CsCCD2L is Involved in the Response to Light Stress by Regulating Zeaxanthin Content in Saffron (Crocus sativus L.)

Saffron, a plant flowering in fall and prized for its medicinal red stigmas, has a unique life cycle. After dormancy, the flower formation process starts from late summer to fall. Post-harvest, it enters the vegetative growth stage from winter to spring. The reason behind its growth pattern remains unknown. In our study, we found that overexpressing carotenoid cleavage dioxygenase 2 (CsCCD2L, a long transcript of CsCCD2) in Arabidopsis thaliana affected the content of zeaxanthin and light tolerance. In saffron, CsCCD2L varies throughout its life cycle, impacting zeaxanthin content. Saffron flowers indoors with its leaves still enclosed in sheathing cataphylls. The expression of CsCCD2L in saffron leaves reached its peak on the day of anthesis, but significantly decreased in the vegetative stage when leaves extend from the sheathing cataphylls for photosynthesis. Intense light during this stage leads to leaf yellowing, a reduction in CsCCD2L expression, and an increase in zeaxanthin content. These results indicate that CsCCD2L regulates the content of zeaxanthin and light tolerance. Moreover, CsCCD2L exhibited the highest expression in the orange stigmas. Subjecting flower buds at the orange stigma stage to intense light significantly reduced the crocin content in mature stigmas. Collectively, these results not only shed light on the unique growth pattern of saffron but also offer promising avenues for enhancing saffron quality through the precise manipulation of light intensity and the expression of CsCCD2L.