Nat. Biotechnol. http://doi.org/bn8c (2016)

Slowing fruit softening to extend shelf life remains a major challenge for tomato improvement, especially considering that the ‘non-ripening mutations’ currently used in production generally compromise the fruit flavour and colour. Selman Uluisik, at the University of Nottingham, UK, and colleagues now develop an effective approach to control tomato softening by manipulating a gene encoding a pectate lyase.

In strawberries, silencing pectate lyase reduces the rate of fruit softening, however in tomato, pectate lyase was the only major pectin-degrading enzyme hitherto lacking investigation. The researchers accordingly surveyed the pectate lyase genes in tomato and focused on one that is highly expressed during ripening. Downregulating this pectate lyase gene using RNAi increased fruit firmness without affecting other traits, such as yield and the contents of metabolites that influence colour, taste and flavour.

Examination of cell walls using microscopy and labelling techniques showed that the pectate lyase mainly acts in the tricellular junction regions where it breaks down the demethylesterified homogalacturonans to more degradable water-soluble pectins, resulting in rapid fruit softening.

The researchers suggest that manipulating the expression of this gene using natural variation or genomic editing can generate products for commercialization. Preliminary genomic editing experiments and quantitative trait locus mapping analysis demonstrated the feasibility of this strategy.