The halotolerant green alga Dunaliella salina accumulates large amounts of beta-carotene when exposed to various stress conditions. Although several studies concerning accumulation and biotechnological production of beta-carotene have been published, the molecular basis and regulation of the genes involved in carotenoid biosynthesis in D. salina are still poorly known. In this paper, we report the isolation and regulation of the lycopene beta-cyclase (Lcy-beta) gene by abiotic stress. The function of this gene was determined by heterologous genetic complementation in E. coli. Gene expression and physiological analyses revealed that D. salina Lcy-beta steady-state transcript and carotenoid levels were up-regulated in response to all stress conditions tested (salt, light and nutrient depletion). The results presented here suggest that nutrient availability is a key factor influencing carotenogenesis as well as carotenoid biosynthesis-related gene expression in D. salina.