Biology subjects

Geelen, D.

Publications and source records attributed to Geelen, D..

8 recordsLinked to original sources

bioRxiv2026

Spatially-restricted metabolic delivery of auxin for selective adventitious root induction

Auxin impacts on nearly every aspect of plant growth and development. Its exogenous application therefore results in pleiotropic growth responses. Exploiting this activity for plant propagation requires avoiding or minimizing such off-target effects and is generally achieved as a trade-off between toxicity and organogenetic efficacity. We recently identified the compound HYSPARIN (HYS) with potent, and uniquely selective adventitious root inductive activity. Unlike other root-inducing compounds, HYS preferentially activates auxin responses in the shoot via an unknown mechanism. Here, we show that HYS acts as a shoot-specific proauxin. Rather than acting through auxin homeostasis, we found that HYS is hydrolysed in planta independently of ILR1/ILL amidohydrolases to release the synthetic auxin MCPA. Structure-activity relationship analysis confirmed a strong dependence on its MCPA moiety for activating auxin responses, and identified its promoiety as a determinant of shoot-specificity and activity. Selective application of MCPA also potently induces AR is consistent with a model in which HYS metabolism produces a spatially restricted, AR inductive auxin signal. The activation mechanism of HYS thus provides a conceptual framework for tissue-specific metabolic delivery of auxin and may enable the programmable delivery of other xenobiotics in plants.

plant biology↗

bioRxiv2026

Belgian endive-derived biostimulant activity in Arabidopsis, lettuce and sweet pepper at different developmental stages, environmental conditions, and application methods

Belgian endive-derived biostimulant (BEE) was previously shown to enhance root and shoot growth of Arabidopsis thaliana and Plectranthus esculentus in in vitro culturing conditions. In this study, we evaluated the effect of BEE on A. thaliana subjected to abiotic stresses and assessed the translatability of its bioactivity on lettuce (Lactuca sativa) and sweet pepper (Capsicum annuum) cultured in substrate and soil. A first set of experiments tested the impact of BEE on protection during, and restoration after, osmotic or salt (NaCl) stress. BEE treatment had little to no rescuing effect when plants were exposed to osmotic stress. In contrast, BEE strongly promoted shoot development and leaf health both under standard and NaCl stress conditions. Under mild stress, BEE enhanced photosynthetic efficiency and chlorophyll content in Arabidopsis, whereas it did not significantly alleviate osmotic stress induced by sorbitol. To evaluate the effect under ex vitro conditions, BEE was applied via root drenching to substrate-grown A. thaliana, lettuce, and sweet pepper. BEE improved leaf greenness and photosynthesis enhancing Arabidopsis rosette development, but it did not increase lettuce head weight. In sweet pepper, BEE increased fruit yield and promoted fruit maturation. Under drought stress conditions, BEE application did not improve sweet pepper yield.

plant biology↗

bioRxiv2025

Constitutive cGAS-STING activation in ALT+ cells

Stimulator of interferon genes (STING) is a pivotal mediator of anti-tumor immunity, activated downstream of cytoplasmic DNA recognition by cyclic GMP-AMP synthase (cGAS). In cells that employ the alternative lengthening of telomeres (ALT) pathway, extrachromosomal telomeric repeats (ECTRs) act as potent activators of the cGAS-STING pathway. Although ALT+ cells were previously thought to evade this pathway through epigenetic silencing, our findings reveal more nuanced adaptive mechanisms that involve the spatial regulation of STING and the clearance of immunostimulatory ECTR species. In the vast majority of ALT+ cells, ongoing ECTR production drives sustained 2'3'-cGAMP synthesis, directing STING to the Golgi apparatus for immune signaling before lysosomal degradation. Lysosomal degradation of STING relies largely on interferon regulatory factor 3 (IRF3), with minimal involvement of TANK-binding kinase 1 (TBK1), pointing at a novel role for IRF3 in STING trafficking in ALT+ cells. Another adaptive mechanism involves the removal of immunogenic cytoplasmic ECTRs through STING-mediated lysosomal degradation. These mechanisms likely cooperate to restrict chronic interferon signaling that might otherwise prevent ALT+ cancers from emerging. These findings refine our understanding of immune sensing in ALT+ cancers, revealing how ALT+ cells respond to continuous ECTR production and suggesting a potential therapeutic target to modulate the microenvironment of ALT+ tumors.

cell biology↗

bioRxiv2024

Light and substrate composition control root exudation rates at the initial stages of soilless lettuce cultivation

Plant root exudation is an inherent metabolic process that enhances various functions of the root system like the mobilization of nutrients and interactions with surrounding microbial communities. The role and extent of root exudation in soilless crop production is poorly investigated. Here, we analyzed soilless lettuce and show that the root exudation rate declines with plant age. Furthermore, the impact of light quality and substrate was assessed by growing soilless lettuce in 100% red light (660 nm), 100% blue light (450 nm), and white light (full-light spectrum) and in 100% perlite, 100% potting soil, or mixtures of both materials. Root exudates were collected at 10, 17 and 24 days after transplanting. The total carbon root exudation rate was influenced by light conditions and substrate composition at the earliest timepoint of the culture but not at later growth stages. The total carbohydrate exudation rate was significantly higher under pure blue and red light compared to white light. The impact of light depended on the presence of perlite in the substrate. The total phenolic compound exudation rate was most strongly influenced by the substrate composition and reached the highest level in either pure potting soil or pure perlite. These findings underscore the importance of root exudation during the initial stages of development. Light and growing media influence the exudation rate at this early stage, suggesting that exudation is an adaptive process of the soilless lettuce culture. HIGHLIGHTAt an initial stage of development, soilless lettuce exudation rates are high and modulated by light and substrate composition, whereas older plants show lower rates that are not influenced by these environmental conditions.

plant biology↗

bioRxiv2024

Ribosome biogenesis factor AtRRB1 confers pollen heat stress tolerance in Arabidopsis

The plant male reproductive system is very sensitive to high temperature stress leading to a reduction in fertility. Damage caused by heat stress is restored by the activation of transcription and the synthesis of chaperones that regulate the heat stress response. Here we report that AtRRB1 is a homolog of the yeast ribosome chaperone protein Rrb1p. AtRRB1 is an essential gene and a T-DNA insertion in the coding region impairs male and female gametogenesis. The heterozygous rrb1-1 mutant shows decreased expression of AtRRB1 and increased transcription of the 60S ribosome proteins RPL3B and RPL4, in line with a chaperone role of AtRRB1 in ribosome biogenesis. Embryo sac development across ovules of a single pistil occurs uncoordinated and about half of the ovules abort. Half of rrb1-1 pollen is substantially smaller and produce shorter pollen tubes than WT pollen. In contrast to the Col-0 pollen, smaller pollen is overly sensitivity to high temperature (24h at 32{degrees}C) treatment, specifically during the early bicellular microspore development stage. Heat stressed rrb1-1 bicellular microspores accumulated excessively rough endoplasmic reticulum stacks, suggesting that loss of AtRRB1 activity causes an arrest in ER associated protein biosynthesis. These findings support a critical requirement for ribosome biogenesis and protein synthesis in bicellular microspores to recover from high temperature stress.

plant biology↗

bioRxiv2023

The selective estrogen receptor modulator clomiphene inhibits sterol biosynthesis in Arabidopsis thaliana

Sterols are produced via complex, multistep biosynthetic pathways involving similar enzymatic conversions in plants, animals and fungi, yielding a variety of sterol metabolites with slightly different chemical properties to exert diverse and specific functions. The role of plant sterols has been studied in the context of cell biological processes, signaling and overall plant development, mainly based on mutants. Due to their essential nature, genetic interference with their function causes pleiotropic developmental defects. An important alternative is to use a pharmacological approach. However, the current toolset for manipulating sterol biosynthesis in plants remains limited. Here, we probed a collection of inhibitors of mammalian cholesterol biosynthesis to identify new inhibitors of plant sterol biosynthesis. We provide evidence that imidazole-type fungicides, bifonazole, clotrimazole and econazole inhibit the obtusifoliol 14-demethylase CYP51, that is highly conserved among eukaryotes. Surprisingly, we found that the selective estrogen receptor modulator, clomiphene, inhibits sterol biosynthesis, in part by inhibiting the plant-specific cyclopropyl-cycloisomerase CPI1. These results demonstrate that rescreening of the animal sterol biosynthesis pharmacology is an easy approach for identifying novel inhibitors of plant sterol biosynthesis. Such molecules can be used as entry points for the development of plant-specific inhibitors of sterol biosynthesis that can be used in agriculture.

plant biology↗

bioRxiv2022

Phase separation-based visualization of protein-protein interactions and kinase activities in plants

Protein activities depend heavily on protein complex formation and dynamic post-translational modifications, such as phosphorylation. Their dynamic nature is notoriously difficult to monitor in planta at cellular resolution, often requiring extensive optimization and high-end microscopy. Here, we generated and exploited the SYnthetic Multivalency in PLants (SYMPL)-vector set to study protein-protein interactions (PPIs) and kinase activities in planta based on phase separation. This technology enabled easy detection of inducible, binary and ternary protein-protein interactions among cytoplasmic, nuclear and plasma membrane proteins in plant cells via a robust image-based readout. Moreover, we applied the SYMPL toolbox to develop an in vivo reporter for SnRK1 kinase activity, allowing us to visualize tissue-specific, dynamic SnRK1 activation upon energy deprivation in stable transgenic Arabidopsis plants. The applications of the SYMPL cloning toolbox lay the foundation for the exploration of PPIs, phosphorylation and other post-translational modifications with unprecedented ease and sensitivity.

plant biology↗

bioRxiv2022

Belgian endive-derived biostimulants promote shoot and root growth in vitro.

Recovering biostimulant compounds from by-products of crops is a promising strategy to add value, enhance sustainability, and increase the environmental safety of the agricultural production chain. Here, we report consistent root and shoot growth-stimulating bioactivity present in water-based extracts from Belgian endive forced roots (Cichorium intybus var. foliosum) over two consecutive harvest years. The shoot and the primary root of in vitro cultivated Arabidopsis thaliana treated with Belgian endive extract were about 30% increased in size compared to plants grown under control conditions. The ornamental species Plectranthus esculentus also showed enhanced in vitro shoot and root growth, suggesting bioactivity on a broad range of species. Fractionation of the Belgian endive extracts into aqueous and organic subfractions coupled with bio-activity measurements showed that the principal root and shoot growth-promoting ingredients are primarily water-soluble. NMR-based characterization of the bioactive aqueous fractions revealed the presence of pre-dominantly sugars and organic acids. Malate and sugars were abundant and common to all water fractions, suggesting these molecules contributed to the growth stimulation phenotype. The findings indicate that Belgian endive roots are a source for the development of organic waste-derived biostimulants with potential for application in tissue culture and putatively for soil-grown crop production.

plant biology↗