Chemical genetics uncovers novel inhibitors of lignification, including p-iodobenzoic acid targeting CINNAMATE-4-HYDROXYLASE

Plant secondary-thickened cell walls are characterized by the presence of lignin, a recalcitrant and hydrophobic polymer that provides mechanical strength and ensures long-distance water transport. Exactly the recalcitrance and hydrophobicity of lignin put a burden on the industrial processing efficiency of lignocellulosic biomass. Both forward and reverse genetic strategies have been used intensively to unravel the molecular mechanism of lignin deposition. As an alternative strategy, we introduce here a forward chemical genetic approach to find candidate inhibitors of lignification. A high-throughput assay to assess lignification in Arabidopsis (Arabidopsis thaliana) seedlings was developed and used to screen a 10-k library of structurally diverse, synthetic molecules. Of the 73 compounds that reduced lignin deposition, 39 that had a major impact were retained and classified into five clusters based on the shift they induced in the phenolic profile of Arabidopsis seedlings. One representative compound of each cluster was selected for further lignin-specific assays, leading to the identification of an aromatic compound that is processed in the plant into two fragments, both having inhibitory activity against lignification. One fragment, p-iodobenzoic acid, was further characterized as a new inhibitor of CINNAMATE 4-HYDROXYLASE, a key enzyme of the phenylpropanoid pathway synthesizing the building blocks of the lignin polymer. As such, we provide proof of concept of this chemical biology approach to screen for inhibitors of lignification and present a broad array of putative inhibitors of lignin deposition for further characterization

Endopolyploidy as a potential alternative adaptive strategy for Arabidopsis leaf size variation in response to UV-B

The extent of endoreduplication in leaf growth is group- or even species-specific, and its adaptive role is still unclear. A survey of Arabidopsis accessions for variation at the level of endopolyploidy, cell number, and cell size in leaves revealed extensive genetic variation in endopolyploidy level. High endopolyploidy is associated with increased leaf size, both in natural and in genetically unstructured (mapping) populations. The underlying genes were identified as quantitative trait loci that control endopolyploidy in nature by modulating the progression of successive endocycles during organ development. This complex genetic architecture indicates an adaptive mechanism that allows differential organ growth over a broad geographic range and under stressful environmental conditions. UV-B radiation was identified as a significant positive climatic predictor for high endopolyploidy. Arabidopsis accessions carrying the increasing alleles for endopolyploidy also have enhanced tolerance to UV-B radiation. UV-absorbing secondary metabolites provide an additional protective strategy in accessions that display low endopolyploidy. Taken together, these results demonstrate that high constitutive endopolyploidy is a significant predictor for organ size in natural populations and is likely to contribute to sustaining plant growth under high incident UV radiation. Endopolyploidy may therefore form part of the range of UV-B tolerance mechanisms that exist in natural populations

New members of the tomato ERF family show specific expression pattern and diverse DNA-binding capacity to the GCC box element

Four new members of the ERF (ethylene-response factor) family of plant-speci¢c DNA-binding (GCC box) factors were isolated from tomato fruit (LeERF1^4). Phylogenetic analysis indicated that LeERF2 belongs to a new ERF class, characterized by a conserved N-terminal signature sequence. Expression patterns and cis/trans binding a⁄nities di¡ered between the LeERFs. Combining experimental data and modeled three-dimensional analysis, it was shown that binding a⁄nity of the LeERFs was a¡ected by both the variation of nucleotides surrounding the DNA cis-element sequence and the nature of critical amino acid residues within the ERF domain

Cellular interactions during tracheary elements formation and function

The survival of higher plant species on land depends on the development and function of an efficient vascular system distributing water and minerals absorbed by roots to all aerial organs. This conduction and distribution of plant sap relies on specialized cells named tracheary elements (TEs). In contrast to many other cell types in plants, TEs are functionalized by cell death that hollows the cell protoplast to make way for the sap. To maintain a stable conducting function during plant development, recovery from vascular damages as well as to adapt to environmental changes, TEs are completely dependent on direct cellular interactions with neighboring xylem parenchyma cells (XPs)

Cellular interactions during tracheary elements formation and function

The survival of higher plant species on land depends on the development and function of an efficient vascular system distributing water and minerals absorbed by roots to all aerial organs. This conduction and distribution of plant sap relies on specialized cells named tracheary elements (TEs). In contrast to many other cell types in plants, TEs are functionalized by cell death that hollows the cell protoplast to make way for the sap. To maintain a stable conducting function during plant development, recovery from vascular damages as well as to adapt to environmental changes, TEs are completely dependent on direct cellular interactions with neighboring xylem parenchyma cells (XPs)

Hexokinase 1 is required for glucose-induced repression of bZIP63, At5g22920, and BT2 in Arabidopsis

Simple sugars, like glucose (Glc) and sucrose (Suc), act as signals to modulate the expression of hundreds of genes in plants. Frequently, however, it remains unclear whether this regulation is induced by the sugars themselves or by their derivatives generated in the course of carbohydrate (CH) metabolism. In the present study, we tested the relevance of different CH metabolism and allocation pathways affecting expression patterns of five selected sugar-responsive genes (bZIP63, At5g22920, BT2, MGD2, and TPS9) in Arabidopsis thaliana. In general, the expression followed diurnal changes in the overall sugar availability. However, under steady growth conditions, this response was hardly impaired in the mutants for CH metabolizing/transporting proteins (adg1, sex1, sus1-4, sus5/6, and tpt2), including also hexokinase1 (HXK1) loss- and gain-of-function plants—gin2.1 and oe3.2, respectively. In addition, transgenic plants carrying pbZIP63::GUS showed no changes in reporter-gene-expression when grown on sugar under steady-state conditions. In contrast, short-term treatments of agar-grown seedlings with 1% Glc or Suc induced pbZIP63::GUS repression, which became even more apparent in seedlings grown in liquid media. Subsequent analyses of liquid-grown gin2.1 and oe3.2 seedlings revealed that Glc -dependent regulation of the five selected genes was not affected in gin2.1, whereas it was enhanced in oe3.2 plants for bZIP63, At5g22920, and BT2. The sugar treatments had no effect on ATP/ADP ratio, suggesting that changes in gene expression were not linked to cellular energy status. Overall, the data suggest that HXK1 does not act as Glc sensor controlling bZIP63, At5g22920, and BT2 expression, but it is nevertheless required for the production of a downstream metabolic signal regulating their expression.Originally published in thesis in manuscript form with the title: The metabolic activity of HEXOKINASE 1 is required for glucose-induced repression of bZIP63, At5g22920 and BT2 in Arabidopsis</p

Hexokinase 1 is required for glucose-induced repression of bZIP63, At5g22920, and BT2 in Arabidopsis

Simple sugars, like glucose (Glc) and sucrose (Suc), act as signals to modulate the expression of hundreds of genes in plants. Frequently, however, it remains unclear whether this regulation is induced by the sugars themselves or by their derivatives generated in the course of carbohydrate (CH) metabolism. In the present study, we tested the relevance of different CH metabolism and allocation pathways affecting expression patterns of five selected sugar-responsive genes (bZIP63, At5g22920, BT2, MGD2, and TPS9) in Arabidopsis thaliana. In general, the expression followed diurnal changes in the overall sugar availability. However, under steady growth conditions, this response was hardly impaired in the mutants for CH metabolizing/transporting proteins (adg1, sex1, sus1-4, sus5/6, and tpt2), including also hexokinase1 (HXK1) loss- and gain-of-function plants—gin2.1 and oe3.2, respectively. In addition, transgenic plants carrying pbZIP63::GUS showed no changes in reporter-gene-expression when grown on sugar under steady-state conditions. In contrast, short-term treatments of agar-grown seedlings with 1% Glc or Suc induced pbZIP63::GUS repression, which became even more apparent in seedlings grown in liquid media. Subsequent analyses of liquid-grown gin2.1 and oe3.2 seedlings revealed that Glc -dependent regulation of the five selected genes was not affected in gin2.1, whereas it was enhanced in oe3.2 plants for bZIP63, At5g22920, and BT2. The sugar treatments had no effect on ATP/ADP ratio, suggesting that changes in gene expression were not linked to cellular energy status. Overall, the data suggest that HXK1 does not act as Glc sensor controlling bZIP63, At5g22920, and BT2 expression, but it is nevertheless required for the production of a downstream metabolic signal regulating their expression.Originally published in thesis in manuscript form with the title: The metabolic activity of HEXOKINASE 1 is required for glucose-induced repression of bZIP63, At5g22920 and BT2 in Arabidopsis</p

Cooperative lignification of xylem tracheary elements

The development of xylem tracheary elements (TEs) – the hydro-mineral sap conducting cells - has been an evolutionary breakthrough to enable long distance nutrition and upright growth of vascular land plants. To allow sap conduction, TEs form hollow laterally reinforced cylinders by combining programmed cell death and secondary cell wall formation. To ensure their structural resistance for sap conduction, TE cell walls are reinforced with the phenolic polymer lignin, which is deposited after TE cell death by the cooperative supply of monomers and other substrates from the surrounding living cells

Теоретические основы электротехники: Ч. 1. Электрические цепи постоянного и однофазного переменного тока

Электронный учебно-методический комплекс дисциплины