Pectins: structure, biosynthesis, and oligogalacturonide-related signaling.

While the chemical nature of reactive oxygen species (ROS) dictates that they are potentially harmful to cells, recent genetic evidence suggests that in planta purely physicochemical damage may be much more limited than previously thought. The most potentially deleterious effect of ROS under most conditions is that at high concentrations they trigger genetically programmed cell suicide events. Moreover, because plants use ROS as second messengers in signal transduction cascades in processes as diverse as mitosis, tropisms and cell death, their accumulation is crucial to plant development as well as defence. Direct ROS signal transduction will ensue only if ROS escape destruction by antioxidants or are otherwise consumed in a ROS cascade. Thus, the major low molecular weight antioxidants determine the specificity of the signal. They are also themselves signal-transducing molecules that can either signal independently or further transmit ROS signals. The moment has come to re-evaluate the concept of oxidative stress. In contrast to this pejorative or negative term, implying a state to be avoided, we propose that the syndrome would be more usefully described as 'oxidative signalling', that is, an important and critical function associated with the mechanisms by which plant cells sense the environment and make appropriate adjustments to gene expression, metabolism and physiology.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2005.01327.x

Oxidant and antioxidant signalling in plants: a re-evaluation of the concept of oxidative stress in a physiological context

I INTRO DUCTION . . . . . . ...... . . . . . . ...... . . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 455 1.1 Criteria of Lignin Detection . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . 457 1.2 Lignin Distribution in the Plant Kingdom: A Reevaluation . . . . . . . . . . . . . . . . . . . . . . . . . 458 1.3 Lignin Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462 2 LIGNIN B IOG ENE SI S AND S TRUCT URE.... .. ... . . .. . . . . . .. . . . . . . . . .. . . . . . . .. . . . ...... . . . 469 2.1 Arogenic Acid . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . """'"'''''''''''''''''''' 470 2.2 p-Coumaric Acid to £and Z-Monolignols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 2.3 Monolignol Transport into the Cell Wall . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . .. . . . . . . . . . . . . . 472 2.4 Lignin Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . .. .. .. . .... . . . . . . . . 473 2.5 Regulation of Lignification . . . . . . . . . . . . . . . . . . . . . . . . .. . " . . "" . . . . . . . . . . . . . . . . . . . . . . ". . . . . . 476 2.6 Lignin Structure . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . .. .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . 477 3 LIGNIN BIO DEGRADATION . . . . . ..... . .... .. . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . .. . 481 3.1 Lignin-like Polymers in White-Rot Fungi .. .. . . . . . . . . . . . . . . . . . . .. .. . . . . . .. ... . .... . . . . . . 481 3.2 Criteria of Lignin Degradation . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 3.3 Lignin Biodegradation by White-Rot Fungi ...... " . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 482 CONCLU SIONS 487

Lignin: Occurrence, Biogenesis and Biodegradation

It is accepted that most fungal avirulence genes encode virulence factors that are called effectors. Most fungal effectors are secreted, cysteine-rich proteins, and a role in virulence has been shown for a few of them, including Avr2 and Avr4 of Cladosporium fulvum, which inhibit plant cysteine proteases and protect chitin in fungal cell walls against plant chitinases, respectively. In resistant plants, effectors are directly or indirectly recognized by cognate resistance proteins that reside either inside the plant cell or on plasma membranes. Several secreted effectors function inside the host cell, but the uptake mechanism is not yet known. Variation observed among fungal effectors shows two types of selection that appear to relate to whether they interact directly or indirectly with their cognate resistance proteins. Direct interactions seem to favor point mutations in effector genes, leading to amino acid substitutions, whereas indirect interactions seem to favor jettison of effector genes.

Fungal Effector Proteins

Biotic and abiotic stresses stimulate the synthesis of jasmonates and ethylene, which, in turn, induce the expression of genes involved in stress response and enhance defense responses. The cev1 mutant has constitutive expression of stress response genes and has enhanced resistance to fungal pathogens. Here, we show that cev1 plants have increased production of jasmonate and ethylene and that its phenotype is suppressed by mutations that interrupt jasmonate and ethylene signaling. Genetic mapping, complementation analysis, and sequence analysis revealed that CEV1 is the cellulose synthase CeSA3. CEV1 was expressed predominantly in root tissues, and cev1 roots contained less cellulose than wild-type roots. Significantly, the cev1 mutant phenotype could be reproduced by treating wild-type plants with cellulose biosynthesis inhibitors, and the cellulose synthase mutant rsw1 also had constitutive expression of VSP. We propose that the cell wall can signal stress responses in plants.

/pdf/the-arabidopsis-mutant-cev1-links-cell-wall-signaling-to-4xv14s99ux.pdf

The Arabidopsis mutant cev1 links cell wall signaling to jasmonate and ethylene responses.

The heptapeptide Tyr-Gly-Arg-Gly-Asp-Ser-Pro containing the sequence Arg-Gly-Asp (RGD--the essential structure recognised by animal cells in substrate adhesion molecules) was tested on epidermal cells of onion and cultured cells of Arabidopsis upon plasmolysis. Dramatic changes were observed on both types of cells following treatment: on onion cells, Hechtian strands linking the cell wall to the membrane were lost, while Arabidopsis cells changed from concave to convex plasmolysis. A control heptapeptide Tyr-Gly-Asp-Gly-Arg-Ser-Pro had no effect on the shape of plasmolysed cells. Protoplasts isolated from Arabidopsis cells agglutinate in the presence of ProNectinF, a genetically engineered protein of 72 kDa containing 13 RGD sequences: several protoplasts may adhere to a single molecule of ProNectinF. The addition of the RGD-heptapeptide disrupted the adhesion between the protoplasts. Purified plasma membrane from Arabidopsis cells exhibits specific binding sites for the iodinated RGD-heptapeptide. The binding is saturable, reversible, and two types of high affinity sites (Kd1 approximately 1 nM, and Kd2 approximately 40 nM) can be discerned. Competitive inhibition by several structurally related peptides and proteins noted the specific requirement for the RGD sequence. Thus, the RGD-binding activity of Arabidopsis fulfils the adhesion features of integrins, i.e. peptide specificity, subcellular location, and involvement in plasma membrane-cell wall attachments.

High affinity RGD-binding sites at the plasma membrane of Arabidopsis thaliana links the cell wall.

The RGD tripeptide sequence, a cell adhesion motif present in several extracellular matrix proteins of mammalians, is involved in numerous plant processes. In plant-pathogen interactions, the RGD motif is believed to reduce plant defence responses by disrupting adhesions between the cell wall and plasma membrane. Photoaffinity cross-linking of [125I]-azido-RGD heptapeptide in the presence of purified plasma membrane vesicles of Arabidopsis thaliana led to label incorporation into a single protein with an apparent molecular mass of 80 kDa. Incorporation could be prevented by excess RGD peptides, but also by the IPI-O protein, an RGD-containing protein secreted by the oomycete plant pathogen Phytophthora infestans. Hydrophobic cluster analysis revealed that the RGD motif of IPI-O (positions 53–56) is readily accessible for interactions. Single amino acid mutations in the RGD motif in IPI-O (of Asp56 into Glu or Ala) resulted in the loss of protection of the 80-kDa protein from labelling. Thus, the interaction between the two proteins is mediated through RGD recognition and the 80-kDa RGD-binding protein has the characteristics of a receptor for IPI-O. The IPI-O protein also disrupted cell wall-plasma membrane adhesions in plasmolysed A. thaliana cells, whereas IPI-O proteins mutated in the RGD motif (D56A and D56E) did not.

/pdf/high-affinity-recognition-of-a-phytophthora-protein-by-2onf9yxfny.pdf

High affinity recognition of a Phytophthora protein by Arabidopsis via an RGD motif.

Vacuolar efflux of malate and its influence of nitrate accumulation in Catharanthus roseus cells

Chorismate mutase from Quercus pedunculata Ehrh leaves has been purified by ammonium sulfate precipitation, molecular sieving and hydroxyapatite chromatography Some results obtained during the purification suggest the presence, in oak, of two isofunctional forms of the enzyme, the one sensitive, the other insensitive to the action of aromatic amino acids The regulable form exhibits a molecular weight of about 45,000 It is inhibited by tyrosine and by phenylalanine and is activated by tryptophan In addition to its activating properties, this latter compound, endowed with a great affinity for the enzyme, reverses the inhibition due to the two other amino acids



The H+ concentration of the medium plays an important role in the sensitivity of the enzyme with regard to its effectors Inhibition by tyrosine and by phenylalanine is maximal at pH 65, at which value the two ligands present an identical effect At alkaline pH values, the rate of inhibition decreases regularly, tyrosine becoming the most effective inhibitor Activation by tryptophan is particularly acute in a mildly acid medium; at pH 65, this effector increases the enzymatic activity threefold Its action is weak (20% activation) in the optimum pH zone (pH 78) and increases towards the more basic pH values As a result, tryptophan maintains a constant level of enzymatic activity throughout a large pH zone (between 65 and pH 90) The physiological significance of these results is discussed

Huguette Bouyssou

Papers

High affinity RGD-binding sites at the plasma membrane of Arabidopsis thaliana links the cell wall.

High affinity recognition of a Phytophthora protein by Arabidopsis via an RGD motif.

Vacuolar efflux of malate and its influence of nitrate accumulation in Catharanthus roseus cells

Allosteric Properties of Chorismate Mutase from Quercus pedunculata

Taxonomic distribution of isoenzymes of dehydroquinate hydrolyase in the angiosperms