Overexpression of the Gene Encoding Solanum lycopersicum Carotenoid Cleavage Dioxygenase 1A (SlCCD1A) Regulates Tomato Flavor Quality

SlCCD1A-OE lines of cherry tomato CI1005 and large-fruited tomato AC were selected to investigate the effect of SlCCD1A on tomato flavor quality. The transgenic plants were identified by real-time polymerase chain reaction (PCR), and the volatile components and major quality traits of the transgenic lines were determined. The results showed that SlCCD1A-OE mainly cleaved lycopene and β-carotene in tomato fruit, and increased the contents of 11 volatile isoprene compounds, including 6-methyl-5-heptene-2-one, compared with the wild type (WT). The total amount of these isoprene compounds was the highest in strain OE-3 from CI1005, which was 5.68 times of that in WT, and it increased 1.88 times in OE-8 from AC compared with WT, significantly enhancing the floral, fruity, and sweet aroma. The soluble solid content, total sugar content, and sugar/acid ratio in strain OE-3 from CI1005 increased to 6.2%, 37.34 mg/g, and 10.37, while the contents of total acid and vitamin C (VC) decreased to 0.36 mg/L and 42.10 mg/L, respectively. The soluble solid content, total sugar content, and sugar/acid ratio in strain OE-7 from AC increased to 4.77%, 20.03 mg/g, and 5.23, while the total acid and VC contents decreased to 0.38 mg/L and 37.10 mg/L, respectively, resulting in high-sweet and low-sour taste. The SlCCD1A gene is beneficial for enhancing the content and richness of carotenoid-derived volatiles in tomato fruit and increasing the contents of soluble solids and total sugars, thereby improving the flavor quality.