Objective  Poplar seed hair is produced by the development of epidermal cells of the placenta at the base of ovary and it has become one of the environmental problems in northern cities of China in recent years. At present, the research on poplar seed hair is not in-depth. In this study, two genes (PeCFL1 and PeCFL2), which are differentially expressed during the development of poplar ovary and related to cotton fiber development, were selected as candidate genes for the regulation of seed hair development. We studied the spatio-temporal specificity of PeCFL1 and PeCFL2 genes expressed in Populus × euramericana ‘Bofeng 3’ to lay a foundation for further study on the regulation of the two genes during the development of poplar seed hair and improvement of poplar varieties by genetic engineering.

  Method  After 4, 5, 6, 7, 8, 12 days of hydroponic culture, the female inflorescences of Populus × euramericana ‘Bofeng 3’ were collected, fixed, paraffin embedded and sliced to observe the ovary development and the morphogenesis of poplar seed hair. Real time quantitative PCR was used to detect the expression patterns of PeCFL1 and PeCFL2 genes during the development of female inflorescence and in vegetative organs such as roots, stems and leaves of ‘Bofeng 3’ poplar. The tissue expression specificity of PeCFL1 and PeCFL2 genes in poplar flower organs was detected by in situ hybridization, and the temporal and spatial expression patterns of candidate genes PeCFL1 and PeCFL2 related to the regulation of poplar floc development were revealed.

  Result  After 12 days of hydroponic culture, fibrous structure appeared at the bottom of ovary placentation and poplar seed hair began to form. PeCFL1 and PeCFL2 were expressed in roots, stems, leaves and axillary buds of female flower branches of ‘Bofeng 3’ poplar. For the female inflorescence of hydroponic culture, a small amount of PeCFL1 and PeCFL2 were expressed from the 4th to the 7th day, and the expression levels began to increase significantly after the 8th day. Then the expression levels continued to increase significantly on the 12th day, at the same time, the fibrous structure at the bottom of placenta could be seen in paraffin section. The results of in situ hybridization showed that PeCFL1 and PeCFL2 genes were expressed in ovary wall and placenta of poplar ovary.

  Conclusion  The expression of PeCFL1 and PeCFL2 is significantly increased when the fibrous structure appeared at the bottom of the placentation in female flowers of Populus × euramericana ‘Bofeng 3’, and they are specifically expressed in the fibrous structure at the bottom of the placenta and the ovary wall, indicating that they are closely related to the regulation of seed hair development, and can be used as target genes for genetic engineering improvement of poplar seed hair.