Abstract
SummaryTomato (Solanum lycopersicum) fruit ripening is regulated co‐operatively by the action of ethylene and a hierarchy of transcription factors, including RIPENING INHIBITOR (RIN) and NON‐RIPENING (NOR). Mutations in these two genes have been adopted commercially to delay ripening, and accompanying textural deterioration, as a means to prolong shelf life. However, these mutations also affect desirable traits associated with colour and nutritional value, although the extent of this trade‐off has not been assessed in detail. Here, we evaluated changes in tomato fruit pericarp primary metabolite and carotenoid pigment profiles, as well as the dynamics of specific associated transcripts, in the rin and nor mutants during late development and postharvest storage, as well of those of the partially ripening delayed fruit ripening (dfd) tomato genotype. These profiles were compared with those of the wild‐type tomato cultivars Ailsa Craig (AC) and M82. We also evaluated the metabolic composition of M82 fruit ripened on or off the vine over a similar period. In general, the dfd mutation resulted in prolonged firmness and maintenance of quality traits without compromising key metabolites (sucrose, glucose/fructose and glucose) and sectors of intermediary metabolism, including tricarboxylic acid cycle intermediates. Our analysis also provided insights into the regulation of carotenoid formation and highlighted the importance of the polyamine, putrescine, in extending fruit shelf life. Finally, the metabolic composition analysis of M82 fruit ripened on or off the vine provided insights into the import into fruit of compounds, such as sucrose, during ripening.
Highlights
When fleshy fruits ripen, they typically undergo changes in colour, flavour, aroma and texture, all of which promote their consumption in order to facilitate seed dispersal (Lorts et al, 2008)
Fruit from dfd, nor and rin, as well as those from the normally softening wild-type (WT) cultivars Ailsa Craig (AC) and M82, were harvested at the breaker (B) stage, or equivalent based on days after pollination (DAP), and were stored at room temperature for up to twelve weeks
The mutant fruits exhibited varying degrees of delayed postharvest ripening phenotypes, including major differences in colour changes (Figure 1a), reduction in weight, which was taken as an indication of water loss (Figure 1b), and firmness, defined here as resistance of intact fruit to compression (Figure 1c)
Summary
They typically undergo changes in colour, flavour, aroma and texture, all of which promote their consumption in order to facilitate seed dispersal (Lorts et al, 2008) These processes are associated with a broad range of metabolic pathways, including those that lead to the accumulation of sugars, organic acids and secondary metabolites, as well as the production of volatile organic compounds (Causse et al, 2010; Klee and Giovannoni, 2011; Rambla et al, 2014; Seymour et al, 2011; Tieman et al, 2012; Tohge et al, 2014). The later stages of ripening are generally accompanied by substantial changes in texture, resulting from cell wall and middle lamella disassembly, as well as transpirational water loss (Seymour et al, 2013a; Uluisik et al, 2016; Vicente et al, 2007; Wang et al, 2018) These processes can lead to ‘over-ripening’ and a loss of palatability (Seymour et al, 2013a). Tomato has emerged as the pre-eminent experimental model for studying fleshy fruit, including the developmental control of ripening and ethylene synthesis and perception (Carrari and Fernie, 2006; Gapper et al, 2013; Giovannoni, 2004; Giovannoni et al, 2017; Hyang et al, 2009; Osorio et al, 2011; Seymour et al, 2013b)
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