Comprehensive expression profiling of the pectin methylesterase gene family during silique development in Arabidopsis thaliana.

Pectin methylesterases (PME, EC. 3.1.1.11) are enzymes that demethylesterify plant cell wall pectins in muro. In Arabidopsis thaliana, putative PME proteins are thought to be encoded by a 66-member gene family. This study used real-time RT-PCR to gain an overview of the expression of the entire family at eight silique developmental stages, in flower buds and in vegetative tissue in the Arabidopsis. Only 15% of the PMEs were not expressed at any of the developmental stages studied. Among expressed PMEs, expression data could be clustered into five distinct groups: 19 PMEs highly or uniquely expressed in floral buds, 4 PMEs uniquely expressed at mid-silique developmental stages, 16 PMEs highly or uniquely expressed in silique at late developmental stages, 16 PMEs mostly ubiquitously expressed, and 1 PME with a specific expression pattern, i.e. not expressed during early silique development. Comparison of expression and phylogenetic profiles showed that, within phylogenetic group 2, all but one PME belong to the floral bud expression group. Similar results were shown for a subset of one of the phylogenetic group, which differed from others by containing most of the PMEs that do not possess any PRO part next to their catalytic part. Expression data were confirmed by two promoter:GUS transgenic plant analysis revealing a PME expressed in pollen and one in young seeds. Our results highlight the high diversity of PME expression profiles. They are discussed with regard to the role of PMEs in fruit development and cell growth.