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

This is the authors' abstract. We don't add key points for this paper.

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.