Identification of novel loci regulating interspecific variation in root morphology and cellular development in tomato.

While the Arabidopsis (Arabidopsis thaliana) root has been elegantly characterized with respect to specification of cell identity, its development is missing a number of cellular features present in other species. We have characterized the root development of a wild and a domesticated tomato species, Solanum pennellii and Solanum lycopersicum 'M82.' We found extensive differences between these species for root morphology and cellular development including root length, a novel gravity set point angle, differences in cortical cell layer patterning, stem cell niche structure, and radial cell division. Using an introgression line population between these two species, we identified numerous loci that regulate these distinct aspects of development. Specifically we comprehensively identified loci that regulate (1) root length by distinct mechanisms including regulation of cell production within the meristem and the balance between cell division and expansion, (2) the gravity set point angle, and (3) radial cell division or expansion either in specific cell types or generally across multiple cell types. Our findings provide a novel perspective on the regulation of root growth and development between species. These loci have exciting implications with respect to regulation of drought resistance or salinity tolerance and regulation of root development in a family that has undergone domestication.