Yilei Wu

Fruit color, a defining characteristic in mulberry, varies markedly across cultivars, ranging from black and red to pink and white. However, the regulatory mechanisms governing pigmentation during fruit development remain poorly characterized. In this study, ATAC-seq and RNA-seq were integrated to investigate genome-wide chromatin accessibility and identify putative transcription factors involved in fruit development in Da10 (Yueshenda10, Morus atropurpurea Roxb.). Differentially accessible chromatin regions and differentially expressed genes were jointly analyzed to generate a genome-wide map of regulatory elements and transcriptional activity. This integrative approach enabled the reconstruction of a transcriptional regulatory network that facilitated the identification of candidate transcription factors and target genes associated with the biosynthesis of bioactive compounds, including sugars, flavonoids, diterpenoids, and anthocyanins. The expression levels of RNA-seq were confirmed by qRT-PCR. Motif enrichment analysis revealed seven and 23 enriched cis-elements at the S1 and S3 developmental stages, respectively. Integration with the transcriptional regulatory network established a robust framework for identifying candidate genes involved in the accumulation of key metabolites. Additionally, the dataset enables exploration of previously uncharacterized traits during turning stages of mulberry fruit development. Collectively, these findings advance our understanding of the regulatory architecture underlying fruit maturation and provide a foundation for future strategies to enhance mulberry fruit quality.

The publication of several high‐quality genomes has contributed greatly to clarifying the evolution of citrus. However, due to their complex genetic backgrounds, the origins and evolution of many citrus species remain unclear. We assembled de novo the 294‐Mbp chromosome‐level genome of a more than 200‐year‐old primitive papeda (DYC002). Comparison between the two sets of homologous chromosomes of the haplotype‐resolved genome revealed 1.2% intragenomic variations, including 1.75 million SNPs, 149,471 insertions and 154,215 deletions. Using this genome as a reference, we resequenced and performed population and phylogenetic analyses of 378 representative citrus accessions. Our study confirmed that the primary origin center of core Citrus species is in South China, particularly in the Himalaya–Hengduan Mountains. Papeda species are an ancient Citrus type compared with C. ichangensis. We found that the evolution of the Citrus genus followed two radiations through two routes (to East China and Southeast Asia) along river systems. Evidence for the origin and evolution of some individual citrus species was provided. Papeda probably played an important role in the origins of Australian finger lime, citrons, Honghe papeda and pummelos; Ichang papeda originated from Yuanjiang city of Yunnan Province, China, and C. mangshanensis has a close relationship with kumquat and Ichang papeda. Moreover, the Hunan and Guangdong Provinces of China are predicted to be the origin center of mandarin, sweet orange and sour orange. Additionally, our study revealed that fruit bitterness was significantly selected against during citrus domestication. Taken together, this study provides new insight into the origin and evolution of citrus species and may serve as a valuable genomic resource for citrus breeding and improvement.

Transposable elements (TEs) significantly contribute to the evolution and diversity of plant genomes. In this study, we explored the roles of TEs in the genomes of Citrus and Citrus-related genera by constructing a pan-genome TE library from 20 published genomes of Citrus and Citrus-related accessions. Our results revealed an increase in TE content and the number of TE types compared to the original annotations, as well as a decrease in the content of unclassified TEs. The average length of TEs per assembly was approximately 194.23 Mb, representing 41.76% (Murraya paniculata) to 64.76% (Citrus gilletiana) of the genomes, with a mean value of 56.95%. A significant positive correlation was found between genome size and both the number of TE types and TE content. Consistent with the difference in mean whole-genome size (39.83 Mb) between Citrus and Citrus-related genera, Citrus genomes contained an average of 34.36 Mb more TE sequences than Citrus-related genomes. Analysis of the estimated insertion time and half-life of long terminal repeat retrotransposons (LTR-RTs) suggested that TE removal was not the primary factor contributing to the differences among genomes. These findings collectively indicate that TEs are the primary determinants of genome size and play a major role in shaping genome structures. Principal coordinate analysis (PCoA) of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) identifiers revealed that the fragmented TEs were predominantly derived from ancestral genomes, while intact TEs were crucial in the recent evolutionary diversification of Citrus. Moreover, the presence or absence of intact TEs near the AdhE superfamily was closely associated with the bitterness trait in the Citrus species. Overall, this study enhances TE annotation in Citrus and Citrus-related genomes and provides valuable data for future genetic breeding and agronomic trait research in Citrus.