Abstract: In mature buds of the dwarf dogwood lineage (DW) of Cornus, petals and filaments form an “x”-like box containing mechanical energy from the filaments to allow explosive pollen dispersal. As a start to understand the molecular mechanisms responsible for the origin of this unique structure in Cornus, we cloned and characterized the sequences of APETALA3 (AP3) homologs from Cornus canadensis of the DW lineage and five other Cornus species, given the function of AP3 on petal and stamen development in Arabidopsis, and tested the function of CorcanAP3 using a stable Agrobacterium-mediated transformation system. The cloned CorAP3s (AP3-like genes in Cornus) were confirmed to belong to the euAP3 lineage. qRT-PCR analysis indicated strong increase of CorcanAP3 expression in floral buds of wildtype C. canadensis. A hairpin construct of CorcanAP3 was successfully introduced into wild type plants of C. canadensis, resulting in significant reduction of CorcanAP3 expression and abnormal floral development. The abnormal floral buds lost the “x” form and opened immaturely due to delay or retard of petal and stamen elongation and the push of style elongation. The results suggested CorcanAP3 may function to regulate the coordinated rate of development of petals and stamens in C. canadensis, necessary for the x-structure formation, although the exact molecular mechanism remains unclear. Comparison among six Cornus species indicated a greater ratio of stamen to petal and style growth in C. canadensis, suggesting an evolutionary change of CorAP3 expression pattern in the DW lineage, leading to the greater growth of filaments to form the “x”-box.

Key words: abnormality in floral development, Cornus canadensis, explosive pollen release, functional validation of APETALA3 homolog, gene expression, genetic transformation