Biology subjects

Hrmova, M.

Publications and source records attributed to Hrmova, M..

5 recordsLinked to original sources

bioRxiv2025

Complete genome sequence assembly elucidates evolution and regulation of 5S rDNA loci in the greater duckweed Spirodela polyrhiza

We resolved the molecular architecture of the 5S rDNA loci in an aquatic monocot Spirodela polyrhiza. Measurements of fluorescence in situ hybridization signals revealed two loci with 5S rDNA clusters. A combination of the extra-long DNA reads and conventional sequencing of 5S rDNA repeats allowed the assembling of complete loci sequences located on ChrSp6 and ChrSp13. The homologous chromosomes of the ChrSp6 locus contain clusters of 40 and >60 copies of 5S rDNA repeat units with intergenic spacer (IGS) of 400 bp. The ChrSp13 locus is represented by 5S rDNA clusters of rRNA genes spaced by IGSs of 1,056 or 1,069 bp arranged in two sub-clusters, suggesting a different rate of repeat homogenization between loci. The G/C-rich 5S rDNA arrays in both loci are embedded in A/T-enriched chromosome regions with possible regulatory functions. The TATA-like boxes of the 5S rDNA repeat on ChrSp6 and ChrSp13 exhibit different affinities for the TATA-binding protein in 3D modeling of protein/DNA interactions, suggesting a locus-specific regulation of rRNA transcription. Our findings shed light on the molecular architecture of the 5S rDNA loci, which could foster an innovative era for the principles of evolution and regulation of rRNA genes in plants.

molecular biology↗

bioRxiv2024

Protein modelling and thermodynamics reveal that plant cation-chloride cotransporters mediate potassium-chloride symport

Plant cation-chloride-cotransporters (CCC) are proposed to be Na+-K+-2Cl- transporting proteins, although phylogenetically they are closer to K+-Cl- cotransporters (KCC). Conserved features of plant CCC and animal KCC include the presence of predicted K+ and Cl- binding sites, and the absence of a Na+ binding site. Here, we investigated grapevine (Vitis vinifera L.) VvCCC using protein structural modelling and heterologous expression. Our modelling data predicted that 3D folds of VvCCC were more similar to DrNKCC1, but sequences of ion binding sites resembled those of hKCC1. The measurements with VvCCC-injected Xenopus laevis oocytes with VvCCC, localising to plasma membranes, indicated that oocytes were depleted of intracellular Cl-, net 86Rb fluxes, which agreed with thermodynamic predictions for KCC co-transport. 86Rb uptake by VvCCC-injected oocytes was Cl--dependent, did not require external Na+, and was partially inhibited by the non-specific CCC blocker bumetanide - these properties are typical of KCC transporters. A loop diuretic-insensitive Na+ conductance in VvCCC-injected oocytes may account for earlier observations of Na+ uptake by plant CCC proteins in oocytes. Our data suggest plant CCC proteins are likely to function as K+-Cl- cotransporters, which opens avenues to define their mechanistic and biophysical properties and roles in physiology. HighlightBased on predictive structural and experimental data, this study presents novel findings to reveal that plant cation-chloride-cotransporters are likely to function as K+-Cl- symporters.

plant biology↗

bioRxiv2023

Barley HvNIP2;1 aquaporin permeates water, metalloids, saccharides, and ion pairs due to structural plasticity and diversification

Aquaporins can facilitate the passive movement of water and small polar molecules and some ions. The barley Nodulin 26-like Intrinsic Protein (HvNIP2;1) embedded in liposomes and examined through stopped-flow light scattering spectrophotometry and Xenopus oocyte swelling assays was found to permeate water, boric and germanic acids, sucrose and L-arabinose but not D-glucose or D-fructose. Other saccharides, such as neutral (D-mannose, D-galactose, D-xylose, D-mannoheptaose) and charged (N-acetyl D-glucosamine, D-glucosamine, D-glucuronic acid) aldoses, disaccharides (lactose, cellobiose, gentiobiose, trehalose), trisaccharide raffinose, and urea, glycerol, and acyclic polyols were permeated to a much lower extent. Apparent permeation of hydrated KCl and MgSO4 ion pairs was observed, while CH3COONa and NaNO3 permeated at significantly lower rates. Experiments with boric acid and sucrose revealed no apparent interaction between solutes when permeated together, and AgNO3 blocked the permeation of all solutes. Full-scale steered molecular dynamics simulations of HvNIP2;1 and spinach SoPIP2;1 revealed possible rectification for water, boric acid, and sucrose transport, and defined key residues interacting with permeants. In a biological context, the simulated sucrose rectification could mediate its apoplastic-to-intracellular transport but not the reverse, thus, constituting a novel element of plant saccharide-transporting machinery. Phylogenomic analyses of 164 Viridiplantae and 2,993 Archaean, bacterial, fungal, and Metazoan aquaporins rationalised solute poly-selectivity in NIP3 sub-clade entries and suggested that they diversified from other sub-clades to acquire a unique specificity of saccharide transporters. Solute specificity definition in NIP aquaporins could inspire developing plants for sustained food production. Significance StatementAquaporins are fundamental to water and solute movements in nearly all living organisms. Solute selectivity inspections of the HvNIP2;1 aquaporin revealed that it transported water, hydroxylated metalloids boric and germanic acids, sucrose, L-arabinose, KCl, and MgSO4 ion pairs, but not D-glucose or D-fructose and to lesser extent urea, and acyclic polyols. This poly-selective transport by HvNIP2;1 classified in the NIP3 sub-clade aquaporins may afford nutritional and protective roles during plant development and in response to abiotic stresses. It is anticipated that the solute specificity definition of HvNIP2;1 inspires protein engineering and in silico mining to develop plants, which when exposed to suboptimal soil conditions of high soil metalloids, would overcome toxicity for sustained food production.

biophysics↗

bioRxiv2020

A single nucleotide substitution in TaHKT1;5-D controls shoot Na+ accumulation in bread wheat

Improving salinity tolerance in the most widely cultivated cereal, bread wheat (Triticum aestivum L.), is essential to increase grain yields on saline agricultural lands. A Portuguese landrace, Mocho de Espiga Branca accumulates up to 6 folds greater leaf and sheath sodium (Na+) than two Australian cultivars, Gladius and Scout, under salt stress. Despite high leaf and sheath Na+ concentrations, Mocho de Espiga Branca maintained similar salinity tolerance compared to Gladius and Scout. A naturally occurring single nucleotide substitution was identified in the gene encoding a major Na+ transporter TaHKT1;5-D in Mocho de Espiga Branca, which resulted in a L190P amino acid residue variation. This variant prevents Mocho de Espiga Branca from retrieving Na+ from the root xylem leading to a high shoot Na+ concentration. The identification of the tissue tolerant Mocho de Espiga Branca will accelerate the development of more elite salt tolerant bread wheat cultivars.

plant biology↗

bioRxiv2018

High affinity Na+ transport by wheat HKT1;5 is blocked by K+

The wheat sodium transporters TmHKT1;5-A and TaHKT1;5-D are encoded by genes underlying major shoot Na+ exclusion loci Nax2 and Kna1 from Triticum monococcum (Tm) and Triticum aestivum (Ta), respectively. In contrast to HKT2 transporters that have been shown to exhibit high affinity K+-dependent Na+ transport, HKT1 proteins have, with one exception, only been shown to catalyse low affinity Na+ transport and no K+ transport. Here, using heterologous expression in Xenopus laevis oocytes we show that both TmHKT1;5-A and TaHKT1;5-D encode dual (high and low) affinity Na+-transporters with the high-affinity component being abolished when external K+ is in excess of external Na+. Based on 3-D structural modelling we propose that tighter binding of K+, compared to that of Na+ in the selectivity filter region by means of additional van der Waals forces, explains the K+ block at the molecular level. The low-affinity component for Na+ transport of TmHKT1;5-A had a lower Km than that of TaHKT1;5-D and was less sensitive to external K+. We propose that these properties underpin the improvements in shoot Na+-exclusion and crop plant salt tolerance following the introgression of TmHKT1;5-A into diverse wheat backgrounds.

plant biology↗