**6. Conclusion**

Plants are constantly exposed to environmental fluctuations, including biotic and abiotic stresses that cause metabolic, morphological, physiological, and molecular changes in plants/algae and all photosynthetic organisms that affect the growth, development, and final production of the plant. In response to these stresses, algaelike plants have evolved various defense systems and have mechanisms to deal with abiotic and biotic stresses. As a result, the stress response in cells begins with perception. Stress clues to living or nonliving factors in cell walls or membranes that are perceived by secondary messengers (such as calcium ions, reactive oxygen species, and hormones) and as intracellular signals. They are transmitted to signal transduction or transduction pathways of downstream signals, such as kinases or phosphatases. Transduction pathways regulate the expression of transcription factors, which in turn modulate the expression of stress-responsive genes in photosynthetic cells.

When a plant is stressed, several adaptive changes occur in plant cells to maintain growth, including over-regulation or under-regulation of various genes. Regulatory proteins act in stress signal transduction by influencing the expression of downstream target genes (functional genes). These regulatory proteins include protein kinases, protein phosphatases, and transcription factors. Transcription factors bind to specific sequences (Cis elements) in the promoter of target genes (stress-related genes), thereby regulating gene expression and affecting biological phenotypes. Transcription factors are key regulatory components of the biotic and abiotic stress signaling pathway.

The chloroplast genome like the nuclear genome is a potential binding site for transcription factors. It can be concluded that environmental stresses affect the regulation of expression and transcription of *D. salina* chloroplast genes.

*Transcription Flexibility of* Dunaliella *Chloroplast Genome DOI: http://dx.doi.org/10.5772/intechopen.105125*
