Plants transitioned from an aquatic to a terrestrial lifestyle during their evolution. On land, fluctuations on water availability in the environment became one of the major problems they encountered. The appearance of morpho-physiological adaptations to cope with and tolerate water loss from the cells was undeniably useful to survive on dry land. Some of these adaptations, such as carbon concentrating mechanisms (CCMs), desiccation tolerance (DT) and root impermeabilization, appeared in multiple plant lineages. Despite being crucial for evolution on land, it has been unclear how these adaptations convergently evolved in the various plant lineages. Recent advances on whole genome and transcriptome sequencing are revealing that co-option of genes and gene regulatory networks (GRNs) is a common feature underlying the convergent evolution of these adaptations. In this review we address how the study of CCMs and DT have provided insight into convergent evolution of GRNs underlying plant adaptation to dry environments, and how these insights could be applied to currently emerging understanding of evolution of root impermeabilization through different barrier cell types. We discuss examples of co-option, conservation, and innovation of genes and GRNs at the cell, tissue and organ levels revealed by recent phylogenomic (comparative genomic) and comparative transcriptomic studies.

Plants transitioned from an aquatic to a terrestrial lifestyle during their evolution. On land, drought became one of the major problems they encountered, as it impacts correct cell functioning necessary to support life. The evolution of morpho-physiological and molecular adaptations to cope with and tolerate drough was undeniably useful to survive on land. Some of these adaptations appeared repeatedly in phylogenetically distant species, showing a signature of convergent evolution. Details of this convergent evolution are now being assessed thanks to recent developments on high throughput phenotyping and whole genome and transcriptome sequencing. Phylogenomic (comparative genomic) and comparative transcriptomic analyses are revealing complex, well-coordinated and intricate gain and loss of genes and co-option of gene regulatory networks underlying cell and tissue specific adaptations to moderate and extreme drought in phylogenetically distant species. Here we review recent research on signatures of convergent evolution of regulatory networks underlying carbon concentrating mechanisms such as C4 and CAM photosynthesis, desiccation tolerance in seeds and resurrection plants, and impermeabilization of root exodermis.