Inhibition of a ubiquitously expressed pectin methyl esterase in Solanum tuberosum L. affects plant growth, leaf growth polarity, and ion partitioning

Abstract

Two pectin methyl esterases (PMEs; EC 3.1.1.11) from Solanum tuberosum were isolated and their expression characterised. One partial clone ( pest1) was expressed in leaves and fruit tissue, while pest2 was a functional full-length clone and was expressed ubiquitously, with a preference for aerial organs. Potato plants were transformed with a chimeric antisense construct that was designed to simultaneously inhibit pest1 and pest2 transcript accumulation; however, reduction of mRNA levels was confined to pest2. The decrease in pest2 transcript was accompanied by up to 50% inhibition of total PME activity, which was probably due to the reduction of only one PME isoform. PME inhibition affected plant development as reflected by smaller stem elongation rates of selected transformants when compared with control plants, leading to a reduction in height throughout the entire course of development. Expansion rates of young developing leaves were measured simultaneously by two displacement transducers in the direction of the leaf tip (proximal-distal axis) and in the perpendicular direction (medial-lateral axis). Significant differences in leaf growth patterns were detected between wild-type and transgenic plants. We suggest that these visual phenotypes could be correlated with modifications of ion accumulation and partitioning within the transgenic plants. The ion-binding capacities of cell walls from PME-inhibited plants were specifically modified as they preferentially bound more sodium, but less potassium and calcium. X-ray microanalysis also indicated an increase in the concentration of several ions within the leaf apoplast of transgenic plants. Moreover, quantification of the total content of major cations revealed differences specific for a given element between the leaves of PME-inhibited and wild-type plants. Reduced growth rates might also be due to effects of PME inhibition on pectin metabolism, predominantly illustrated by an accumulation of galacturonic acid over other cell wall components.

Pectin Methylesterification Impacts the Relationship Between Photosynthesis and Plant Growth in Arabidopsis thaliana

“…Indeed, over-expression of pectin methylesterase inhibitors results in longer root cells (Lionetti et al, 2007). Therefore, the degree of methylation and demethylation of pectin determines the delicate balance between cell wall extensibility and rigidity with consequent effects on growth and shape of cells (Burton et al, 2000;Pilling et al, 2004;Lionetti et al, 2007;Wolf et al, 2009;Xiao and Anderson, 2013;Kim et al, 2015). Consistent with this notion, overexpression of pectin methyltransferases, CGR2 or CGR3, led to enhanced rosette size and fresh weight in Arabidopsis (Kim et al, 2015).…”

“…The plant cell wall controls expansion and positioning of cells of photosynthetic tissues and therefore, changes in cell wall properties will have a direct impact on the above properties. Although there is evidence for changes in leaf architecture as a result of alterations in genes that affect the synthesis and properties of the cell wall (Burton et al, 2000;Kim and Delaney, 2002;Pilling et al, 2004;Wolf et al, 2009;Kim et al, 2015), an in-depth analysis of effects on leaf gas exchange and overall plant growth under such circumstances has not yet been conducted.…”

Structural Basis for the Interaction between Pectin Methylesterase and a Specific Inhibitor Protein

“…By generating free carboxylic groups, PMEs also affect the wall pH and consequently influence the activity of a wide range of hydrolytic enzymes, including PMEs (Grignon and Sentenac, 1991;Denes et al, 2000;Goldberg et al, 2001). PMEs produced by plants take part in important physiological processes, such as microsporogenesis, pollen growth, seed germination, root development, polarity of leaf growth, stem elongation, fruit ripening, and loss of tissue integrity (Tieman and Handa, 1994;Wen et al, 1999;Micheli et al, 2000;Pilling et al, 2000;Micheli, 2001;Pilling et al, 2004). They have also been reported to play a role in response to fungal pathogens (Wietholter et al, 2003) and are required for the systemic spread of Tobacco mosaic virus through the plant (Dorokhov et al, 1999;Chen et al, 2000;Chen and Citovsky, 2003).…”

Inhibition of pectin methyl esterase activity by green tea catechins

“…Furthermore, the exogenous application of small molecule inhibitors offers a method for fine control of enzymatic activity during isolated life stages and tissues. Previous work using antisense technology to inhibit PME (e.g., Pilling et al, 2004) has shown systemic effects of PME inhibition, but are difficult to confine to particular plant parts or life stages, nor are they tractable for field experiments on non-model systems. Therefore, we endeavored to identify appropriate small molecules that have shown efficacy as enzymatic inhibitors, as a starting point for identifying candidate PME inhibitors.…”