Plants cannot move and have not evolved a nervous system or an adaptive immune system. Nevertheless, there are currently 300,000 flowering plant species that have colonized nearly the entire land surface of the Earth. These plants include some of the largest and most long-lived organisms on this planet. One of the major factors enabling this tremendous evolutionary success is that plants have evolved an unmatched ability to adjust their growth and development to the environment by responding to numerous exogenous signals. In addition, many plant species are able to thrive in diverse environments because strains have genetically adapted to exhibit different responses to the same environmental stimulus. This adaptive capacity has allowed humankind to spread crop plants over the whole globe, laying the foundation for our modern civilization.
One organ that is crucial for plant survival is the root. Much like the gut of an animal, the root acquires all nutrients and water. However, as plants are generally immobile, acquisition of often sparsely distributed nutrients and water is primarily achieved by growing the root system to forage the soil. The root system begins as a single primary root that branches to develop lateral roots. As the abundance of nutrients and water dramatically varies over time and in different soil types, roots must constantly process numerous external cues and prioritize growth of individual root tips. Principles guiding this prioritization process need to be different for plants adapted to different environments. In areas with frequent rainfall, water will be assigned a different priority than in areas of sparse rain fall. Despite the remarkable natural variation for root growth between and within plant species, very little is known about the genes and the molecular mechanisms in which genetic variation determines root growth and its responses, and how it relates to local adaptation. We make use of the remarkable root growth variation between accessions (i.e., strains collected from the wild) of the model plants Arabidopsis thaliana and Lotus japonicus to identify genes, their genetic variants and the molecular mechanism that determine root growth and its responses to the environment. For this, we utilize the full power of genomics, statistical genetics and systems biology. Because both species we work with, display a broad range of habitats (e.g. strains of the model species Arabidopsis thaliana naturally occur from North-Sweden to North-Africa – and everywhere in between), we can also relate root growth and its regulation to environmental adaptation.