Abstract:A novel knotted1-like homeobox (knox) gene, Pttkn1 (Populus tremula×tremuloides knotted1), isolated from the cambial region of hybrid aspen, was introduced into Petunia hybrida Vilm. using the leaf-disc method mediated by Agrobacterium. A series of novel phenotypes was observed in transgenic petunia plants, including the formation of ectopic spikes on the adaxial surface of corollas and small petals on the abaxial surface of corollas, fusion of floral organs, shortening of corolla midribs, the formation of tumor-like knots along the midrib on the abaxial surface and serrated lobs of corolla margins, and alterations in petal color; except for changes in the leaves and plant architecture, RT-PCR showed that the Pttkn1 gene was expressed in the leaves of different petunia transgenic plants, whereas no signal was detected in wild-type plants. The possible function of Pttkn1 in leaf and flower development is discussed.