Sadhukhan, Ayan

Extremophile land plants have evolved convergently to become tough survivors in harsh soil and climatic conditions, such as extremes of soil pH, temperature, drought, high salinity, heavy metals, high light intensity, and UV radiation. Thus, the extremophile plants hold the potential key to improving stress-resilience in crop plants in the face of global climate change and desertification. Moreover, extremophile plants also exhibit industrial importance, being the source of active pharmaceuticals, new fuels, and essential chemicals. Transcriptome analysis of extremophiles is a common approach towards discovering genes and molecular mechanisms for adaptation to stress apart from identifying the pathways responsible for the biosynthesis of commercially essential metabolites. Again, the current scenario in extremophile research ranges from the study of extremophile plant models, e.g., Arabidopsis lyrata, to various plants of economic and ecological significance. The genetic signatures obtained from the transcriptome libraries of these extremophiles are utilized towards their conservation by employing the genome-editing approaches apart from extending their applicability towards the introgression of abiotic tolerance traits into agronomically important crop plants. This chapter aims to summarize the recent transcriptome analyses of extremophile species from the Indian Thar desert and other extreme eco-regions of the world.

Aluminum (Al) toxicity in acid soil is one of the most severe environmental stress factors that limit world food production. Al ion (Al 3+) is highly reactive with negatively charged ligands of the cell and disturbs cell division and expansion at sub-micromolar levels. Since the harmful effects are caused by both cyto- and genotoxicities of Al, plant cells show various dose- and time-dependent responses. On the other hand, plants have evolved different Al tolerance strategies that protect sensitive cells from Al 3+ . These include restructuring of the cell wall to prevent deposition of Al 3+ and organic acid release by plasma membrane transporters to chelate out and exclude Al 3+ in the rhizosphere, regulated by the transcription factor STOP1 or its orthologs, and internal detoxification mechanisms including root-to-shoot translocation, antioxidant defense, and Al sequestration in vacuoles to prevent cytotoxicity. In recent years, genomics approaches, particularly genome-wide association studies and transcriptome analyses, have provided genetic evidence of well-known genes’ involvement in Al tolerance and uncovered new Al tolerance genes in plants. This chapter summarizes the findings from recent genomic studies that add to our understanding of the complex plant responses to Al toxicity.