The present invention is related to a birch BpCol2 nucleic acid sequence and BpCol2-like nucleic acid sequences, which are related to CONSTANS (CO) gene family, and gene products thereof as well as methods and use therein for influencing growth of a plant or roots of a plant. Particularly the invention is related to cloning and expression of BpCol2 gene in plants. The invention is further related to DNA constructs, vectors, transgenic cells, plants and seeds comprising said nucleic acid sequences and gene products.