Biology subjects

Coomey, J. H.

Publications and source records attributed to Coomey, J. H..

5 recordsLinked to original sources

bioRxiv2026

Microtubules in Arabidopsis pollen tubes are oriented away from the tube apex and are actin-independent at the cortex

Pollen tubes are dynamic tip-growing cells that deliver sperm nuclei to female gametes in flowering plants, allowing for sexual reproduction and seed formation. Actin and microtubule cytoskeletons both play important roles in directional pollen tube growth and guidance. While actin dynamics are well-studied in pollen tubes, the role of microtubules and the interactions between these two cytoskeletal filaments are less well understood. To address this knowledge gap, we imaged growing Arabidopsis thaliana pollen tubes co-expressing fluorescently-labeled tubulin and actin markers and observed partial co-localization of actin and microtubule filaments. We found that treatment with microtubule disrupting drugs did not affect the actin cytoskeleton. In contrast, when actin filaments were depolymerized, microtubules in the medial region of pollen tubes were disrupted, while microtubules at the cell cortex remained intact. Thus, the microtubule cytoskeleton in A. thaliana pollen tubes relies on the actin cytoskeleton in a spatially dependent manner. Furthermore, we utilized native expression of the microtubule plus-end binding protein EB1b to track microtubule orientation in growing pollen tubes. We found the microtubule array to be largely parallel, with plus ends growing away from the tube apex. Together, these findings offer new insights into the dynamics and organization of microtubules in growing pollen tubes and the interactions between actin filaments and microtubules.

plant biology↗

bioRxiv2025

Temperature signals drive grass secondary cell wall thickening

In grasses, stem elongation is driven by intercalary meristems at node-internode junctions, where cells divide, elongate, and in some cell types secondary wall maturation. Cellulose is the predominant polymer in plant cells and the most abundant biopolymer on Earth. It is synthesized at the plasma membrane by multi-protein complexes that include CELLULOSE SYNTHASE A (CESA) proteins. To investigate the spatiotemporal regulation of cellulose deposition during development, we developed a CESA8 luciferase gene expression reporter system in Brachypodium distachyon. High bioluminescence was observed in stem nodes, a specific region of elongating internodes, and the inflorescence, indicating sites of active secondary wall deposition. Within internodes, luminescence followed a distinct pattern, with a "dark zone" directly above the node with minimal signal, followed by a "bright zone" approximately 5 mm above the node where bioluminescence peaked. Histological, biophysical, and transcript analysis confirmed that luminescence intensity correlates with thickened secondary cell walls, increased cellulose crystallinity, and elevated CESA8 transcript levels. Time-lapse imaging revealed that CESA8 expression follows a robust diurnal rhythm governed by thermocycles alone, with peak expression occurring in the early morning. Temperature pulse experiments revealed an immediate but transient response of CESA8 to temperature shifts, which we modeled as an incoherent feed-forward loop. Finally, we found a strong correlation between CESA8 expression and stem elongation, highlighting the role of secondary cell wall thickening in supporting upright growth. These findings provide new insights into the regulation of secondary wall formation and its integration with environmental cues, advancing our understanding of grass stem development. SIGNIFICANCEUnderstanding how grasses build strong stems is essential for improving biomass production and crop resilience. In grasses, stem elongation and secondary cell wall thickening occur in distinct zones, yet the precise timing and regulation of this process remain unclear. To investigate this phenomenon, we developed a real-time imaging system to track the expression of CESA8, a key gene involved in cellulose synthesis. Our findings reveal that secondary wall thickening follows a daily rhythm controlled by temperature rather than light. These insights provide a foundation for optimizing plant architecture in bioenergy crops, improving their efficiency and sustainability.

plant biology↗

bioRxiv2023

Mechanosensitive ion channel MSL8 is required for pulsatile growth and cell wall dynamics in Arabidopsis pollen tubes

HIGHLIGHTPollen tube growth requires tight control of apical wall expansion. We present evidence for a mechanosensitive ion channel, MSL8, as a braking signal in growth dynamics through cell wall regulation. The male gametophyte in flowering plants, pollen, both performs the critical role of fertilization and represents a unique and accessible system for interrogating plant cell mechanics. Pollen endures multiple mechanical hurdles during its lifecycle: desiccation in the anther, rapid rehydration on the stigma, and germination to produce a rapidly growing pollen tube that will eventually reach the ovule. A key component in this robust mechanical system is MscS-Like 8 (MSL8), a mechanosensitive ion channel. We previously proposed that that MSL8 serves as an "osmotic safety valve", regulating pressure in the germinating pollen tube by releasing anions in response to plasma membrane tension, thereby preventing pollen tube rupture. However, we subsequently identified defects in the cell walls of msl8 mutant pollen, suggesting that it plays a role independent of osmoregulation, a conclusion also supported by mathematical modeling. Here, we show that pollen tubes lacking MSL8 channel function by genetic knockout or channel-blocking point mutation lose major growth pauses, have altered pectin esterification patterns, and are sensitive to pectin crosslinking. Together, these data suggest a mechanism whereby tension-gated ion release through mechanosensitive channels regulates apoplastic function and cell wall dynamics.

plant biology↗

bioRxiv2021

Touch-triggered bZIP translocation regulates elongation and secondary wall biosynthesis

AbstractPlant growth requires the integration of internal and external cues, perceived and transduced into a developmental program of cell division, elongation, and wall thickening. Mechanical forces contribute to this regulation, and thigmomorphogenesis typically includes reducing stem height, increasing stem diameter, and a canonical transcriptomic response. We present data on a bZIP transcription factor involved in this process in grasses. Brachypodium distachyon SECONDARY WALL INTERACTING bZIP (SWIZ) protein translocated into the nucleus following mechanostimulation. Classical touch responsive genes were upregulated in B. distachyon roots following touch, including significant induction of the glycoside hydrolase 17 family, which may be unique to grass thigmomorphogenesis. SWIZ protein binding to an E-box variant in exons and introns was associated with immediate activation followed by repression of gene expression. SWIZ overexpression resulted in plants with reduced stem and root elongation. These data further define plant touch-responsive transcriptomics and physiology, offering insights to grass mechanotranduction dynamics.

plant biology↗

bioRxiv2019

Changes in ambient temperature are the prevailing cue in determining Brachypodium distachyon diurnal gene regulation

O_LIPlants are continuously exposed to diurnal fluctuations in light and temperature, and spontaneous changes in their physical or biotic environment. The circadian clock coordinates regulation of gene expression with a 24-hour period, enabling the anticipation of these events. C_LIO_LIWe used RNA sequencing to characterize the Brachypodium distachyon transcriptome under light and temperature cycles, as well as under constant conditions. C_LIO_LIApproximately 3% of the transcriptome was regulated by the circadian clock, a smaller proportion reported in most other species. For most transcripts that were rhythmic under all conditions, including many known clock genes, the period of gene expression lengthened from 24 to 27 h in the absence of external cues. To functionally characterize the cyclic transcriptome in B. distachyon, we used Gene Ontology enrichment analysis, and found several terms significantly associated with peak expression at particular times of the day. Furthermore we identified sequence motifs enriched in the promoters of similarly-phased genes, some potentially associated with transcription factors. C_LIO_LIWhen considering the overlap in rhythmic gene expression and specific pathway behavior, thermocycles was the prevailing cue that controlled diurnal gene regulation. Taken together, our characterization of the rhythmic B. distachyon transcriptome represents a foundational resource with implications in other grass species. C_LI

plant biology↗