. multistriata allow the reconstruction of changes occurring in diatoms in a key phase of their life cycle, providing hints on the evolution and putative function of their genes and empowering studies on sexual reproduction

Temperature trends of late Cambrian through the middle Ordovician : implications for Oridovician climate and biodiversification

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The Ordovician Period includes both the largest and longest period of sustained biodiversification--the Great Ordovician Biodiversification Event (GOBE)--and the second-largest mass extinction of the Phanerozoic--the end Ordovician mass extinction. Climate change has been invoked as a contributing factor to both events. Much research has focused on the end Ordovician extinction and thus, paleotemperatures of the last 15 million years of the period are relatively well documented. Data for the Early and Middle Ordovician are much more limited. Although the number of Early to Middle Ordovician climate studies has increased over the last decade, the record of climate change leading into the GOBE is still incomplete. To begin to address this problem, I generated [delta][superscript 18] O data at three new localities and increased sampling density at a fourth. New data combined with previous records suggest that cooling occurred between the latest Cambrian and Early Ordovician, that little change occurred during the Early Ordovician, and that additional cooling occurred by the Middle Ordovician. However, temperatures remained above modern levels through the GOBE. While climate change may have played a role in the GOBE, the relatively low magnitude and relatively late timing of the cooling argue that cooling is unlikely to be the primary trigger for the event.by Laura SpeirIncludes bibliographical reference

Effect of synthetic dairy factory effluent containing different acids (H3PO4, HNO3 and CH3COOH) on soil microbial and chemical properties and nutrient leaching

The effects of addition of synthetic dairy factory effluent (DFE) containing phosphoric, nitric or acetic acids as cleaning agents on soil chemical and microbial properties and potential nutrient leaching from a dairy farm soil were studied in an 84-day open incubation/leaching experiment and in a short-term (24 days) closed incubation. Dairy factory effluent resulted in increased leaching of Na and Ca . The main anion leached in the DFE treatments was Cl , whilst in the control treatments it was NO . Leachates from DFE-treated soil had a greater electrical conductivity (EC) and lower pH than those from controls, but type of acid had little effect on the ionic content or composition of leachates. At the conclusion of the experiment, soils from DFE treatments showed a large accumulation of exchangeable Na , a reduction in exchangeable Ca and significant increases in microbial biomass C, basal respiration and β-glucosidase and arylsulphatase activities. Microbial activity was greatest from the acetic acid-DFE treatment. There was a significant increase in extractable P in the phosphoric acid-DFE treatment, but addition of nitric acid-DFE did not increase leaching of NO . In the short-term incubation experiment, EC increased over time in all treatments, while pH, microbial biomass and basal respiration decreased. During the first few days after a one-off DFE addition, there was an increase in both microbial biomass C and basal respiration, but these differences dissipated after 3 days. It was concluded that while additions of DFE have significant effects on chemical and microbial soil properties, a change in the form of acid present in the DFE has relatively minor effects on these properties