Local adaptation of trophic strategy determined the tolerance of coral Galaxea fascicularis to environmental fluctuations.

The escalation of global change has resulted in heightened frequencies and intensities of environmental fluctuations within coral reef ecosystems. Corals originating from marginal reefs have potentially enhanced their adaptive capabilities in response to these environmental variations through processes of local adaptation. However, the intricate mechanisms driving this phenomenon remain a subject of limited investigation. This study aimed to investigate how corals in Luhuitou reef, a representative relatively high-latitude reef in China, adapt to seasonal fluctuations in seawater temperature and light availability. We conducted a 190-day plantation experiment with the widespread species, Galaxea fascicularis, in Luhuitou local, and from Meiji reef, a typical offshore tropical reef, to Luhuitou as comparison. Drawing upon insights from physiological adaptations, we focused on fatty acid (FA) profiles to unravel the trophic strategies of G. fascicularis to cope with environmental fluctuations from two origins. Our main findings are threefold: 1) Native corals exhibited a stronger physiological resilience compared to those transplanted from Meiji. 2) Corals from both origins consumed large quantities of energy reserves in winter, during which FA profiles of local corals altered, while the change of FA profiles of corals from Meiji was probably due to the excessive consumption of saturated fatty acid (SFA). 3) The better resilience of native corals is related to high levels of functional polyunsaturated fatty acid (PUFA), while insufficient nutrient reserves, possibly due to weak heterotrophic ability, result in the obstruction of the synthesis pathway of PUFA for corals from Meiji, leading to their intolerance to environmental changes. Consequently, we suggest that the tolerance of G. fascicularis to environmental fluctuations is determined by their local adapted trophic strategies. Furthermore, our findings underscore the notion that the rapid adaptation of relatively high-latitude corals to seasonal environmental fluctuations might not be readily attainable for their tropical counterparts within a brief timeframe.

Life-stage specificity and temporal variations in transcriptomes and DNA methylomes of the reef coral Pocillopora damicornis in response to thermal acclimation.

Understanding the acclimation capacity of reef corals across generations to thermal stress and its underlying molecular underpinnings could provide insights into their resilience and adaptive responses to future climate change. Here, we acclimated adult brooding coral Pocillopora damicornis to high temperature (32 °C vs. 29 °C) for three weeks and analyzed the changes in phenotypes, transcriptomes and DNA methylomes of adult corals and their brooded larvae. Results showed that although adult corals did not show noticeable bleaching after thermal exposure, they released fewer but larger larvae. Interestingly, larval cohorts from two consecutive lunar days exhibited contrasting physiological resistance to thermal stress, as evidenced by the divergent responses of area-normalized symbiont densities and photochemical efficiency to thermal stress. RNA-seq and whole-genome bisulfite sequencing revealed that adult and larval corals mounted distinct transcriptional and DNA methylation changes in response to thermal stress. Remarkably, larval transcriptomes and DNA methylomes also varied greatly among lunar days and thermal treatments, aligning well with their physiological metrics. Overall, our study shows that changes in transcriptomes and DNA methylomes in response to thermal acclimation can be highly life stage-specific. More importantly, thermally-acclimated adult corals could produce larval offspring with temporally contrasting photochemical performance and thermal resilience, and such variations in larval phenotypes are associated with differential transcriptomes and DNA methylomes, and are likely to increase the likelihood of reproductive success and plasticity of larval propagules under thermal stress.

Effects of elevated temperature and copper exposure on the physiological state of the coral Galaxea fascicularis.

The co-occurrence of elevated seawater temperature and local stressors (heavy metal contamination) affects the ecophysiology of phototrophic species, and represents a risk to the environmental quality of coral reefs. Therefore, we investigated the effects of both Cu alone and Cu in combination with elevated temperature (ET) on the physiology of the coral Galaxea fascicularis, and measured the parameters related to the photo-physiology and oxidative state. G.fascicularis is one of the dominant coral species in the South China Sea which exhibits strong adaptability to environmental stress. We exposed the common coral species G.fascicularis to a series of environmentally relevant concentrations of Cu at 29 °C (normal temperature, NT) and 32 °C (elevated temperature, ET) for 96 h. Single polyps were used in the experiments, which reduced individual variability when compared to the coral colonies. The results suggested that: i) Cu or ET had significant negative effects on the actual operating ability of photosystem Ⅱ (PSII), but not on the maximal chlorophyll fluorescence in darkness (Fv/Fm). ii) Symbiodiniaceae density was significantly reduced by high Cu concentrations, for Cu-NT and Cu-ET, a high concentration of Cu (40 µg/L) significantly impacted Symbiodiniaceae density, causing a 75.4% and 81.0% decrease, respectively. iii) the content of malondialdehyde (MDA) in coral tissues increased significantly under Cu-ET. iv) a certain range of copper concentration (25-30 µg/L) increased the pigment content of the Symbiodiniacea. Our results indicated that the combined stressors of Cu and ET made the coral tissue sloughed, caused the coral tissue damaged by lipid oxidation, reduced the photosynthetic capacity of the Symbiodiniacea, and led to the excretion of Symbiodiniacea.

Genome-Wide Identification of bZIP Transcription Factors in Faba Bean Based on Transcriptome Analysis and Investigation of Their Function in Drought Response.

Faba bean is an important cool-season edible legume crop that is constantly threatened by abiotic stresses such as drought. The basic leucine zipper (bZIP) gene family is one of the most abundant and diverse families of transcription factors in plants. It regulates plant growth and development and plays an important role in the response to biotic and abiotic stresses. In this study, we identified 18 members of the faba bean bZIP transcription factor family at the genome-wide level based on previous faba bean drought stress transcriptome sequencing data. A phylogenetic tree was constructed to group the 18 VfbZIP proteins into eight clades. Analysis of cis-acting elements in the promoter region suggested that these 18 VfbZIPs may be involved in regulating abiotic stress responses such as drought. Transcriptome data showed high expression of seven genes (VfbZIP1, VfbZIP2, VfbZIP5, VfbZIP7, VfbZIP15, VfbZIP17, and VfbZIP18) in the drought-tolerant cultivar under drought stress, in which VfbZIP1, VfbZIP2, and VfbZIP5 were consistently expressed as detected by quantitative real-time polymerase chain reaction (qRT-PCR) compared to the transcriptome data. Ectopic overexpression of the three VfbZIPs in tobacco, based on the potato Virus X (PVX) vector, revealed that VfbZIP5 enhanced the drought tolerance. Overexpressed VfbZIP5 in plants showed lower levels of proline (PRO), malondialdehyde (MDA), and peroxidase (POD) compared to those overexpressing an empty vector under 10 days of drought stress. Protein-protein interaction (PPI) analysis showed that VfbZIP5 interacted with seven proteins in faba bean, including VfbZIP7 and VfbZIP10. The results depict the importance of VfbZIPs in response to drought stress, and they would be useful for the improvement of drought tolerance.

Rapid shifts in thermal reaction norms and tolerance of brooded coral larvae following parental heat acclimation.

Thermal priming of reef corals can enhance their heat tolerance; however, the legacy effects of heat stress during parental brooding on larval resilience remain understudied. This study investigated whether preconditioning adult coral Pocillopora damicornis to high temperatures (29°C and 32°C) could better prepare their larvae for heat stress. Results showed that heat-acclimated adults brooded larvae with reduced symbiont density and shifted thermal performance curves. Reciprocal transplant experiments demonstrated higher bleaching resistance and better photosynthetic and autotrophic performance in heat-exposed larvae from acclimated adults compared to unacclimated adults. RNA-seq revealed strong cellular stress responses in larvae from heat-acclimated adults that could have been effective in rescuing host cells from stress, as evidenced by the widespread upregulation of genes involved in cell cycle and mitosis. For symbionts, a molecular coordination between light harvesting, photoprotection and carbon fixation was detected in larvae from heat-acclimated adults, which may help optimize photosynthetic activity and yield under high temperature. Furthermore, heat acclimation led to opposing regulations of symbiont catabolic and anabolic pathways and favoured nutrient translocation to the host and thus a functional symbiosis. Notwithstanding, the improved heat tolerance was paralleled by reduced light-enhanced dark respiration, indicating metabolic depression for energy saving. Our findings suggest that adult heat acclimation can rapidly shift thermal tolerance of brooded coral larvae and provide integrated physiological and molecular evidence for this adaptive plasticity, which could increase climate resilience. However, the metabolic depression may be maladaptive for long-term organismal performance, highlighting the importance of curbing carbon emissions to better protect corals.

Ocean acidification elicits differential bleaching and gene expression patterns in larval reef coral Pocillopora damicornis under heat stress.

The successful dispersal of coral larvae is vital to the population replenishment and reef recovery and resilience. Despite that this critical early stage is susceptible to ocean warming and acidification, little is known about the responses of coral larvae to warming and acidification across different biological scales. This study explored the influences of elevated temperature (29 °C versus 33 °C) and pCO2 (500 µatm versus 1000 µatm) on brooded larvae of Pocillopora damicornis at the organismal, cellular and gene expression levels. Heat stress caused bleaching, depressed light-enhanced dark respiration, photosynthesis and autotrophy, whereas high pCO2 stimulated photosynthesis. Although survival was unaffected, larvae at 33 °C were ten-times more likely to settle than those at 29 °C, suggesting reduced capacity to disperse and differentiate suitable substrate. Remarkably, heat stress induced greater symbiont loss at ambient pCO2 than at high pCO2, while cell-specific pigment concentrations of symbionts at 33 °C increased twofold under ambient pCO2 relative to high pCO2, suggesting pCO2-dependent bleaching patterns. Considerable increases in activities of host antioxidants superoxide dismutase (SOD) and catalase (CAT) at 33 °C indicated oxidative stress, whereas lipid peroxidation and caspase activities were contained, thereby restraining larval mortality at 33 °C. Furthermore, the coral host mounted stronger transcriptional responses than symbionts. High pCO2 stimulated host metabolic pathways, possibly because of the boosted algal productivity. In contrast, host metabolic processes and symbiont photosystem genes were downregulated at 33 °C. Interestingly, the upregulation of extracellular matrix genes and glycosaminoglycan degradation pathway at 33 °C was more evident under ambient pCO2 than high pCO2, suggesting compromised host tissue integrity that could have facilitated symbiont expulsion and bleaching. Our results provide insights into how coral larvae respond to warming and acidification at different levels of biological organization, and demonstrate that ocean acidification can mediate thermal bleaching and gene expression in coral larvae under heat stress.