Combining single-cell RNA sequencing with spatial transcriptome analysis reveals dynamic molecular maps of cambium differentiation in the primary and secondary growth of trees

The primary and secondary growth of a tree stem is responsible for the corresponding increases in height and diameter in the trunk. However, our molecular understanding of the biological processes underlying the two growth events is not yet complete. In this study, we used single-cell RNA sequencing (scRNA-seq) and spatial transcriptome sequencing (ST-seq) to get the transcription landscapes of the stem primary and secondary growth tissues in the Populus tree. The results of a comparison between the cell atlas and the differentiation trajectory in primary and secondary growth revealed different regulatory networks in cell differentiation from cambium to xylem precursors and phloem precursors. These regulatory networks may be controlled through the accumulation and distribution of auxin. The cell differentiation trajectory analysis suggests that vessel and fiber development followed a sequential pattern of progressive transcriptional regulation. The research gives new insights into the processes of cell identity and differentiation that occur throughout the primary and secondary growth of tree stems, which would help in the understanding of the cellular differentiation dynamics that occur during the stem growth of perennial trees.