Abstract
BackgroundShoot branching is an important determinant of plant architecture and influences various aspects of growth and development. Selection on branching has also played an important role in the domestication of crop plants, including sunflower (Helianthus annuus L.). Here, we describe an investigation of the genetic basis of variation in branching in sunflower via association mapping in a diverse collection of cultivated sunflower lines.ResultsDetailed phenotypic analyses revealed extensive variation in the extent and type of branching within the focal population. After correcting for population structure and kinship, association analyses were performed using a genome-wide collection of SNPs to identify genomic regions that influence a variety of branching-related traits. This work resulted in the identification of multiple previously unidentified genomic regions that contribute to variation in branching. Genomic regions that were associated with apical and mid-apical branching were generally distinct from those associated with basal and mid-basal branching. Homologs of known branching genes from other study systems (i.e., Arabidopsis, rice, pea, and petunia) were also identified from the draft assembly of the sunflower genome and their map positions were compared to those of associations identified herein. Numerous candidate branching genes were found to map in close proximity to significant branching associations.ConclusionsIn sunflower, variation in branching is genetically complex and overall branching patterns (i.e., apical vs. basal) were found to be influenced by distinct genomic regions. Moreover, numerous candidate branching genes mapped in close proximity to significant branching associations. Although the sunflower genome exhibits localized islands of elevated linkage disequilibrium (LD), these non-random associations are known to decay rapidly elsewhere. The subset of candidate genes that co-localized with significant associations in regions of low LD represents the most promising target for future functional analyses.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0458-9) contains supplementary material, which is available to authorized users.
Highlights
Shoot branching is an important determinant of plant architecture and influences various aspects of growth and development
We identified candidate genes involved in hormonal or transcriptional regulation that mapped in close proximity to significant associations
In comparing the map positions of these genes to the locations of SNPs exhibiting significant associations, we identified 13 potential candidate branching genes that mapped in close proximity to various branching traits (Figure 5)
Summary
Shoot branching is an important determinant of plant architecture and influences various aspects of growth and development. Selection on branching has played an important role in the domestication of crop plants, including sunflower (Helianthus annuus L.). Shoot branching is a major determinant of plant architecture and plays an important role in the adaptation of plants to their environment. In cultivated sunflower (Helianthus annuus L.), selection during domestication resulted in the production of an apically dominant, unbranched growth form that differs markedly from its highly branched wild progenitor (common sunflower; H. annuus) [7,8,9,10]. The modern-day cultivated sunflower gene pool exhibits substantial variation in plant architecture, making it an ideal system to study the genetics of branching
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