Analysis of a dehiscence zone endo-polygalacturonase in oilseed rape (Brassica napus) and Arabidopsis thaliana: evidence for roles in cell separation in dehiscence and abscission zones, and in stylar tissues during pollen tube growth

The oilseed rape (Brassica napus) endo-polygalacturonase (endo-PG) RDPG1 is involved in middle lamella breakdown during silique opening. We investigated tissue-specific expression of RDPG1 in transgenic Arabidopsis thaliana. Cellular localization of endo-PG protein in Arabidopsis siliques was determined by immuno-electron microscopy. An Arabidopsis orthologue, ADPG1, was isolated and aligned with the sequence of RDPG1. The proximal 5 sequences as well as introns are largely conserved. Analysis of the histological GUS-staining pattern of two RDPG1 promoter-GUS (-glucuronidase) constructs in transgenic Arabidopsis revealed that the conserved proximal part of the 5-flanking region directs expression in dehiscence zones of siliques and anthers, floral abscission zones and stylar tissues during pollen tube growth, branch points between stems and pedicel and expression associated with the apical meristem of seedlings, while the distal part of theRDPG1 5-flanking region contains elements involved in vascular-associated expression in petals, cotyledons and roots. Subsequent RT-PCR analysis, on RNA from the corresponding rape tissues, confirms the staining pattern revealed in transgenic Arabidopsis, thereby justifying the use of Arabidopsis as a reliable model system for analysis of oilseed rape regulatory sequences.