Transcriptome Analysis and Physiological Responses of Economic Macroalga Gracilariopsis lemaneiformis under Sulfate Deficiency

Abstract

Sulfur is an essential macronutrient for the growth of all photosynthetic organisms and plays important roles in different metabolic pathways. However, sulfur metabolism and its related research on macroalgae with important ecological value is rather limited. In this study, marine ecological valued macroalga Gracilariopsis lemaneiformis was used to study the general physiological responses and transcriptome profiling under the sulfate deficiency. The relative growth rate of algae under sulfate deficiency was statistically significantly lower than that of control after 6 days. However, no significant differences were observed in the pigments content and Fv/Fm value, indicating that the photosynthesis was not obviously affected under the sulfate deficiency. Furthermore, the significantly increased soluble protein and carbohydrate contents, and indistinctively differentially expressed sulfate transporter/permease (ST) and ATP sulfurylase (ATPS) genes suggesting that G. lemaneiformis cells did not use sulfur from internal protein and carbohydrate pools but utilize stored sulfur from vacuole to satisfy their nutritional requirements during the sulfate deficiency. Transcriptome data showed that most annotated differentially expressed genes (DEGs) were down-regulated under the sulfate deficiency, including a large proportion of genes involved in the pathway of sulfur metabolism. Therefore, it was concluded that the pathway of sulfur metabolism was suppressed under the sulfate deficiency in G. lemaneiformis. The results and analysis in this study provide a comprehensive understanding for the physiological and molecular response of G. lemaneiformis to sulfate deficiency.