Biology subjects

Munnik, T.

Publications and source records attributed to Munnik, T..

5 recordsLinked to original sources

bioRxiv2026

Salt stress reverses root circumnutation, -skewing and -growth direction in Arabidopsis

Plant roots exhibit remarkable developmental plasticity, resulting in the adaptation of growth direction and architecture upon environmental changes. Previously, we demonstrated that inorganic phosphate (Pi) triggers Arabidopsis roots to skew to the left when grown on tilted agar plates. This so-called 'phosphate-dependent skewing' (PDS) is caused by a right-handed (clockwise, CW) circumnutation of the root tip, which is driven by a left-handed (counterclockwise, CCW) cell file rotation (CFR) of epidermal cells in the root elongation zone, and involves the cortical microtubule cytoskeleton (Sheng et al., 2024). In the present study, we demonstrate that NaCl triggers a skewing response in the opposite direction and that all other helical movements are also reversed. Thus, 'Salt-Induced Rightward Skewing' (SIRS) is accompanied by a right-handed (CW) epidermal CFR, a left-handed (CCW) circumnutation of the root tip, and hence, a left-handed (CCW) helical root growth. Comparing different Na+- and Cl- salts revealed that SIRS is predominantly caused by cations, and can be induced by K+ and osmotic stress as well, although Na+ is most efficient. To get further insight into the mechanism underlying this response, we tested candidate genes from an earlier GWAS on root responses to salt stress (Deolu-Ajayi et al., 2019) for their potential involvement. This identified GLT1 and DOB1 as being involved in the root skewing response to Pi and NaCl, respectively. Our findings reveal that Pi and salinity elicit opposing effects on root circumnutation, and hence root skewing and growth direction. Understanding the molecular machinery driving this helical behaviour may help explain adaptive mechanisms, including changes in the spatial architecture of roots, and may facilitate the optimization of crop yield under abiotic stress conditions through breeding or crop management strategies. Our results also shed new light on halotropism, which is typically measured as a change in root growth direction to the right, which in the present study has been identified to represent SIRS.

plant biology↗

bioRxiv2023

Ectopic Expression of Distinct PLC Genes Identifies 'Compactness' as Novel Architectural Shoot Strategy to Cope with Drought Stress

Phospholipase C (PLC) has been implicated in several stress responses, including drought. Overexpression (OE) of PLC has been shown to improve drought tolerance in various plant species. Arabidopsis contains nine PLC genes, subdivided into four clades. Earlier, OE of PLC3, -5 or -7 were found to increase Arabidopsis drought tolerance. Here, we confirm this for three other PLCs: PLC2, the only constitutively expressed AtPLC; PLC4, reported to have reduced salt tolerance; and PLC9, of which the encoded enzyme was presumed to be catalytically inactive. To compare each PLC and to discover any other potential phenotype, two independent OE lines of six AtPLC genes, representing all four clades, were simultaneously monitored with the GROWSCREEN FLUORO phenotyping platform, under both control- and mild drought conditions. To investigate which tissues were most relevant to achieve drought survival, we additionally expressed AtPLC5 using 13 different cell- or tissue-specific promoters. While no significant differences in plant size, biomass or photosynthesis were found between PLC lines and wild-type (WT) plants, all PLC-OE lines, as well as those tissue-specific lines that promoted drought survival, exhibited a stronger decrease in convex hull perimeter (= increase in compactness) under water deprivation compared to WT. Increased compactness has not been associated with drought or decreased water loss before, though a hyponastic decrease in compactness in response to increased temperatures has been associated with water loss. We pose that increased compactness leads to decreased water loss and potentially provides a new breeding trait to select for drought tolerance.

plant biology↗

bioRxiv2020

A nanodomain anchored-scaffolding complex is required for PI4K? function and localization in plants

Phosphoinositides are low-abundant lipids that participate in the acquisition of membrane identity through their spatiotemporal enrichment in specific compartments. PI4P accumulates at the plant plasma membrane driving its high electrostatic potential, and thereby facilitating interactions with polybasic regions of proteins. PI4K1 has been suggested to produce PI4P at the plasma membrane, but how it is recruited to this compartment is unknown. Here, we pin-point the mechanism that tethers PI4K1 to the plasma membrane via a nanodomain-anchored scaffolding complex. We identified that PI4K1 is part of a complex composed of proteins from the NO-POLLEN-GERMINATION, EFR3-OF-PLANTS, and HYCCIN-CONTAINING families. Comprehensive knock-out and knock-down strategies revealed that subunits of the PI4K1 complex are essential for pollen, embryonic and post-embryonic development. We further found that the PI4K1 complex is immobilized in plasma membrane nanodomains. Using synthetic mis-targeting strategies, we demonstrate that a combination of lipid anchoring and scaffolding localizes PI4K1 to the plasma membrane, which is essential for its function. Together, this work opens new perspectives on the mechanisms and function of plasma membrane nanopatterning by lipid kinases.

plant biology↗

bioRxiv2019

The BIR2/BIR3-interacting Phospholipase D gamma 1 negatively regulates immunity in Arabidopsis

Plants have evolved effective strategies to defend themselves against pathogen invasion. Starting from the plasma membrane with the recognition of microbe-associated molecular patterns (MAMPs) via pattern recognition receptors, internal cellular signaling pathways are induced to ultimately fend off the attack. Phospholipase D (PLD) hydrolyzes membrane phospholipids to produce phosphatidic acid (PA), which has been proposed to play a second messenger role in immunity. The Arabidopsis PLD family consists of 12 members and for some a specific function in resistance towards a subset of pathogens has been shown. We demonstrate here that Arabidopsis PLD{gamma}1, but not its close homologs PLD{gamma}2 and PLD{gamma}3, is specifically involved in plant immunity. Genetic inactivation of PLD{gamma}1 resulted in increased resistance towards the virulent bacterium Pseudomonas syringae pv. tomato DC3000 and the necrotrophic fungus Botrytis cinerea. As pld{gamma}1 mutant plants responded with elevated levels of reactive oxygen species to MAMP-treatment, a negative regulatory function for this PLD isoform is proposed. Importantly, PA levels in pld{gamma}1 mutants were not affected compared to stressed wild-type plants, suggesting that alterations in PA levels are unlikely the cause for the enhanced immunity in the pld{gamma}1 line. Instead, the plasma-membrane-attached PLD{gamma}1 protein colocalized and associated with the receptor-like kinases BIR2 and BIR3, which are known negative regulators of pattern-triggered immunity. Moreover, complex formation of PLD{gamma}1 and BIR2 was further promoted upon MAMP-treatment. Hence, we propose that PLD{gamma}1 acts as a negative regulator of plant immune responses in complex with immunity-related proteins BIR2 and BIR3.\n\nOne-sentence summaryA phospholipase D is a novel negative regulator of plant immunity and forms complexes with regulatory receptor-like kinases.

plant biology↗

bioRxiv2018

Arabidopsis inositol phosphate kinases, IPK1 and ITPK1, constitute a metabolic pathway in maintaining phosphate homeostasis

Emerging studies have implicated a close link between inositol phosphate (InsP) metabolism and cellular phosphate (Pi) homeostasis in eukaryotes; however, whether a common InsP species is deployed as an evolutionarily conserved metabolic messenger to mediate Pi signaling remains unknown. Here, using genetics and InsP profiling combined with Pi starvation response (PSR) analysis in Arabidopsis thaliana, we showed that the kinase activity of inositol pentakisphosphate 2-kinase (IPK1), an enzyme required for phytate (inositol hexakisphosphates; InsP6) synthesis, is indispensable for maintaining Pi homeostasis under Pi-replete conditions, and inositol 1,3,4-trisphosphate 5/6-kinase 1 (ITPK1) plays an equivalent role. Although both ipk1-1 and itpk1 mutants exhibited decreased levels of InsP6 and diphosphoinositol pentakisphosphate (PP-InsP5; InsP7), disruption of another ITPK family enzyme, ITPK4, which correspondingly caused depletion of InsP6 and InsP7, did not display similar Pi-related phenotypes, which precludes these InsP species as effectors. Notably, the level of D/L-Ins(3,4,5,6)P4 was concurrently elevated in both ipk1-1 and itpk1 mutants, which implies a potential role for InsP4 in regulating Pi homeostasis. However, the level of D/L-Ins(3,4,5,6)P4 is not responsive to Pi starvation that instead manifests a shoot-specific increase in InsP7 level. This study demonstrates a more nuanced picture of intersection of InsP metabolism and Pi homeostasis and PSR than has previously been elaborated, and additionally establishes intermediate steps to phytate biosynthesis in plant vegetative tissues.\n\nSignificance StatementRegulation of phosphate homeostasis and adaptive responses to phosphate limitation is critical for plant growth and crop yield. Accumulating studies implicate inositol phosphates as regulators of phosphate homeostasis in eukaryotes; however, the relationship between inositol phosphate metabolism and phosphate signaling in plants remain elusive. This study dissected the step where inositol phosphate metabolism intersects with phosphate homeostasis regulation and phosphate starvation responses.

plant biology↗