Analysis of expression profiles of three peroxidase genes associated with lignification in Arabidopsis thaliana.

We have investigated the mechanism of lignification during tracheary element (TE) differentiation using a Zinnia elegans xylogenic culture. In the process, we isolated ZPO-C, a peroxidase gene of Z. elegans that is expressed specifically in differentiating TEs. ZPO-C is suggested to be involved in lignification of Z. elegans TEs in vivo and in vitro. Furthermore, a peroxidase gene of Arabidopsis thaliana (AtPrx66), which is homologous to ZPO-C, was identified. The expression profile and functions of the gene in planta remain to be investigated. In this study, we performed promoter::beta-glucuronidase (GUS) assays to investigate the expression profiles and functions of the ZPO-C-like peroxidases in A. thaliana. We generated transgenic A. thaliana lines carrying AtPrx66, AtPrx47 or AtPrx64 (peroxidases showing high sequence similarity to AtPrx66) promoter::GUS reporter gene fusions. The GUS activities of AtPrx66, AtPrx47 and AtPrx64 promoter::GUS lines were arranged concentrically from the center to the periphery in the roots of seedlings. Furthermore, histochemical GUS assays using inflorescence stems showed that AtPrx66, AtPrx47 and AtPrx64 promoter-driven GUS were mainly expressed in the differentiating vessels, xylem parenchyma and sclerenchyma, respectively. These results suggest that the gene expressions of these three peroxidases, which showed high sequence similarity to one another, are differentially regulated in various tissues and organs. In addition, our results suggest that while AtPrx66 and AtPrx47 are associated with lignification of vessels, AtPrx64 is associated with lignification of sclerenchyma.