Argyranthemum frutescens, which belongs to the Anthemideae (Asteraceae), is widely cultivated as an ornamental plant. In this study, the complete chloroplast genome of A. frutescens was obtained based on the sequences generated by Illumina HiSeq. The chloroplast genome of A. frutescens was 149,626 base pairs (bp) in length, containing a pair of inverted repeats (IR, 24,510 bp) regions separated by a small single-copy (SSC, 18,352 bp) sequence and a large single-copy (LSC, 82,254 bp) sequence. The genome contained 132 genes, consisting of 85 coding DNA sequences, 37 tRNA genes, and 8 rRNA genes, with nineteen genes duplicated in the IR region. A comparison chloroplast genome analysis among ten species from the tribe of Anthemideae revealed that the chloroplast genome size varied, but the genome structure, gene content, and oligonucleotide repeats were highly conserved. Highly divergent regions, e.g., ycf1, trnK-psbK, petN-psbM intronic, were detected. Phylogenetic analysis supported Argyranthemum as a separate genus. The findings of this study will be helpful in the exploration of the phylogenetic relationships of the tribe of Anthemideae and contribute to the breeding improvement of A. frutescens.

BZIP transcription factors play important roles in regulating plant development and stress responses. Although bZIPs have been identified in many plant species, there is little information on the bZIPs in Chrysanthemum. In this study, bZIP TFs were identified from the leaf transcriptome of C. mongolicum, a plant naturally tolerant to drought. A total of 28 full-length bZIP family members were identified from the leaf transcriptome of C. mongolicum and were divided into five subfamilies based on their phylogenetic relationships with the bZIPs from Arabidopsis. Ten conserved motifs were detected among the bZIP proteins of C. mongolicum. Subcellular localization assays revealed that most of the CmbZIPs were predicted to be localized in the nucleus. A novel bZIP gene, designated as CmbZIP9, was cloned based on a sequence of the data of the C. mongolicum transcriptome and was overexpressed in tobacco. The results indicated that the overexpression of CmbZIP9 reduced the malondialdehyde (MDA) content and increased the peroxidase (POD) and superoxide dismutase (SOD) activities as well as the expression levels of stress-related genes under drought stress, thus enhancing the drought tolerance of transgenic tobacco lines. These results provide a theoretical basis for further exploring the functions of the bZIP family genes and lay a foundation for stress resistance improvement in chrysanthemums in the future.

Chrysanthemum mongolicum and Chrysanthemum vestitum belong to the Asteraceae family, which occupy a wider range of ecological niches and represent extensive biotic resistance and abiotic tolerance. However, the genetic information about these two species is poorly known, which restricts their utilization. Here, the leaf transcriptomes of the two Chrysanthemum species were investigated and compared. In total, 21,856 differentially expressed genes (DEGs) were identified between C. vestitum and C. mongolicum, of which 12,076 DEGs were up-regulated and 9780 were down regulated in C. vestitum compared to C. mongolicum. Functional enrichment analysis revealed that stress resistance categories had significant proportions. The up-regulated DEGs related to “ABC transporters”, “Flavonoid biosynthesis” and “Monoterpenoid biosynthesis” were significantly enriched in C. vestitum compared with C. mongolicum. While the DEGs involved in “Biosynthesis of unsaturated fatty acids”, “Proteasome”, “Phenylpropanoid biosynthesis”, “Oxidative phosphorylation”, “Plant-pathogen interaction”, “Starch and sucrose metabolism”, “Glutathione metabolism”, as well as “MAPK signaling pathway” were mostly up-regulated in C. mongolicum compared with C. vestitum, suggesting their important roles in C. mongolicum. These results might explain the differences in morphology and provide potential molecular mechanisms for the ecological adaptation of the two Chrysanthemum species in extreme environments. Together, the results of this study provide a genetic resource that may greatly benefit the genetic improvement of cultivated chrysanthemums and will be helpful for plant conservation and sustainable utilization in the future.