He S.; Wang X.; Du Z.; Liang P.; Zhong Y.; Wang L.; Zhang Y.-Y. and Shen Y. 2023. Frontiers in Plant Science 14.

Mangrove forests inhabit tropical or subtropical intertidal zones and have remarkable abilities in coastline protection. Kandelia obovata is considered the most cold-tolerant mangrove species and has been widely transplanted to the north subtropical zone of China for ecological restoration. However, the physiological and molecular mechanisms of K. obovata under colder climate was still unclear. Here, we manipulated the typical climate of cold waves in the north subtropical zone with cycles of cold/recovery and analyzed the physiological and transcriptomic responses of seedlings. We found that both physiological traits and gene expression profiles differed between the first and later cold waves, indicating K. obovata seedlings were acclimated by the first cold experience and prepared for latter cold waves. 1,135 cold acclimation-related genes (CARGs) were revealed, related to calcium signaling, cell wall modification, and post-translational modifications of ubiquitination pathways. We identified the roles of CBFs and CBF-independent transcription factors (ZATs and CZF1s) in regulating the expression of CARGs, suggesting both CBF-dependent and CBF- independent pathways functioned in the cold acclimation of K. obovata. Finally, we proposed a molecular mechanism of K. obovata cold acclimation with several key CARGs and transcriptional factors involved. Our experiments reveal strategies of K. obovata coping with cold environments and provide prospects for mangrove rehabilitation and management.

Physiological and transcriptomic responses of K. obovata seedlings to circles of cold and recovery. Enzyme activity changes of malondialdehyde (MDA) (A), peroxidase (POD) (B), and superoxide dismutase (SOD) (C). (D) PCA results of transcriptome analysis. Circles mean warm conditions (CTR and REC-1/2), triangles mean cold treatments (COLD-1/2/4). (E) The Veen plot of 2,681 DEGs between the cold treatments (COLD-1/2/4) and the warm conditions (CTR and REC-1/2). The bold value represented the number of cold acclimation related genes (CARGs). The definition of CARGs was based on the analysis results of DEGs. CTR, REC-1, and REC-2 were set as ‘Warm’ status, genes differentially expressed (|log2FoldChange| > 2 and padj < 0.01) between COLD-1/Warm versus COLD-2/Warm or COLD-4/Warm were named CARGs.