Resilience and self-regulation processes of microalgae under UV radiation stress

The apparent increase in solar ultraviolet (UV) radiations on the Earth’s surface, due to continuous depletion or diminishing of the stratospheric ozone shield has triggered serious ecological as well as biological consequences on several life-forms, including microalgae. UV radiation tends to damage the key cellular machinery, cells may adapt by developing several defense mechanisms as a response to such damage; otherwise, the cellular destiny is cell-death. Since microalgae are one of the primary biotic components, any drastic effects caused by UV radiation may imbalance the entire ecosystems. However, survival of microalgae under billions of years of fluctuating environmental changes has pressurized them to develop a number of tolerance mechanisms against environmental UV stress. The high resilience of the microalgal community in the face of UV stress is attributed to the activation of several photo/dark repair mechanisms, antioxidant systems, and biosynthesis of UV-photoprotectants such as mycosporine-like amino acids (MAAs), scytonemin (Scy), carotenoids and polyamines. The focus of this review underlies an overview of various resilience mechanisms adopted by microalgae, by which cells are able to survive under UV stressed environment. Moreover, the current progress on genetic engineering to enhance the survival of microalgae in response to intense solar UV radiation has also been conferred.