Genetic transformation of lignin degrading fungi facilitated by Agrobacterium tumefaciens

Ramesh C Kuhad,Krishna K Sharma

doi:10.1186/1472-6750-10-67

Abstract

BackgroundWhite-rot fungi are primarily the major degraders of lignin, a major obstacle for commercial exploitation of plant byproducts to produce bioethanol and other industrially important products. However, to improve their efficacy for lignin degradation, it has become necessary to genetically modify these organisms using appropriate vectors. Agrobacterium tumefaciens, a soil phytopathogenic bacterium, generally transforms plants by delivering a portion of the resident Ti- plasmid, the T-DNA (transfer DNA). The trans-Kingdom gene transfer is initiated by the activity of Ti-plasmid encoded vir (virulence) genes in response to low-molecular-mass phenolic compounds such as acetosyringone. A. tumefaciens played a major role in plant genetic engineering and basic research in molecular biology, accounting for nearly 80% of the transgenic plants produced so far. Initially, it was believed that only dicotyledons, gymnosperms and a few monocotyledonous species could be transformed by this bacterium; but recent reports have totally changed this scenario by demonstrating that many 'recalcitrant' species not included in its natural host range can also be transformed, especially filamentous fungi.ResultsThis paper describes an efficient and convenient Agrobacterium-mediated gene transformation system for successful delivery of T-DNA, carrying the genes coding for β-glucuronidase (uidA), green fluorescent protein (gfp) and hygromycin phosphotransferase (hpt) to the nuclear genome of lignin degrading white-rot fungi such as Phanerochaete chrysosporium, Ganoderma sp. RCKK-02, Pycnoporous cinnabarinus, Crinipellis sp. RCK-1, Pleurotus sajor-caju and fungal isolate BHR-UDSC without supplementation of acetosyringone. The fungal transformants were confirmed by PCR and Southern hybridization. The expression vector pCAMBIA 1304-RCKK was constructed by the addition of GPD promoter from plasmid p416 to the binary vector backbone pCAMBIA1304, which controls uidA and gfp gene. Transmission Electron Microscope (TEM) analysis revealed the attachment of bacterial cells to the fungal hyphae. Transformation frequency varied from 50 to 75% depending on the fungal species used in this study. The transformation efficiency was maximum at 20°C whereas no transfer was observed at temperature above 29°C.ConclusionThese findings provide a rapid and reproducible transformation method without external addition of acetosyringone, which could be useful for improving white-rot fungi for their various biotechnological applications.

Highlights

White-rot fungi are primarily the major degraders of lignin, a major obstacle for commercial exploitation of plant byproducts to produce bioethanol and other industrially important products
The fungal cultures when co-cultured with A. tumefaciens harboring hpt gene resulted in development of hygromycin-resistant (Hygr) mycelia (Figure 2B)
The DNA transfer events were studied by monitoring the transgene associated with T-DNA in Hygr colonies

Summary

Introduction

White-rot fungi are primarily the major degraders of lignin, a major obstacle for commercial exploitation of plant byproducts to produce bioethanol and other industrially important products. To improve their efficacy for lignin degradation, it has become necessary to genetically modify these organisms using appropriate vectors. Agrobacterium tumefaciens, a soil phytopathogenic bacterium, generally transforms plants by delivering a portion of the resident Ti- plasmid, the T-DNA (transfer DNA). Agrobacterium-mediated transformation (AMT) leads to homologous recombination and facilitated gene knock-out. Using diverse Agrobacterium strains and isolates, vectors and number of inoculation and selection techniques, transgenics have been produced, which were previously thought to be ‘recalcitrant’ to Agrobacterium mediated gene transformation. The Agrobacterium mediated transformation of fungal as well as human cell line (HeLa, HEK293 and neuronal PC12 cells) have been reported [9]

Methods

Results

Conclusion