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Functional Analyses of Laccase Genes from Fusarium oxysporum

Six laccase genes, lcc1, lcc2, lcc3, lcc4, lcc5, and lcc9, of the vascular wilt fungus Fusarium oxysporum were isolated and characterized. All genes have the characteristic conserved domains for copper binding of phenol oxidase enzymes. Targeted inactivation of lcc1, lcc3, and lcc5 resulted in a significant decrease of extracellular laccase activity. Reverse transcription-polymerase chain reaction showed that lcc1, lcc2, and lcc9 were constitutively expressed in culture, whereas lcc3 and lcc5 appeared down and up-regulated, respectively, by PacC. Oxidative stress conditions and phenolic compounds altered the growth rate of the Δlcc3 mutant compared with the wild-type. lcc1, lcc3, and lcc9 were expressed in roots and stems during the infection process. However, inactivation of lcc1, lcc3, and lcc5 had no detectable effects on virulence on tomato plants.