miR166, as an ancient and large family of plant microRNAs, has been demonstrated to participate in plant growth and development as well as responses to abiotic stress. However, at present, the functions of miR166 gene family members and the mechanism by which miR166 participates in the salt stress response of Chrysanthemums have not been fully studied. This study verified the function of identified miR166 family members in Chrysanthemum, confirming that miR166 positively regulates salt stress tolerance in Arabidopsis thaliana. The miR166 family of Chrysanthemum consists of 10 members, and their mature sequences are highly conserved among different plants; The precursor sequence of cgr-miR166d is approximately 200 bp in length and has a typical hairpin structure, showing a relatively close genetic relationship to ath-miR166f of Arabidopsis thaliana. By constructing the pBI121-cgr-miR166-GUS vector and using the dipping method for genetic transformation of Arabidopsis thaliana, seven cgr-miR166 overexpression transgenic plants were screened and obtained. The expression levels of Arabidopsis thaliana HD-ZipIII family members were suppressed in transgenic plants. Under salt treatment, the seed germination rate and root length of transgenic Arabidopsis plants were significantly higher than those of the wild type. The activities of POD and CAT were significantly increased, while MDA showed no significant change. Additionally, under IAA and ABA induction, miR166 expression was significantly upregulated in both leaf and root tissues of Chrysanthemums. Based on heterologous expression experiments in Arabidopsis, the study demonstrates that the cgr-miR166 gene family exerts a positive regulatory role in plant resistance to salt stress. This gene may achieve its function by targeting and regulating members of the HD-ZipIII family, and it is also related to plant hormones. This study reveals that miR166 is a candidate regulator mediating the salt stress response in Chrysanthemums, providing a theoretical basis for further research on salt-tolerant Chrysanthemum breeding.
Zhang et al. (Wed,) studied this question.