The homeodomain-leucine zipper (HD-Zip) transcription factor family is a key transcription factor family and unique to the plant kingdom. It consists of a homeodomain and a leucine zipper that serve in combination as a dimerization motif. The family can be classified into four subfamilies, and these subfamilies participate in the development of hormones and mediation of hormone action and are involved in plant responses to environmental conditions. However, limited information on this gene family is available for the important chrysanthemum ornamental species (Chrysanthemum morifolium). Here, we characterized 17 chrysanthemum HD-Zip genes based on transcriptome sequences. Phylogenetic analyses revealed that 17 CmHB genes were distributed in the HD-Zip subfamilies I and II and identified two pairs of putative orthologous proteins in Arabidopsis and chrysanthemum and four pairs of paralogous proteins in chrysanthemum. The software MEME was used to identify 7 putative motifs with E values less than 1e-3 in the chrysanthemum HD-Zip factors, and they can be clearly classified into two groups based on the composition of the motifs. A bioinformatics analysis predicted that 8 CmHB genes could be targeted by 10 miRNA families, and the expression of these 17 genes in response to phytohormone treatments and abiotic stresses was characterized. The results presented here will promote research on the various functions of the HD-Zip gene family members in plant hormones and stress responses.

Plant-specific TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) proteins play critical roles in plant development and stress responses; however, their functions in chrysanthemum (Chrysanthemum morifolium) have not been well-studied. In this study, we isolated and characterized the chrysanthemum TCP transcription factor family gene CmTCP13, a homolog of AtTCP13. This gene encoded a protein harboring a conserved basic helix–loop–helix motif, and its expression was induced by salinity stress in chrysanthemum plants. Subcellular localization experiments showed that CmTCP13 localized in the nucleus. Sequence analysis revealed the presence of multiple stress- and hormone-responsive cis-elements in the promoter region of CmTCP13. The heterologous expression of CmTCP13 in Arabidopsis plants enhanced their tolerance to salinity stress. Under salinity stress, CmTCP13 transgenic plants exhibited enhanced germination, root length, seedling growth, and chlorophyll content and reduced relative electrical conductivity compared with those exhibited by wild-type (WT) plants. Moreover, the expression levels of stress-related genes, including AtSOS3, AtP5CS2, AtRD22, AtRD29A, and AtDREB2A, were upregulated in CmTCP13 transgenic plants than in WT plants under salt stress. Taken together, our results demonstrate that CmTCP13 is a critical regulator of salt stress tolerance in plants.

Callus induction is the foundation for large-scale and rapid plant propagation, and explant age is a key factor affecting callus induction efficiency and in vitro culture outcomes. Pedicels are the main explants for Agapanthus praecox tissue culture. This study analyzed three pedicel developmental stages (S1: immature, S2: semi-mature, S3: mature) and their induced calli (C1, C2, C3). We integrated transcriptomics, metabolomics (LC-MS/GC-MS), quantitative real-time PCR (qRT-PCR), and weighted gene co-expression network analysis (WGCNA) to clarify the physiological and molecular mechanisms of pedicel regenerative potential. Results showed that S2 exhibited the highest callus induction rate, while C2 showed superior proliferation coefficients and regenerative potential. In pedicel samples, differentially expressed genes were significantly enriched in the MAPK signaling pathway and plant hormone signal transduction pathway, while differentially accumulated metabolites were linked to energy metabolism, amino acid/nucleotide metabolism, and stress responses. Key metabolites (e.g., carbohydrates, amino acids, thidiazuron, and β-chlorogenin) played specific roles in maintaining the meristematic capacity of pedicels. qRT-PCR further confirmed that S2 maintained balanced endogenous hormone signaling and proper cell wall modification. Furthermore, WGCNA identified a key module associated with oxidative stress responses along with S2. Overall, the regenerative potential of pedicel is mediated by the balanced hormone signal transduction, metabolic reprogramming, and epigenetic regulation in A. praecox.

Haworthia cooperi var. pilifera is a succulent plant with ornamental value. The white–green leaf mutant (wl) showed a significant difference in leaf color from the wild-type plant (WT). In this study, we integrated the transcriptomes of wl and WT plants to screen differentially expressed genes related to leaf color variation. The results of transcriptome analysis showed that 84,163 unigenes were obtained after de novo assembly and the NR database annotated the largest number of unigenes, which accounted for 57.13%, followed by NT (43.02%), GO (39.84%), Swiss-Prot (39.25%), KEGG (36.06%), and COG (24.88%). Our finding showed that 2586 genes were differentially expressed in the two samples, including 1996 down-regulated genes and 590 up-regulated genes. GO analysis predicted that these differentially expressed genes (DEGs) participate in 12 cellular components, 20 biological processes, and 13 molecular function terms and KEGG analysis showed that metabolic pathways, plant–pathogen interaction, glycerophospholipid metabolism, endocytosis, plant hormone signal transduction, and ether lipid metabolism were enriched among all identified pathways. Through functional enrichment analysis of DEGs, we found that they were involved in chloroplast division and the biosynthesis of plant pigments, including chlorophyll, carotenoids, anthocyanin, and transcription factor families, which might be related to the formation mechanism of leaf color. Taken together, these results present insights into the difference in gene expression characteristics in leaves between WT and wl mutants and provide a new insight for breeding colorful leaf phenotypes in succulent plants.

Chrysanthemum (Chrysanthemum morifolium) is a globally significant ornamental plant, whose growth, development, and ornamental quality are frequently impaired by salt stress. DOF (DNA-binding with one finger) family transcription factors extensively act as crucial regulators in medicating reactions to environmental pressures on plants. But their specific functions in regulating salt stress tolerance in chrysanthemum still remain largely elusive and require further investigation. Here, we isolated CmDOF2, a DOF family transcription factor from chrysanthemum, whose expression was up-regulated in chrysanthemums under salt stress. Functional analysis demonstrated that CmDOF2 functions as a nuclear-localized transcriptional activator. Comprehensive phenotypic and physiological characterization showed that heterologous expression of CmDOF2 in Arabidopsis thaliana conferred markedly increased salt stress tolerance, as reflected by higher chlorophyll, leaf relative water, and proline content; lower leaf relative electric conductivity and malondialdehyde content; and increased activities of superoxide dismutase, peroxidase, and catalase. Furthermore, qRT-PCR analyses confirmed that stable expression of CmDOF2 in Arabidopsis led to increased transcript levels of key salt-responsive genes, including stress marker genes (AtRD29A, AtRD29B), components of the SOS signaling pathway (AtSOS1, AtSOS2, AtSOS3), genes involved in osmotic adjustment (AtP5CS1, AtP5CS2), and genes encoding antioxidant enzymes (AtSOD1, AtPOD34, AtCAT3). Collectively, our data demonstrate that CmDOF2 serves as a nuclear-localized transcriptional regulator with activation activity and positively regulates salt stress tolerance by mediating the transcript levels of stress-related genes in multiple signaling pathways.

Cenchrus alopecuroides Thunb. 1794 is a warm-season ornamental grass with glossy foliage and showy inflorescence, which is widely distributed from eastern Asia to Australia. Although this species is of great economic importance, little genomic sequence data are available. Here, we report the complete chloroplast genome sequence of C. alopecuroides, which provides valuable plastid genomic resources for further studies on this ornamental grass. The chloroplast genome of C. alopecuroides was 138,053 bp in length and exhibited a typical quadripartite structure, which comprised a pair of inverted repeat regions (22,331 bp) separated by a large (81,177 bp) and a small single copy (12,214 bp) region. In total, 110 unique genes were annotated in the chloroplast genome, containing 76 protein-coding genes, 30 transfer RNAs and four ribosomal RNAs. The overall GC content of the chloroplast genome was 38.6%. Phylogenetic analysis based on 11 whole-chloroplast genome sequences of Cenchrus species suggested that C. alopecuroides and C. compressus were sisters to each other and joint sisters to C. clandestinus.