**1. Introduction**

Microalgae are worldwide microscopic organisms capable of producing valuable bioactive components from biomass to molecules with drug properties. The rapid growth, utilization of a wide variety of water sources, and photosynthetic activity are the reason for microalgae's success in producing such compounds. High photosynthesis efficiency in microalgae and acclimation power in various ecosystems make microalgae attractive model organisms for the investigation of tolerance mechanisms.

*Dunaliella* is one of the important microalgae Genus with special characteristics in the dominated territory. *Dunaliella* spices also have wonderful ecological attributes, for example, *Dunaliella acidophila* can survive in pH 1 and *D. salina can live* in hypersaline even crystallizer ponds.

Though the genus and its species have been studied for over a century and a half, there are still a lot of unanswered questions about its magic tools for such behavior.

The interest in *D. salina* and the hired methods and used strategies by it to survive in intolerable environments for other photosynthetic organisms dates back to the 1870s. Till now the research on those strategies has reached molecular levels, and

regulating the expression of genes involved in cellular metabolic pathways leads to acclimation and adaptation to diverse environments. It is thought that the flexibility of nuclear and organellar gene expression is one of these mysterious tools.

So, in this chapter, an attempt has been made to be paid a slight aspect of the flexibility of *D. salina,* this particular cell, in the regulation of chloroplast gene expression focusing on **transcription factors**.
