Biology subjects

Welti, R.

Publications and source records attributed to Welti, R..

4 recordsLinked to original sources

bioRxiv2025

Autopolyploidy exacerbates dominance masking under negative frequency-dependent selection: evidence from sporophytic self-incompatibility in Arabidopsis arenosa and A. lyrata

Polyploidy is a widespread phenomenon in flowering plants, with up to 30% of extant species being recent polyploids. Whether and how polyploidy modulates the action of natural selection remains debated, and the particular case of balancing selection has been poorly explored. This study investigates the impact of autopolyploidy on sporophytic self-incompatibility in plants, a striking example of a genetic system evolving under a special form of balancing selection (strong negative frequency-dependent selection). Numerical simulations reveal that under strict codominance, the number of S-alleles maintained in tetraploid populations is expected to double as compared to diploid populations. However, under a model with strict hierarchical dominance among alleles, the number of S-alleles increases only slightly, but gene diversity and observed heterozygosity are substantially lower in tetraploids as compared to diploids, due to enhanced dominance masking effects. Empirical data on Arabidopsis arenosa and A. lyrata confirm the latter predictions, showing similar levels of allelic diversity but dramatically lower observed and expected heterozygosity at the self-incompatibility locus in tetraploids compared to diploids. The study highlights the significant impact of autopolyploidy on patterns of diversity at the self-incompatibility locus, emphasizing the increased dominance effect in tetraploids. The results also allow us to reject a scenario of strong founder effects associated with evolution of the polyploid lineages.

evolutionary biology↗

bioRxiv2024

Drosophila Models Uncover Substrate Channeling Effects on Phospholipids and Sphingolipids in Peroxisomal Biogenesis Disorders

Peroxisomal Biogenesis Disorders Zellweger Spectrum (PBD-ZSD) disorders are a group of autosomal recessive defects in peroxisome formation that produce a multi-systemic disease presenting at birth or in childhood. Well documented clinical biomarkers such as elevated very long chain fatty acids (VLCFA) are key biochemical diagnostic findings in these conditions. Additional, secondary biochemical alterations such as elevated very long chain lysophosphatidylcholines are allowing newborn screening for peroxisomal disease. In addition, a more widespread impact on metabolism and lipids is increasingly being documented by metabolomic and lipidomic studies. Here we utilize Drosophila models of pex2 and pex16 as well as human plasma from individuals with PEX1 mutations. We identify phospholipid abnormalities in Drosophila larvae and brain characterized by differences in the quantities of phosphatidylcholine (PC) and phosphatidylethanolamines (PE) with long chain lengths and reduced levels of intermediate chain lengths. For diacylglycerol (DAG) the precursor of PE and PC through the Kennedy pathway, the intermediate chain lengths are increased suggesting an imbalance between DAGs and PE and PC that suggests the two acyl chain pools are not in equilibrium. Altered acyl chain lengths are also observed in PE ceramides in the fly models. Interestingly, plasma from human subjects exhibit phospholipid alterations similar to the fly model. Moreover, human plasma shows reduced levels of sphingomyelin with 18 and 22 carbon lengths but normal levels of C24. Our results suggest that peroxisomal biogenesis defects alter shuttling of the acyl chains of multiple phospholipid and ceramide lipid classes, whereas DAG species with intermediate fatty acids are more abundant. These data suggest an imbalance between de novo synthesis of PC and PE through the Kennedy pathway and remodeling of existing PC and PE through the Lands cycle. This imbalance is likely due to overabundance of very long and long acyl chains in PBD and a subsequent imbalance due to substrate channeling effects. Given the fundamental role of phospholipid and sphingolipids in nervous system functions, these observations suggest PBD-ZSD are diseases characterized by widespread cell membrane lipid abnormalities.

genetics↗

bioRxiv2021

Polar lipids are linked to nanoparticles in xylem sap of temperate angiosperm species

Xylem sap of angiosperm species has been found to include low concentrations of polar lipids and nanoparticles, including surfactant-coated nanobubbles. Although the nanoparticles have been suggested to consist of polar lipids, no attempt has been made to determine if nanoparticle and lipid concentrations are related. Here, we examined concentrations of nanoparticles and lipids in xylem sap and contamination control samples of six temperate angiosperm species with a NanoSight device and based on mass spectrometry. We found (1) that the concentration of nanoparticles and lipids were both diluted when an increasing amount of sap was extracted, (2) that their concentrations were significantly correlated in three species, (3) that their concentrations were affected by vessel anatomy, and (4) that concentrations of nanoparticles and lipids were very low in contamination-control samples. Moreover, there was little seasonal difference, no freezing-thawing effect on nanoparticles, and little seasonal variation in lipid composition. These findings indicate that lipids and nanoparticles are related to each other, and largely do not pass interconduit pit membranes. Further research is needed to examine the formation and stability of nanoparticles in xylem sap in relation to lipid composition, and the complicated interactions among the gas, liquid, and solid phases in xylem conduits.

plant biology↗

bioRxiv2019

Lipids in xylem sap of woody plants across the angiosperm phylogeny

Lipids have been observed attached to lumen-facing surfaces of mature xylem conduits of several plant species, but there has been little research on their functions or effects on water transport, and only one lipidomic study of the xylem apoplast. Therefore, we conducted lipidomic analyses of xylem sap from woody stems of seven plants representing six major angiosperm clades, including basal magnoliids, monocots, and eudicots, to characterize and quantify phospholipids, galactolipids, and sulfolipids in sap using mass spectrometry. Locations of lipids in vessels of Laurus nobilis were imaged using TEM and confocal microscopy. Xylem sap contained the galactolipids di- and mono-galactosyldiacylglycerol (DGDG and MGDG), as well as all common plant phospholipids, but only traces of sulfolipids, with total lipid concentrations in extracted sap ranging from 0.18 to 0.63 nmol / mL across all seven species. Contamination of extracted sap from lipids in cut living cells was found to be negligible. Lipid composition of sap was compared to wood in two species and was largely similar, suggesting that sap lipids, including galactolipids, originate from cell content of living vessels. Seasonal changes in lipid composition of sap were observed for one species. Lipid layers coated all lumen-facing vessel surfaces of Laurus nobilis, and lipids were highly concentrated in inter-vessel pits. The findings suggest that apoplastic, amphiphilic xylem lipids are a universal feature of angiosperms. The findings require a reinterpretation of the cohesion-tension theory of water transport to account for the effects of apoplastic lipids on dynamic surface tension and hydraulic conductance in xylem.

plant biology↗