How to make a tumour: cell type specific dissection of Ustilago maydis-induced tumour development in maize leaves.

The biotrophic fungus Ustilago maydis causes smut disease on maize (Zea mays), which is characterized by immense plant tumours. To establish disease and reprogram organ primordia to tumours, U. maydis deploys effector proteins in an organ-specific manner. However, the cellular contribution to leaf tumours remains unknown. We investigated leaf tumour formation at the tissue- and cell type-specific levels. Cytology and metabolite analysis were deployed to understand the cellular basis for tumourigenesis. Laser-capture microdissection was performed to gain a cell type-specific transcriptome of U. maydis during tumour formation. In vivo visualization of plant DNA synthesis identified bundle sheath cells as the origin of hyperplasic tumour cells, while mesophyll cells become hypertrophic tumour cells. Cell type-specific transcriptome profiling of U. maydis revealed tailored expression of fungal effector genes. Moreover, U. maydis See1 was identified as the first cell type-specific fungal effector, being required for induction of cell cycle reactivation in bundle sheath cells. Identification of distinct cellular mechanisms in two different leaf cell types and of See1 as an effector for induction of proliferation of bundle sheath cells are major steps in understanding U. maydis-induced tumour formation. Moreover, the cell type-specific U. maydis transcriptome data are a valuable resource to the scientific community.

Cell wall modification in tobacco by differential targeting of recombinant endoglucanase from Trichoderma reesei.

BACKGROUND: The development of transgenic plants as a production platform for biomass-degrading enzymes is a promising tool for an economically feasible allocation of enzymes processing lignocellulose. Previous research has already identified a major limitation of in planta production such as interference with the structure and integrity of the plant cell wall resulting in a negative influence on plant growth and development. RESULTS: Here, we describe the in planta expression of endoglucanase TrCel5A from the mesophilic fungus Trichoderma reesei with differential intracellular targeting and evaluate its impact on the tobacco cell wall composition. Targeting of the enzyme to the apoplast leads to distinct changes in cell polysaccharides such as glucose level in the matrix polysaccharides (MPS). These effects are combined with severe changes in plant development. Retention of TrCel5A in the endoplasmic reticulum (ER) could avoid visible effects on plant growth under the chosen conditions, but exhibits changes in the composition of the MPS. CONCLUSIONS: These results give new insights into the complex interaction of heterologous cellulase expression with cell wall development and it outlines novel promising strategies to engineer plant cell walls for improved biomass processing.

Ethanol inducible expression of a mesophilic cellulase avoids adverse effects on plant development.

BACKGROUND: Plant-produced biomass-degrading enzymes are promising tools for the processing of lignocellulose to fermentable sugars. A major limitation of in planta production is that high-level expression of such enzymes could potentially affect the structure and integrity of the plant cell wall and negatively influence plant growth and development. RESULTS: Here, we evaluate the impact on tobacco plant development of constitutive versus alcohol-inducible expression of the endoglucanase TrCel5A from the mesophilic fungus Trichoderma reesei. Using this system, we are able to demonstrate that constitutive expression of the enzyme, controlled by the doubled Cauliflower Mosaic Virus promoter, leads to lower cellulose content of the plant combined with severe effects on plant growth. However, using an alcohol-inducible expression of the endoglucanase in the plant leaves, we achieved similar enzymatic expression levels with no changes in the crystalline cellulose content. CONCLUSION: We were able to produce significant amounts of cellulase in the plant leaves without detrimental effects to plant development. These results demonstrate the potential feasibility of an inducible expression system for producing biomass degrading enzymes in plants.