Cuihua Gu

Cuphea hookeriana (Lythraceae) is an evergreen flowering shrub native to tropical and subtropical regions, serving as an ornamental plant in landscaping and as a raw material for industry and agriculture. Here, we assembled a haplotype-resolved chromosomal genome for C. hookeriana (2n = 3x = 24) based on HiFi and Hi-C sequencing datasets. The genome was assembled into 16 chromosomes with a total size of 498,761,099 bp, comprising 248,233,948 bp and 240,972,969 bp for haplotypes A and B, respectively. BUSCO evaluation indicated an assembly completeness of 97.7% C value. Approximately 30,000 genes were annotated for each haplotype, achieving a BUSCO complete score of 97%.

Chimonanthus spp. has attracted much attention due to its great ornamental value and potential medicinal value. The flowers of Chimonanthus praecox and C. salicifolius exude a strong aroma. Terpenoids are the main components of the floral volatile organic compounds (VOCs), and the synthesis of these compounds is closely related to the terpene synthase (TPS) gene. In this study, headspace-solid phase microextraction combined with gas chromatography-mass spectrometry (HS–SPME–GC–MS) was used to identify the floral components of C. praecox and C. salicifolius. 25 and 31 floral VOCs were identified from C. praecox and C. salicifolius, respectively. Combined with the published VOCs of Chimonanthus leaf, we found that monoterpenoids take most relative content of volatile in flowers while in leaves, both monoterpenoids and sesquiterpenoids have high relative content. We identified 63 and 48 TPS genes from the genomes of C. praecox and C. salicifolius. Transcriptome analysis showed that TPS-b subfamily genes (related to monoterpene synthesis) showed high expression levels in flowers and leaves, while TPS-a subfamily genes (related to sesquiterpene synthesis) showed strong expression in leaves. The TPS genes with high expression in leaves mainly evolved through tandem duplication, suggesting that tandem duplication of TPS genes may promote the synthesis of terpenoids in leaves. This study revealed the expression pattern of TPS genes in Chimonanthus plants, and proposed that the tandem duplication of TPS gene family may play an important role in the synthesis of monoterpenes in the leaves of Chimonanthus species.

The protein phosphatase 2 C (PP2C) plays a crucial role in the growth and development of plants. However, limited information on the PP2C genes in Chimonanthus spp. is available. Therefore, the comprehensive genome-wide identification and analysis of the PP2Cs gene family is necessary in Chimonanthus spp. to provide basic information for further study. In this work, 93 members of the CsPP2C gene family and 85 members of the CpPP2C gene family were identified. Based on the phylogenetic analysis, 93 CsPP2Cs and 85 CpPP2Cs genes were classified into 13 subgroups. Based on RNA-Seq data, specific expression patterns of CsPP2Cs in different tissues were identified. CsPP2C28, CsPP2C55, and CsPP2C17 showed high expression during leaf senescence, and combined with cis-element analysis, it is speculated that they may participate in regulating plant senescence. CsPP2C47, CsPP2C27, CsPP2C42, and CsPP2C41 may play an important role in responding to abscisic acid during seed dormancy and germination. These results contribute to a deeper understanding of the functions of the CsPP2C gene family and CpPP2C gene family, and providing candidate genes for genetic engineering and breeding to enhance important traits such as stress resistance and growth development in C. salicifolius and C. praecox.

Lagerstroemia indica, a species renowned for its ornamental attributes, occupies a vital position in garden landscaping, and CYP450 constitutes a group of proteins functioning as monooxygenases, which are extensively implicated in plant growth, development, and various other life processes. There are 314 members in total belonging to the CYP450 family, which were identified within the genome of Lagerstroemia indica, with their distribution spanning 23 chromosomes. Based on diverse structural domains as well as evolutionary analysis, the CYP450 family is divided into nine subfamilies; segmental duplication serves as the chief amplification mode during the development trajectory of the CYP450 gene family, the CYP75 subfamily genes LiF3'H and LiF3'5'H, which were found to localize to the cell membrane and promote anthocyanin synthesis. The results obtained from this study are of great significance as they delve deeper into the functional contributions of CYP450 genes by establishing a firm basis and for investigating the molecular processes involved in anthocyanin synthesis in Lagerstroemia indica.

Lagerstroemia indica is popular for its bright flower colors and long bloom period. However, although L. indica has a long flowering period, the flowering time of a single flower is short, lasting only 1−2 d. Petal expansion is a key process that affects the length and ornamental quality of the flowering period. However, the molecular mechanism of petal expansion in L. indica remains unclear. The molecular mechanisms underlying flower opening in L. indica were investigated through transcriptome sequencing of flower buds and blooms at four developmental stages. Analysis of differentially expressed genes (DEGs) indicated enrichment in cellular processes, metabolic regulation, and biological signaling pathways. KEGG pathway analysis revealed significant roles for carbohydrate, lipid, and amino acid metabolism in the flowering process. Additional pathway analysis identified key genes and processes related to carbohydrate utilization, hormone signaling, water transport, and cell wall expansion that contribute to petal opening regulation. A comprehensive examination of the expansin gene family proteins, known for promoting cell wall loosening and extension, identified 27 expansin genes in L. indica, which were categorized into four subfamilies with conserved structures and motifs. Of these, LiEXPA10, LiEXPA19, LiEXLA1, and LiEXLA2 showed heightened expression in the later stages of flowering (S3−S4), suggesting a central role in petal expansion. Functional validation in Arabidopsis thaliana demonstrated that LiEXLA1 and LiEXLA2 promote accelerated flowering and enhanced petal expansion in transgenic lines. These findings offer new insights into the genetic and molecular basis of flower opening in L. indica and provide a foundation for breeding strategies aimed at improving ornamental traits.

Floral fragrance is an important ornamental trait of horticultural crops. However, research on the physiological and molecular biology of the floral volatile compounds in Chinese rose is limited. This study conducted metabolomic and transcriptomic analyses on the floral volatile compounds of Rosa chinensis (R. chinensis) 'Old Blush' ('OB') and R. chinensis 'Chilong Hanzhu' ('CH'). A total of 22 major volatile organic compounds (VOCs) were detected in the blooming flowers of 'OB' and 'CH'. The main VOCs emitted from 'OB' petals was 1,3,5-trimethoxybenzene (TMB), while that from 'CH' petals was 2-phenylethanol (2-PE). The GO and KEGG enrichment on differentially expressed genes (DEGs) revealed the essential role of phenylpropanoid pathway in the difference of floral fragrance between two cultivars, and a total of 15 key genes involved in the biosynthesis of phenylpropanoid were identified in R. chinensis flowers. The overexpression of RcCH_AADC-1 in transgenic tobacco plants led to the accumulation of 2-PE. In contrast, no significant change in the level of 2-PE was observed after the transient transformation of RcCH_PAR1 or RcCH_PAR1_Like into tobacco plants. These findings provide valuable insight for enhancing the accumulation of 2-PE in R. chinensis.

The basic helix-loop-helix (bHLH) family is one of the three major transcription factor families that play important transcriptional regulatory roles in plant growth and development. One of the most crucial elements in defining Lagerstroemia indica’s decorative qualities is flower color. However, the function of the bHLH transcription factor family in L. indica anthocyanin glycoside synthesis has not been clarified. Using the transcriptome data of flower color, 79 LibHLH genes were found in this study. Phylogenetic analysis showed that the LibHLH genes can be divided into 16 subfamilies, and most of the genes in the same subfamily have similar conserved motifs. The total anthocyanin glycoside content of L. indica ‘Zihua Guifei’ petals was determined during three developmental stages of the petals’ growth. The results showed that the total anthocyanin glycoside content grew gradually with growth and development, and that it accumulated most during the full bloom stage. By using gene expression analysis, protein interaction network analysis, and bioinformatics, it was possible to determine which member of the III f family, LibHLH29, is important for the synthesis of anthocyanin glycosides in L. indica. Its expression was confirmed by qRT-PCR, and the results were essentially compatible with the transcriptome data. It was more prominent in the light-colored bloom stage the color-transition stage of L. indica ‘Zihua Guifei’. It can be further investigated as a major candidate gene for regulating anthocyanin glycoside synthesis in L. indica, thus laying the foundation for an in-depth study of the interactions among transcription factors.