Herman Höfte

• French National Institute for Agriculture, Food, and Environment (INRAE)

P4B (2-phenyl-1-[4-(6-(piperidin-1-yl) pyridazin-3-yl) piperazin-1-yl] butan-1-one) is a novel cellulose biosynthesis inhibitor (CBI) discovered in a screen for molecules to identify inhibitors of Arabidopsis (Arabidopsis thaliana) seedling growth. Growth and cellulose synthesis inhibition by P4B were greatly reduced in a novel mutant for the cellu...

Pressurized cells with strong walls make up the hydrostatic skeleton of plants. Assembly and expansion of such stressed walls depend on a family of secreted RAPID ALKALINIZATION FACTOR (RALF) peptides, which bind both a membrane receptor complex and wall-localized LEUCINE-RICH REPEAT EXTENSIN (LRXs) in a mutually exclusive way. Here we show that, i...

Plant cell wall researchers were asked their view on what the major unanswered questions are in their field. This article summarises the feedback that was received from them in five questions. In this issue you can find equivalent syntheses for researchers working on bacterial, unicellular parasite and fungal systems.

Microscale thermophoresis (MST) is a simple but powerful tool to study the in vitro interaction among biomolecules, and to quantify binding affinities. MST curves describe the change in the fluorescence level of a fluorescent target as a result of an IR-laser-induced temperature change. The degree and nature of the change in fluorescence signal dep...

Assembly of cell wall polysaccharides into specific patterns is required for plant growth. A complex of RAPID ALKALINIZATION FACTOR 4 (RALF4) and its cell wall–anchored LEUCINE-RICH REPEAT EXTENSIN 8 (LRX8)–interacting protein is crucial for cell wall integrity during pollen tube growth, but its molecular connection with the cell wall is unknown. H...

Cells maintain a constant dialog between the extracellular matrix and their plasma membrane to fine tune signal transduction processes. We found that the receptor kinase FERONIA (FER), which is a proposed cell wall sensor, modulates phosphatidylserine plasma membrane accumulation and nano-organization, a key regulator of Rho GTPase signaling in Ara...

One of the many legacies of the work of Michel Caboche is our understanding of plant cell wall synthesis and metabolism thanks to the use of Arabidopsis mutants. Here I describe how he was instrumental in initiating the genetic study of plant cell walls. I also show, with a few examples for cellulose and pectins, how this approach has led to import...

Cadmium (Cd) accumulation is highly variable among Arabidopsis halleri populations. To identify cell wall (CW) components that contribute to the contrasting Cd accumulation between PL22-H (Cd-hyperaccumulator) and I16-E (Cd-excluder), Cd absorption capacity of CW polysaccharides, CW mono- and poly- saccharides contents and CW glycan profiles were c...

The de-methylesterification of the pectic polysaccharide homogalacturonan (HG) by pectin methylesterases (PMEs) is a critical step in the control of plant cell expansion and morphogenesis. Plants have large gene families encoding PMEs but also PME inhibitors (PMEIs) with differ in their biochemical properties. The Arabidopsis thaliana PECTIN METHYL...

A rapidly increasing body of literature suggests that many biological processes are driven by phase separation within polymer mixtures. Liquid-liquid phase separation can lead to the formation of membrane-less organelles, which are thought to play a wide variety of roles in cell metabolism, gene regulation or signaling. One of the characteristics o...

Growth of etiolated Arabidopsis hypocotyls is biphasic. During the first phase, cells elongate slowly and synchronously. At 48hrs after imbibition, cells at the hypocotyl base accelerate their growth. Subsequently, this rapid elongation propagates through the hypocotyl from base to top. It is largely unclear what regulates the switch from slow to f...

The cells of all organisms are sugarcoated with polysaccharides, glycoproteins, and glycolipids. In multicellular organisms these polymers not only have a structural role in the organization of tissues and organs, but also have signaling activities. In the animal extracellular matrix for instance, the negatively charged hyaluronic acid (HA) polymer...

Three types of treatments of miscanthus were performed, alkali, silanization and the combination of both. There is a direct inverse relation between the amount of sugar-containing molecules extracted from miscanthus and the mechanical strength of the concrete blocks. The use of alkali treated stems as fillers increased remarkably the strength of th...

Somatic polyploidy caused by endoreplication is observed in arthropods, molluscs, and vertebrates, but is especially prominent in higher plants where it has been postulated to be essential for cell growth and fate maintenance. However, a comprehensive understanding of the physiological significance of plant endopolyploidy has remained elusive. Here...

The growth of plants, like that of other walled organisms, depends on the ability of the cell wall to yield without losing its integrity. In this context, plant cells can sense the perturbation of their walls and trigger adaptive modifications in cell wall polymer interactions. Catharanthus roseus receptor-like kinase 1-like (CrRLK1L) THESEUS1 (THE...

Plants actively perceive and respond to perturbations in their cell walls which arise during growth, biotic and abiotic stresses. However, few components involved in plant cell wall integrity sensing have been described to date. Using a reverse-genetic approach, we identified the Arabidopsis thaliana leucine-rich repeat receptor kinase MIK2 as an i...

The role of MIK2-LIKE in responses triggered by cellulose biosynthesis inhibition and control of root growth angle. (A) Phylogenetic tree based on homology in the C-terminal domain of MIK2 proteins in Arabidopsis thaliana (A.t.), Arabidopsis lyrata (A.l.) and Brassica rapa (B.r.). Regions homologous to Arabidopsis thaliana MIK2 amino acids 620–1045...

ISX-induced CESA3 internalization in mik2-1 and the1-1 mutant background. (A,B) Confocal images of GFP-CESA3 in cesa3je5, cesa3je5 mik2-1, or cesa3je5 the1-1 genetic background. Four-day-old Arabidopsis seedlings were mock treated or treated with 0.1 μM ISX for 2 h. Panel A displays the cell surface, while panel B displays a cross section through t...

Mik2 and the1 have distinct effects on cell wall structure in the root tip. (A) Quantification of the orientation of cellulose microfibrils relative to the direction of cell elongation in root tips of 7-day-old Arabidopsis seedlings. Values of 3 independent experiments were combined. Error bars represent standard error of n = 10 roots. (B,C) FT-IR...

The role of atlure receptor complex components in response to cellulose biosynthesis inhibition and control of root growth angle. (A) Immune marker gene expression in 13-day-old Arabidopsis seedlings determined by qRT-PCR. Seedlings were mock treated, or treated with 0.6 μM ISX for 9 h. Expression of the immune marker gene CYP81F2 was normalized re...

MIK2, MIK2-LIKE and THE1 expression in different organs. Expression of MIK2, MIK2-LIKE, and THE1 in different organs [80]. (TIF)

MIK2 is not required for hypocotyl growth reduction in prc1-1 genetic background. Five-day-old seedlings grown in an upright position in the dark on MS agar medium supplemented with 1% sucrose. Hypocotyl length was quantified. Error bars represent standard error of n = 18 biological replicas. Different letters indicate statistically significant dif...

Biochemical analysis of cell wall composition in Col-0, mik2-1, the1-1, and mik2-1 the1-1 plants. Levels of cellulose, pectin (galacturonic acid (GA)), and monosaccharides derived from hemi-cellulose or pectin, in roots of 7-day-old Arabidopsis seedlings. Values are expressed per mg root tissue. Depicted is the average of four independent experimen...

Root tip morphology in mik2-1, the-1 and mik2-1 the1-1. mik2-1, the1-1 and mik2-1 the1-1 mutants do not display any apparent defects in phloem continuity or root meristem morphology. (A) Confocal microscopy pictures of the root meristem of 7-day-old seedlings of the indicated genotypes stained with propidium iodide (red). Protophloem is visible as...

Dry weight of mik2-1, the1-1 and mik2-1 the1-1 after mock or NaCl treatment. Dry weight of Arabidopsis plants treated with or without NaCl, as described in Fig 4B. Different letters indicate statistically significant differences between genotypes (Left panel: ANOVA and Holm-Sidak test (p < 0.05), right panel: Kruskal-Wallis ANOVA on ranks followed...

Characterization of MIK2. (A) Gene models for MIK2 indicating the positions of the T-DNA insertions (yellow triangles), and the primers (green arrows) used for detection of MIK2.1 and MIK2.2. (B,C) MIK2.1 and MIK2.2 (B) and immune marker gene (C) expression in 13-day-old Arabidopsis seedlings determined by qRT-PCR. MIK2.1 is the more abundant splic...

The role of THE1 in control of root growth angle, salt tolerance and resistance to F. oxysporum. (A) Nine-day-old Arabidopsis seedlings grown in an upright position (under a 10° angle relative to the direction of gravity) on MS agar medium with 1% sucrose. Root angle relative to the vertical growth axis, and root length were quantified. Error bars...

Assessment of susceptibility of the mik2-1 mutant to bacterial and fungal pathogens. (A) Growth of Pseudomonas syringae pv. tomato DC3000 in Col-0 and mik2-1 mutant plants. The hypersusceptible mutant fls2c was included as a control. Plants were sprayed with a P. syringae bacterial suspension (OD600 = 0.02), and material was harvested two days late...

Because the plant cell wall provides the first line of defence against biotic and abiotic assaults, its functional integrity needs to be maintained under stress conditions. Through a phenotype-based compound screening approach we identified a novel cellulose synthase inhibitor, designated C17. C17 administration depletes cellulose synthase complexe...

A major challenge in plant systems biology is the development of robust, predictive multiscale models for organ growth. In this context it is important to bridge the gap between the, rather well-documented, molecular scale and the organ scale by providing quantitative methods to study within-organ growth patterns. Here, we describe a simple method...

The localization of proteins in specific domains or compartments in the 3D cellular space is essential for many fundamental processes in eukaryotic cells. Deciphering spatial or- ganization principles within cells is a challenging task, in particular because of the large morphological variations between individual cells. We present here an approach...

Complex shapes in biology depend on the ability of cells to shift from isotropic to anisotropic growth during development. In plants, this growth symmetry breaking reflects changes in the extensibility of the cell walls. The textbook view is that the direction of turgor-driven cell expansion depends on the cortical microtubule (CMT)-mediated orient...

The fourth author’s name is spelled incorrectly. The correct name is: Claire L. Alvim-Kamei. The correct citation is: Mansoori N, Timmers J, Desprez T, Alvim-Kamei CL, Dees DCT, Vincken J-P, et al. (2014) KORRIGAN1 Interacts Specifically with Integral Components of the Cellulose Synthase Machinery. PLoS ONE 9(11): e112387. doi:10.1371/journal.pone....

Understanding how developmental and environmental signals control plant cell expansion requires an intimate knowledge of the architecture of the primary cell wall and the chemo-rheological processes that underlie cell wall relaxation. In this review I discuss recent findings that reveal a more prominent role than previously suspected for covalent b...

Polysaccharides are major components of extracellular matrices and are often extensively modified post-synthetically to suit local requirements and developmental programmes. However, our current understanding of the spatiotemporal dynamics and functional significance of these modifications is limited by a lack of suitable molecular tools. Here, we...

Cellulose is synthesized by the so called rosette protein complex and the catalytic subunits of this complex are the cellulose synthases (CESAs). It is thought that the rosette complexes in the primary and secondary cell walls each contains at least three different non-redundant cellulose synthases. In addition to the CESA proteins, cellulose biosy...

Cellulose synthesis is driven by large plasma membrane-inserted protein complexes, which in plants have six-fold symmetry. In Arabidopsis functional cellulose synthesis complexes (CSC) are composed of at least three different cellulose synthase catalytic subunits (CESA) but the actual ratio of the CESA isoforms within the CSCs remains unresolved. I...

Significance Plant growth and development depend on the biosynthesis and remodeling of the cell wall. To coordinate these two processes, surveillance mechanisms have evolved to monitor the state of the cell wall. The brassinosteroid (BR) hormone signaling pathway plays an essential role in growth control and regulates the expression of a plethora o...

The synthesis and composition of cell walls is dynamically adapted in response to many developmental and environmental signals. In this respect, cell wall proteins involved in controlling cell elongation are critical for cell development. Transcriptome analysis identified a gene in Arabidopsis thaliana, which was named proline-rich protein-like, At...

Plant lignocellulosic biomass, mostly composed of cell walls, is one of the largest, mostly untapped, reserves of renewable carbon feedstock on the planet. Energy-rich poly-saccharide polymers of plant cell walls can be broken down to produce fermentable sugars used to produce bioethanol. However, the complex structure of plant cell walls, and in p...

Plant growth and organ formation depend on the oriented deposition of load-bearing cellulose microfibrils in the cell wall. Cellulose is synthesized by a large molecular weight (MW) Cellulose Synthase Complex (CSC), which comprises at least three distinct cellulose synthases (CESAs). Cellulose synthesis in plants or bacteria also requires the activ...

Despite an increasingly detailed understanding of endogenous and environmental growth-controlling signals and their signaling networks, little is known on how these networks are integrated with the cell expansion machinery. Members of the CrRLK1L family control cell wall properties and cell expansion in a variety of developmental and environmental...

The remarkable mechanical strength of cellulose reflects the arrangement of multiple β-1,4-linked glucan chains in a para-crystalline fibril. During plant cellulose biosynthesis, a multimeric cellulose synthesis complex (CSC) moves within the plane of the plasma membrane as many glucan chains are synthesized from the same end and in close proximity...

Background and AimsIn Arabidopsis thaliana, the degree of methylesterification (DM) of homogalacturonans (HGs), the main pectic constituent of the cell wall, can be modified by pectin methylesterases (PMEs). In all organisms, two types of protein structure have been reported for PMEs: group 1 and group 2. In group 2 PMEs, the active part (PME domai...

During cytokinesis a new crosswall is rapidly laid down. This involves the formation at the cell equator of a tubulo-vesicular membrane network (TVN). This TVN evolves into a tubular network (TN) and a planar fenestrated sheet, which extends at its periphery before fusing to the mother cell wall. The role of cell wall polymers in cell plate assembl...

ArabinoGalactan Proteins (AGPs) are a complex family of cell wall proteoglycans, which are thought to have major roles in plant growth and development. Genetic approaches studying AGP function have met limited success so far, presumably due to redundancy within the large gene families encoding AGP backbones. Here we used an alternative approach for...

The new model plant for temperate grasses, Brachypodium distachyon offers great potential as a tool for functional genomics. We have established a sodium azide-induced mutant collection and a TILLING platform, called “BRACHYTIL”, for the inbred line Bd21-3. The TILLING collection consists of DNA isolated from 5530 different families. Phenotypes wer...

Amino acid sequences of putative COMT proteins used for phylogenetic analysis in Figure 3 . (DOCX)

Background Along the root axis of Arabidopsis thaliana, cells pass through different developmental stages. In the apical meristem repeated cycles of division increase the numbers of cells. Upon leaving the meristem, these cells pass the transition zone where they are physiologically and mechanically prepared to undergo subsequent rapid elongation....

240 differentially expressed genes upon 3hr 5μM ACC treatment. The genes (locus identifiers) are presented together with their expression ratio and Bonferroni P-values.

Expression profiles in the root of the genes presented in Table 2. Data were extracted from the Arabidopsis eFP browser. A) ethylene-related genes, B) auxin-related genes, C) AGPs and HRGPs, D) peroxidases, E) 10 most up regulated genes, F) 10 most down regulated genes.

Enriched Gene Ontology (GO) terms in the differentially expressed genes. A) cluster of up regulated genes, B) cluster of down regulated genes, with the legend linking the numbers to the GI terms.

qPCR analysis of the 10 most up and down regulated genes upon 3 hr 5μM ACC addition to Arabidopsis roots. Expression is presented as relative % towards the gene’s expression under control conditions.

Brassinosteroid (BR) signaling is required for normal plant growth as shown by the dwarf phenotype of loss-of-function BR biosynthetic or perception mutants. Despite a detailed understanding of the BR signaling network [1-3], it is not clear how exactly BRs control growth. For instance, genetic sector analysis shows that BRs, in contrast to most ot...

Lignins are complex aromatic heteropolymers that reinforce the cell walls of terrestrial plants. A new study identifies an ATP-binding cassette ABC transporter that pumps a monolignol lignin precursor across the plasma membrane.

Plant cell walls are highly dynamic and heterogeneous structures, which vary between cell types, growth stages but also between microdomains within a single cell wall. In this review, we summarize the imaging techniques using fluorescent tags that are currently being used and which should in the coming years revolutionize our understanding of the d...

How is the extensibility of growing plant cell walls regulated? In the past, most studies have focused on the role of the cellulose/xyloglucan network and the enigmatic wall-loosening agents expansins. Here we review first how in the closest relatives of the land plants, the Charophycean algae, cell wall synthesis is coupled to cell wall extensibil...

Organ growth depends on two distinct, yet integrated, processes: cell proliferation and post-mitotic cell expansion. Although the regulatory networks of plant cell proliferation during organ growth have begun to be unveiled, the mechanisms regulating post-mitotic cell growth remain mostly unknown. Here, we report the characterization of three EXIGU...

Agarose gel electrophoresis of RT-PCR amplification products obtained from CESA8 transcripts. RNA was extracted from exi1-1 (lanes 1, 2) and Ler (lanes 3, 4) rosettes collected 21 DAS, reverse transcribed and PCR amplified using the EXI1_3bF and EXI1_3R primers (Table S1). Lane 5: 1 kb DNA ladder (Invitrogen). (TIF)

Additive phenotype of the exi2 exi5 double mutant. Pictures of (A) exi2 and (B) exi2 exi5 were taken 27 DAS. Scale bars indicate 3 mm. (TIF)

Mutants carrying T-DNA insertional alleles of the EXI genes. Rosettes are shown from (A) Col-0, (B) irx1–5 (Salk_026812), (C) irx5-4 (Salk_084627) and (D) irx3–4 (Salk_029940). Pictures were taken 21 DAS. Scale bars indicate 2 mm. (TIF)

Primers used in this work. (DOCX)

Plant development is highly plastic and dependent on light quantity and quality monitored by specific photoreceptors. Although we have a detailed knowledge of light signaling pathways, little is known about downstream targets involved in growth control. Cell size and shape are in part controlled by cellulose microfibrils extruded from large cellulo...

Tissue mechanics have been shown to play a key role in the regulation of morphogenesis in animals [1-4] and may have an equally important role in plants [5-9]. The aerial organs of plants are formed at the shoot apical meristem following a specific phyllotactic pattern [10]. The initiation of an organ from the meristem requires a highly localized i...

Plant leaves and flowers are positioned along the stem in a regular pattern. This pattern, which is referred to as phyllotaxis, is generated through the precise emergence of lateral organs and is controlled by gradients of the plant hormone auxin. This pattern is actively maintained during stem growth through controlled cell proliferation and elong...

It is generally believed that cell elongation is regulated by cortical microtubules, which guide the movement of cellulose synthase complexes as they secrete cellulose microfibrils into the periplasmic space. Transversely oriented microtubules are predicted to direct the deposition of a parallel array of microfibrils, thus generating a mechanically...

Plant cell walls have the remarkable property of combining extreme tensile strength with extensibility. The maintenance of such an exoskeleton creates nontrivial challenges for the plant cell: How can it control cell wall assembly and remodeling during growth while maintaining mechanical integrity? How can it deal with cell wall damage inflicted by...

• We focused on a developmentally regulated growth acceleration in the dark-grown Arabidopsis hypocotyl to study the role of changes in cell wall metabolism in the control of cell elongation. • To this end, precise transcriptome analysis on dissected dark-grown hypocotyls, Fourier transform infrared (FT-IR) microspectroscopy and kinematic analysis...

A mutant of tomato (Solanum lycopersicum) with reduced abscisic acid (ABA) production (sitiens) exhibits increased resistance to the necrotrophic fungus Botrytis cinerea. This resistance is correlated with a rapid and strong hydrogen peroxide-driven cell wall fortification response in epidermis cells that is absent in tomato with normal ABA product...

Plant shoots have thick, polylamellate outer epidermal walls based on crossed layers of cellulose microfibrils, but the involvement of microtubules in such wall lamellation is unclear. Recently, using a long-term movie system in which Arabidopsis seedlings were grown in a biochamber, the tracks along which cortical microtubules move were shown to u...

How are the different secondary cell wall deposition patterns generated in the vascular cells of plants? The use of a novel Arabidopsis mesophyll cell culture that transdifferentiates into vascular cells shows a crucial role for a complex of two microtubule-binding proteins.

Plant growth and development depend on anisotropic cell expansion. Cell wall yielding provides the driving force for cell expansion, and is regulated in part by the oriented deposition of cellulose microfibrils around the cell. Our current understanding of anisotropic cell expansion combines hypotheses generated by more than 50 years of research. H...

Three subfamilies of grasses, the Ehrhartoideae, Panicoideae and Pooideae, provide the bulk of human nutrition and are poised to become major sources of renewable energy. Here we describe the genome sequence of the wild grass Brachypodium distachyon (Brachypodium), which is, to our knowledge, the first member of the Pooideae subfamily to be sequenc...

Plant cell walls, like a multitude of other biological materials, are natural fiber-reinforced composite materials. Their mechanical properties are highly dependent on the interplay of the stiff fibrous phase and the soft matrix phase and on the matrix deformation itself. Using specific Arabidopsis thaliana mutants, we studied the mechanical role o...

A recent report shows that cells in the Arabidopsis apical meristem orientate their cortical microtubules along mechanical stress patterns generated during tissue morphogenesis. This in turn is expected to influence the mechanical properties of the cell via the modification of the cortical microtubule network and the cell wall. This feedback loop c...

Plant growth and organ formation depend on the oriented deposition of load-bearing cellulose microfibrils in the cell wall. Cellulose is synthesized by plasma membrane-bound complexes containing cellulose synthase proteins (CESAs). Here, we establish a role for the cytoskeleton in intracellular trafficking of cellulose synthase complexes (CSCs) thr...

Plant organs are produced from meristems in a characteristic pattern. This pattern, referred to as phyllotaxis, is thought to be generated by local gradients of an information molecule, auxin. Some studies propose a key role for the mechanical properties of the cell walls in the control of organ outgrowth. A major cell-wall component is the linear...

The growth of plant cells involves a constant adjustment of synthesis and rearrangement of cell wall polymers. Recently, three plasma membrane-bound receptor kinases related to CrRLK1 have been shown to be involved in the negative control of cell growth in different contexts. THESEUS1 is activated in mutants deficient for cellulose and may act as a...

Pectins are a family of highly complex multifunctional cell wall polysaccharides. Little is known on the relation between pectin structure, hydrodynamic properties, and cellular function. In this study, we took advantage of the Arabidopsis pectin mutant quasimodo2 (qua2), which specifically lacks half of its homogalacturonan blocks, to study the re...

The dissolution of cotton fibres has been studied at different development stages before and after the onset of secondary wall deposition in solvents of varying quality. We show that the dissolution of the primary wall is inefficient even in good solvents. In moderately good solvents, the inside of the secondary wall dissolves by fragmentation, whe...

In all land plants, cellulose is synthesized from hexameric plasma membrane complexes. Indirect evidence suggests that in vascular plants the complexes involved in primary wall synthesis contain three distinct cellulose synthase catalytic subunits (CESAs). In this study, we show that CESA3 and CESA6 fused to GFP are expressed in the same cells and...

The recent visualization of the motion of fluorescently labeled cellulose synthase complexes by Alexander Paredez and colleagues heralds the start of a new era in the science of the plant cell wall. Upon drug-induced complete depolymerization, the movement of the complexes does not become disordered but instead establishes an apparently self-organi...

A major challenge is to understand how the walls of expanding plant cells are correctly assembled and remodeled, often in the presence of wall-degrading micro-organisms. Plant cells, like yeast, react to cell-wall perturbations as shown by changes in gene expression, accumulation of ectopic lignin, and growth arrest caused by the inhibition of cell...

Pectins are a family of complex cell-wall polysaccharides, the biosynthesis of which remains poorly understood. We identified dwarf mutants with reduced cell adhesion at a novel locus, QUASIMODO2 (QUA2). qua2-1 showed a 50% reduction in homogalacturonan (HG) content compared with the wild type, without affecting other cell-wall polysaccharides. The...

The composition and permeability of the cuticle has a large influence on its ability to protect the plant against various forms of biotic and abiotic stress. WAX INDUCER1 (WIN1) and related transcription factors have recently been shown to trigger wax production, enhance drought tolerance, and modulate cuticular permeability when overexpressed in A...

New findings reveal that many membrane proteins undergo regulated trafficking between intracellular compartments and the plasma membrane. This also appears to be a common regulatory mechanism in the control of cell wall metabolism.

Quantitative trait loci (QTL) analysis was used to identify genes underlying natural variation in primary cell wall composition in Arabidopsis (Arabidopsis thaliana). The cell walls of dark-grown seedlings of a Bay-0 x Shahdara recombinant inbred line population were analyzed using three miniaturized global cell wall fingerprinting techniques: mono...