The walls of plant cells play essential roles in many cellular functions, such as providing shape and mechanical support to the different cell types, intercellular communication and defense responses against potential pathogens. Deeper understanding of these functions can be gained by studying cell wall structure, biosynthesis and regulation.
Plant cell walls are basically composed of lignocellulose which comprises different groups of carbohydrate polymers (cellulose, hemicellulose, pectin), and an aromatic polymer (lignin). Together these polymers form a complex network with a large variety of chemical linkages. Plant cell walls have been brought into focus as renewable resources for fuels and basic chemicals. Our research elucidates biosynthetic pathways for cell wall synthesis as well as beneficial traits for subsequent lignocellulose processing using combined wet and dry lab approaches.
Plants invest a significant amount of their resources into the production of an extracellular matrix built primarily of polysaccharides. Cell wall polysaccharides represent the most abundant and useful polymers on Earth, but their biosynthesis and functions are still poorly understood. We tackle these challenges using Arabidopsis thaliana seed coat epidermal (SCE) cells as a model system.
Arabidopsis SCE cells synthesize copious amounts of cell wall polysaccharides at a very specific stage of development and secrete them in a polar manner. Upon hydration of mature seeds, these polymers are released as a large mucilage capsule that can be easily stained or extracted for chemical analysis. More than 35 genes are known to affect mucilage properties, but only four of these encode putative glycosyltransferases (Voiniciuc et al., 2015). This highlights that despite many detailed studies of Arabidopsis mucilage production, most of the molecular players directly involved in polysaccharide synthesis in SCE cells remain to be discovered. Through a co-expression search for MUCILAGE-RELATED (MUCI) genes, we have identified additional enzymes involved in the production of cell wall polymers. Surprisingly, MUCI genes are indispensable for the production of hemicellulose, rather than pectin, the most abundant mucilage polymer. Biochemical data indicates that Arabidopsis mucilage is more than just pectin and contains at least two hemicelluloses [1]. In addition to revealing novel players involved in cell wall synthesis, the MUCI screen demonstrates that hemicelluloses are essential for the architecture of mucilage, despite their low abundance.
[1] C. Voiniciuc, B. Yang, M. H.-W. Schmidt, M. Günl, B. Usadel (2015) “Starting to gel: How Arabidopsis seed coat epidermal cells produce specialized secondary cell walls” International Journal of Molecular Sciences 16(2):3452-73
Plant cell walls are a major resource which can be used for biofuels or as raw materials. Whilst the last few years have seen major advances in our understanding of how the plant cell walls are constructed and can be decomposed, we are still far away from tailoring lignocellulose to our needs. We therefore investigate the cell wall composition of naturally occurring plant species or variants (e.g. wild relatives) to identify potentially beneficial traits that could be introduced into modern breeding varieties. Specifically, we focus on the use of residual material such as plant parts that would end up as straw and thus don’t compete with food or feed usage. To identify new candidate genes involved in specific cell wall traits Quantitative Trait Loci (QTLs) identification and Genome-Wide Association Studies (GWAS) are used on different plant accession such as Arabidopsis thaliana or introgression lines (ILs) such as tomato.
A detailed understanding of plant cell wall architecture and biosynthesis is a prerequisite for an optimal industrial utilization of lignocellulose. The identification of beneficial traits for biomass fractionation or hydrolysis is required for the implementation of crop plants into economically feasible processes.
The group has established standardized techniques for a detailed lignocellulose characterization. This platform is used to evaluate different types of biomass such as novel energy crops like Sida hermaphrodita but also transgenic biomass modified for enhanced processing.
Enzymatic conversion of lignocellulose is a key technology in novel bio-refineries and this technology is currently the subject of intensive research. The group uses several bioinformatics tools based on sequence homology, domain structure and database analysis to build models for the identification of novel enzyme for lignocellulose degradation such as glycosyl-hydrolases, esterases, laccases. The established models can then be used for high throughput database screening or whole genome screening.