CCT39 Transcription Factor Promotes Chlorophyll Biosynthesis and Photosynthesis in Poplar.

Chlorophyll serves as a crucial pigment in plants, essential for photosynthesis, growth, and development. Our previous study has shown that PpnCCT39 can increase leaf chlorophyll content and photosynthesis rate in poplar. However, the underlying molecular mechanisms remain unknown. In this study, we observed that overexpression of PpnCCT39 not only elevates chlorophyll content and photosynthesis, but also induces alterations in leaf morphology, basal diameter, and chloroplast structure. By performing RNA-seq on terminal buds and leaves at leaf positions 1, 3, 5, and 10, we determined that PpnCCT39 predominantly exerts its effects in young leaves. Chromatin Immunoprecipitation Sequencing (ChIP-seq) performed on PpnCCT39-overexpressing poplars identified 17 194 potential regulatory target genes. By integrating RNA-seq and ChIP-seq datasets along with validation assays for protein-DNA interactions, we determined that PpnCCT39 directly stimulated the transcription of three key genes involved in the chlorophyll biosynthesis and photosynthesis pathways: PagHO1, PagLIL3, and PagPYG7. Furthermore, protein interaction assays revealed that PpnCCT39 interacts with PagRD19 and PagATP2, localized in vesicles and mitochondria respectively, with these interactions occurring within chloroplasts. This study elucidates the molecular mechanism by which the PpnCCT39 transcription factor in poplar promotes chlorophyll biosynthesis and photosynthesis. It also highlights the critical role of PpnCCT39 in nucleocytoplasmic interactions. These findings underscore the significance of PpnCCT39 in regulating chlorophyll biosynthesis and enhancing photosynthesis through molecular design.