6 Conclusions and perspectives
The appearance and diversification of adaptations to dry environments and their underlying GRNs have been tightly shaped at cell, tissue and organismal levels during evolution. These adaptations were crucial for plants to colonize dry lands and survive variations on water availability in the environment. Carbon concentration mechanisms, desiccation tolerance and root impermeabilization are among the main plant adaptations to dry environments and share a similar pattern of convergent evolution in phylogenetically distant organisms. However, we are only starting to understand the evolutionary paths of the GRNs underpinning these adaptations in individual lineages. More comparative research between independent evolutions will inform us of the possible GRN evolutionary paths, including finding out if the same molecular and regulatory changes have occurred in independent lineages.
Detailed physiological and histological studies combined with advanced genome and transcriptome sequencing techniques such as TRAP-seq and single-cell sequencing (Heiman, Kulicke, Fenster, Greengard, & Heintz, 2014; Reynoso et al., 2015; Thellmann, Andersen, & Vermeer, 2020) will allow us to assess how these adaptations evolved through millions of years. This information in combination with novel methods to simulate drought conditions (e.g. Marchin, Ossola, Leishman, and Ellsworth (2019)) and technologies for plant genetic modification (e.g. CRISPR/Cas9) will have the power to help on the improvement of plant performance in dry environments, especially in the current scenario of increasing climate change. These data will also provide knowledge about key TFs working upstream of GRNs controlling DT pathways, which are of potential interest for engineering more drought tolerant crops.