Ectopic expression of a BZR1-1D transcription factor in brassinosteroid signalling enhances carotenoid accumulation and fruit quality attributes in tomato

The brassinosteroid (BR) response transcription factor Brassinazole resistant 1 (BZR1)-mediated BR signalling regulates many specific developmental processes including fruit ripening. Here, we report the effect of 2,4-epibrassinolide (EBR) and BZR1-1D overexpression on carotenoid accumulation and quality attributes of tomato (Solanum lycopersicum) fruit. EBR-treated pericarp discs of ethylene-insensitive mutant, Never ripe, accumulated significantly more carotenoid than those of the control. The results suggest that BR seems to be involved in modulating pigments accumulation. When three independent transgenic lines overexpressing the Arabidopsis BZR1-1D were used to evaluate the role of BZR1 in regulating tomato fruit carotenoid accumulation and quality attributes, fruits of all three transgenic lines exhibited enhanced carotenoid accumulation and increased soluble solid, soluble sugar and ascorbic acid contents during fruit ripening. In addition, the fruits of two transgenic lines showed dark green shoulder at mature green stage, in accordance with the up-regulated expression level of SlGLK2, which is involved in chloroplast development. Our results indicate the importance of BZR1-centred BR signalling in regulating carotenoid accumulation and quality attributes of tomato fruit and the potential application of the BZR1-like(s) for improvement of nutritional quality and flavour of tomato through genetic engineering.