Abstract
BackgroundBark plays important roles in photosynthate transport and storage, along with physical and chemical protection. Bark texture varies extensively among species, from smooth to fissured to deeply furrowed, but its genetic control is unknown. This study sought to determine the main genomic regions associated with natural variation in bark features and stem diameter. Quantitative trait loci (QTL) were mapped using an interspecific pseudo-backcross pedigree (Populus trichocarpa x P. deltoides and P. deltoides) for bark texture, bark thickness and diameter collected across three years, two sites and three biological replicates per site.ResultsQTL specific to bark texture were highly reproducible in shared intervals across sites, years and replicates. Significant positive correlations and co-localization between trait QTL suggest pleiotropic regulators or closely linked genes. A list of candidate genes with related putative function, location close to QTL maxima and with the highest expression level in the phloem, xylem and cambium was identified.ConclusionCandidate genes for bark texture included an ortholog of Arabidopsis ANAC104 (PopNAC128), which plays a role in lignified fiber cell and ray development, as well as Pinin and Fasciclin (PopFLA) genes with a role in cell adhesion, cell shape and migration. The results presented in this study provide a basis for future genomic characterization of genes found within the QTL for bark texture, bark thickness and diameter in order to better understand stem and bark development in Populus and other woody perennial plants. The QTL mapping approach identified a list of prime candidate genes for further validation using functional genomics or forward genetics approaches.
Highlights
Bark plays important roles in photosynthate transport and storage, along with physical and chemical protection
Fissured bark typical for P. trichocarpa was not found in this backcross pedigree (P. deltoides x P. trichocarpa hybrid backcrossed with P. deltoides)
The phenotypic correlations at the Oregon site (OR) site within the same year for bark texture ranged from r = 0.58 to 0.76; for diameter, r = 0.38 to 0.45 and for bark thickness, r = 0.40 to 0.56, all at p ≤ 0.0001 (Additional file 2: Table S1)
Summary
Bark plays important roles in photosynthate transport and storage, along with physical and chemical protection. Bark texture varies extensively among species, from smooth to fissured to deeply furrowed, but its genetic control is unknown. Despite its important roles including photosynthate transport [3], photosynthesis [4, 5], storage [6], mechanical support [7] and protection [8,9,10,11], the molecular basis of bark formation remains poorly understood (for reviews see: [12, 13]). Bark texture varies among species, and even among genotypes within species, and has notable phenotypic diversity ranging from smooth, peeling, fractured, fissured to plated [14]. Ecological and industrial value of bark, the genetic basis of bark’s features remains undefined
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