The developmental transcriptome dynamics of current-year shoot utilized as scion in Camellia chekiangoleosa.

Background: Camellia chekiangoleosa is the most widely planted red-flowered and large-fruited oil-camellia species, with high value in edible oil production and landscaping. To better understand the weak scion development and slow graft-union healing underlying grafting propagation challenges in C. chekiangoleosa, we conducted temporal RNA-seq on current-year shoots with five time points determined according to changes in cell wall composition, aiming to reveal dynamic developmental regulation.

Results: Analysis of temporal expression characteristics of genome-wide genes and differentially expressed genes (DEGs) revealed that genes differentially patterned between stem and apical bud were enriched in functions related to cell division and differentiation, hormone responses, and vascular or flower development. Coexpression network analysis revealed that red/far-red light and gibberellin (GA) signaling were closely correlated with flowering development in C. chekiangoleosa shoots. We further analyzed a unique module showing a negative correlation between the module and traits (cell wall composition, i.e., lignin, cellulose, and hemicellulose content). Genes in the top-scored sub-cluster of this module were enriched in shoot development-related processes, including cell wall dynamics, xylem development, secondary cell wall biogenesis, lignin biosynthesis, and procambium histogenesis. WOX4 and PXY, known markers of cambium cells, were identified as key hub genes, along with the actin-binding protein WLIM1. These coexpressed hub genes associated with vascular system development peaked in June in stems and were validated by qRT-PCR, suggesting that June may be an optimal grafting season for C. chekiangoleosa.

Conclusions: Integrating transcriptomics and physiology defined the dynamic signature of changes in composition of cell wall and gene activity during the development of current-year shoots in C. chekiangoleosa. Our findings provide insights into a potential molecular strategy for breeders, targeting key regulators specific to cambium differentiation, and physiological strategy for hormone or light supplied artificially to enhance grafting productivity of C. chekiangoleosa.