(1) Background: Brassinosteroids (BRs) are important hormones involved in almost all stages of plant growth and development, and sterol dehydrogenase is a key enzyme involved in BRs biosynthesis. However, the sterol dehydrogenase gene family of Populus yunnanensis Dode (P. yunnanensis) has not been studied. (2) Methods: The PyDET2 (DEETIOLATED2) gene family was identified and analyzed. Three genes were screened based on RNA-seq of the stem tips, and the PyDET2e was further investigated via qRT-PCR (quantitative real-time polymerase chain reaction) and subcellular localization. (3) Results: The 14 DET2 family genes in P. yunnanensis were categorized into four groups, and 10 conserved protein motifs were identified. The gene structure, chromosome distribution, collinearity, and codon preference of all PyDET2 genes in the P. yunnanensis genome were analyzed. The codon preference of this family is towards the A/U ending, which is strongly influenced by natural selection. The PyDET2e gene was expressed at a higher level in September than in July, and it was significantly expressed in stems, stem tips, and leaves. The PyDET2e protein was localized in chloroplasts. (4) Conclusions: The PyDET2e plays an important role in the rapid growth period of P. yunnanensis. This systematic analysis provides a basis for the genome-wide identification of genes related to the brassinolide biosynthesis process in P. yunnanensis, and lays a foundation for the study of the rapid growth mechanism of P. yunnanensis.

DNA methylation is an important mechanism for epigenetic modifications that have been shown to be associated with responses to plant development. Previous studies found that inverted Populus yunnanensis cuttings were still viable and could develop into complete plants. However, the growth status of inverted cuttings was weaker than that of upright cuttings, and the sprouting time of inverted cuttings was later than that of upright cuttings. There is currently no research on DNA methylation patterns in inverted cuttings of Populus yunnanensis. In this study, we detected genome-wide methylation patterns of stem tips of Populus yunnanensis at the early growth stage and the rapid growth stage by Oxford Nanopore Technologies (ONT) methylation sequencing. We found that the methylation levels of CpG, CHG, CHH, and 6mA were 41.34%, 33.79%, 17.27%, and 12.90%, respectively, in the genome of inverted poplar cuttings, while the methylation levels of the four methylation types were higher in the genome of upright poplar cuttings than in inverted cuttings, 41.90%, 34.57%, 18.09%, and 14.11%, suggesting important roles for DNA methylation in poplar cells. In all comparison groups, CpG-type methylation genes in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway were annotated to pathways associated with carbon metabolism, ribosome biogenesis in eukaryotes, glycolysis/gluconeogenesis, pyruvate metabolism, and mRNA detection pathways, suggesting that different biological processes are activated in upright and inverted cuttings. The results show that methylation genes are commonly present in the poplar genome, but only a few of them are involved in the regulation of expression in the growth and development of inverted cuttings. From this, we screened the DET2 gene for significant differences in methylation levels in upright or inverted cuttings. The DET2 gene is a key gene in the Brassinolide (BRs) synthesis pathway, and BRs have an important influence on the growth and development process of plants. These results provide important clues for studying DNA methylation patterns in P. yunnanensis.

(1) Background: Brassinosteroids (BRs) are an important hormone that participates in almost all stages of plant growth and development, and sterol dehydrogenase is a key enzyme that is involved in the biosynthesis of BRs. However, the steroid dehydrogenase gene family in Populus yunnanensis Dode (P. yunnanensis) has not been studied; (2) Methods: The PyDET2 gene family was identified and bioinformatics analyzed. Three genes were screened based on the RNA-seq of stem tip, the PyDET2e was further investigated by RT-qPCR (real-time quantitative polymerase chain reaction) and subcellular localization; (3) Results: We identified 14 DET2 family genes in P. yunnanensis that were classified into 4 groups according to sequence similarity and phylogenetic relationship, and 10 conserved protein motifs had been identified. The gene structure, chromosome distribution, collinearity, and codon preference of all PyDET2 genes identified in the genome of P. yunnanensis were analyzed. The codon of this family is biased to the end of A/U, and natural selection has a great influence on it. The expression level of PyDET2e in September was higher than in July, and it was significantly expressed in stems, stem tips, and leaves. The PyDET2e protein was localized in chloroplasts; (4) Conclusions: The PyDET2e is involved in the development of P. yunnanensis in the rapid growth stage. The systematic analysis provided a basis for the genome-wide identification of genes related to brassinolide biosynthesis processes in P. yunnanensis, and laid a foundation for the study on the mechanism of rapid growth of P. yunnanensis.