So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Plants are responsive to temperature, and some species can distinguish differences of 1°C In Arabidopsis, warmer temperature accelerates flowering and increases elongation growth (thermomorphogenesis) However, the mechanisms of temperature perception are largely unknown We describe a major thermosensory role for the phytochromes (red light receptors) during the night Phytochrome null plants display a constitutive warm-temperature response, and consistent with this, we show in this background that the warm-temperature transcriptome becomes derepressed at low temperatures We found that phytochrome B (phyB) directly associates with the promoters of key target genes in a temperature-dependent manner The rate of phyB inactivation is proportional to temperature in the dark, enabling phytochromes to function as thermal timers that integrate temperature information over the course of the night

/pdf/phytochromes-function-as-thermosensors-in-arabidopsis-lwuqgydk16.pdf

Phytochromes function as thermosensors in Arabidopsis

Ambient temperature regulates many aspects of plant growth and development, but its sensors are unknown. Here, we demonstrate that the phytochrome B (phyB) photoreceptor participates in temperature perception through its temperature-dependent reversion from the active Pfr state to the inactive Pr state. Increased rates of thermal reversion upon exposing Arabidopsis seedlings to warm environments reduce both the abundance of the biologically active Pfr-Pfr dimer pool of phyB and the size of the associated nuclear bodies, even in daylight. Mathematical analysis of stem growth for seedlings expressing wild-type phyB or thermally stable variants under various combinations of light and temperature revealed that phyB is physiologically responsive to both signals. We therefore propose that in addition to its photoreceptor functions, phyB is a temperature sensor in plants.

/pdf/phytochrome-b-integrates-light-and-temperature-signals-in-3vulvf4epl.pdf

Phytochrome B integrates light and temperature signals in Arabidopsis

Abiotic stresses and soil nutrient limitations are major environmental conditions that reduce plant growth, productivity and quality. Plants have evolved mechanisms to perceive these environmental challenges, transmit the stress signals within cells as well as between cells and tissues, and make appropriate adjustments in their growth and development in order to survive and reproduce. In recent years, significant progress has been made on many fronts of the stress signaling research, particularly in understanding the downstream signaling events that culminate at the activation of stress- and nutrient limitation-responsive genes, cellular ion homeostasis, and growth adjustment. However, the revelation of the early events of stress signaling, particularly the identification of primary stress sensors, still lags behind. In this review, we summarize recent work on the genetic and molecular mechanisms of plant abiotic stress and nutrient limitation sensing and signaling and discuss new directions for future studies.

Plant abiotic stress response and nutrient use efficiency.

Contents Summary I. Introduction II. Cold stress and physiological responses in plants III. Sensing of cold signals in plants IV. Messenger molecules involved in cold signal transduction V. Cold signal transduction in plants VI. Conclusions and perspectives Acknowledgements References SUMMARY: Cold stress is a major environmental factor that seriously affects plant growth and development, and influences crop productivity. Plants have evolved a series of mechanisms that allow them to adapt to cold stress at both the physiological and molecular levels. Over the past two decades, much progress has been made in identifying crucial components involved in cold-stress tolerance and dissecting their regulatory mechanisms. In this review, we summarize recent major advances in our understanding of cold signalling and put forward open questions in the field of plant cold-stress responses. Answering these questions should help elucidate the molecular mechanisms underlying plant tolerance to cold stress.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.15696

Advances and challenges in uncovering cold tolerance regulatory mechanisms in plants.

ELF3 controls thermoresponsive growth in Arabidopsis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) induces immune-mediated type 1 interferon (IFN-1) production, the pathophysiology of which involves sterile alpha motif and histidine-aspartate domain-containing protein 1 (SAMHD1) tetramerization and the cytosolic DNA sensor cyclic-GMP-AMP synthase (cGAS)–stimulator of interferon genes (STING) signaling pathway. As a result, type I interferonopathies are exacerbated. Aspirin inhibits cGAS-mediated signaling through cGAS acetylation. Acetylation contributes to cGAS activity control and activates IFN-1 production and nuclear factor-κB (NF-κB) signaling via STING. Aspirin and dapsone inhibit the activation of both IFN-1 and NF-κB by targeting cGAS. We define these as anticatalytic mechanisms. It is necessary to alleviate the pathologic course and take the lag time of the odds of achieving viral clearance by day 7 to coordinate innate or adaptive immune cell reactions.

/pdf/covid-19-molecular-pathophysiology-acetylation-of-1mbfpo3l.pdf

COVID-19 Molecular Pathophysiology: Acetylation of Repurposing Drugs

Temperature is one of the most important abiotic environmental regulators of plant growth and development. The temperature-dependent elongation of the Arabidopsis thaliana hypocotyls (seedling stems) is a well-characterised environmental response. The aim of this study was to identify allelic variants underlying Quantitative Trait Loci (QTL) responsible for the natural genetic variation of hypocotyl length in response to ambient temperatures. 
The Arabidopsis thaliana accessions were phenotyped for hypocotyl length at 12°C, 17°C, 22°C and 27°C ambient temperature environments and substantial genetic variation was established. This facilitated a forward genetic approach by performing a QTL analysis to identify the genetic basis of thermal sensitivity. Firstly, fine-mapped QTL were identified for hypocotyl length in response to different temperatures. SMALL AUXIN UPREGULATED RNA 38 (SAUR38) is a novel candidate gene for a QTL. Another major-effect QTL ‘Temp22.2’ was also identified which harbours the candidate gene PHYTOCHROME B (PHYB). Secondly, fine-mapped ‘Environmental QTL’ were also discovered for the genotype by environment (G x E) interaction. PHYTOCHROME D (PHYD) is a candidate for a temperature-responsiveness QTL. 
For QTL cloning, functional characterisation of SAUR38 and PHYB was carried out by knockout analysis and transgenic allelic complementation. The results showed that SAUR38 controlled natural variation in the Tsu-0 accession by increasing elongation. The PHYB alleles of Ct-1, Sf-2 and Col-0 accessions explain the Temp22.2 QTL. Ct-1 and Sf-2 alleles are positive regulators increasing elongation, whereas Col-0 allele is a negative regulator. Temp22.2 QTL was cloned and novel alleles were discovered revealing the molecular basis of quantitative variation in hypocotyl length in response to temperature.

Natural variation in Arabidopsis thaliana growth in response to ambient temperatures

Some physicians use dapsone as part of the standard treatment of severe COVID-19 patients entering the ICU, though some do not. To obtain an indication of whether dapsone is helping or not, we undertook a retrospective chart review of 29 consecutive ICU COVID-19 patients receiving dapsone and 30 not receiving dapsone. As we previously reported, of those given dapsone, 9/29 (30%) died, while of those not given dapsone, 18/30 (60%) died. We looked back on that data set to determine if there might be basic laboratory findings in these patients that might give an indication of a mechanism by which dapsone was acting. We found that the neutrophil-to-lymphocyte ratio decreased in 48% of those given dapsone and in 30% of those not given dapsone. We concluded that dapsone might be lowering that ratio. We then reviewed collected data on neutrophil related inflammation pathways on which dapsone might act as presented here. As this was not a controlled study, many variables prevent drawing any conclusions from this work; a formal, randomized controlled study of dapsone in severe COVID-19 is warranted.

https://www.mdpi.com/1422-0067/23/24/15563/pdf?version=1670918867

Asif Khan Khattak

Papers

Phytochromes function as thermosensors in Arabidopsis

ELF3 controls thermoresponsive growth in Arabidopsis

COVID-19 Molecular Pathophysiology: Acetylation of Repurposing Drugs

Natural variation in Arabidopsis thaliana growth in response to ambient temperatures

Dapsone Lowers Neutrophil to Lymphocyte Ratio and Mortality in COVID-19 Patients Admitted to the ICU