Plant Cell Wall
The plant cell wall is a natural and developmentally dynamic nanostructure consisting of the polymers cellulose, cross-linking glycans, pectins and structural proteins. The variable composition of the wall matrix in a plant species is determined within a complex interaction of developmental or stress cues with wall precursor biosynthesis and cell wall modification in situ, and reflects its local structural, chemical and mechanical requirements. Despite considerable efforts, the question of how changes in the wall nanostructure relate to changes in its biophysical properties remains elusive. In this laboratory we have investigated how the structural protein, extensin, and its cross-linking into a three-dimensional network, can alter cell wall properties. Recently, we were able to demonstrate that extensin cross-linking by endogenous extensin peroxidases causes primary cell wall dehydration, leading to the formation of a thinner and denser matrix, with significant consequences to wall polymer spacing and thermomobility. The results suggest the formation of the extensin network may be one of the main means by which the plant effects localised changes in primary wall rigidity during the formation of cell-cell contacts and the regulation of cell elongation.
The plant cell wall and apoplast-cell membrane interface also hosts a plethora of proteins with functions ranging from matrix modification in situ to the transduction of signals from the environment to mobilise adaptive responses. A further area of research therefore concerns changes in the apoplast proteome in response to environmental stress, a major part of which is mobilised or regulated by reactive oxygen species (ROS) signalling. We have chosen wounded Medicago as the model system for study. A robust data set of 90 apoplastic proteins was identified, a third of which was shown to be wound-responsive. By using pharmacological inhibitors of ROS production, we were able to identify those wound-responsive proteins mobilised by ROS signals originating within the first 3 min after wounding. The results so far obtained with this reproducible system form the basis of on-going work to identify early-activated components of ROS signalling pathways in stressed Medicago.
A new area of research concerns the comparative exploration of Ascomycota secretomes for enzyme mixtures appropriate for the biodegradation of lignocellulosic substrates, including those destined for the production of bioethanol. In conjunction with the laboratory of Physiology of Environmentally Conditioned Microbiota, we have recently used both Gel-based MALDI-TOF/TOF and 1D LC-MS to explore the secretome of Neurospora sitofila, a major fungal habitant on maturing cork planks, and which has possible consequences on cork stopper properties. The data has revealed a surprising complexity in secreted proteins, ranging from abundant endo and exocelluloses, to minor constituents consisting of other glycolytic hydrolases and enzymes active against aromatic wall compounds.
- Luis Goulão, Invited Researcher
- Ada Dorothea Vatulescu, PhD Student
- Samarpita Lahiri, Undergraduate Student
- Nelson C. Soares, Jolanta Wojtkowska, Phil A. Jackson (2011). A proteomic analysis of the wound response in Medicago leaves reveals the early activation of a ROS-sensitive signal pathway. J. Proteomics. DOI:10.1016/j.jprot.2011.03.017
- Luis F. Goulao, Sara Vieira-Silva and Phil A. Jackson (2011). Association of hemicellulose- and pectin-modifying gene expression with Eucalyptus globulus secondary growth. Plant Phys. & Biochem. DOI:10.1016/j.plaphy.2011.02.020
- Silva Pereira, C., Ribeiro, M. J., Vatulescu, A. D., Kacurakova, M., Findlay, K., MacDougall, A.J. and Jackson, P. A. (2011). Extensin network formation in Vitis vinifera callus cells is an essential and causal event in rapid and H2O2-induced reduction in primary cell wall hydration. BMC Plant Biology 2011, 11:106. DOI:10.1186/1471-2229-11-106
A parede celular das plantas é uma estrutura complexa que tem inúmeras proteínas importantes para a sua construção, modificação e defesa, e para a transmissão de sinais do exterior para o interior da célula, que permite à planta adaptar-se durante o seu desenvolvimento e em condições de stress. O Laboratório de Parede Celular das Plantas investiga as proteínas da parede celular com o intuito de alargar o nosso conhecimento sobre relevantes processos bioquímicos e moleculares que ocorrem nesta importante estrutura.
One major activity in 2006-2007 was directed towards the role of apoplastic proteins in the response to plant wounding. Plant wounding occurs via abiotic stress, such as hail and wind, but also biotic factors including herbivore feeding, and can cause considerable damage to economically important crops. Plants have developed the means to reduce the damage caused by such factors, not the least of which is the production of herbivore deterrents and rapid wound-healing to prevent facultative pathogen ingress. Despite the importance of these defensive responses, the underlying biochemical and molecular bases involved in their coordination remain poorly understood. We have established a robust data-set of the Medicago leaf apoplast proteome, currently covering 108 unique proteins. Using this proteomic data set and pharmacological inhibitors, we have recently established that the apoplast is an important site for the expression of early defensive measures to wounding, and that reactive oxygen species (ROS)-signalling is one of the early regulatory pathways involved.
A further activity (2007) has been directed to extensin peroxidases (EPs), which have proposed as the class III peroxidases responsible for extensin network formation in muro. Several lines of evidence indicates that we have successfully identified such a peroxidase in grapevine, including exceptionally high extensin cross-linking activities in vitro and in muro, and its co-localisation with extensin in planta. Structural modelling of this EP reveals some interesting topological features surrounding the substrate access channel, which might promote closer interaction of this EP with its macromolecular substrate, extensin. We now intend to pursue finer structural and biochemical studies of the interaction this EP has with extensin-like small peptides via crystallography, NMR and RAMAN.