Proteomics analysis reveals the mechanism of growth retardation under a specific nitrogen environment for Caulerpa lentillifera

Abstract

Caulerpa lentillifera is a macroalgae with high economic value in tropical and subtropical regions. To date, the influence of nitrogen sources on the growth of C. lentillifera is unclear, and the biological relevance behind the nonlinear growth phenomenon of C. lentillifera under different nitrogen concentrations remains unknown. In this study, besides traditional growth observation and photosynthetic pigment content analysis, a quantitative proteomics method was applied to investigate the molecular mechanisms of C. lentillifera in response to 55, 110, 220, 440, and 880 mu mol/L nitrate concentrations. Our results showed that neither the number of branches nor the percentage weight gain of C. lentillifera increased linearly with nitrate concentration during the 12-day culture. Growth retardation was observed at 220 mu mol/L nitrate concentration (4x condition), but the concentrations of chlorophyll a, chlorophyll b, and beta-carotene extracted from C. lentillifera showed no difference under all nitrate conditions. Proteomics analysis results coupled with principal component analysis demonstrated that 4x condition is a unique culture condition for C. lentillifera. In addition, proteins with substantial expression changes were involved in different biological functions, such as protein synthesis, genetic information processing, protein ubiquitination, and cytoskeleton formation. Quantitative proteomics analysis further confirmed that 17 proteins were significantly upregulated under the 4x condition, while three proteins were downregulated, indicating that this culture condition is an environmental stress to C. lentillifera and causes growth retardation. Moreover, according to the protein-protein interaction network, eukaryotic translation initiation factor 4A-1 (eIF4A), one of 17 protein upregulated was suggested as a potential marker of the growth retardation phenomenon of C. lentillifera. Our findings provide the first molecular evidence for understanding the mechanism under different nitrate conditions and propose a potential growth marker for the cultivation of C. lentillifera.