Format: ORAL

Vernica S. Di Stilio and Anthony G. Garca

Department of Biology, University of Washington, Seattle, USA

Wind pollination has evolved repeatedly in flowering plants, yet the developmental genetics of floral traits associated with this pollination mode remains elusive. Thalictrum (Ranunculaceae) have transitioned repeatedly between insect and wind pollination and exhibit intermediate floral morphs with mixed pollination, providing an ideal system to test the correlated evolution of floral morphology, developmental genetics and pollination mode. Prior data broadly supports the existence of detectable flower morphs from convergent evolution to wind pollination in Thalictrum, consisting of small, inconspicuous, and mostly dioecious flowers with extended stigmatic surfaces on long styles or dangling stamens. MIXTA family transcription factors are known to modulate the differentiation of cellular outgrowths (conical cells and trichomes) on the epidermis of land plants and were tested here as potential candidates for the longer stigmatic papillae and extended stigmas found in wind-pollinated species. A single copy ortholog from diploid T. thalictroides, paleoMIXTA (TthPMX), was functionally characterized via targeted gene silencing and overexpression, followed by comparative transcriptomics to investigate the gene regulatory network. The reduction in stigmatic papillae length under targeted gene silencing and their extension under over-expression suggest that TthPMX has a novel role in promoting stigmatic papillae cell elongation. Elevated expression of specific PMX paralogs in carpels of polyploid taxa further suggests that duplications in PMX may have facilitated the evolution of the long stigmatic papillae found in plumose stigmas of wind-pollinated species.