Absorption and Transport of Inorganic Carbon in Kelps with Emphasis on Saccharina japonica

Abstract

Due to the low CO2 concentration in seawater, macroalgae including Saccharina japonica have developed mechanisms for using the abundant external pool of HCO3 − as an exogenous inorganic carbon (Ci ) source. Otherwise, the high photosynthetic efficiency of some macroalgae indicates that they might possess CO2 concentrating mechanisms (CCMs) to elevate CO2 concentration intracellularly around the active site of ribu‐ lose-1, 5-bisphosphate carboxylase/oxygenase (RuBisCo). As the photosynthetic modes of macroalgae are diverse (C3, C4 or a combination of C3 and C4 pathway), CCMs in different carbon fixation pathways should vary correspondingly. However, both in C3 and C4 pathways, carbonic anhydrase (CA) plays a key role by supplying either CO2 to RuBisCO or HCO3 − to PEPC. Over the past decade, although CA activities have been detected in a number of macroalgae, genes of CA family, expression levels of CA genes under different CO2 concentrations, as well as subcellular location of each CA have been rarely reported. Based on analysis the reported high-throughput sequencing data of S. japonica, 12 CAs of S. japonica (SjCA) genes were obtained. Neighbor-Joining (NJ) phylogenetic tree of SjCAs constructed using Mega6.0 and the subcellular location prediction of each CA by WoLFPSORT are also conducted in this article.