Microcosm study on cold adaptation and recovery of an exotic mangrove plant, Laguncularia racemosa in China

High-quality genome of a pioneer mangrove Laguncularia racemosa explains its advantages for intertidal zone reforestation

Ecological restoration of mangrove ecosystems that became susceptible to recent habitat perturbations is crucial for tropical coast conservation. The white mangrove Laguncularia racemosa, a pioneer species inhabiting intertidal environments of the Atlantic East Pacific (AEP) region, has been used for reforestation in China for decades. However, the molecular mechanisms underlying its fast growth and high adaptive potential remain unknown. Using PacBio single-molecule real-time sequencing, we completed a high-quality L. racemosa genome assembly covering 1105 Mb with scaffold N50 of 3.46 Mb. Genomic phylogeny shows that L. racemosa invaded intertidal zones during a period of global warming. Multi-level genomic convergence analyses between L. racemosa and three native dominant mangrove clades show that they experienced convergent changes in genes involved in nutrient absorption and high salinity tolerance. This may explain successful L. racemosa adaptation to stressful intertidal environments after introduction. Without recent whole-genome duplications or activated transposable elements, L. racemosa has retained many tandem gene duplications. Some of them are involved in auxin biosynthesis, intense light stress and cold stress response pathways, associated with L. racemosa's ability to grow fast under high light or cold conditions when used for reforestation. In summary, our study identifies shared mechanisms of intertidal environmental adaptation and unique genetic changes underlying fast growth in mangrove-unfavourable conditions and sheds light on the molecular mechanisms of the white mangrove utility in ecological restoration.

Unraveling molecular mechanisms underlying low-temperature adaptation in Laguncularia racemosa

Laguncularia racemosa (L.) C.F. Gaertn is a controversial species in China, in terms of being a pioneer species for mangrove restoration and a putative invasive species occupying natural habitats. The tolerance to chilling stress allows L. racemosa to adapt to extreme climate change. However, little is known about the molecular-level chilling resistance mechanisms in L. racemosa, which restricts our understanding of its biological features and invasion potential. In this study, L. racemosa seedlings were treated with freezing temperature (0 °C) at four durations (0 h, 3 h, 12 h and 24 h of recovery after treatment), and both physiological and transcriptional regulations underlying chilling stress resistance were investigated. Chilling stress caused damage to the cell membrane system and reduced photosynthesis efficiency of L. racemosa seedlings. To combat the adverse impacts, plasma membrane biosynthesis and antioxidant processes were substantially enhanced. After 24 h of recovery, the seedlings nearly recovered to normal growth condition, except for the processes related to photosynthesis, indicating their vigorous adaptation to short-term chilling stress. Importantly, the individuals from higher latitude displayed better adaptation to chilling injury than those from lower latitude, highlighting the role of long-term heredity × environment interactions in promoting the chilling resistance capacity of L. racemosa. These features allow L. racemosa to survive in extremely cold weather, but may also increase its risk of invasion into intertidal ecosystems. Together, our findings present a comprehensive view of the chilling-adaptative mechanisms of L. racemosa, which provide clues for better evaluating the invasive potential of L. racemosa.