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Abstract Background Cultivated chrysanthemums are susceptible to abiotic stress, and the intricate polyploidy complicates the discovery of resistance genes. Chrysanthemum indicum is a native diploid species with strong resistance, which makes it an important resource for investigating stress resistance genes and improving genetic traits in ornamental chrysanthemum plants. Results In this study, we cloned the CiHY5 gene and generated both overexpressing CiHY5 (OE-CiHY5) and suppressing CiHY5 (RNAi-CiHY5) transgenic chrysanthemum lines. After salt stress treatment, compared with the WT plants, the OE-CiHY5 plants exhibited a lower Malondialdehyde content and less leaf electrolyte leakage and significantly greater antioxidant enzyme activity. In contrast, the physiological parameters of the RNAi-CiHY5 plants exhibited opposite trends. Moreover, the Na+/K+ ratio in both the leaves and roots of the OE-CiHY5 plants significantly decreased in contrast with that in the leaves and roots of the WT and RNAi-CiHY5 plants. The qRT‒PCR results showed that the expression levels of downstream stress response genes, such as CiRAB18, CiERF1, CiABF2, CiABF4, and CiDREB1D, were significantly greater in the OE-CiHY5 plants than in the WT plants. Additionally, a yeast one-hybrid assay revealed that CiHY5 could directly bind to the promoter of CiABF4 and activate CiABF4 expression. Transient overexpression of CiABF4 in C. indicum leaf discs also improved salt stress tolerance. Conclusions Overall, we concluded that overexpressing CiHY5 enhanced but RNAi-CiHY5 reduced salt tolerance in C. indicum, acting as a pivotal candidate stress resistance gene that participates in the salt stress response at least partially in an ABA-dependent manner. The above findings demonstrated the molecular mechanisms underlying the CiHY5-mediated salt stress response and laid the foundation for the molecular breeding of chrysanthemum plants to improve resistance.
Xia et al. (Wed,) studied this question.