guildfordcycads

Abstract

Key message

Our results from transcriptomics extend the understanding of the gene expression and major events associated with embryogenesis progression in Taxodium distichum × Taxodium mucronatum.

Abstract

Zygotic embryogenesis is a critical process during seed development in which the plant body plan is established and the meristems responsible for all post-embryonic growth are determined. Taxodium ‘Zhongshanshan’ is a series of superior interspecies hybrids of T. distichum and T. mucronatum and has been widely planted in southeastern China. Understanding the molecular, cellular and metabolic processes of embryonic development will provide important information on the somatic embryogenesis of T. ‘Zhongshanshan’ and further developing zygotic embryogenesis research. In the present study, we sequenced the transcriptomes of zygotic T. distichum × T. mucronatum embryos at several developmental stages, covering most of embryogenesis. Total RNA samples from six zygotic embryo developmental stages were collected for high-throughput RNA sequencing. In total, 46,798 unigenes were identified, and 12,846 differentially expressed genes were annotated. Genes involved in carbohydrate metabolic, such as glycoside hydrolase-, alpha-xylosidase- and xyloglucan endotransglycosylase-encoding genes, were over-represented in early embryogenesis. Genes associated with auxin, gibberellin, and cytokinin signaling pathways and epigenetic genes related to chromatin remodeling, DNA methylation, and histone deacetylase showed significant differential expression during the embryo development process. Moreover, a number of transcription factors related to embryonic development were identified, among which WUSCHEL HOMEOBOX (WOX), NO APCAL MERISTEM (NAM), and LEAFY COTYLEDON1 (LEC1) being more relevant during early and mid-embryogenesis stages. Our results will provide a valuable resource for future studies and will be helpful to the research of T. ‘Zhongshanshan’ breeding programs.

Abstract

Pisonia grandis R. Br. is a tree commonly found in urban coastal and tropical regions, valued for its ornamental beauty and utility in agroforestry and traditional medicine. To facilitate its propagation, particularly through in vitro techniques, this study aimed to refine a propagation system by inducing adventitious buds from node explants of mature tree. The study revealed that the Murashige and Skoog (MS) medium, supplemented with 30 g L⁻¹ sucrose and 2.0 mg L⁻¹ thidiazuron (TDZ), effectively stimulated bud break. Furthermore, a combination of 1.0 mg L⁻¹ TDZ and 0.5 mg L⁻¹ α-naphthalene acetic acid (NAA) yielded optimal shoot multiplication, resulting in an average of 16.0 shoots per explant with a length of 5.9 cm. In contrast, utilizing 1.0 mg L⁻¹ 6-benzylaminopurine (BAP) and 0.5 mg L⁻¹ NAA led to producing 10.0 shoots with a height of 3.7 cm. Incorporating TDZ significantly enhanced shoot numbers, size, and overall health of the shootlets. Microscopic analysis revealed that leaves and petioles derived from the TDZ and NAA combination exhibited desirable features, such as a thick cuticle, well-differentiated epidermis, mesophyll, vascular tissues, stomata, and improved vein density compared to those derived from BAP and NAA. The maximum root percentage (87.5%) and adventitious root formation (averaging 8.0 roots with a length of 6.2 cm) were observed on half-strength media supplemented with 1.5 mg L⁻¹ indole-3-butyric acid (IBA). Conversely, NAA fortification resulted in lower rooting percentages (77.8% response with an average of 4.7 roots measuring 4.0 cm in length). Subsequently, the rooted plantlets were successfully acclimatized using a mixture of soilrite®, cocopeat, and garden soil (1:1:1 v/v ratio), with a survival rate of 92.0% in the field. This study contributes valuable insights into the optimized use of growth regulators for the large-scale propagation of P. grandis and related species, ensuring the production of micro-morpho-structurally stable plantlets.