Biology subjects

Ketelaar, T.

Publications and source records attributed to Ketelaar, T..

6 recordsLinked to original sources

bioRxiv2026

Genotype and farm effects on yield and morphology reveal potential for breeding and site selection for sugar kelp

Seaweed cultivation has recently gained increased attention in North-West Europe as a sustainable source of biomass for biobased products. However, yields need to increase to make the seaweed sector economically viable. To achieve this, higher yielding varieties can be bred but this requires variation for yield and yield-related traits among genotypes. To reliably select high-yielding genotypes, an understanding is required of how both within-farm and between-farm environmental differences affect phenotypes and how to identify simple and reliable proxies for yield. In this study we evaluated growth of nine Saccharina latissima genotypes on two farms, 12 km apart, within the same season. We observed a threefold difference in yield among genotypes, demonstrating the potential for improvement through selection and breeding. Blade thickness and blade size-related traits were strongly correlated with yield, highlighting their potential to serve as rapid and non-destructive proxies for yield, thereby accelerating selection. Furthermore, we demonstrated the importance of adequate replication in farm trials to improve genotype performance estimation by correcting for within-farm spatial variation. Moreover, phenotypic variation was most explained by the genotype and environment, highlighting the importance of both genotype and site selection. Although genotype by environment interactions (GxE) were significant, its contributions were small, indicating stable genotype ranking across farms. Overall, these results are promising for breeding improved S. latissima as it indicates that genotype performance is consistent across close by locations and that local S. latissima populations harbour substantial phenotypic variation that can be used to breed for increased yield. Highlights- Local genetic resources harbour substantial variation in yield and morphology for breeding. - Minor GxE allows for breeding across farms. - Blade thickness and blade size related traits are good predictors of yield. - Correction for on-farm spatial variation improves genotype performance estimation.

genetics↗

bioRxiv2026

Bacteria orchestrate gametophyte growth, oogenesis and sporophyte development in Saccharina latissima in a sex-dependent manner

O_LIMarine organisms, including green and brown macroalgae, exhibit a broad dependency on their microbiome which has been demonstrated in model species including Ulva compressa and Ectocarpus siliculosus with relatively simple building plans. However, it remains elusive if and how Saccharina latissima, a complex brown macroalgae with high degrees of organ and tissue differentiation, is controlled by its microbiome. C_LIO_LIWe monitored gametophyte cultures of mixed sexes, induced oogenesis and followed sporophyte development both under axenic conditions and in cultures complemented with bacterial isolates from the sugar kelp core microbiome. C_LIO_LIFemale gametophytes generally performed better in the presence of bacteria while males performed worse. Some bacterial isolates inhibit oogenesis in females entirely, whereas others have a stimulating effect. Under axenic conditions sporophytes did form, but growth, pigmentation and the establishment of an apical-basal polarization axis were severely disrupted. These defects could be resolved by complementation with many bacteria from the S. latissima core microbiome. C_LIO_LISugar kelp depends heavily on specific bacterial symbionts for growth, reproduction and development and their effect is sex-dependent in gametophytes. This work provides a platform to investigate the precise methods of cross-kingdom communication which has a large potential in the kelp production industry. C_LI

developmental biology↗

bioRxiv2025

Microtubules in the coenocyte Phytophthora function in nuclear positioning and sustaining tip growth

The microtubule cytoskeleton consists of dynamic intracellular filaments and is involved in numerous processes, ranging from nuclear division to intracellular transport. Some of these microtubule-mediated processes are conserved in all eukaryotic lineages while others are specific for certain groups of organisms. Here, we focus on the microtubule cytoskeleton of oomycetes in the genus Phytophthora, a group of harmful plant pathogens. For visualizing microtubule organization and dynamics, we generated transgenic Phytophthora palmivora lines expressing GFP-tagged -tubulin. Besides a conserved localization in the mitotic spindle, we observed cytoplasmic microtubules originating from microtubule-organizing centers associated with nuclei in the coenocytic hyphae. These dynamic microtubules initiated long-lasting, antiparallel connections with microtubules originating from adjacent nuclei. After mitosis, these microtubules rapidly increased in length while maintaining their antiparallel interaction. Frequent buckling events suggest that microtubule-based force generation plays a role in nuclear spacing. This idea was strengthened by erratic nuclear motility and positioning in hyphae exposed to the microtubule depolymerizing drug oryzalin. Besides aberrant nuclear positioning we also observed defects in hyphal growth; in oryzalin-treated hyphae lacking microtubules, tip growth was less sustained than in non-treated hyphae. This suggests that microtubules radiating into the hyphal tip from the apical nucleus have a function in sustaining tip growth. Altogether, this study provides novel insights in the localization, dynamics and functions of the microtubule cytoskeleton in the coenocytic Phytophthora hyphae.

cell biology↗

bioRxiv2022

Cell wall extensin arabinosylation is required for root directional response to salinity

Soil salinity is a major contributor to crop yield losses. To improve our understanding of root responses to salinity, we developed and exploit here a real-time salt-induced tilting assay (SITA). This method follows root growth upon both gravitropic and salt challenges, revealing that root bending upon tilting is modulated by salinity, but not by osmotic stress. Next, this salt-specific response was measured in 345 natural Arabidopsis accessions and we discovered a genetic locus, encoding for the cell-wall modifying enzyme EXTENSIN ARABINOSE DEFICIENT TRANSFERASE (ExAD), to be associated with root bending in salt. Extensins are a class of structural cell wall glycoproteins [hydroxyproline-rich glycoproteins (HRGPs)] which are post-translationally modified by O-glycosylation mostly in the form of hydroxyproline (Hyp)-arabinosylation. We show that salt induces ExAD-dependent Hyp-arabinosylation, influencing root bending responses and cell wall thickness. We report that roots of exad mutants, which lack extensin Hyp-Araf4 modifications, display increased root epidermal cell wall thickness and porosity and altered gravitropic root bending in salt, as well as a reduced salt avoidance response. Our results suggest that extensin modification via Hyp-arabinosylation represents a novel salt-specific cellular process that is required for the directional response of roots exposed to salinity.

plant biology↗

bioRxiv2018

Exocyst subunit Sec6 is positioned by microtubule overlaps in the moss phragmoplast prior to the arrival of cell plate membrane

During plant cytokinesis a radially expanding membrane-enclosed cell plate is formed from fusing vesicles that compartmentalizes the cell in two. How fusion is spatially restricted to the site of cell plate formation is unknown. Aggregation of cell-plate membrane starts near regions of microtubule overlap within the bipolar phragmoplast apparatus of the moss Physcomitrella patens. Since vesicle fusion generally requires coordination of vesicle tethering and subsequent fusion activity we analysed the subcellular localization of several subunits of the exocyst, a tethering complex active during plant cytokinesis. We found that Sec6, but neither Sec3 or Sec5 subunits localized to microtubule overlap regions in advance of cell plate construction started in moss. Moreover, Sec6 exhibited a conserved physical interaction with an orthologue of the Sec1/Munc18 protein KEULE, an important regulator for cell-plate membrane vesicle fusion in Arabidopsis. Recruitment of PpKEULE and vesicles to the early cell plate was delayed upon Sec6 gene silencing. Our findings thus suggest that vesicle-vesicle fusion is in part enabled by a pool of exocyst subunits at microtubule overlaps that is recruited independent of the delivery of vesicles.\n\nSummary statementWe performed a time-resolved localization screen of multiple subunits of the exocyst complex throughout moss cytokinesis and show that each subunit has a unique spatiotemporal recruitment pattern.

cell biology↗

bioRxiv2017

Stacks off tracks: A role for the golgin AtCASP in plant endoplasmic reticulum - Golgi apparatus tethering

The plant Golgi apparatus modifies and sorts incoming proteins from the endoplasmic reticulum (ER), and synthesises cell wall matrix material. Plant cells possess numerous motile Golgi bodies, which are connected to the ER by yet to be identified tethering factors. Previous studies indicated a role of cis-Golgi plant golgins (long coiled-coil domains proteins anchored to Golgi membranes) in Golgi biogenesis. Here we show a tethering role for the golgin AtCASP at the ER-Golgi interface. Using live-cell imaging, Golgi body dynamics were compared in Arabidopsis thaliana leaf epidermal cells expressing fluorescently tagged AtCASP, a truncated AtCASP-{Delta}CC lacking the coiled-coil domains, and the Golgi marker STtmd. Golgi body speed and displacement were significantly reduced in AtCASP-{Delta}CC lines. Using a dual-colour optical trapping system and a TIRF-tweezer system, individual Golgi bodies were captured in planta. Golgi bodies in AtCASP-{Delta}CC lines were easier to trap, and the ER-Golgi connection was more easily disrupted. Occasionally, the ER tubule followed a trapped Golgi body with a gap, indicating the presence of other tethering factors. Our work confirms that the intimate ER-Golgi association can be disrupted or weakened by expression of truncated AtCASP-{Delta}CC, and suggests that this connection is most likely maintained by a golgin-mediated tethering complex.\n\nHighlightHere we show that the Golgi-associated Arabidopsis thaliana protein AtCASP may form part of a golgin-mediated tethering complex involved in anchoring plant Golgi stacks to the endoplasmic reticulum (ER).

plant biology↗