Two seminars IJPB/SPS: Prof. Daniel J. Cosgrove
"Growing cell walls - connecting mechanics to structure", Monday 1st July, 2024 10 am
and "Contrasting Actions of Three Classes of Expansins", Monday 8th July, 2024 2 pm
Monday 1st July, 2024 10 am
For over a century, plant biologists have investigated wall mechanical properties, seeking to relate them to growth and wall structure. Progress has been limited by the lack of molecular models of primary cell walls that quantitatively predict wall mechanical properties and how tensile forces are transmitted between wall polymers. Molecular dynamics models in combination with detail mechanical studies have begun to bridge this gap. In experimental stretching assays, onion epidermal walls show elasticity and plasticity, but little strain-rate dependence, thus differing from classical notions of viscoelastic materials like pectin. Arabidopsis stems behave similarly. A coarse-grained molecular model offers insights into the structure, assembly, and mechanics of primary cell walls. Noncovalent adhesion between cellulose microfibrils enables formation of a strong yet extensible fibrillar network, potentially modulated by pectins and hemicelluloses. Wall elasticity is based on straightening/bending of the cellulose network, plasticity emerges from force-driven sliding of aligned cellulose-cellulose junctions and the yield threshold depends on the strength of adhesion between cellulose microfibrils. Plasticity and creep are two forms of irreversible wall deformation that differ in their biological roles, the timescale of deformation, the wall stress conditions under which deformation occurs, and the involvement of protein-mediated wall loosening (e.g. by expansins).
Invitation: Rawen Ben Malek et Grégory Mouille, contact, "Cell to Cell Adhesion and Communication" ACCI
Monday 8th July, 2024 2 pm
Expansins comprise an ancient group of cell wall loosening proteins ubiquitous in land plants and their algal ancestors. During cell growth, they facilitate passive yielding (creep) of the wall’s cellulose network to turgor-generated tensile stresses, without evidence of enzymatic activity. Expansins are also implicated in fruit softening and other developmental processes and in adaptive responses to environmental stresses and pathogens. The major expansin families in plants include α-expansins (EXPAs) that act on cellulose-cellulose junctions and β-expansins (EXPBs) that can act on xylans, but may have other targets as well. EXPAs mediate ‘acid growth’ which contributes to wall enlargement by auxin and other growth agents. In Arabidopsis, EXPAs are encoded by 26 genes divided into 11 ancient clades based on their sequence and microsynteny analysis. A long outstanding question is whether the various expansin proteins are functionally equivalent in terms of their wall loosening activity. Because recombinant expression of plant expansins has proved difficult, it has been challenging to address this question satisfactorily. During the seminar will be discussed recent attempts to resolve this point by Daniel J. Cosgrove et al.. EXPA7 and EXPA18 are specifically expressed in and required for root hair elongation beyond the early initiation stage. Using CRISPR the hairless double mutant expa7/expa18 has been created to test the functionality of expansin genes by genetic complementation of the root hair phenotype. The results have brought some surprises that will be discussed. The second major group of plant expansins are EXPBs whose activities are known mainly from a maize pollen protein. Its function differs from EXPA characterized to date, in that it releases arabinoxylans from grass cell walls, particularly from the middle lamella which may be its prime target in the grass stigma and style. Microbial expansins (designated EXLX) comprise a third group of diverse proteins. The genomes of diverse microbes, including many plant pathogens, encode EXLXs, which are largely unexplored. We have surveyed 200 microbial expansin genes for their expression in E. coli and their ability to bind cellulose and to loosen cell walls, which is very different than the action of plant expansins. There is still much to be discovered in the mechanism and biological roles of these unusual proteins.
Invitation: Heman Höfte, "Primary Cell Wall" PAR team
Prof. Daniel J. Cosgrove, Department of Biology, Penn State University, USA
In connection with the research developed at theInstitute Jean-Pierre Bourgin for Plant Sciences.
For over a century, plant biologists have investigated wall mechanical properties, seeking to relate them to growth and wall structure. Progress has been limited by the lack of molecular models of primary cell walls that quantitatively predict wall mechanical properties and how tensile forces are transmitted between wall polymers. Molecular dynamics models in combination with detail mechanical studies have begun to bridge this gap. In experimental stretching assays, onion epidermal walls show elasticity and plasticity, but little strain-rate dependence, thus differing from classical notions of viscoelastic materials like pectin. Arabidopsis stems behave similarly. A coarse-grained molecular model offers insights into the structure, assembly, and mechanics of primary cell walls. Noncovalent adhesion between cellulose microfibrils enables formation of a strong yet extensible fibrillar network, potentially modulated by pectins and hemicelluloses. Wall elasticity is based on straightening/bending of the cellulose network, plasticity emerges from force-driven sliding of aligned cellulose-cellulose junctions and the yield threshold depends on the strength of adhesion between cellulose microfibrils. Plasticity and creep are two forms of irreversible wall deformation that differ in their biological roles, the timescale of deformation, the wall stress conditions under which deformation occurs, and the involvement of protein-mediated wall loosening (e.g. by expansins).
Invitation: Rawen Ben Malek et Grégory Mouille, contact, "Cell to Cell Adhesion and Communication" ACCI
Monday 8th July, 2024 2 pm
Expansins comprise an ancient group of cell wall loosening proteins ubiquitous in land plants and their algal ancestors. During cell growth, they facilitate passive yielding (creep) of the wall’s cellulose network to turgor-generated tensile stresses, without evidence of enzymatic activity. Expansins are also implicated in fruit softening and other developmental processes and in adaptive responses to environmental stresses and pathogens. The major expansin families in plants include α-expansins (EXPAs) that act on cellulose-cellulose junctions and β-expansins (EXPBs) that can act on xylans, but may have other targets as well. EXPAs mediate ‘acid growth’ which contributes to wall enlargement by auxin and other growth agents. In Arabidopsis, EXPAs are encoded by 26 genes divided into 11 ancient clades based on their sequence and microsynteny analysis. A long outstanding question is whether the various expansin proteins are functionally equivalent in terms of their wall loosening activity. Because recombinant expression of plant expansins has proved difficult, it has been challenging to address this question satisfactorily. During the seminar will be discussed recent attempts to resolve this point by Daniel J. Cosgrove et al.. EXPA7 and EXPA18 are specifically expressed in and required for root hair elongation beyond the early initiation stage. Using CRISPR the hairless double mutant expa7/expa18 has been created to test the functionality of expansin genes by genetic complementation of the root hair phenotype. The results have brought some surprises that will be discussed. The second major group of plant expansins are EXPBs whose activities are known mainly from a maize pollen protein. Its function differs from EXPA characterized to date, in that it releases arabinoxylans from grass cell walls, particularly from the middle lamella which may be its prime target in the grass stigma and style. Microbial expansins (designated EXLX) comprise a third group of diverse proteins. The genomes of diverse microbes, including many plant pathogens, encode EXLXs, which are largely unexplored. We have surveyed 200 microbial expansin genes for their expression in E. coli and their ability to bind cellulose and to loosen cell walls, which is very different than the action of plant expansins. There is still much to be discovered in the mechanism and biological roles of these unusual proteins.
Invitation: Heman Höfte, "Primary Cell Wall" PAR team
Prof. Daniel J. Cosgrove, Department of Biology, Penn State University, USA
In connection with the research developed at theInstitute Jean-Pierre Bourgin for Plant Sciences.
Back
