Adaptation of Photoautotrophs in Extraterrestrial Environments: Responses and Mechanisms of Survival

In the last few decades, impeccable progress has been made in the field of astrobiological research whose purpose was to search for efficient Earth organisms capable of surviving in space environment followed by using them as tools for human space exploration. Among the investigated organisms, photoautotrophs constitute the most rigorously studied group. In the present chapter, responses and survival strategies of photoautotrophs in space and/or simulated extraterrestrial conditions have been discussed in detail. Space exposure and survival-related studies on photoautotrophs have mainly been performed using cyanobacteria, algae, lichens and higher plants. Reports accumulated over 60 years reflected that many species belonging to these photoautotrophic groups have an outstanding ability to survive in space. However, the exact mechanisms of their survival in space have not yet been completely explored. In order to unveil the survival strategies of photoautotrophs in space environment, various plant species i.e. Arabidopsis thaliana, Brassica rapa var. nipposinica, Ceratopteris richardii and Oryza sativa, have recently been studied thoroughly through mRNAseq and microarray-based transcriptomic analyses. Results obtained from these studies denoted that plants exhibit a myriad of survival responses like cell wall remodelling, oxidative stress, activation of antioxidative machineries, lipid utilization, cell cycle regulation, increased telomerase activity, reduced genome oxidation, altered hormone signalling, protection of photosynthetic apparatus etc. Few identical responses like oxidative stress, activation of antioxidant machineries, increased lipid metabolism and protection of photosynthetic apparatus have also been noticed in cyanobacteria and algae when they have been exposed to space like stratospheric and high-altitude environments respectively, followed by being subjected to gene expression analysis. Interestingly, complete absence of such studies has been recorded for lichens, hence the space survival mechanisms of this photoautotrophic group still remain absolutely unknown. Despite a large number of researches on this topic, only a few review articles have been written so far and those reviews have either focussed on only plants’ survival responses in space or that of cyanobacteria and algae. Therefore, the present chapter will be very useful to the upcoming researchers in this field as it meticulously elaborates the survival responses and strategies of all groups of photoautotrophs in space conditions.