Abstract
CONSTANS (CO) and CONSTANS-LIKE (COL) transcription factors have been known to regulate a series of cellular processes, including the transition from vegetative growth to flower development in plants. However, their role in regulating the content of chlorophyll in fruit is poorly understood. In this study, SlCOL1, the tomato (Solanum lycopersicum) ortholog of Arabidopsis CONSTANS, was shown to play key roles in the control of fruit chlorophyll. The suppression of SlCOL1 expression was found to lead to a reduction in the content of chlorophyll in the immature green fruit. In contrast, the overexpression of SlCOL1 increased the content of chlorophyll in the immature green fruit. An analysis of protein-protein interactions indicated that SlCOL1 forms a complex with GOLDEN2-LIKE (GLK2), which promotes the stability of its protein. The overexpression of SlCOL1 in the glk2 null mutation background of tomato failed to promote the accumulation of chlorophyll in the immature green fruit, which suggests that GLK2 is required for the function of SlCOL1 in the regulation of the content of chlorophyll. These results shed new light into the mechanisms used by COL1 and GLK2 to regulate fruit development and the accumulation of chlorophyll in tomato.