Integrated Application of Transcriptomics and Metabolomics Reveals the Energy Allocation-Mediated Mechanisms of Growth-Defense Trade-Offs in Crassostrea gigas and Crassostrea angulata

Abstract

Understanding the genetic basis of trait variations and their coordination between relative species or populations distributing in different environmental conditions is important in evolutionary biology. In marine ectotherms, growth-defense trade-offs are a common ecological and evolutionary phenomenon. However, the biochemical and molecular mechanisms that govern these trade-offs in marine ectotherms in the evolutionary perspective remain poorly investigated. Oysters are among the most important species in global aquaculture. Crassostrea gigas (C. gigas) and Crassostrea angulata (C. angulata) are two allopatric congeneric dominant oyster species that inhabit the northern and southern intertidal areas of China. Wild C. gigas and C. angulata were spawned, and their F1 progeny were cultured in the same sites to reduce the environmental effects. Untargeted metabolomics and transcriptomics, together with phenotypic parameters including morphological traits (growth performance), nutritional content (glycogen, crude fat, and fatty acid content), physiology (normalized oxygen consumption rate and total antioxidant capacity) were applied to assess metabolic and transcript divergences between C. gigas and C. angulata. Integrated analyses of metabolites and transcriptomes showed that C. gigas allocated more energy to storage and defense by suppressing glycolysis, fatty acid oxidation and by upregulating fatty acid synthesis, antioxidant gene expression, and related metabolites. The metabolic and transcript results were further confirmed by the phenotypic data that C. gigas has higher glycogen and crude fat content and fatty acid unsaturation and stronger antioxidant capacity than C. angulata. In contrast, C. angulata exhibited better growth performance and a higher oxygen consumption rate. These findings suggest that C. angulata allocates more energy to growth, which is embodied in its stronger aerobic capacity and higher levels of protein synthesis genes, metabolites, and growth-related biomarkers. This study will help to enlighten the evolutionary patterns and genetic basis of growth-defense trade-offs in marine ectotherms and the biochemical and molecular mechanisms underlying energy allocation. Also, the key genes and metabolites of glycogen and fatty acids pathway identified in this study will be applied for meat quality improvement in the oyster industry.

Cis- andTrans-variations of Stearoyl-CoA Desaturase Provide New Insights into the Mechanisms of Diverged Pattern of Phenotypic Plasticity for Temperature Adaptation in Two Congeneric Oyster Species

“…Moreover, the expression of the metabolic gene Scd expression further demonstrated that it was also induced by low temperatures in both species, and C. gigas had significantly higher expression of Scd than C. angulata under both normal temperature (control) and cold conditions; however, it exhibited a lower magnitude of upregulation under cold stress compared with that in C. angulata ( C. gigas 1.67-fold; C. angulata 2.67-fold). The diverged trait means and plasticity of oleic acid (C18:1) content and Scd gene expression in two oyster species support our previous findings that fatty acid composition/ Scd is an important temperature adaptive trait/gene and that adaptive divergence of plasticity occurs ( Li et al 2021 ; Wang, Li, Wang, Cong, et al 2021 ). The content of UFAs and their corresponding metabolic gene Scd constitute an ideal system to study the underlying molecular mechanisms and genetic basis of diverged pattern of plasticity for temperature adaptation.…”

“…The Y-box factor positively activates Scd transcription and specifically binds to “CCAAT” cis -element in human cultured keratinocytes ( Didier et al 1988 ; Zhang et al 2001 ; Eliseeva et al 2011 ). And our previous transcriptome had demonstrated that the Y-box factor was not induced by environmental stress and there was no difference between C. gigas and C. angulata ( Li et al 2021 ; Wang, Li, Wang, Cong, et al 2021 ). Therefore, our findings suggest that the mutation of binding sites for a constitutively active transcription factor (Y-box factor in this study) might lead to increased redundancy in gene expression under different environmental cues, ultimately resulting in the decoupling of genes expression from the environment ( Pfennig and Ehrenreich 2014 ).…”

“…Small interfering RNA (siRNA) was synthesized by GenePharma (Shanghai, China) and used for the RNAi experiments (sequences of the siRNA are shown in supplementary table S1, Supplementary Material online). Thirty C. gigas were cleaned and reared in a 500-l tank for acclimation, and fed with 4 g/m 3 commercial Spirulina powder once per day ( Wang, Li, Wang, Cong, et al 2021 ). After 1 week, individuals were anesthetized as previously described ( Suquet et al 2009 ) (500 g MgCl 2 + 5 l seawater + 5 l freshwater) and then divided into two groups: the siRNA ( n = 15) and the negative control (NC) groups ( n = 15).…”

“…Relative expression levels were calculated using the 2 −△△CT method ( Livak and Schmittgen 2001 ). A detailed comparison between the two species has been previously described ( Li et al 2019 ; Wang, Li, Wang, Cong, et al 2021 ).…”

“…These two species serve as an important model for investigating the evolution of temperature adaption ( Sebens 2002 ; Li et al 2017 , 2021 ). Crassostrea gigas and C. angulata adapt to an environmental temperature gradient, reflected by differential thermal tolerance and differential fatty acid content and composition (especially oleic acid C18:1; Ghaffari et al 2019 ; Wang, Li, Wang, Cong, et al 2021 ). And previous study has observed the adaptive divergence of plasticity in environmentally responsive genes between C. gigas and C. angulata ( Li et al 2019 , 2021 ).…”