Pectin Methylesterase Isoforms in Tomato (Lycopersicon esculentum) Tissues (Effects of Expression of a Pectin Methylesterase Antisense Gene)

Abstract

We have identified two major groups of pectin methylesterase (PME, EC 3.1.1.11) isoforms in various tissues of tomatoes (Lycopersicon esculentum). These two groups exhibited differential immuno-cross-reactivity with polyclonal antibodies raised against tomato fruit PME or flax callus PME and differences in their accumulation patterns in tissues of wild-type and transgenic tomato plants expressing a PME antisense gene. The group I isoforms with isoelectric points (pls) of 8.2, 8.4, and 8.5 are specific to fruit tissue, where they are the major forms of PME activity. The group II PME isoforms, with pl values of 9 and above, are observed in both vegetative and fruit tissues. The group I isoforms cross-react with polyclonal antibodies raised to a PME isoform purified from fruit, whereas the group II isoforms cross-react with antibodies to a PME purified from flax callus. Expression of a fruit-specific PME anti-sense gene impairs accumulation of the group I PME isoforms, with no apparent effect on the accumulation of the group II PME isoforms. The absence of any noticeable effects on growth and development of transgenic plants suggests that the group I PME isoforms are not involved in plant growth and development and may play a role under special circumstances such as cell separation during fruit ripening.

Molecular cloning and characterisation of a putative pectin methylesterase cDNA in Arabidopsis thaliana (L.)

“…The third isoform has a pI of 5.7 closer to the neutrality and was essentially detected in the inflorescence. As in other plant species [22], the presence of multiple PME isoforms in Arabidopsis suggests that they have their own specialised function, specifically and temporarily associated with a particular cell type, tissue or organ during plant development. Particularly, the most basic PME isoform in Arabidopsis has a pI and a pattern similar to the ubiquitous basic PME isoforms of pI 9.0 and above which are detected in tomato [22].…”

“…As in other plant species [22], the presence of multiple PME isoforms in Arabidopsis suggests that they have their own specialised function, specifically and temporarily associated with a particular cell type, tissue or organ during plant development. Particularly, the most basic PME isoform in Arabidopsis has a pI and a pattern similar to the ubiquitous basic PME isoforms of pI 9.0 and above which are detected in tomato [22]. In this plant species, it is suggested that these basic isoforms might contribute to pectin de-esterification within growing organs subject to cell enlargement.…”

Methanol Emission from Leaves (Enzymatic Detection of Gas-Phase Methanol and Relation of Methanol Fluxes to Stomatal Conductance and Leaf Development)

“…Obendorf et al (1990), who measured the accumulation of free methanol in maturing soybean seeds, reviewed earlier observations of methanol production during seed growth and maturation and suggested that pectin methylesters in cell walls are a likely source of methanol. Methanol is known to be a product of pectin demethylation in the cell walls of roots, stems, leaves, and fruits by pectin methylesterase (reviewed by Gaffe et al, 1994). Pectin demethylation occurs during growth and development as well as during aging and senescence of plant tissues.…”

Silencing of the Major Salt-Dependent Isoform of Pectinesterase in Tomato Alters Fruit Softening

“…This activity, as in other plants, is associated with multiple isoforms (Gaffe et al, 1994). Thus, tomato fruit tissues express at least three isoforms of PE, which have been termed PE1, PE2, and PE3 (Tucker et al, 1982), while at least five isoforms have been detected in leaf tissue (Gaffe et al, 1994). The fruit isoforms have been most intensively studied.…”