Zinc-finger proteins are important transcription factors in plants, responding to adversity and regulating the growth and development of plants. However, the roles of the BBX gene family of zinc-finger proteins in wintersweet (Chimonanthus praecox) have yet to be elucidated. In this study, a group IV subfamily BBX gene, CpBBX19, was identified and isolated from wintersweet. Quantitative real-time PCR (qRT-PCR) analyses revealed that CpBBX19 was expressed in all tissues and that expression was highest in cotyledons and inner petals. CpBBX19 was also expressed in all flower development stages, with the highest expression detected in early initiating bloom, followed by late initiating bloom and bloom. In addition, the expression of CpBBX19 was induced by different abiotic stress (cold, heat, NaCl, and drought) and hormone (ABA and MeJA) treatments. Heterologous expression of CpBBX19 in Arabidopsis thaliana (Arabidopsis) enhanced the tolerance of this plant to salt and drought stress as electrolyte leakage and malondialdehyde (MDA) concentrations in transgenic Arabidopsis after stress treatments were significantly lower than those in wild-type (WT) plants. In conclusion, this research demonstrated that CpBBX19 plays a role in the abiotic stress tolerance of wintersweet. These findings lay a foundation for future studies on the BBX gene family of wintersweet and enrich understanding of the molecular mechanism of stress resistance in wintersweet.

Chimonanthus praecox (Calycanthaceae family) is a unique ornamental and economic flowering tree in China, and after thousands of years of cultivation, it has produced several varieties and varietal types. Notably, male sterility is common in flowering plants and is an important tool for the genetic improvement in plants and optimization using hybrid plant technology; however, there have been no reports on male-sterile material or related studies on C. praecox. To our knowledge, this is the first time that C. praecox male sterility is dissected unveiling the involvement of key metabolic pathways. Notably, male sterility in C. praecox was observed during the budding period and likely occurred during the premature stage of pollen cell maturation. Additionally, differentially expressed genes in the starch and sucrose metabolism pathway and the plant hormone signal transduction pathway showed regular expression trends. This study reports on significant genetic differences that contribute to male sterility in C. praecox and provides a basis for further research and breeding strategies.

Chimonanthus praecox, a member of the Calycanthaceae family, is a unique, traditional, and famous flowering economic tree species in China. Despite the existence of several varieties, only a few cultivars have been formally named. Currently, expression sequence tag–simple sequence repeat (EST-SSR) markers are extensively used to identify different species and varieties; a large number of microsatellites can be identified from transcriptome databases. A total of 162,638 unigenes were assembled using RNA-seq; 82,778 unigenes were annotated using the Nr, Nt, Swiss-Prot, Pfam, GO, KOG, and KEGG databases. In total, 13,556 SSR loci were detected from 11,691 unigenes, with trinucleotide repeat motifs being the most abundant among the six repeat motifs. To develop the markers, 64,440 pairs of SSR primers with polymorphism potential were designed, and 75 pairs of primers were randomly selected for amplification. Among these markers, seven pairs produced amplified fragments of the expected size with high polymorphism. Using these markers, 12 C. praecox varieties were clustered into two monophyletic clades. Microsatellites in the transcriptome of C. praecox exhibit rich types, strong specificity, and great polymorphism potential. These EST-SSR markers serve as molecular technical methods for identifying different varieties of C. praecox and facilitate the exploration of a large number of candidate genes associated with important traits.

Plant senescence is a complex process that is controlled by developmental regulation and genetic programs. A senescence-related gene CpSRG1, which belongs to the 2OG-Fe(II) dioxygenase superfamily, was characterized from wintersweet, and the phylogenetic relationship of CpSRG1 with homologs from other species was investigated. The expression analysis by qRT-PCR (quantitative real-time PCR) indicated that CpSRG1 is abundant in flower organs, especially in petals and stamens, and the highest expression of CpSRG1 was detected in stage 6 (withering period). The expression patterns of the CpSRG1 gene were further confirmed in CpSRG1pro::GUS (β-glucuronidase) plants, and the activity of the CpSRG1 promoter was enhanced by exogenous Eth (ethylene), SA (salicylic acid), and GA₃ (gibberellin). Heterologous overexpression of CpSRG1 in Arabidopsis promoted growth and flowering, and delayed senescence. Moreover, the survival rates were significantly higher and the root lengths were significantly longer in the transgenic lines than in the wild-type plants, both under low nitrogen stress and GA₃ treatment. This indicated that the CpSRG1 gene may promote the synthesis of assimilates in plants through the GA pathway, thereby improving growth and flowering, and delaying senescence in transgenic Arabidopsis. Our study has laid a satisfactory foundation for further analysis of senescence-related genes in wintersweet and wood plants. It also enriched our knowledge of the 2OG-Fe(II) dioxygenase superfamily, which plays a variety of important roles in plants.

Chimonanthus praecox, also known as wintersweet, is a traditional ornamental plant in China. It blooms during the cold winter months and emits a long-lasting fragrance. The WUSCHEL-related homeobox (WOX) transcription factor family is a plant-specific family of homeodomain (HD) transcription factors that plays diverse roles in plant development. We identified 13 WOX family genes (CpWOX1–CpWOX12 and CpWUS) and systematically analysed their physicochemical properties, evolutionary relationships, conserved domains, and expression regulation characteristics. The subcellular localization prediction indicates that all CpWOX proteins are localized in the nucleus and contain a conserved homeobox domain, with the WUS clade specifically containing a WUS-box motif. Phylogenetic analysis revealed that these genes are divided into three evolutionary branches: the WUS, ancient, and intermediate clades. Promoter analysis suggests that CpWOX genes may be involved in hormone responses, abiotic stress, developmental regulation, and encodes a nuclear-localised protein with self-activating activity. It is highly expressed in the stamen and root and is induced by low and high temperatures, salt stress, and methyl jasmonate. This study revealed the evolutionary characteristics of the WOX family genes in wintersweet and the function of CpWUS in regulating flowering time and root development, providing a theoretical basis for understanding the developmental regulatory mechanisms in wintersweet.

Camellia (Camellia japonica) is a semi-shaded plant that is highly vulnerable to heat stress. To investigate the mechanisms underlying heat stress in C. japonica, two C. japonica cultivars, “Xiaotaohong” and “Zhuapolian”, which exhibit significant differences in heat tolerance, were selected from four common cultivars. The selection methods included phenotypic observations and physiological index detection, including relative electric conductivity (REC), malondialdehyde (MDA) content, superoxide dismutase (SOD) enzyme activity, relative water content (RWC), and chlorophyll content. RNA-seq analysis yielded 980 million reads and identified 68,455 differentially expressed genes (DEGs) in the two C. japonica cultivars during heat stress compared to the control samples. Totals of 12,565 and 16,046 DEGs were differentially expressed at 16 h and 32 h, respectively, in “Xiaotaohong” during heat stress. In “Zhuapolian”, 40,280 and 37,539 DEGs were found at 16 h and 32 h, respectively. KEGG enrichment analysis revealed that both cultivars were enriched in the “plant hormone signal transduction” and “circadian rhythm” pathways at two stages, indicating the critical role these pathways play in the heat stress response. The differences in the tolerance between the two cultivars are likely linked to pathways such as “plant hormone signal transduction”, “photosynthesis”, and “circadian rhythm”. Some members of heat shock proteins (HSPs) are associated with the heat stress response. It is speculated that transcription factor families contributing to the tolerance differences include AP2/ERF, C3H, bHLH, bZIP, and MYB-related with a small number of heat shock factors (HSFs) also induced by the stress. In conclusion, these results reveal the changes in the physiological indices and molecular networks of two C. japonica cultivars under heat stress. This study lays the foundation for the breeding of superior heat-resistant C. japonica cultivars and for further molecular research.