Isolation of a flax pectin methylesterase promoter and its expression in transgenic tobacco.

Pectin methylesterases (PME) catalyze the de-esterification of methoxylated pectins in plant cell walls. We have isolated a 1.9 kb regulatory region upstream from the Lupme3 coding sequence of Linum usitatissimum L. (flax) using a 'Polymerase Chain Reaction (PCR) walking' strategy. Two 5' truncated deletion fragments (1.5 and 0.44 kb) of this potential promoter sequence were inserted upstream of the gus reporter gene in order to study their expression in transgenic plants. These constructs were transferred into Nicotiana tabacum, a heterologous system using Agrobacterium tumefaciens. Expression of the reporter gene was analyzed in regenerated transgenic plants and calli to study the promoter activities of these sequences. This expression was observed in calli with both constructs. In contrast, expression in organs was only detected in tobacco plants transformed with the largest (1.5 kb) construct. This long fragment triggered expression in roots and immature or vitrified leaves. Expression in both organs was localized in the vasculature, but also detected in the root meristem. These results are the first evidence, to our knowledge, of the spatial and temporal regulation of a specific pme promoter of flax. Localization of Lupme3 promoter activity in vascular tissues of immature organs provides an insight into the role of this PME isoform in cell elongation and differentiation.