Potato tuber pectin structure is influenced by pectin methyl esterase activity and impacts on cooked potato texture

Abstract

Although cooked potato tuber texture is an important trait that influences consumer preference, a detailed understanding of tuber textural properties at the molecular level is lacking. Previous work has identified tuber pectin methyl esterase activity (PME) as a potential factor impacting on textural properties. In this study, tuber PME isoform and gene expression profiles have been determined in potato germplasm with differing textural properties as assessed using an amended wedge fracture method and a sloughing assay, revealing major differences between the potato types. Differences in pectin structure between potato types with different textural properties were revealed using monoclonal antibodies specific for different pectic epitopes. Chemical analysis of tuber pectin clearly demonstrated that, in tubers containing a higher level of total PME activity, there was a reduced degree of methylation of cell wall pectin and consistently higher peak force and work done values during the fracture of cooked tuber samples, demonstrating the link between PME activity, the degree of methylation of cell wall pectin, and cooked tuber textural properties.

Wounding coordinately induces cell wall protein, cell cycle and pectin methyl esterase genes involved in tuber closing layer and wound periderm development

“…Importantly, the elevated StTLRP expression after 28 d suggests a role for this gene in phellogen cell wall thickening and strengthening after cessation of meristematic activity. This hypothesis is consistent with the results of Ross et al (2011) and Kloosterman et al (2010) who showed that StTLRP was more highly expressed in firm tuber tissues.…”

“…Domingo et al (1994) determined that TLRP participates in cross-linking of proteins to cell walls and can be linked to aromatic side chains of lignin. This cell wall protein was also found to be expressed at higher levels in potato tubers within a population that displayed firmer cooked tuber texture (Ross et al, 2011). Collectively, these studies suggest that expression of extensin and TLRP genes may be linked to wound-healing events and wound-periderm maturation.…”

“…Certain cell wall proteins and pectins may have key roles in strengthening phellogen cell walls after meristematic inactivation, making them more resistance to fracture and the periderm more resistant to excoriation (Sabba and Lulai, 2002, 2004Kloosterman et al, 2010;Ross et al, 2011). Extensins are a family of hydroxyproline-rich glycoproteins (HRGPs) which are major components in cell walls of dicots and are characterized by a pentapeptide motif of Ser-Hyp 4 which is repeated throughout the protein (Showalter, 1993).…”

“…Also, Deepak et al (2007) showed that there were higher levels of HRGP transcripts and associated protein in a cultivar of pearl millet resistant to Sclerospora graminicola, the causative agent of pearl millet downy mildew. Another protein involved in cell wall structure is pectin methyl esterase (PME); this gene product can increase the content of unesterified uronic acid residues allowing pectin to have higher Ca 2+ binding efficiency, thereby increasing tissue firmness (Ross et al, 2011). Contiguous patterns of de-esterification of homogalacturonan molecules by PME leads to what Siedlecka et al (2008) described as egg-box structures, which contribute to pectin stabilization and cell wall stiffening.…”

High-Resolution Mapping of a Fruit Firmness-Related Quantitative Trait Locus in Tomato Reveals Epistatic Interactions Associated with a Complex Combinatorial Locus

“…Studies with transgenic tomato lines containing reduced levels of a PME isoform (Pmeu1) showed enhanced softening (Phan et al, 2007), indicating that the expression of this PME gene is positively related to increased fruit firmness. Furthermore, elevated expression of the PME gene PEST1 was associated with improved texture in potato (Solanum tuberosum; Ross et al, 2011). These results indicate that PME may play an important role in enhancing fruit texture when expressed at high levels.…”