Cinnamomum camphora is an ecologically and economically significant species, highly valued for its essential oil production and environmental benefits. Although a tissue culture system has been established for C. camphora, large-scale propagation remains limited due to the inconsistent formation of adventitious roots (ARs). This study investigated AR formation from callus tissue, focusing on associated physiological changes and gene expression dynamics. During AR induction, contents of soluble sugars and proteins decreased, alongside reduced activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO). Levels of indole-3-acetic acid (IAA) and abscisic acid (ABA) decreased significantly throughout AR formation. Zeatin riboside (ZR) levels initially declined and then rose, whereas gibberellic acid (GA) levels displayed the opposite trend. Comparative transcriptomic and temporal expression analyses identified differentially expressed genes (DEGs), which were grouped into four distinct expression patterns. KEGG pathway enrichment indicated that 67 DEGs are involved in plant hormone signaling pathways and that 38 DEGs are involved in the starch and sucrose metabolism pathway. Additionally, protein–protein interaction network (PPI) analysis revealed ten key regulatory genes, which are mainly involved in auxin, cytokinin, GA, ABA, and ethylene signaling pathways. The reliability of the transcriptome data was further validated by quantitative real-time PCR. Overall, this study provides new insights into the physiological and molecular mechanisms underlying AR formation in C. camphora and offers valuable guidance for optimizing tissue culture systems.

A pluripotent callus is central to genetic transformation in Cinnamomum parthenoxylon; however, the molecular and cellular mechanisms regulating callus formation and subsequent differentiation remain unelucidated, hindering progress in its genetic improvement. This study systematically investigated the dynamic changes during the in vitro regeneration of C. parthenoxylon through morphological observations, physiological assays, and transcriptomic analyses, while comparing differences in callus formation under varying induction conditions to elucidate the mechanism of its high-efficiency regeneration. The results showed that the formation of a pluripotent callus is a critical step in C. parthenoxylon regeneration, characterized by the presence of highly proliferative cell zones. Compared to an ordinary callus (P3C), a pluripotent callus (P3) exhibited higher activities of polyphenol oxidase (PPO) and indole-3-acetic acid oxidase (IAAO), as well as elevated levels of zeatin riboside (ZR) and abscisic acid (ABA). In contrast, P3 showed lower levels of soluble sugars, soluble proteins, malondialdehyde (MDA), indole-3-acetic acid (IAA), and gibberellins (GA), a reduced IAA/ZR ratio, and diminished peroxidase (POD) activity. Weighted gene co-expression network analysis (WGCNA) identified 27 hub transcription factors (TFs) strongly associated with IAA/ZR, primarily from the ERF, bHLH, MYB, WRKY, and C3H families. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed the significant enrichment of differentially expressed genes (DEGs) related to plant hormone signal transduction and cell wall metabolism during pluripotent callus acquisition. Further investigations revealed that five genes encoding a putative indole-3-acetic acid-amido synthetase GH3.1, protein TIFY 10A, a two-component response regulator ARR2-like isoform X2, and xyloglucan endotransglucosylase/hydrolase, likely promoting callus pluripotency by modulating plant hormone signaling and cell wall metabolism, thereby enhancing in vitro regeneration in C. parthenoxylon. In summary, this study provides critical insights into the molecular mechanisms of C. parthenoxylon regeneration and offers valuable germplasm resources for establishing an efficient and stable genetic transformation system via tissue culture.

Polyploidization produces abundant phenotypic variation. Little is currently known about adventitious root (AR) development variation due to polyploidization. In this study, we analyzed the morphological, cytological, and physiological variations in AR development between tetraploid and diploid Populus plants during in vitro rooting culture. Compared to the diploids, the AR formation times and rooting rates of the tetraploids’ stem explants had non-significant changes. However, the tetraploid ARs exhibited significantly slower elongation growth than the diploid ARs. Cytological observation showed that the tetraploid ARs were characterized by shorter root meristems and reduced meristem cell numbers, suggesting the reasons for the slow AR elongation. Analysis of hormones and related metabolites during AR development demonstrated that the total auxin, cytokinin, and jasmonic acid contents were significantly lower in the tetraploid ARs than in those of the diploids, and that the ratio of total auxins to total CKs at 0 h of AR development was also lower in the tetraploids than in the diploids, whereas the total salicylic acid content of the tetraploids was consistently higher than that of the diploids. qPCR analysis showed that the expression levels of several hormone signaling and cell division-related genes in the tetraploid ARs significantly differed from those in the diploids. In conclusion, the slow elongation of the tetraploid ARs may be caused by the endogenous hormone-mediated meristem shortening. Our findings enhance the understanding of polyploidization-induced variation in AR development of forest trees.

Cinnamomum kanehirae is a species of high economic worth, as it produces abundant aromatic oils for industrial use and its heartwood acts as an optimal sub