title: Association mapping in sunflower (Helianthus annuus L.) reveals independent control of apical vs. basal branching.
abstract: BACKGROUND
  Shoot 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.
  
  
  RESULTS
  Detailed 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.
  
  
  CONCLUSIONS
  In 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.
authors.affiliation: Department of Plant Biology, Miller Plant Sciences, University of Georgia, Athens, GA, 30602, USA. sunamb@uga.edu.|Present address: Department of Horticulture, University of Georgia, Athens, GA, 30602, USA. sunamb@uga.edu.
authors.forename: Savithri U
authors.initials: SU
authors.lastname: Nambeesan
authors.affiliation: Department of Plant Biology, Miller Plant Sciences, University of Georgia, Athens, GA, 30602, USA. jennifer.r.mandel@gmail.com.|Present address: Department of Biological Sciences, University of Memphis, Memphis, TN, 38152, USA. jennifer.r.mandel@gmail.com.
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Mandel
authors.affiliation: Department of Plant Biology, Miller Plant Sciences, University of Georgia, Athens, GA, 30602, USA. jebowers@uga.edu.
authors.forename: John E
authors.initials: JE
authors.lastname: Bowers
authors.affiliation: North Central Regional Plant Introduction Station, Iowa State University/USDA-ARS, Ames, IA, 50014, USA. lmarek@iastate.edu.
authors.forename: Laura F
authors.initials: LF
authors.lastname: Marek
authors.affiliation: Department of Botany, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. dpebert@gmail.com.
authors.forename: Daniel
authors.initials: D
authors.lastname: Ebert
authors.affiliation: Department of Plant Biology, Miller Plant Sciences, University of Georgia, Athens, GA, 30602, USA. corbijonathan@gmail.com.|Present address: Department of Crop and Soil Sciences, University of Georgia, Athens, GA, 30602, USA. corbijonathan@gmail.com.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Corbi
authors.affiliation: Department of Botany, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. loren.rieseberg@botany.ubc.ca.
authors.forename: Loren H
authors.initials: LH
authors.lastname: Rieseberg
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA, 95616, USA. steve.knapp@monsanto.com.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Knapp
authors.affiliation: Department of Plant Biology, Miller Plant Sciences, University of Georgia, Athens, GA, 30602, USA. jmburke@uga.edu.
authors.forename: John M
authors.initials: JM
authors.lastname: Burke
mesh_terms: D017343:Genes, Plant; D006368:Helianthus / Q000235:genetics* / Q000254:growth & development*; D020641:Polymorphism, Single Nucleotide