Molecular cloning and functional characterization of apple MdPIF1

In the angiosperm seed, the decision to germinate is dependent on the interaction of various environmental factors, including temperature and light. Light is sensed and perceived by photoreceptors. Till now, several photoreceptors have been characterized from various plant species. Among them, phytochromes (phys) are the red and far-red light photoreceptors that mediate multiple responses in plant growth and development. Here, we showed that the MdPIF1, a bHLH gene, which encodes a PIF-like protein, was constitutively expressed at different levels in various apple tissues, and was significantly induced during seed germination. Functional complementation assay in Arabidopsis pil5 mutant suggested that MdPIF1 was a negative regulator in the phy-mediated inhibition of hypocotyl elongation, and seed germination was inhibited after MdPIF1 overexpression in the transgenic pil5 mutant lines. In addition, MdPIF1 regulated the germination of apple seeds and dormancy breaking in apple buds based on our study. Moreover, we observed that MdPIF1 inhibited growth via phy-mediated pathways in apple calluses. These findings suggested MdPIF1 acts as an important regulator in phy-mediated plant growth and development.