Synergistic integration of light signal, hormone dynamics, and carbohydrate metabolism orchestrates rhizome bud development in Arundo donax.

Main conclusion: The rhizome bud development is governed by light signal, hormonal dynamics, carbohydrate metabolism, and cell cycle regulation in Arundo donax. Rhizomatous plants reproduce asexually through transplantation of rhizome segments bearing buds, which develop into new individuals. However, the regulatory mechanism governing rhizome bud differentiation and development is still unknown. In this study, cytological observations were conducted on rhizome buds of Arundo donax at different developmental stages, and RNA sequencing and differentially expressed gene analysis were performed on rhizomes and preparatory rhizome buds (PR). The results showed that rhizome buds elongated outward from internal structure of the rhizomes. During PR initiation, the far-red light receptor PHYA and photosystem-related genes in the light-signal pathway were significantly upregulated, indicating that far-red light promoted PR initiation. In the IAA signal pathway, transport inhibitor protein 1 (TIR1) and auxin response factor (ARF) genes were significantly upregulated, while in the CTK signal pathway, the cytokinin receptor (AHK), histidine-containing phosphotransfer protein (AHP), and the type-A Arabidopsis response regulator (A-ARR) were significantly upregulated, with the type-B Arabidopsis response regulator (B-ARR) downregulated. These results suggested that IAA and CTK signal promoted cell division and differentiation. In addition, genes responsible for starch degradation into glucose were upregulated during this process, indicating that glucose served as the primary energy source. The cell cycle regulators D-type cyclin (CYCD) and cyclin-dependent kinase 2 (CDK2) were significantly upregulated, demonstrating active cell division and differentiation activities. This analysis constructed a multi-dimensional regulatory network of rhizome bud development, revealing that PR development is regulated by multiple coordinated pathways, including light signal, hormone dynamics, carbohydrate metabolism, and cell cycle regulation in A. donax.