Medicinal Plant Research 2024, Vol.14, No.2, 71-84 http://hortherbpublisher.com/index.php/mpr 76 species. Wild chrysanthemums, due to their unique genetic makeup and superior traits, are often used as genetic resources for introducing new traits. Understanding the evolutionary history and genetic relationships of Chrysanthemum morifolium, as well as the genetic characteristics of specific traits, provides a theoretical basis for breeding strategies aimed at improving the ornamental and medicinal properties of Chrysanthemum morifolium. 4.2 Adaptation to environmental stresses In recent years, due to global climate change, excessive use of water resources, and intensified human activities, Chrysanthemum morifolium has significantly declined or degraded. Maintaining a certain level of genetic diversity is crucial for the adaptation and evolution of organisms and is of great importance for the management and conservation of species. Li et al. (2023) studied the phenotypic and genetic changes in Chrysanthemum morifoliumto analyze its environmental adaptation mechanisms. Heterosis, or hybrid vigor, is a common genetic phenomenon in the biological world. Chrysanthemum morifolium is a predominantly outcrossing plant, and hybridization can produce a wide range of variation types and gene combinations. DNA methylation is a highly conserved epigenetic modification that primarily regulates gene transcription and expression, playing a crucial role in maintaining genome stability and responding to abiotic stresses (Xin et al., 2015). DNA methylation is closely related to heterosis; hybridization results in significant changes in DNA methylation levels as well as the loss and gain of genetic fragments, which can produce genotypes adapted to new environmental conditions (Wang et al., 2014). The expression levels of genes, such as CmTM6-mu, can regulate flowering time in plants and their stress responses to external environmental factors affecting growth and development. Liu et al. (2022) identified key regulatory genes controlling flower development and flowering time (Figure 2). Figure 2 Chrysanthemum samples used for transcriptome sequencing and gene expression levels and correlation analysis results (Adopted from Liu et al., 2022) Image caption: (A–C) Leaf, ray floret, and disc floret, respectively, of Chrysanthemum morifoliumRamat “Pink Carpet”; (D) Gene expression levels in each sample; (E) Gene expression level statistics of each sample (Adopted from Liu et al., 2022)
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