Showing papers by "Attila Fehér published in 2020"

Timely removal of exogenous cytokinin and the prevention of auxin transport from the shoot to the root affect the regeneration potential of Arabidopsis roots

Abstract: In vitro regeneration of Arabidopsis from roots is generally achieved via indirect organogenesis. First, transdifferentiation of lateral root primordia to calli is achieved by a balanced auxin-to-cytokinin ratio that is followed by the induction of shoot meristem formation using a high cytokinin level. Here we demonstrate that if the root explants were transferred onto a hormone-free medium after a transient (4-days) cytokinin treatment, embryogenic marker genes (LEC1, LEC2, FUS3) started to be expressed. App. 50% of the regeneration foci developed into plantlets with trichome-less cotyledon-like leaves. Moreover, the somatic embryogenesis defective lec1 mutant could regenerate only shoots with trichome-bearing leaves under this condition. Based on these observations, the mixed accomplishment of shoot organogenesis and somatic embryogenesis is hypothesized in the Arabidopsis root explants cultured under hormone-free conditions following cytokinin induction. Using whole seedlings instead of root explants in the same experimental set up, no regenerates were formed on the roots. Applying the auxin transport inhibitor TIBA to the root-to-shoot junction of the seedlings, the regeneration ability of the root could be restored. The observations indicate that shoot-derived endogenous auxin blocks the cytokinin-induced regeneration process in the roots of whole seedlings. The expression of the wound-induced transcription factor WIND1 could be detected in the roots of unwounded seedlings if the shoot-to-root auxin transport was inhibited. Manipulating the exogenous cytokinin level together with the endogenous shoot-to-root auxin transport therefore could mimic the effect of wounding (removal of shoot) on plant regeneration from roots. Transferring root explants from high cytokinin to hormone-free conditions resulted in the expression of embryogenic markers. Inhibiting the shoot-to-root auxin transport had similar effect on regeneration as wounding.

Increased adaptation of an energy willow cultivar to soil salinity by duplication of its genome size

Abstract: Soil salinity can limit the use of marginal lands for biomass production based on cultivation of short-rotation woody crops as energy willow. Here, we compare salt stress responses of the diploid, productive cultivar (Energo), and its artificially produced autotetraploid (PPE-2; PPE-7; PPE-13) variants. After pre-testing the effects of various salt concentrations, willow plants with different genome sizes were exposed to 1.5 g NaCl kg−1 soil (electrical conductivity (EC) value: 7.04 mS/cm). Digital imaging of shoot surface area (green pixel) and root surface (white pixel) indicated variable improvements in growth responses of tetraploids relative to diploid ones in saline soils. After nine weeks of salt stress, increase in salt adaptation capability of tetraploid plants was indicated by larger biomass, leaf and root weights under salinity (1.5 g NaCl kg−1 soil) relative to diploids. Biomass weights were significantly higher in the case of tetraploid PPE-2 plants with increased water consumption and leaf water content than of diploid plants. The inhibitory effect of salt stress on photosynthetic assimilation rates was less significant in plants with doubled genome. The Na+ accumulation was reduced in leaves of tetraploids and increased in their roots, while the K+ ion content was higher in their leaves than in diploids. Tetraploidy improved K+/Na+ ratio in leaves and roots of willow plants under normal soil condition. This parameter was less reduced in tetraploid leaves exposed to salt stress. The described tetraploid energy willow genotypes with salt tolerance can play a role in the extended use of green energy.

Posttranslational modification of the RHO of plants protein RACB by phosphorylation and cross-kingdom conserved ubiquitination

Abstract: Small RHO-type G-proteins act as signaling hubs and master regulators of polarity in eukaryotic cells. Their activity is tightly controlled, as defective RHO signaling leads to aberrant growth and developmental defects. Two major pathways regulate G-protein activity: canonical switching of the nucleotide bound state and posttranslational modification (PTM). PTMs can support or suppress RHO signaling, depending on each individual case. In plants, regulation of Rho of plants (ROPs) has been shown to act through nucleotide exchange and hydrolysis, as well as through lipid modification, but there is little data available on phosphorylation or ubiquitination of ROPs. Hence, we applied proteomic analyses to identify PTMs of the barley ROP RACB. We observed in vitro phosphorylation by barley ROP Binding Kinase 1 and in vivo ubiquitination of RACB. Comparative analyses of the newly identified RACB phosphosites and human RHO protein phosphosites revealed conservation of modified amino acid residues, but no overlap of actual phosphorylation patterns. However, the identified RACB ubiquitination site is present in all ROPs from Hordeum vulgare, Arabidopsis thaliana and Oryza sativa. Since this highly conserved amino acid residue is likewise ubiquitinated in mammalian Rac1 and Rac3, we suggest that RHO family proteins from different kingdoms could be generally regulated by ubiquitination of this site.

Molecular plant physiology

Abstract: The Plant Molecular Physiology textbook is designed to introduce undergraduate students into the life of plants. First, the genetic basis of the growth and development of plants is described. The first chapter explores the molecular regulatory factors with high importance in functioning of the genome and controlling the expression of genes. The second chapter introduces the specific organisation of plant cells and cellular organelles. Following chapters discuss the demand of plants for minerals, the uptake and transport of water and nutrients, and the mechanisms and significance of photosynthesis. The main endogenous factors (plant hormones) and the most important exogenous signal (light) and related signalling events affecting plant life and adaptation are also discussed. The plant-specific aspects of these biological processes, their regulatory and signalling mechanisms are also described. Then, the key points of plant ontogenesis including growth and development, reproduction and senescence are highlighted.

The Arabidopsis RLCK VI_A2 Kinase Controls Seedling and Plant Growth in Parallel with Gibberellin.

Abstract: The plant-specific receptor-like cytoplasmic kinases (RLCKs) form a large, poorly characterized family. Members of the RLCK VI_A class of dicots have a unique characteristic: their activity is regulated by Rho-of-plants (ROP) GTPases. The biological function of one of these kinases was investigated using a T-DNA insertion mutant and RNA interference. Loss of RLCK VI_A2 function resulted in restricted cell expansion and seedling growth. Although these phenotypes could be rescued by exogenous gibberellin, the mutant did not exhibit lower levels of active gibberellins nor decreased gibberellin sensitivity. Transcriptome analysis confirmed that gibberellin is not the direct target of the kinase; its absence rather affected the metabolism and signalling of other hormones such as auxin. It is hypothesized that gibberellins and the RLCK VI_A2 kinase act in parallel to regulate cell expansion and plant growth. Gene expression studies also indicated that the kinase might have an overlapping role with the transcription factor circuit (PIF4-BZR1-ARF6) controlling skotomorphogenesis-related hypocotyl/cotyledon elongation. Furthermore, the transcriptomic changes revealed that the loss of RLCK VI_A2 function alters cellular processes that are associated with cell membranes, take place at the cell periphery or in the apoplast, and are related to cellular transport and/or cell wall reorganisation.