Functional characterization of a Chrysanthemum dichrum stress-related promoter

Transcriptome and Metabolome Analyses of the Flowers and Leaves of Chrysanthemum dichrum

Chrysanthemum dichrum is an important wild species in the family Asteraceae. However, because of a lack of genetic information, there has been relatively little research conducted on the molecular mechanisms in C. dichrum. There is no report describing the transcriptome and metabolome of C. dichrum flowers and leaves at different developmental stages. In this study, high-throughput sequencing and RNA-seq analyses were used to investigate the transcriptome of C. dichrum leaves, flower buds, and blooming flowers. Additionally, these three tissues also underwent a metabolomics analysis. A total of 447,313,764 clean reads were assembled into 77,683 unigenes, with an average length of 839 bp. Of the 44,204 annotated unigenes, 42,189, 28,531, 23,420, and 17,599 were annotated using the Nr, Swiss-Prot, KOG, and KEGG databases, respectively. Furthermore, 31,848 differentially expressed genes (DEGs) were detected between the leaves and flower buds, whereas 23,197 DEGs were detected between the leaves and blooming flowers, and 11,240 DEGs were detected between the flower buds and blooming flowers. Finally, a quantitative real-time Polymerase Chain Reaction (qRT-PCR) assay was conducted to validate the identified DEGs. The metabolome data revealed several abundant metabolites in C. dichrum leaves, flower buds, and blooming flowers, including raffinose, 1-kestose, asparagine, glutamine, and other medicinal compounds. The expression patterns of significant DEGs revealed by the transcriptome analysis as well as the data for the differentially abundant metabolites in three C. dichrum tissues provide important genetic and metabolic information relevant for future investigations of the molecular mechanisms in C. dichrum. Moreover, the results of this study may be useful for the molecular breeding, development, and application of C. dichrum resources.

Ambient temperature enhanced freezing tolerance of Chrysanthemum dichrum CdICE1 Arabidopsis via miR398

Background

ICE (Inducer of CBF Expression) family genes play an important role in the regulation of cold tolerance pathways. In an earlier study, we isolated the gene CdICE1 from Chrysanthemum dichrum and demonstrated that freezing tolerance was enhanced by CdICE1 overexpression. Therefore, we sought to determine the mechanism by which ICE1 family genes participate in freezing tolerance.

Results

Using EMSA (Electrophoretic Mobility Shift Assay) and yeast one-hybrid assays, we confirmed that CdICE1 binds specifically to the MYC element in the CdDREBa promoter and activates transcription. In addition, overexpression of CdICE1 enhanced Arabidopsis freezing tolerance after transition from 23°C to 4°C or 16°C. We found that after acclimation to 4°C, CdICE1, like Arabidopsis AtICE1, promoted expression of CBFs (CRT/DRE Binding Factor) and their genes downstream involved in freezing tolerance, including COR15a (Cold-Regulated 15a), COR6.6, and RD29a (Responsive to Dessication 29a). Interestingly, we observed that CdICE1-overexpressing plants experienced significant reduction in miR398. In addition, its target genes CSD1 (Copper/zinc Superoxide Dismutase 1) and CSD2 showed inducible expression under acclimation at 16°C, indicating that the miR398-CSD pathway was involved in the induction of freezing tolerance.

Conclusions

Our data indicate that CdICE1-mediated freezing tolerance occurs via different pathways, involving either CBF or miR398, under acclimation at two different temperatures.