Biology subjects

Heller, N.

Publications and source records attributed to Heller, N..

5 recordsLinked to original sources

bioRxiv2025

Disturbance provides limited respite for native fish against invaders

Understanding how flow-related disturbance regimes influence species interactions is critical for conserving threatened species in freshwater ecosystems, where both the alteration of these regimes and the invasion of non-native species pose major threats. Using 30 years of sampling data from a well-studied river system in Aotearoa New Zealand, we applied empirically- parameterized Lotka-Volterra competition models across a gradient of flood disturbance regimes to assess the potential for coexistence between threatened native galaxiids and invasive trout. Our models suggest trout dominate under low disturbance regimes, leading to galaxiid extinction. Coexistence peaks at intermediate disturbance regimes, though native fish densities are highly suppressed. Only at high disturbance regimes do native fish prevail, but priority effects are likely. Thus, restoration and conservation efforts focused solely on high disturbance habitats without accompanying biological interventions may not ensure native fish persistence. Further, prioritizing such habitats at the expense of others risks misdirecting resources towards sub-optimal conditions, particularly under climate change.

ecology↗

bioRxiv2025

Population and adaptation history of 739 Thlaspi arvense natural accessions

Pennycress (Thlaspi arvense) is a promising intermediate oilseed crop, producing oil suitable for conversion to biofuels--including aviation fuels. While domestication efforts are ongoing, a deeper understanding of the genetic architecture of traits is crucial for informing future breeding efforts. Here, we conducted the largest genomic and phenotypic survey of pennycress to date, analyzing 739 accessions collected across four continents. Leveraging whole-genome sequencing and field-collected phenotypes, we characterized the standing genetic variation underlying key agronomic traits and climate resilience. Our findings revealed multiple independent migration events to North America, with substantial genetic admixture. We identified homologs of Arabidopsis thaliana flowering-time genes that contribute to adaptation and demonstrated the agronomic benefits of winter-type pennycress. Furthermore, through multi-season field trials, we identified a genomic region containing a cluster of mTERF genes strongly associated with green canopy coverage, a critical trait for biomass retention and yield stability. These insights provide a genomic roadmap for accelerating pennycress domestication and improving its resilience to climate variability.

genomics↗

bioRxiv2025

Loss of PIF7 attenuates shade and elevated temperature responses throughout the lifecycle in Pennycress

Pennycress (Thlaspi arvense) is being developed as a winter annual intermediate oilseed bioenergy crop in the Midwest during typical fallow periods. Crucial work remains to domesticate and optimize pennycress for incorporation into cropping systems and increasing resilience to rising temperatures. We found that increased planting density reduces biomass and hastens time to flowering and maturity, which are associated with shade avoidance responses. In controlled conditions, we found that pennycress elongates in response to foliar shade and increased ambient temperatures (28 {degrees}C). We applied the knowledge base from Arabidopsis thaliana to manipulate genes in the PHYB signaling pathway to simultaneously decrease the shade avoidance response during interseeding and tissue responses to elevated temperatures. Evaluation of CRISPR alleles of PIF7 shows that pif7 reduces organ elongation to competition and heat cues and retains a compact rosette when exposed to shade or elevated temperature and their combination. Crucially, yield and oil content were unaltered in pif7 and plants maintained earlier flowering in stress conditions. Furthermore, indicators of plant health, such as hue, chlorophyll indices, and root system architecture, were improved between wild type and pif7. This is evidence that plant architecture and physiological health can be uncoupled under competition and heat conditions, supporting our efforts to attenuate morphological responses to environmental cues. We propose this strategy for reducing SAR, improving pennycress performance at high densities, for during interseeding establishment in standing crops, and in a warming climate.

plant biology↗

bioRxiv2021

Hepatocyte androgen receptor in females mediates androgen-induced hepatocellular glucose mishandling and systemic insulin resistance

Androgen excess is one of the most common endocrine disorders of reproductive-aged women, affecting up to 20% of this population. Women with elevated androgens often exhibit hyperinsulinemia and insulin resistance. The mechanisms of how elevated androgens affect metabolic function are not clear. Hyperandrogenemia in a dihydrotestosterone (DHT)-treated female mouse model induces whole body insulin resistance possibly through activation of the hepatic androgen receptor (AR). We investigated the role of hepatocyte AR in hyperandrogenemia-induced metabolic dysfunction by using several approaches to delete hepatic AR via animal-, cell-, and clinical-based methodologies. We conditionally disrupted hepatocyte AR in female mice developmentally (LivARKO) or acutely by tail vein injection of an adeno-associated virus with a liver-specific promoter for Cre expression in ARfl/fl mice (adLivARKO). We observed normal metabolic function in littermate female Control (ARfl/fl) and LivARKO (ARfl/fl; Cre+/-) mice. Following chronic DHT treatment, female Control mice treated with DHT (Con-DHT) developed impaired glucose tolerance, pyruvate tolerance, and insulin tolerance, not observed in LivARKO mice treated with DHT (LivARKO-DHT). Further, during an euglycemic hyperinsulinemic clamp, the glucose infusion rate was improved in LivARKO-DHT mice compared to Con-DHT mice. Liver from LivARKO, and primary hepatocytes derived from LivARKO, and adLivARKO mice were protected from DHT-induced insulin resistance and increased gluconeogenesis. These data support a paradigm in which elevated androgens in females disrupt metabolic function via hepatic AR and insulin sensitivity was restored by deletion of hepatic AR.

molecular biology↗

bioRxiv2017

A Very Oil Yellow1 modifier of the Oil Yellow1-N1989 allele uncovers a cryptic phenotypic impact of cis-regulatory variation in maize

Forward genetics determines the function of genes underlying trait variation by identifying the change in DNA responsible for changes in phenotype. Detecting phenotypically-relevant variation outside protein coding sequences and distinguishing this from neutral variants is not trivial; partly because the mechanisms by which DNA polymorphisms in the intergenic regions affect gene regulation are poorly understood. Here we utilized a dominant genetic marker with a convenient phenotype to investigate the effect of cis and trans-acting regulatory variation. We performed a forward genetic screen for natural variation that suppress or enhance the semi-dominant mutant allele Oy1-N1989, encoding the magnesium chelatase subunit I of maize. This mutant permits rapid phenotyping of leaf color as a reporter for chlorophyll accumulation, and mapping of natural variation in maize affecting chlorophyll metabolism. We identified a single modifier locus segregating between B73 and Mo17 that was linked to the reporter gene itself, which we call very oil yellow1. Based on the variation in OY1 transcript abundance and genome-wide association data, vey1 is predicted to consist of multiple cis-acting regulatory sequence polymorphisms encoded at the wild-type oy1 alleles. The vey1 allele appears to be a common polymorphism in the maize germplasm that alters the expression level of a key gene in chlorophyll biosynthesis. These vey1 alleles have no discernable impact on leaf chlorophyll in the absence of the Oy1-N1989 reporter. Thus, use of a mutant as a simple and efficient reporter for magnesium chelatase activity resulted in the detection of expression-level polymorphisms not readily visible in the laboratory.

genetics↗