Strigolactone (GR24) regulates fruit ripening in yft3 tomatoes by altering ABA biosynthesis

Color development in tomato fruits is a key indicator of ripening, and is driven by complex hormonal and molecular interactions. The present study investigated the effects of exogenous treatment with abscisic acid (ABA), GR24 (a synthetic strigolactone analog), and water (ddH₂O as control) on tomato fruit ripening, ethylene emission, carotenoid biosynthesis, ABA metabolism, and chromoplast development in yft3 and wild-type (WT cv. M82) tomato fruits at 35, 47, and 54 days post-anthesis (dpa). Results showed that GR24 significantly accelerated ripening in yft3, transitioning from green to deep orange at 54 dpa, whereas ABA had a moderate effect. In cv. M82, both treatments enhanced color development, leading to a deep red phenotype. GR24 increased ethylene emission and upregulated the expression of ethylene related genes (ACO1, ACS2/4), with yft3 showing increased sensitivity than cv. M82. Carotenoid profiling revealed higher lycopene and β-carotene contents in yft3, with GR24 enhancing β-carotene and lutein, whereas ABA increased lycopene. GR24 and ABA strongly induced the expression of carotenoid-related genes (CRTISO, PSY1, and CYCB), particularly in yft3 at 54 dpa. Moreover, ABA-content and the expression of genes involved in ABA biosynthesis (NCED, AAO), catabolism (CYP707A), conjugation (GT), and activation (BG) were significantly altered by ABA and GR24 treatments. Furthermore, ultrastructural analysis revealed that GR24 promoted plastoglobule formation and chromoplast differentiation, with yft3 exhibiting a stronger response than cv. M82. These findings highlight that GR24 plays vital roles in regulating tomato fruit ripening, ethylene biosynthesis, carotenoids accumulation, as well as ABA-metabolism, with implications for improving fruit quality in tomatoes.