1. Department of Plant Biology and Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA.
2. Forestry Program, Natural Resources Research Institute, University of Minnesota, Duluth, MN 55811, USA.
3. Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
4. Department of Plant Breeding and Biotechnology, Swedish University of Agricultural Sciences, Alnarp, Sweden.