Biology subjects

Cousins, A.

Publications and source records attributed to Cousins, A..

4 recordsLinked to original sources

bioRxiv2024

Realisation of a key step in the evolution of C4 photosynthesis in rice by genome editing.

C4 photosynthesis is a repeatedly evolved adaptation to photosynthesis that functions to reduce energy loss from photorespiration. The recurrent evolution of this adaptation is achieved through changes in the expression and localisation of several enzymes and transporters that are conventionally used in non-photosynthetic metabolism. These alterations result in the establishment of a biochemical CO2 pump that increases the concentration of CO2 around rubisco in a cellular environment where rubisco is protected from oxygen thus preventing the occurrence of photorespiration. A key step in the evolution of C4 photosynthesis is the change in subcellular localisation of carbonic anhydrase (CA) activity from the mesophyll cell chloroplast to the cytosol, where it catalyzes the first biochemical step of the C4 pathway. Here, we achieve this key step in C4 evolution in the C3 plant Oryza sativa (rice) using genome editing. We show that editing the chloroplast transit peptide of the primary CA isoform in the leaf results in relocalisation of leaf CA activity from the chloroplast to the cytosol. Through analysis of fluorescence induction kinetics in these CA relocalisation lines we uncover a role a new role for chloroplast CA in photosynthetic induction. We also reveal that relocalisation of CA activity to the cytosol causes no detectable perturbation to plant growth or leaf-level CO2 assimilation. Collectively, this work uncovers a novel role for chloroplast CA in C3 plants, and demonstrates that it is possible to achieve a key step in the evolution of C4 photosynthesis by genome editing. Significance statementC4 photosynthesis is a highly efficient adaptation to photosynthesis that fuels the worlds most productive crop plants. It evolved from conventional C3 photosynthesis through a series of changes in leaf biochemistry and anatomy. Here we achieve a key evolutionary step on the path to C4 photosynthesis in rice using genome editing. Specifically, we alter the primary location of carbonic anhydrase activity in the rice leaf from the chloroplast to the cytosol. In doing so, we uncover a novel role for carbonic anhydrase in facilitating the rapid induction kinetics of photosystem II, and initiate a new era of C4 engineering using precision breeding techniques.

plant biology↗

bioRxiv2021

Increased signal to noise ratios within experimental field trials by regressing spatially distributed soil properties as principal components.

Environmental variability poses a major challenge to any field study. Researchers attempt to mitigate this challenge through replication. Thus, the ability to detect experimental signals is determined by the degree of replication and the amount of environmental variation, noise, within the experimental system. A major source of noise in field studies comes from the natural heterogeneity of soil properties which create micro-treatments throughout the field. To make matters worse, the variation within different soil properties is often non-randomly distributed across a field. We explore this challenge through a sorghum field trial dataset with accompanying plant, microbiome and soil property data. Diverse sorghum genotypes and two watering regimes were applied in a split-plot design. We describe a process of identifying, estimating, and controlling for the effects of spatially distributed soil properties on plant traits and microbial communities using minimal degrees of freedom. Importantly, this process provides a tool with which sources of environmental variation in field data can be identified and removed, improving our ability to resolve effects of interest and to quantify subtle phenotypes. IMPORTANCEData from field experiments are notoriously noisy. Proper field designs with high replication aid in mitigating this challenge, yet true biological correlations are still often masked by environmental variability. This work identifies soil property composition as a spatially distributed source of variance to three types of characteristics: plant phenotype, microbiome composition, and leaf traits. We show that once identified, spatial principal component regression was able to account for these effects so that more precise estimates of experimental factors were obtained. This generalizable method is applicable to diverse field experiments.

systems biology↗

bioRxiv2018

Temperature response of Rubisco kinetics in Arabidopsis thaliana: thermal breakpoints and implications for reaction mechanisms

Optimization of Rubisco kinetics could improve photosynthetic efficiency, ultimatly resulting in increased crop yield. However, imprecise knowledge of the reaction mechanism and the individual rate constants limit our ability to optimize the enzyme. Membrane inlet mass spectrometery (MIMS) may offer benefits over traditional methods for determining individual rate constants of the Rubisco reaction mechanism, as it can directly monitor concentration changes in CO2, O2, and their isotopologs during assays. However, a direct comparsion of MIMS to the traditional Radiolabel method of determining Rubisco kinetic parameters has not been made. Here, the temperature responses of Rubisco kinetic parameters from Arabidopsis thaliana were measured using the Radiolabel and MIMS methods. The two methods provided comparable parameters above 25 {degrees}C, but temperature responses deviated at low temperature as MIMS derived catalytic rates of carboxylation, oxygenation, and CO2/O2 specificity showed thermal breakpoints. Here we discuss the variability and uncertainty surrounding breakpoints in the Rubisco temperature response and relavance of individual rate constants of the reaction mechanisms to potential breakpoints.

plant biology↗

bioRxiv2018

A genetic link between whole-plant water use efficiency and leaf carbon isotope composition in the C4 grass Setaria

Increasing whole plant water use efficiency (yield per transpiration; WUEplant) through plant breeding can benefit the sustainability of agriculture and improve crop yield under drought. To select for WUEplant, an efficient phenotyping method that reports on the genetic contribution of component traits such as transpiration efficiency (TEi; rate of CO2 assimilation per stomatal conductance) must be developed. Leaf carbon stable isotope composition ({delta}13Cleaf) has been proposed as a high-throughput proxy for TEi, and a negative correlation between {delta}13Cleaf and both WUEplant and TEi has previously been demonstrated in several C4 grass species. Therefore, the aim of the research presented here was to determine if the same loci control {delta}13Cleaf, WUEplant, and TEi under well-watered and water-limited conditions in a recombinant inbred line (RIL) population of closely related C4 grasses Setaria viridis and S. italica. Three quantitative trait loci (QTL) for {delta}13Cleaf were co-localized with transpiration, biomass, and a linear model of WUE. When WUEplant was calculated for allele classes based on the three QTL for {delta}13Cleaf, {delta}13Cleaf was negatively correlated with WUEplant as theory predicts when WUEplant is in part driven by differences in TEi. In any population, multiple traits can influence WUEplant; however, the analysis of {delta}13Cleaf in this RIL population demonstrates that there is genetic control of TEi that significantly contributes to WUEplant. Furthermore, this research suggests that {delta}13Cleaf can be used in marker-assisted breeding to select for TEi and as a tool to better understand the physiology and genetic architecture of TEi and WUEplant in C4 species.\n\nSignificance StatementOverextended water resources and drought are major agricultural problems worldwide. Therefore, selection for increased plant water use efficiency (WUEplant) in food and biofuel crop species is an important trait in plant breeding programs. Leaf carbon isotopic composition ({delta}13Cleaf) has potential as a rapid and effective high throughput phenotyping method for intrinsic transpiration efficiency (TEi), an important leaf-level component trait of WUEplant. Our research shows that {delta}13Cleaf and WUEplant share a common genetic architecture through their shared relationship with TEi. This suggests that {delta}13Cleaf can be used as a screen for TEi in marker-assisted plant breeding programs to improve crop drought resistance and decrease agricultural water consumption.

plant biology↗