Characterization of two lycopene beta-cyclases reveal their essential roles in photoprotection in Nicotiana tabacum

Carotenoids are essential isoprenoids with vital roles in photoprotection and antioxidative processes in photosynthetic organisms. Lycopene Beta-cyclase (β-LCY) is a key enzyme in carotenoid biosynthesis; however, the role of β-LCY in photoprotection is still unclear. In this study, we characterized two β-LCY genes in an allotetraploid tobacco cultivar K326, that are primarily expressed in leaves. Reduction of β-LCY expression by RNA interfercnce (RNAi) resulted in decreased carotenoid content, leaf variegation, impaired photosynthetic efficiency, and abnormal chloroplast morphology. β-LCY RNAi plants exhibited hypersensitivity to high light and lower non-photochemical quenching (NPQ) values under both normal and high light conditions. The stability of D1, a core subunit of photosystem II reaction center, was dramatically impaired β-LCY RNAi plants upon exposure to high light, suggesting severe photodamage of photosystem. Furthermore, reactive oxygen species (ROS) content was increased in β-LCY RNAi plants compared to WT plants under both normal and high light conditions. These results indicate that β-LCY is crucial for NPQ, D1 stability and ROS homeostasis, thus protecting photosystem from photooxidative damage. These findings contribute to our understanding on the function of plant β-LCY and its potential implications for plant growth, development, and photoprotection.