Abstract

Laccases are widely distributed oxido-reductases that catalyse the biological oxidation-reduction of polyphenols with a concomitant reduction of molecular oxygen to water. Genome analysis ofMagnaporthe grisea using bioinformatic approach showed the presence of multiple laccases, which encode proteins with three domains of multicopper oxidase. The transcript levels of all M. grisea laccases were analysed by quantitative RT-PCR, in order to study their expression patterns in normal and nitrogen starved conditions. The highest relative expression was observed forMGG_08127 (MgLac1) in normal conditions. The highest induction was observed forMGG_02876 (MgLac2) in nitrogen starvation. Since total fungal protein extracts would contain multiple laccases, heterologous gene expression, purification and further enzyme characterisation was carried out to analyse the function of these two laccases from M. grisea. Thus, we identified a novel multifunctional laccase, MgLac2, in M. grisea which showed lignin-like dye decolourising activity, 1, 8-dihydroxynapthalene (DHN) polymerisation ability and also ferroxidase activity. Its optimum pH and maximum thermostability were at 4 to 4.5 and 30°C, respectively. MgLac1 also showed dye decolourization activity, its optimum pH and maximum thermostability were at 4 to 5 and 30°C, respectively. We found that the laccases expressed in normal conditions and in conditions which mimic pathogenicity are different biochemically.

Key words: Magnaporthe grisea, laccase, dye decolourization, DHN polymerisation, ferroxidaseactivity, glutathione-S-transferase (GST).