An ortholog of MIXTA-like2 controls epidermal cell shape in flowers of Thalictrum.
Here, we investigated the genetic underpinnings of pollination-related floral phenotypes in Thalictrum, a ranunculid with apetalous flowers. The variable presence of petaloid features in other floral organs correlates with distinct adaptations to insect vs. wind pollination. Conical cells are present in sepals or stamens of insect-pollinated species, and in stigmas. We characterized a Thalictrum ortholog of the Antirrhinum majus transcription factor MIXTA-like2, responsible for conical cells, from three species with distinct floral morphologies, representing two pollination syndromes. Genes were cloned by PCR and analysed phylogenetically. Expression analyses were conducted by quantitative PCR and in situ hybridization, followed by functional studies in transgenic tobacco. The cloned genes encode R2R3 MYB proteins closely related to Antirrhinum AmMYBML2 and Petunia hybrida PhMYB1. Spatial expression by in situ hybridization overlaps areas of conical cells. Overexpression in tobacco induces cell outgrowths in carpel epidermis and significantly increases the height of petal conical cells. We have described the first orthologs of AmMIXTA-like2 outside the core eudicots, likely ancestral to the MIXTA/MIXTA-like1 duplication. The conserved role in epidermal cell elongation results in conical cells, micromorphological markers for petaloidy. This adaptation to attract insect pollinators was apparently lost after the evolution of wind pollination in Thalictrum.
Di Stilio
Verónica S
VS
Department of Biology, University of Washington, Box 351800, Seattle WA 98195-1800, USA.
Martin
Cathie
C
Department of Cell and Developmental Biology, John Innes Centre, Norwich UK NR4 7UH, UK.
Schulfer
Anjelique F
AF
Department of Biology, University of Washington, Box 351800, Seattle WA 98195-1800, USA.
Connelly
Caitlin F
CF
Department of Biology, University of Washington, Box 351800, Seattle WA 98195-1800, USA.
D000595:Amino Acid Sequence; D044822:Biodiversity; D001681:Biological Assay; D048430:Cell Shape; D003001:Cloning, Molecular; D035264:Flowers / Q000166:cytology / Q000235:genetics / Q000648:ultrastructure; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010802:Phylogeny; D019441:Plant Epidermis / Q000166:cytology* / Q000648:ultrastructure; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D031949:Thalictrum / Q000166:cytology* / Q000235:genetics / Q000648:ultrastructure; D014026:Nicotiana / Q000166:cytology
D010940:Plant Proteins