Introgression of a dominant phototropin1 mutant enhances carotenoids and boosts flavour-related volatiles in genome-edited tomato RIN mutants.

The tomato (Solanum lycopersicum) ripening inhibitor (rin) mutation is known to completely repress fruit ripening. The heterozygous (RIN/rin) fruits have extended shelf life, ripen normally, but have inferior taste/flavour. To address this, we used genome editing to generate newer alleles of RIN (rin CR ) by targeting the K-domain. Unlike previously reported CRISPR alleles, the rin CR alleles displayed delayed onset of ripening, suggesting that the mutated K-domain represses the onset of ripening. The rin CR fruits had extended shelf life and accumulated carotenoids at an intermediate level between rin and progenitor line. Besides, the metabolites and hormonal levels in rin CR fruits were more akin to rin. To overcome the negative attributes of rin, we crossed the rin CR alleles with Nps1, a dominant-negative phototropin1 mutant, which enhances carotenoid levels in tomato fruits. The resulting Nps1/rin CR hybrids had extended shelf life and 4.4-7.1-fold higher carotenoid levels than the wild-type parent. The metabolome of Nps1/rin CR fruits revealed higher sucrose, malate, and volatiles associated with tomato taste and flavour. Notably, the boosted volatiles in Nps1/rin CR were only observed in fruits bearing the homozygous Nps1 mutation. The Nps1 introgression into tomato provides a promising strategy for developing cultivars with extended shelf life, improved taste, and flavour.