Production and characterization of fungal β-glucosidase and bacterial cellulases by tobacco chloroplast transformation

Abstract

The high capacity of the chloroplast genome to integrate and express transgenes at high levels makes transplastomic technology a good option for overexpressing proteins of interest. This report presents the stable expression of β-glucosidase (bgl1 gene) from Aspergillus niger and two cellulases (celA and celB genes) from Thermotoga neapolitana into the chloroplast genome of tobacco. The pES6, pHM4, pHM5 and pHM6 vectors were derived from the pES4 plasmid containing bgl1, celA-celB, celA and celB synthetic genes, respectively. All of the genes were flanked by a synthetic rrn16 promoter and the 3′UTR from rbcL gene. The integration of the genes into intergenic regions rrn16 and 3′rps12 of the inverted repeats was confirmed by Southern blot analysis. Stable expression and processing of monocistronic mRNA were confirmed by Northern blot analysis, and protein functionality was analysed via enzymatic activity assay. The recombinant enzymes exhibited high enzymatic activity at pH 5 (β-glucosidase: 30.45 U mg−1 of TSP, celA-celB 58 U mg−1 of TSP, celA 49.10 U mg−1 of TSP and celB 48.72 U mg−1 of TSP). In addition, β-glucosidase exhibited high activity at 40 °C, whereas cellulases type A (celA) and type B (celB) showed high activity at 65 °C. NtpES6, NtpHM5 and NtpHM6 plants showed a similar phenotype compared with the wild type plants; however, NtpHM4 plants presented an abnormal phenotype with variegated leaves. This study, demonstrated that hydrolytic genes such as bgl1, celA and celB could be integrated and expressed correctly in the chloroplast genome. This work provides new information on methods and strategies for the expression of hydrolytic enzymes that are potentially useful for biotechnological applications using transplastomic plants.