A Chloroplast-Localized SlABCC21 Contributes to Plastid Development and Carotenoid Accumulation during Tomato Fruit Ripening

Abstract Carotenoids accumulate massively as tomato (Solanum lycopersicum) fruit ripen, a process coupled to the transition of chloroplasts into chromoplasts, yet the membrane transporters that contribute to this plastid remodeling remain poorly understood. Here, we identify SlABCC21, a chloroplast-localized ATP-binding cassette subfamily C transporter that displays a uniquely ripening-associated expression pattern. CRISPR/Cas9-mediated knockout of SlABCC21 delayed fruit degreening and produced a mottled red-and-yellow phenotype. Transmission electron microscopy showed that the chloroplast-to-chromoplast transition was delayed in the slabcc21 mutants, with retained thylakoids and fewer plastoglobules. Loss of SlABCC21 redirected carotenoid flux from lycopene and β-carotene toward xanthophylls and lowered endogenous free abscisic acid (ABA). These findings establish that plant ABCC transporters can act within plastid-associated metabolic networks and identify SlABCC21 as a target for engineering carotenoid composition and nutritional quality in tomato fruit.