Mutation breeding is considered to be economic and efficient in plant improvement, and the use of chemical mutagens such as ethyl methanesulfonate (EMS) can potentially address plant breeding challenges. The aim of this study was to induce morphological mutants in C. indicum var. aromaticum using EMS treatments with different doses, and to analyze the morphological and physiological traits of obtained mutants in expectation of finding favorable mutants. Results revealed significant effects of EMS doses on seed germination. The sample germination rate significantly decreased with increasing of EMS doses. The obtained morphological mutants were two viable types, containing leaf and stem mutants. Overall leaf size was significantly larger as a result of EMS treatments. And the height of mutant plants was significantly higher. Anatomical characteristics exhibited changes in both leaves and stems of the mutant plants. The puncture strength of the bent stem from the mutant plants was low, with weak penetration resistance. The total lignin and cellulose contents of mutant plants stem decreased significantly as a result of the EMS treatments. These results demonstrate the efficiency of EMS to induce mutations in C. indicum var. aromaticum, and this method can be useful in the future to assist breeding of this plant.
Terpenoids are important secondary metabolites in plants. The synthesis of terpenoids involves a key enzyme, 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR). In an aromatic ornamental plant, Chrysanthemum indicum var. aromaticum, terpenoids were found to be an important component in leaf secretions. To study the regulatory mechanism of terpenoid synthesis in C. indicum var. aromaticum, we cloned the DXR gene from C. indicum var. aromaticum, named CiDXR, based on transcriptome data. CiDXR is 1419 bp, encoding a polypeptide chain of 472 amino acids. Comparative and bioinformatic analysis showed that CiDXR was highly similar to DXRs from other plant species. The protein product of CiDXR was analyzed for physical and chemical properties, and secondary and tertiary structures. Methyl jasmonate (MeJA) is an effective exogenous elicitor that can impact the synthesis of secondary metabolites by regulating the expression of a series of specific key enzymes. In our study, MeJA treatment was used to study the relationship between CiDXR expression and terpenoid metabolism. The expression pattern of CiDXR was analyzed by quantitative real-time polymerase chain reaction. Leaves expressed the highest level of CiDXR mRNA. In addition, CiDXR expression was found to be activated by MeJA, up to 20-fold at 24 h post induction. The MeJA treatment significantly affected the relative contents of the secretion products, and the induction effect was maximal at 24 h, consistent with the expression of CiDXR. This study shows that CiDXR may play a key regulatory role in the control of terpenoid synthesis in C. indicum var. aromaticum.
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