Distinguishing two genetic factors that control yellow fruit color in tomato

Carotenoids are tetraterpenes (40-carbon isoprenoids) derived from the five-carbon isoprene units, isopentenyl diphosphate (IDP) and its isomer dimethylallyl diphosphate (DMADP). These molecules are the major determinants of fruit pigmentation in many plant species, including tomato. The IDP isomerase (IDI) catalyzes the isomerization of IDP to DMADP. Phytoene synthase (PSY) catalyzes the dimerization of two diterpenes from geranylgeranyl pyrophosphate to phytoene, which is the rate-limiting step in carotenoid biosynthesis. Mutations in the tomato PSY1, yellow flesh, are widely used for breeding yellow tomatoes. We report a series of allelic variations in yellow flesh, and in the newly identified apricot, which has yellow fruit as a result of a mutation in IDI1. In HPLC analysis, both the cultivars showed yellow ripe fruits that lacked carotenoids. However, unlike wild type and yellow flesh, apricot mutants had reduced carotenoid levels in flowers. The allelic variations in yellow flesh were determined to have a deletion in the promoter region and a nonsense mutation in the PSY1 gene, whereas apricot contained a ‘T’ insertion that resulted in premature termination codon in the IDI1 gene. DNA markers to identify allelic variations in two yellow flesh and three apricot mutant lines were developed. These markers and germplasms would be useful for breeding yellow tomatoes.