Biology subjects

Helliker, B.

Publications and source records attributed to Helliker, B..

5 recordsLinked to original sources

bioRxiv2026

Leaves in Transition: Single nuclei RNA sequencing provides insights into sorghums juvenile and adult phases

The transition from juvenile to adult phase (JA) is a key developmental process in plants, driven by conserved pathways that shape growth and stress responses. In monocots such as sorghum, this transition influences traits linked to environmental resilience, yet the regulation of micro-anatomical features such as trichomes and bulliform cells remains poorly understood. Here, we use single-nucleus RNA sequencing (snRNA-seq) to generate high-resolution gene expression maps of juvenile and adult sorghum leaves. Contrary to the traditional developmental model, we find that trichomes are present in both juvenile and adult leaves, with stage-dependent differences in gene expression. We also observe that bulliform cells, typically considered adult-specific, are present in juvenile leaves. At the transcriptomic level, cell populations cluster more strongly by developmental stage than by cell type, with juvenile cells grouping with other juvenile cells and adult cells with adult counterparts, indicating a dominant effect of developmental state on gene expression. In addition, we identify enrichment of dhurrin biosynthetic genes in trichome-associated cells as well as elevated expression of aquaporin genes in these cells, pointing to a potential role for trichomes in coordinating defense and water-related processes. Together, these findings refine current models of sorghum development and suggest that key epidermal cells and their associated functions may be established earlier than previously known. Collectively, this study provides a single nucleus resolved framework for understanding how developmental stage shapes gene expression in sorghum leaves.

plant biology↗

bioRxiv2020

The legacy of C4 evolution in the hydraulics of C3 and C4 grasses

The anatomical reorganization required for optimal C4 photosynthesis should also impact plant hydraulics. Most C4 plants possess large bundle-sheath cells and high vein density, which should also lead to higher leaf hydraulic conductance (Kleaf) and capacitance. Paradoxically, the C4 pathway reduces water demand and increases water-use-efficiency, creating a potential mis-match between supply capacity and demand in C4 plant water relations. We use phylogenetic analyses, physiological measurements, and models to examine the reorganization of hydraulics in closely-related C4 and C3 grasses. Evolutionarily young C4 lineages have higher Kleaf, capacitance, turgor-loss-point, and lower stomatal conductance than their C3 relatives. In contrast, species from older C4 lineages show decreased Kleaf and capacitance, indicating that over time, C4 plants have evolved to optimize hydraulic investments while maintaining C4 anatomical requirements. The initial "over-plumbing" of C4 plants disrupts the positive correlation between maximal assimilation rate and Kleaf, decoupling a key relationship between hydraulics and photosynthesis generally observed in vascular plants.

ecology↗

bioRxiv2020

Optimal reorganization of photosynthesis after the evolution of C4

C3 and C4 are major functional types in terrestrial biosphere models, with photosynthesis traits as important input parameters. The evolution of C4 required reorganizations of Calvin-Benson-cycle and coordination of C4-cycle enzymes, resulting in divergences of physiological traits between C3 and C4. In addition, photosynthesis further optimized after the evolution of C4 causing diversification within C4 lineages due to different evolutionary histories. We combined optimality modeling, physiological measurements and phylogenetic analysis to examine how various aspects of C4 photosynthetic machinery were reorganized and coordinated within C4 lineages and as compared to closely-related C3 in grasses. Optimality models and measurements indicated a higher maximal electron transport to maximal Rubisco carboxylation ratio (Jmax/Vcmax) in C4 than C3, consistent with the optimal prediction to maximize photosynthesis. The coordination between Calvin-Benson and C4 cycles (Vpmax/Vcmax), however, is in line with the optimal modeling results under 200 ppm, as opposed to current CO2. Such inconsistencies can be explained by a slowly declining assimilation rate beyond optimal Vpmax/Vcmax. Although rapid coordination occurred early in C4 evolution, C4 is still under optimizing processes and photosynthetic measures have continued to increase across time. Lastly, better understandings of Jmax/Vcmax, Vpmax/Vcmax and fluorescence-based-electron-transport proffer enhanced approaches to parameterize terrestrial biosphere models.

ecology↗

bioRxiv2020

Lineage Functional Types (LFTs): Characterizing functional diversity to enhance the representation of ecological behavior in Earth System Models

Process-based vegetation models attempt to represent the wide range of trait variation in biomes by grouping ecologically similar species into plant functional types (PFTs). This approach has been successful in representing many aspects of plant physiology and biophysics, but struggles to capture biogeographic history and ecological dynamics that determine biome boundaries and plant distributions. Grass dominated ecosystems are broadly distributed across all vegetated continents and harbor large functional diversity, yet most Earth System Models (ESMs) summarize grasses into two generic PFTs based primarily on differences between temperate C3 grasses and (sub)tropical C4 grasses. Incorporation of species-level trait variation is an active area of research to enhance the ecological realism of PFTs, which form the basis for vegetation processes and dynamics in ESMs. Using reported measurements, we developed grass functional trait values (physiological, structural, biochemical, anatomical, phenological, and disturbance-related) of dominant lineages to improve ESM representations. Our method is fundamentally different from previous efforts, as it uses phylogenetic relatedness to create lineage-based functional types (LFTs), situated between species-level trait data and PFT-level abstractions, thus providing a realistic representation of functional diversity and opening the door to the development of new vegetation models.

ecology↗

bioRxiv2017

Deriving C4 photosynthesis parameters by fitting intensive A/Ci curves

Measurements of photosynthetic assimilation rate as a function of intercellular CO2 (A/Ci curves) are widely used to estimate photosynthetic parameters for C3 species, yet few parameters have been reported for C4 plants, because of a lack of estimation methods. Here, we extend the framework of widely-used estimation methods for C3 plants to build estimation tools by exclusively fitting intensive A/Ci curves (6-8 more sampling points) for C4 using three versions of photosynthesis models with different assumptions about carbonic anhydrase processes and ATP distribution. We use simulation-analysis, out-of-sample tests, existing in vitro measurements and chlorophyll-fluorescence-measurements to validate the new estimation methods. Of the five/six photosynthetic parameters obtained, sensitivity analyses show that maximal-Rubisco-carboxylation-rate, electron-transport-rate, maximal-PEP-carboxylation-rate and carbonic-anhydrase were robust to variation in the input parameters, while day-respiration and mesophyll-conductance varied. Our method provides a way to estimate carbonic anhydrase activity, a new parameter, from A/Ci curves, yet also shows that models that do not explicitly consider carbonic anhydrase yield approximate results. The two photosynthesis models, differing in whether ATP could freely transport between RuBP and PEP regeneration processes yielded consistent results under high light, but they may diverge under low light intensities. Modeling results show selection for Rubisco of low specificity and high catalytic rate, low leakage of bundle sheath and high PEPC affinity, which may further increase C4 efficiency.

plant biology↗