Author(s)

Malay Das^1,2, Monica Fernández-Aparicio³, Zhenzhen Yang⁴, Kan Huang⁵, Norman J. Wickett⁶, Shannon Alford¹, Eric K. Wafula⁴, Claude dePamphilis⁴, Harro Bouwmeester⁷, Michael P. Timko⁵, John I. Yoder⁸, James H. Westwood¹

¹Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, USA.
²Department of Biological Sciences, Presidency University, Kolkata, India.
³Institute for Sustainable Agriculture, Department of Plant Breeding, Spanish National Research Council, Córdoba, Spain.
⁴Department of Biology, Institute of Molecular Evolutionary Genetics, Pennsylvania State University, University Park, PA, USA.
⁵Department of Biology, University of Virginia, Charlottesville, VA, USA.
⁶Chicago Botanic Garden, Glencoe, IL, USA.
⁷Laboratory of Plant Physiology, Wageningen University, Wageningen, Netherlands.
⁸Department of Plant Sciences, University of California, Davis, Davis, CA, USA.

Strigolactones are plant hormones with multiple functions, including regulating various aspects of plant architecture such as shoot branching, facilitating the colonization of plant roots by arbuscular mycorrhizal fungi, and acting as seed germination stimulants for certain parasitic plants of the family Orobanchaceae. The obligate parasitic species Phelipanche aegyptiaca and Striga hermonthica require strigolactones for germination, while the facultative parasite Triphysaria versicolor does not. It has been hypothesized that P. aegyptiaca and S. hermonthica would have undergone evolutionary loss of strigolactone biosynthesis as a part of their mechanism to enable specific detection of exogenous strigolactones. We analyzed the transcriptomes of P. aegyptiaca, S. hermonthica and T. versicolor and identified genes known to act in strigolactone synthesis (D27, CCD7, CCD8, and MAX1), perception (MAX2 and D14) and transport (PDR12). These genes were then analyzed to assess likelihood of function. Transcripts of all strigolactone-related genes were found in P. aegyptiaca and S. hermonthica, and evidence points to their encoding functional proteins. Gene open reading frames were consistent with homologs from Arabidopsis and other strigolactone-producing plants, and all genes were expressed in parasite tissues. In general, the genes related to strigolactone synthesis and perception appeared to be evolving under codon-based selective constraints in strigolactone-dependent species. Bioassays of S. hermonthica root extracts indicated the presence of strigolactone class stimulants on germination of P. aegyptiaca seeds. Taken together, these results indicate that Phelipanche aegyptiaca and S. hermonthica have retained functional genes involved in strigolactone biosynthesis, suggesting that the parasites use both endogenous and exogenous strigolactones and have mechanisms to differentiate the two.

Broomrape, Phelipanche, Striga, Strigolactone, Triphysaria, Witchweed

Das, M. , Fernández-Aparicio, M. , Yang, Z. , Huang, K. , Wickett, N. , Alford, S. , Wafula, E. , dePamphilis, C. , Bouwmeester, H. , Timko, M. , Yoder, J. and Westwood, J. (2015) Parasitic Plants Striga and Phelipanche Dependent upon Exogenous Strigolactones for Germination Have Retained Genes for Strigolactone Biosynthesis. American Journal of Plant Sciences, 6, 1151-1166. doi: 10.4236/ajps.2015.68120.