Picturing Natural Variation in Arabidopsis Root Architecture in Response to Salinity by Merging Growth Parameters and Genomic Information

Soil salinity is one of the most severe abiotic stress factors threatening agriculture worldwide. Hence, particular interest exists in unravelling mechanisms leading to salt tolerance and improved crop plant performance on saline soils. Salinity tolerance is understood to be polygenically controlled and the plant response to salt stress in different parts of plant body takes place at different spatial and temporal scales. Roots are exposed directly to salt and regulate ion, nutrient and water uptake as well as the transport within the plant. Therefore, understanding the effect of salinity on the root system is a prerequisite for plant improvement. Nineteen accessions of A. thaliana (Bur-0, Can-0, Col-0, Ct-1, Edi-0, Hi-0, Kn-0, Ler-0, Mt-0, No-0, Oy-0, Po-0, Rsch-4, Sf-2, Tsu-0, Wil-2, Ws-0, Wu-0, Zu-0) were tested for alterations in primary, lateral and total root length, as well as lateral root count after thirteen days of growth on MS medium with or without 50 mM NaCl or 100 mM NaCl. Clustering analysis was performed to detect similarities in root architecture among those accessions and revealed groups of distinct growth responses. A clear dose-dependent root response was observed since the clustering differed depending on the level of salinity. From available genome sequence data of those accessions, polymorphisms in coding sequences were extracted and matched with root response pattern, directly linking genotype and phenotype. Gene candidates identified by this approach are involved in phytohormone-related signalling, while for some of them no function is described yet. Testing of T-DNA insertion lines of these genes for their salt stress response confirmed their putative role in the root’s adjustment to salinity.