Abstract
The plant cell wall is an abundant and renewable resource for lignocellulosic applications such as the production of biofuel. Due to structural and compositional complexities, the plant cell wall is, however, recalcitrant to hydrolysis and extraction of platform sugars. A cell wall engineering strategy to reduce this recalcitrance makes use of microbial cell wall modifying enzymes that are expressed directly in plants themselves. Previously, we constructed transgenic Arabidopsis thaliana constitutively expressing the fungal hemicellulases: Phanerochaete carnosa glucurnoyl esterase (PcGCE) and Aspergillus nidulans α-arabinofuranosidase (AnAF54). While the PcGCE lines demonstrated improved xylan extractability, they also displayed chlorotic leaves leading to the hypothesis that expression of such enzymes in planta resulted in plant stress. The objective of this study is to investigate the impact of transgenic expression of the aforementioned microbial hemicellulases in planta on the host arabidopsis. More specifically, we investigated transcriptome profiles by short read high throughput sequencing (RNAseq) from developmentally distinct parts of the plant stem. When compared to non-transformed wild-type plants, a subset of genes was identified that showed differential transcript abundance in all transgenic lines and tissues investigated. Intriguingly, this core set of genes was significantly enriched for those involved in plant defense and biotic stress responses. While stress and defense-related genes showed increased transcript abundance in the transgenic plants regardless of tissue or genotype, genes involved in photosynthesis (light harvesting) were decreased in their transcript abundance potentially reflecting wide-spread effects of heterologous microbial transgene expression and the maintenance of plant homeostasis. Additionally, an increase in transcript abundance for genes involved in salicylic acid signaling further substantiates our finding that transgenic expression of microbial cell wall modifying enzymes induces transcriptome responses similar to those observed in defense responses.
Highlights
Plant cell walls are primarily composed of lignocellulose, which represents a structural complex of cellulose, hemicellulose, and lignin cross-linked through various covalent and non-covalent interactions [1]
The high cost of the enzymes required for lignocellulosic fractionation and hydrolysis remains a major hurdle that needs to be overcome for the adoption of economically viable lignocellulosic applications [3]
Transcriptomes from non-transformed wild-type arabidopsis Columbia 0 (Col-0) were included for comparison
Summary
Plant cell walls are primarily composed of lignocellulose, which represents a structural complex of cellulose, hemicellulose, and lignin cross-linked through various covalent and non-covalent interactions [1]. One barrier to the aforementioned lignocellulosic applications is the biological recalcitrance of plant cell walls, and in particular, resistance to enzymatic hydrolysis This is due in part to the presence of lignin as a physical barrier that is thought to surround cellulose fibrils resulting in a multitude of non-specific molecular interactions, limited accessibility, and inhibition of enzymatic activities [2]. Such hindrance leads to an increase in enzyme loading, hydrolysis time, and the requirement of additional pretreatment procedures. The high cost of the enzymes required for lignocellulosic fractionation and hydrolysis remains a major hurdle that needs to be overcome for the adoption of economically viable lignocellulosic applications [3]
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