To date, little is known about the evolution of fern genomes, with only two small genomes published from the heterosporous Salviniales. Here we assembled the genome of Alsophila spinulosa, known as the flying spider-monkey tree fern, onto 69 pseudochromosomes. The remarkable preservation of synteny, despite resulting from an ancient whole-genome duplication over 100 million years ago, is unprecedented in plants and probably speaks to the uniqueness of tree ferns. Our detailed investigations into stem anatomy and lignin biosynthesis shed new light on the evolution of stem formation in tree ferns. We identified a phenolic compound, alsophilin, that is abundant in xylem, and we provided the molecular basis for its biosynthesis. Finally, analysis of demographic history revealed two genetic bottlenecks, resulting in rapid demographic declines of A. spinulosa. The A. spinulosa genome fills a crucial gap in the plant genomic landscape and helps elucidate many unique aspects of tree fern biology.

Wood formation involves consecutive developmental steps, including cell division of vascular cambium, xylem cell expansion, secondary cell wall (SCW) deposition, and programmed cell death. In this study, we identified PagMYB31 as a coordinator regulating these processes in Populus alba × Populus glandulosa and built a PagMYB31-mediated transcriptional regulatory network. PagMYB31 mutation caused fewer layers of cambial cells, larger fusiform initials, ray initials, vessels, fiber and ray cells, and enhanced xylem cell SCW thickening, showing that PagMYB31 positively regulates cambial cell proliferation and negatively regulates xylem cell expansion and SCW biosynthesis. PagMYB31 repressed xylem cell expansion and SCW thickening through directly inhibiting wall-modifying enzyme genes and the transcription factor genes that activate the whole SCW biosynthetic program, respectively. In cambium, PagMYB31 could promote cambial activity through TRACHEARY ELEMENT DIFFERENTIATION INHIBITORY FACTOR (TDIF)/PHLOEM INTERCALATED WITH XYLEM (PXY) signaling by directly regulating CLAVATA3/ESR-RELATED (CLE) genes, and it could also directly activate WUSCHEL HOMEOBOX RELATED4 (PagWOX4), forming a feedforward regulation. We also observed that PagMYB31 could either promote cell proliferation through the MYB31-MYB72-WOX4 module or inhibit cambial activity through the MYB31-MYB72-VASCULAR CAMBIUM-RELATED MADS2 (VCM2)/PIN-FORMED5 (PIN5) modules, suggesting its role in maintaining the homeostasis of vascular cambium. PagMYB31 could be a potential target to manipulate different developmental stages of wood formation.

NACs (NAM, ATAF1/2, and CUC2) are plant-specific transcription factors that play diverse roles in various plant developmental processes. In this study, we identified the NAC gene family in birch (Betula pendula) and further analyzed the function of BpNACs. Phylogenetic analysis reveals that the 114 BpNACs can be divided into seven subfamilies. We investigated the expression levels of these BpNACs in different tissues of birch including roots, xylem, leaves, and flowers, and the results showed that the BpNACs seem to be expressed higher in xylem and roots than leaves and flowers. In addition to tissue-specific expression analysis, we investigated the expression of BpNACs under low-temperature stress. A total of 21 BpNACs were differentially expressed under low-temperature stress, of which 17 were up-regulated, and four were down-regulated. Using the gene expression data, we reconstructed the gene co-expression network for the 21 low-temperature-responsive BpNACs. In conclusion, our results provide insight into the evolution of NAC genes in the B. pendula genome, and provide a basis for understanding the molecular mechanism for BpNAC-mediated cold responses in birch.

Background: Pinus koraiensis is an evergreen tree species with strong cold resistance. However, the transcriptomic patterns in response to cold stress are poorly understood for P. koraiensis. In this study, global transcriptome profiles were generated for P. koraiensis under cold stress (− 20 °C) over time by high-throughput sequencing. Results: More than 763 million clean reads were produced, which assembled into a nonredundant data set of 123,445 unigenes. Among them, 38,905 unigenes had homology with known genes, 18,239 were assigned to 54 gene ontology (GO) categories and 18,909 were assigned to 25 clusters of orthologous groups (COG) categories. Comparison of transcriptomes of P. koraiensis seedlings grown at room temperature (20 °C) and low temperature (− 20 °C) revealed 9842 differential expressed genes (DEGs) in the 6 h sample, 9250 in the 24 h sample, and 9697 in the 48 h sample. The number of DEGs in the pairwise comparisons of 6 h, 24 h and 48 h was relatively small. The accuracy of the RNA-seq was validated by analyzing the expression patterns of 12 DEGs by quantitative real-time PCR (qRT-PCR). In this study, 34 DEGs (22 upregulated and 12 downregulated) were involved in the perception and transmission of cold signals, 96 DEGs (41 upregulated and 55 downregulated) encoding 8 transcription factors that regulated cold-related genes expression, and 27 DEGs (17 upregulated and 10 downregulated) were involved in antioxidant mechanisms in response to cold stress. Among them, the expression levels of c63631_g1 (annexin D1), c65620_g1 (alpha-amylase isozyme 3C), c61970_g1 (calcium-binding protein KIC), c51736_g1 (ABA), c58408_g1 (DREB3), c66599_g1 (DREB3), c67548_g2 (SOD), c55044_g1 (CAT), c71938_g2 (CAT) and c11358_g1 (GPX) first increased significantly and then decreased significantly with the extension of stress time. Conclusions: A large number of DEGs were identified in P. koraiensis under cold stress, especially the DEGs involved in the perception and transmission of cold signals, the DEGs encoding TFs related to cold regulation and the DEGs removing ROS in antioxidation mechanisms. The transcriptome and digital expression profiling of P. koraiensis could facilitate the understanding of the molecular control mechanism related to cold responses and provide the basis for the molecular breeding of conifers.