Abstract
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.
Highlights
The root system is of vital importance to plants because it anchors the plant and its cells absorb and transport water, nutrients, and solutes to the shoot
Root Growth and Development Differ at the Morphological and Cellular Level between the Wild (S. pennellii) and Domesticated Tomato Species
Roots of domesticated tomato were significantly longer than those of the wild species for each day up to 6 d after germination and had an increased growth rate for the domesticated cv M82 compared with S. pennellii (12.8 mm d–1 versus 5.1 mm d–1, respectively; Fig. 1, A and B)
Summary
The root system is of vital importance to plants because it anchors the plant and its cells absorb and transport water, nutrients, and solutes to the shoot. The use of stable mapping populations such as a homozygous introgression line (IL) between two different species provides a stable genetic pool from which to repeatedly phenotype different cellular and morphological aspects of root architecture and integrate them into a common model This quantitative genetic analysis is typically conducted using quantitative trait locus (QTL) mapping, which has identified loci or, in a small number of cases, genes that regulate root length in monocots and dicots (Bettey et al, 2000; Mouchel et al, 2004; Loudet et al, 2005; Fitz Gerald et al, 2006; Reymond et al, 2006; Fita et al, 2008; Khan et al, 2012). These studies have typically been limited to the analysis of large-effect loci (Loudet et al, 2005; Reymond et al, 2006) and have not coordinately dissected root architecture at both the morphological and cellular levels
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