Format: ORAL

Natalia Pabn-Mora1, Angie D. Gonzlez2, Andrea Ramrez-Ramrez1, Juan F. Alzate3, 4, Elena M. Kramer5, Charles C. Davies5, Jeff P. Mower6, Favio Gonzlez7

1. Instituto de Biología, Universidad de Antioquia, Medellín, Colombia. 2. Departamento de Biología, Facultad de Ciencias, Universidad Nacional de Colombia, Bogotá, Colombia. 3. Centro Nacional de Secuenciación Genómica—CNSG, Sede de Investigación Universitaria—SIU, Universidad de Antioquia, Medellín, Colombia 4. Grupo de Parasitología, Facultad de Medicina, Universidad de Antioquia, Medellín, Colombia 5. Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, USA 6. Center for Plant Science Innovation, University of Nebraska, Lincoln, USA. 7. Universidad Nacional de Colombia, Sede Bogotá, Facultad de Ciencias, Instituto de Ciencias Naturales, Bogotá, Colombia

Plant-plant parasitism has independently evolved 12 times in angiosperms. The ca. 4750 parasitic plants constitute only 2% of all angiosperm diversity; however, they exhibit some of the most outstanding genome reductions and extraordinary modifications in terms of development, structural adaptations, and reproductive strategies. The most dramatic developmental reductions occur in the endoholoparasites, which grow completely inside of their hosts as parenchymatic cells, lack typical roots, shoots and leaves, and become visible only through emerging flowers and fruits. We have focused on documenting the atypical developmental transitions occurring in the Apodanthaceae, specifically in the Salicaceae parasite Apodanthes and the Fabaceae parasite Pilostyles. These plants have no root (RAM) or shoot (SAM) apical meristems; however, flowers initiate in contact to the host vascular tissue, completely inside the host, and emerge having completed organogenesis. Using comparative genomics, we are currently characterizing plastome reduction and are documenting extensive horizontal gene transfer in the mitogenomes. Using comparative transcriptomics (derived from the host, the parasite, and mixed tissues), we have addressed the mechanisms through which Pilostyles maintains stem cells in the absence of primary meristems, the signals perceived for reproductive transitions in the absence of typical photoperiod sensing leaves, and the endogenous capacity for organogenesis in the dark, fully embedded inside of the host. We will present data on: 1) the substantial reduction in the SAMs genetic machinery; 2) the regulation of cell division during the endophytic phase until the completion of flower development, 3) potential recruitment of host flowering regulators by the holoparasites; and 4) expression analyses of endogenous LEAFY and MADS-box floral organ identity homologs in these atypical flowering plants. We will discuss our results in comparison with emerging developmental data from other holoparasitic plants to determine convergent mechanisms in the evolution of parasitism.