Biology subjects

Regan, S.

Publications and source records attributed to Regan, S..

5 recordsLinked to original sources

bioRxiv2025

Generation of Chlorella vulgaris starch mutants and their biomass and lipid productivities under different culture media

BackgroundMicroalgae are an important feedstock for the production of a wide variety of products, including biodiesel. Biodiesel, composed of fatty acid alkyl esters, is produced through the transesterification reaction of triacylglycerol (TAG). Microalgae store their energy reserves primarily as starch and TAGs. Therefore, several studies have focused on understanding the partitioning of carbon precursors between starch and TAG biosynthetic pathways. In this study, 5 starch mutants of Chlorella vulgaris were developed and cultured on different culture media. ResultsChlorella vulgaris starch mutants were generated through UV-random mutagenesis. Five starch mutants were selected for this study: four low-starch producing mutants (st27, st29, st43 and st54) and one high-starch producing mutant (st80). The starch mutants were cultured on media with different organic carbon sources, and lipid and biomass productivity were measured. Mixotrophic growth on glucose resulted in the highest lipid productivity in all the mutants, including st80, without compromising growth, whereas photoautotrophic growth generally did not result in changes in lipid productivity of the starch mutants. The highest increase in lipid productivity was observed for st27, with a 3.8-fold higher lipid productivity than wildtype. ConclusionsAll starch mutants increased their lipid productivities when grown mixotrophically on glucose, suggesting the overflow hypothesis could explain the partitioning of carbon between starch and TAGs. Out of the mutants generated in this work, st27 resulted in the highest increases in lipid productivities, reaching an increase of 380% when grown mixotrophically on glucose, without compromising growth. The high-starch producing mutant st80 provides insight into a possibility to develop starch- and TAG-rich microalgal biomass.

bioengineering↗

bioRxiv2025

Surveying the Hormonome of Hazelnut Catkins During Winter Dormancy

BackgroundDeciduous woody perennials, such as hazelnut, undergo winter dormancy to protect sensitive tissues, such as flowers, from harsh conditions. The reproductive success of the tree is dependent on the release of dormancy under favorable conditions. To bloom, the tree must first experience a certain amount of chilling, followed by a certain amount of warmth. With global warming, many trees risk not being able to accumulate enough chilling to release dormancy. Also, when trees accustomed to warm climates are brought into cold climates, they might bloom prematurely at the first sign of spring, and risk freezing damage. The latter is the case for hazelnut, recently adopted as a crop in Ontario, Canada. The present study investigates the hormonal regulation of dormancy in hazelnuts male flowers (catkins) by generating hormone profiles in early and late-blooming accessions throughout the dormant season. Abscisic acid (ABA), gibberellin (GA), auxin, cytokinin (CTK), their metabolites, as well as the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), were measured. ResultsABA decreased with dormancy progression, while GA increased. This correlation implies ABA is primarily responsible for dormancy maintenance in catkins and GA works antagonistically to ABA. Indeed, the ABA/GA ratio steadily decreased throughout dormancy. For the first time, CTKs have been reported to steadily increase during dormancy. Auxin and ethylene appear to primarily play a role in the onset of dormancy. Interestingly, early blooming accessions failed to accumulate the auxin conjugate, IAA-Asp and had higher ACC levels throughout most of dormancy. ConclusionsCumulatively, the present study has generated the most comprehensive hormone profile in dormant flowers of deciduous woody perennials and has identified potential strategies for the delay of bloom in hazelnut catkins through the manipulation of hormones.

plant biology↗

bioRxiv2025

Corylus avellana disease management: using metagenomics to illuminate the rhizosphere microbiome of Corylus

The European hazelnut, Corylus avellana, is one of the most economically important tree nut crops globally. The biotrophic ascomycete pathogen Anisogramma anomala, found naturally associated with wild C. americana, continues to pose a significant threat to European hazelnut production across North America. Here, metagenomics was used to examine the taxonomic and functional features of the rhizosphere microbial communities of hazelnut trees differing in their levels of resistance to A. anomala: highly tolerant Corylus americana, and resistant and susceptible Corylus avellana. No statistically significant differences in microbial alpha diversity or beta diversity were noted between the three rhizosphere groups. Compared to bulk soil, all three rhizosphere groups were enriched for the fungal phylum Basidiomycota and bacterial phylum "Candidatus Rokubacteriota". At the genus level, the bacterial genera Actinospica, Occallatibacter, and "Candidatus Sulfotelmatobacter" were under-represented, while the genus Rhizobacter was over-represented, in the resistant and susceptible C. avellana rhizosphere samples compared to the bulk soil. A total of 45 dereplicated, high-quality metagenome-assembled genomes (MAGs) were generated, corresponding to 41 bacteria and 4 archaea. Many of the MAGs carried multiple biosynthetic gene clusters, including MAGs corresponding to the genera Lysobacter and Actinospica. Overall, the low differentiation of the rhizosphere microbiomes suggest that differences in A. anomala disease expression are likely not associated with differences in the rhizosphere microbiome. Nevertheless, the results shed new light on the rhizosphere communities of two species of hazelnut, and woody perennials more broadly, and identify potential avenues for future research into the development of microbial inoculants for Corylus spp..

microbiology↗

bioRxiv2025

Hepatic cellular stress response pathways exhibit species differences in basal and inducible activity

Cellular stress response pathways such as the NRF2 oxidative stress response, endoplasmic reticulum (ER) stress response and macroautophagy afford protection against many forms of drug toxicity, including the liver toxicity associated with the formation of reactive drug metabolites. To maximise the translatability of preclinical toxicology studies, an understanding of the relative hepatic stress response capacities of humans and widely-used preclinical animal species is vital. In control liver tissue, the basal gene and protein expression of stress response pathway components was found to be greater in rodents than non-rodent preclinical species and humans. In addition, following in vitro exposure to pharmacological modulators of the NRF2 and ER stress responses, rodent hepatocytes generally displayed a greater capacity, relative to those of non-rodent preclinical species and humans, for adaptation to cellular stress. Consistent with the reported lower concordance of drug toxicity between humans and rats, the latter displayed a greater level of Torin1-induced autophagic flux than all other species, while the robust transcriptional responses to thapsigargin-induced endoplasmic reticulum stress and Bardoxolone- or Ki696-mediated NRF2 activation were comparable between mouse and rat hepatocytes. In all, our results indicate that rodent preclinical species possess a greater basal and adaptive hepatic capacity for mitigation of chemical insult than non- rodent preclinical species and humans. This study represents the first to provide a comprehensive comparison of stress response pathway capacity of humans and the animal species most commonly used for preclinical drug safety assessment. Our findings can be used to inform the selection of species for safety testing of drugs with a liability for reactive metabolite-mediated liver toxicity.

pharmacology and toxicology↗

bioRxiv2023

Differential response of Senna occidentalis L. to arsenic and cadmium contaminated soil

We investigated the phytoremediation potential of Senna occidentalis L., a pantropical plant that has been associated with tolerance to heavy metal-contaminated soils around mining sites. Seedlings of S. occidentalis were exposed to cadmium chloride (CdCl2) and sodium arsenate (Na3AsO4) at concentrations of 200, 300, and 400 mg L-1 under greenhouse conditions. Heavy metal tolerance was assessed by comparing biomass and stress indicators such as chlorophyll, proline, and hydrogen peroxide content. Arsenic treatment had more toxic effects than cadmium on Senna physiology. Regardless of concentration of arsenic applied, the biomass decreased by 50% as compared to control and cadmium-treated plants. Chlorophyll content decreased with exposure to both heavy metals. Higher concentration of Cd and As (400 mg L-1) resulted in 50% reduction in chlorophyll content. Proline and hydrogen peroxide levels were higher in arsenic-treated plants compared to controls and cadmium-treated plants, indicating an enhanced stress response when exposed to arsenic. When heavy metal content was measured, there was a significant accumulation of arsenic in the leaves, stems, and roots, indicating that arsenic in these tissues was responsible for the profound changes in biomass, proline, and hydrogen peroxide content. In contrast, although significant, there was less cadmium uptake by Senna and tolerance can be seen, which was reflected by normal biomass, proline, and hydrogen peroxide levels. High translocation of metals from soil into roots and low translocation from root to shoot tissues suggests the potential for S. occidentalis to be used for phytostabilization of arsenic- and cadmium-contaminated soils.

plant biology↗