Single-Cell Transcriptome Atlas of Leaves at Different Developmental Stages in Populus alba × Populus glandulosa Clone 84K

Leaves are crucial photosynthetic plant organs. The development of poplar leaves has spatio-temporal specificity and it is of great significance to study the single-cell transcription atlas of leaves to reveal the temporal regulation of gene expression in different cell types. Here, single-cell RNA sequencing was performed on 17,768 tender leaf and 5846 functional leaf cells of Poplar 84K to construct a transcriptome atlas and developmental trajectory. The results showed that there were five and six cell types in tender and functional leaves, respectively. According to a pseudo-time trajectory analysis and the clustering of expressed genes into different cell types, the development of tender and functional leaves was divided into two temporal stages. Tender leaf epidermal cells developed earliest and were enriched with genes related to cell division and growth, indicating that tender leaves were in the stage of cell expansion and functional differentiation. Functional leaf palisade mesophyll cells were enriched with genes related to photosynthesis and carbon metabolism and cell types performing different functions tended to mature, indicating that functional leaves were in the stage of leaf development and the initial formation of photosynthesis. Our in-depth analysis of the transcriptional regulation at the single-cell level during leaf development provides an important basis for studying the mechanisms involved in cell differentiation and leaf development in poplar as well as other plants.