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Background Magonlia denudata is an important perennial tree species of the Magnoliaceae family, known for its ornamental value, resistance to smoke pollution and wind, role in air purification, and robust cold tolerance. In this study, a high-throughput transcriptome analysis of leaf buds was performed, and gene expression following artificial acclimation 22 °C, 4 °C and 0 °C, was compared by RNA sequencing. Results Over 426 million clean reads were produced from three libraries (22 °C, 4 °C and 0 °C). A total of 74,503 non-redundant unigenes were generated, with an average length of 1173.7 bp (N50 = 1548). Based on transcriptional results, 357 and 235 unigenes were identified as being upregulated and downregulated under cold stress conditions, respectively. Differentially expressed genes were annotated using Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes pathway analyses. The transcriptomic analysis focused on carbon metabolism and plant hormone signal transduction associated with cold acclimation. Transcription factors such as those in the basic helix-loop-helix and AP2/ERF families were found to play an important role in M. denudata cold acclimation. Conclusion M. denudata exhibits responses to non-freezing cold temperature (4 °C) to increase its cold tolerance. Cold resistance was further strengthened with cold acclimation under freezing conditions (0 °C). Cold tolerance genes, and cold signaling transcriptional pathways, and potential functional key components for the regulation of the cold response were identified in M. denudata. These results provide a basis for further studies, and the verification of key genes involved in cold acclimation responses in M. denudata lays a foundation for developing breeding programs for Magnoliaceae species.

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AGAMOUS/SEEDSTICK (AG/STK) subfamily genes play crucial roles in the reproductive development of plants. However, most of our current knowledge of AG/STK subfamily genes is restricted to core eudicots and grasses, and the knowledge of ancestral exon–intron structures, expression patterns, protein–protein interaction patterns and functions of AG/STK subfamily genes remains unclear. To determine these, we isolated AG/STK subfamily genes (MawuAG1, MawuAG2 and MawuSTK) from a woody basal angiosperm Magnolia wufengensis (Magnoliaceae). MawuSTK arose from the gene duplication event occurring before the diversification of extant angiosperms, and MawuAG1 and MawuAG2 may result from a gene duplication event occurring before the divergence of Magnoliaceae and Lauraceae. Gene duplication led to apparent diversification in their expression and interaction patterns. It revealed that expression in both stamens and carpels likely represents the ancestral expression profiles of AG lineage genes, and expression of STK-like genes in stamens may have been lost soon after the appearance of the STK lineage. Moreover, AG/STK subfamily proteins may have immediately established interactions with the SEPALLATA (SEP) subfamily proteins following the emergence of the SEP subfamily; however, their interactions with the APETALA1/FRUITFULL subfamily proteins or themselves differ from those found in monocots and basal and core eudicots. MawuAG1 plays highly conserved roles in the determinacy of stamen, carpel and ovule identity, while gene duplication contributed to the functional diversification of MawuAG2 and MawuSTK. In addition, we investigated the evolutionary history of exon–intron structural changes of the AG/STK subfamily, and a novel splice-acceptor mode (GUU-AU) and the convergent evolution of N-terminal extension in the euAG and PLE subclades were revealed for the first time. These results further advance our understanding of ancestral AG/STK subfamily genes in terms of phylogeny, exon–intron structures, expression and interaction patterns, and functions, and provide strong evidence for the significance of gene duplication in the expansion and evolution of the AG/STK subfamily.