| Summary: | Low temperature is a limiting factor affecting plant growth and development. Casuarina equisetifolia, a typical tropical and subtropical tree important for the ecological restoration of coastal beaches, is sensitive to cold stress. By comparing cold tolerance between C. equisetifolia and Arabidopsis, we investigated the molecular basis underlying the cold sensitivity of C. equisetifolia. Transcriptomic analysis showed that the number of cold-induced genes in C. equisetifolia was significantly less than that in Arabidopsis, and notably, the response of cold-induced genes was also delayed in C. equisetifolia. Among the cold-induced genes, C-repeat binding factors (CBFs), the major transcription factors in cold acclimation in Arabidopsis, showed a delayed cold-induced expression in C. equisetifolia, despite that C. equisetifolia CBFs could restore the low temperature-sensitive phenotype of Arabidopsis cbfs triple mutants. Interestingly, some key cold-responsive genes (e.g., COR15A and COR15B) targeted by Arabidopsis CBF were absent in the C. equisetifolia genome and many cold-responsive genes in C. equisetifolia lacked the DRE element (i.e., CBF binding cis-element). Moreover, like in C. equisetifolia, many COR genes in other tropical/subtropical plants lacked the DRE element or were directly missing. These two factors could be the underlying reasons for the low-temperature sensitivity of C. equisetifolia and other tropical/subtropical plants.
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