LAUSR

Abstract In this study, Populus tomentosa hybrid poplar 741 seedlings were used for transcriptome analysis; growth characteristics under blue-light treatment were examined at different durations (1, 2, and 5 d), with white-light treatment used as the control, to reveal the response mechanism under blue light. The results showed height growth of poplar 741 were higher under blue light than under control at 1, 2, and 5 d, and increased by 380%, 216%, and 173%, respectively. The chlorophyll and carotenoid contents increased under blue light, indicating blue light was beneficial to photosynthetic pigments biosynthesis. The net photosynthetic rate (Pn), stomatal conductance, and Fv/Fm values were higher under blue light, with Pn, which was significantly increased by 20.47% at 2 d and 83.68% at 5 d, indicating blue light improved photosynthesis. In total, 505, 755, and 680 differentially expressed genes (DEGs) were detected at 1, 2, and 5 d, respectively. Twenty-six DEGs related to chlorophyll, photosynthesis, plant hormone, and blue light receptors were identified, and most of these were upregulated, indicating poplar 741 coped with blue light by regulating the expression of DEGs in porphyrin and chlorophyll metabolism, terpenoid backbone biosynthesis, diterpenoid biosynthesis, and circadian rhythm-plant pathways. This study revealed the physiological responses of poplar 741 to blue light and identified the potential pathways and candidate genes, which will provide information to explore the growth regulatory mechanism of poplar 741 under different light qualities.