Biology subjects

Howell, A. H.

Publications and source records attributed to Howell, A. H..

3 recordsLinked to original sources

bioRxiv2024

Developmental variability in cotton fiber cell wall properties linked to important agronomic traits

The economic value of cotton is based on its long, thin, strong, and twisted trichoblasts that emerge from the ovule epidermis. The mature dried fiber cell reflects the outcome of a rapid tapering of the nascent trichoblast, weeks of polarized diffuse growth, followed by a transition to persistent secondary cell wall synthesis. Highly conserved and dynamic microtubule and cellulose microfibril-based anisotropic growth control modules are central to all of these phases. In this paper, we developed novel quantitative phenotyping and computational modeling pipelines to analyze fiber growth behaviors at a daily resolution. We uncovered unexpected variability in growth rate, cell wall properties, and cell geometry across a critical window of fiber development. Finite element computational modeling of fiber growth was used to analyze the instability of cell diameter control and predict how spatial gradients of fiber and matrix material properties can interact to dictate the patterns of shape change. As an initial step toward gaining insight into the molecular orchestration of cellulose biosynthesis, expression profiles of a broad set of relevant genes were quantified across the same developmental timeline and correlated with fiber phenotypes. This analysis identified specific candidate genes that may serve as targets for fiber quality improvement.

plant biology↗

bioRxiv2024

A high-resolution model of gene expression during Gossypium hirsutum (cotton) fiber development

Cotton fiber development relies on complex and intricate biological processes to transform newly differentiated fiber initials into the mature, extravagantly elongated cellulosic cells that are the foundation of this economically important cash crop. Here we extend previous research into cotton fiber development by employing controlled conditions to minimize variability and utilizing time-series sampling and analyses to capture daily transcriptomic changes from early elongation through the early stages of secondary wall synthesis (6 to 24 days post anthesis; DPA). A majority of genes are expressed in fiber, largely partitioned into two major coexpression modules that represent genes whose expression generally increases or decreases during development. Differential gene expression reveals a massive transcriptomic shift between 16 and 17 DPA, corresponding to the onset of the transition phase that leads to secondary wall synthesis. Subtle gene expression changes are captured by the daily sampling, which are discussed in the context of fiber development. Coexpression and gene regulatory networks are constructed and associated with phenotypic aspects of fiber development, including turgor and cellulose production. Key genes are considered in the broader context of plant secondary wall synthesis, noting their known and putative roles in cotton fiber development. The analyses presented here highlight the importance of fine-scale temporal sampling on understanding developmental processes and offer insight into genes and regulatory networks that may be important in conferring the unique fiber phenotype.

cell biology↗

bioRxiv2024

Electric charge controls plasmodesma conductivity

While plant cells are enclosed by rigid cell walls that counteract intracellular hydrostatic pressure1, their plasma membrane, cytosol, and endoplasmic reticulum (ER) remain connected through plasmodesmata, nanoscopic cell wall pores2. Plasmodesmal cell-to-cell transport occurs in the cytosolic sleeve between the plasma membrane and the ER membrane3-5, and is generally thought to be limited by the size of the moving particle alone6. Given that biological membranes carry negative electric surface charges7-9, this steric notion conflicts with physical theory of ion diffusion in nanometer-sized pores with charged walls10. Quantifying the movements of differently sized and charged fluorescent dyes in Tradescantia stamen hairs, we found that anionic fluorophores of up to 1 kDa traversed plasmodesmata whereas much smaller cationic ones did not. While this agrees with theoretical expectations of different size exclusion limits for cations and anions, it questions current dogma concerning plasmodesma function and also structure, as it implies positively rather than negatively charged surfaces within plasmodesmal pores. Our findings call for re-evaluations of current models of symplasmic transport, especially of charged molecules like the phytohormone auxin (indole-acetic acid) and certain amino acids.

cell biology↗