Isolation and characterisation of a family of laccases in maize

Plant laccases are enzymes that have been proposed to participate in the last step of lignin biosynthesis. The polymerisation event remains still much unknown, implicating other enzymes such as peroxidases. To gain more insight in how this polymerisation process takes place in maize, we isolated by differential screening of an elongation maize root cDNA library four cDNA clones encoding a family of laccases. Three of them (ZmLac2, ZmLac4, ZmLac5) were basic enzymes, while one of them (ZmLac3) was an acidic enzyme. Southern analysis indicates that laccases belong to a multigene family in maize. Phylogenetic analysis reveals that ZmLac2, ZmLac4, and ZmLac5 are closely related enzymes, whereas ZmLac3 is a slightly different enzyme. The pattern of mRNA accumulation of ZmLac2, ZmLac3, ZmLac4, and ZmLac5 genes correlates with the maize regions undergoing lignification. Moreover, ZmLac3 is induced by wounding, whereas ZmLac2 and ZmLac5 are repressed and ZmLac4 gene expression is not affected.Taken together, our results suggest that the acidic ZmLac3 enzyme could be involved in the polymerisation of phenolic compounds in maize. Instead, and in agreement with the idea that laccases are enzymes involved in a wide range of physiological processes, results obtained with ZmLac2, ZmLac4, and ZmLac5 lead us to exclude a direct role of these laccases in lignin polymerisation.