Many mangrove forests have undergone major changes as a result of human activity and global climate change. Sonneratia caseolaris is a common tree located in inner mangroves, and its range extends inland along tidal creeks, as far as the influence of salinity extends. This study investigated the physiological and molecular response mechanisms of S. caseolaris by analyzing its antioxidant defense capacity, including its differentially expressed genes (DEGs) under similar salt stress conditions. Salt treatment significantly affected the osmoprotectants and lipid peroxidation in S. caseolaris seedlings, which increased proline (Pro) content by 31.01–54.90% during all sample periods and decreased malonaldehyde (MDA) content by 12.81 and 18.17% at 25 and 40 days under 3.0% NaCl treatment. Antioxidant enzyme activities increased significantly following 3.0% NaCl treatment. Transcriptome analysis following De novo assembly showed 26,498 matched unigenes. The results showed that 1,263 DEGs responded to transcription factors (TFs) and plant phytohormones and mediated oxidoreductase activity to scavenge reactive oxygen species (ROS) in the control vs. 3.0% NaCl comparison. In addition, the transcription levels of genes associated with auxin and ethylene signal transduction also changed. Under salt stress, ROS scavenging genes (POD, CAT, and APX) and part of AP2, MYB, NAC, C2C2, bHLH, and WRKY TFs were upregulated. This study identified important pathways and candidate genes involved in S. caseolaris salinity tolerance and provided suggestions for further research into the mechanisms of salt tolerance in S. caseolaris.

Acanthus ebracteatus is a typical true mangrove species with great ecological and medicinal values. However, it has become endangered in China. Moreover, because of the similar morphology and distribution, it is commonly confused with the congeneric mangrove species, A. ilicifolius , which poses challenges to the protection and proper medicinal utilization of A. ebracteatus . Plastomes provide a solution for molecular identification and adaptive evolution investigation of plants. In this study, we dissected the complete plastome for A. ebracteatus and performed comparative analysis to A. ilicifolius and three non‐mangrove relatives ( A. montanus , A. leucostachyus and A. mollis ). Both plastome sequences and structure are highly conserved between the two mangrove species, while less similar between mangrove and non‐mangrove species. Phylogenetic analysis suggested that the mangrove species were divergent from the non‐mangrove groups at approximately 15.15 million years ago (Mya), where early to middle Miocene global warming and high sea level might act as one of the main forces driving the mangrove lineage entering into intertidal environments. Furthermore, 12 single nucleotide polymorphisms (SNPs) and 10 insertions/deletions (indels) were detected between the plastomes of A. ebracteatus and A. ilicifolius . PCR validation further demonstrated the effectiveness of the plastid marker in distinguishing the two sibling mangrove species. Taken together, our study broadens the understanding of the origin and evolution of Acanthus mangrove plants, and provided valuable information on the correct identification and protection of endangered mangrove species A. ebracteatus .

The DEAD-box family has been shown to play an important role in a variety of abiotic stresses, but little is known in studies of mangrove plants. Here, the effects of cold stress on various physiological changes and the role of the DEAD-box RNA helicase family in response to cold stress were determined. First, we identified 73 DEAD-box RNA helicase family members in L. littorea. Second, the evolutionary relationships between the DEAD family in L. littorea and the model species Arabidopsis thaliana were investigated by evolutionary phylogenetic analysis. Finally, qRT-PCR study of representative DEAD-box genes showed that DEAD-box genes played a major role in the low-temperature stress response of L. littorea. Furthermore, we found that LlDEAD48, LlDEAD36, and LlDEAD47 might be involved in the maintenance of chlorophyll function, and LlDEAD43 might play a role in the maintenance of mitochondrial function in L. littorea under cold stress.

Here, we describe, illustrate and compare a new natural hybrid, Sonneratia × zhongcairongii Y. S. Wang & S. H. Shi (Sonneratiaceae), with its possible parent species. Based on its morphological characteristics and habitat conditions, this taxon is considered to represent a sterile hybrid between S. alba and S. apetala. In China, the new hybrid is only reported in the mangrove forest in Dongzhai Harbour, Hainan Island. It has intermediate characteristics with its parents by elliptical leaf blades, peltate stigma, terminal or axillary inflorescence with 1–3 flower dichasia, cup – shaped calyx (4–6 calyx lobes) and no petals. We also provide a key for the identification of Sonneratia species.