Characterization of Laccase-like Multicopper Oxidases (LMCOs) in Arabidopsis thaliana

Abstract

Laccase-like multicopper oxidases (LMCOs) have repeatedly been associated with the process of lignification in plants, and previous work suggested that these enzymes might be acting as specific marker for highly localized, small-scale lignification events in tissues not typically thought of as lignified. However, plant LMCOs typically occur as members of gene families and different family members can display disparate enzyme activities and overlapping patterns of expression in bulk tissues. This study used reporter genes and knockout mutants to document the involvement of a specific Arabidopsis thaliana LMCO family member (At2g30210 ) in early root development, specifically with development of endodermal tissues. Expression of the gene product was found to be under the control of sucrose levels, but the gene also responded to fluctuations in salt concentrations. The expression patterns of this gene were consistent with its involvement in the formation of suberin in the Casparian strip of root endodermis. An additional LMCO (At5g58910) displayed a more generalized expression in the radicles emergent seedlings. Additional members of the Arabidopsis LMCO family (At2g29130, At5g01190, and At5g05390) were also investigated with reporter gene constructs and knockout mutants. Expression of these LMCOs was associated with lignifying xylem, and the genes had over-lapping expression. Single knockout mutants did not display obvious phenotypes, suggesting that the gene products might have degenerate functionality that could compensate for loss of a single LMCO function.