Molecular biology of plant laccases in relation to lignin formation

The lack of monocot laccase sequence data has been held as an argument against laccases playing a role in lignin polymerization. This overview focuses on plant laccase molecular biology in relation to lignin formation with emphasis on recently cloned monocot laccases from ryegrass (Lolium perenne). Laccase is found within the major seed plant groupings. Furthermore, as laccases have probably been duplicated before and after division into monocots, dicots and gymnosperms, it is hypothesized that all higher plants encode a multitude of laccases. Work published during the past decade indicates the existence of a strong relationship between laccase expression and lignification in several plant species. Likewise, analysis of the first plant laccase promoter shows that this laccase is putatively regulated by a group of transcription factors that have been shown to regulate several enzymes of the phenylpropanoid pathway. It is suggested that laccases may also serve other roles than participation in lignin formation in plant biology.