Carbonic anhydrase isoforms of Neopyropia yezoensis: Intracellular localization and expression profiles in response to inorganic carbon concentration and life stage

Overexpression of Rboh enhances inorganic carbon acquisition through coordinating with carbonic anhydrase in Pyropia yezoensis

Pyropia yezoensis is an important intertidal economic macroalgae, which is periodically affected by various stresses, such as the limitation of inorganic carbon (Ci) deficiency. Under such environment, the redox homeostasis within the cells of P. yezoensis is seriously affected, and the reactive oxygen species (ROS) signal transduction system would be activated to regulate the photosynthetic activity. Therefore, how P. yezoensis manage ROS to maintain effective photosynthetic carbon fixation has aroused great interest. Here, we characterize transformants overexpressing respiratory burst oxidase homolog (Rboh), an important gene that can actively produce ROS, at the levels of cellular physiology, biochemistry, and transcriptomics. Our data indicated the expression of Rboh significantly increased, accompanied by a significant upregulated expression of alpha-type carbonic anhydrase 3 (αCA3) and increased extracellular carbonic anhydrase activity in the Rboh overexpressing strains. Interestingly, compared with the wild type, the photosynthetic activity of transgenic strains was significantly higher under the low Ci and high light condition, implying that the ROS signal triggered by overexpression of Rboh was involved in regulating the Ci absorption and utilization in P. yezoensis when the Ci source was limited. In summary, this study provided evidence supporting the correlation between the ROS production and the Ci utilization under stress environments in P. yezoensis.

Genetic evidence for functions of Chloroplast CA in Pyropia yezoensis: decreased CCM but increased starch accumulation

In response to the changing intertidal environment, intertidal macroalgae have evolved complicated Ci utilization mechanisms. However, our knowledge regarding the CO2 concentrating mechanism (CCM) of macroalgae is limited. Carbonic anhydrase (CA), a key component of CCM, plays essential roles in many physiological reactions in various organisms. While many genes encode CA in the Pyropia yezoensis genome, the exact function of specific CA in P. yezoensis remains elusive. To explore the particular function of chloroplast CA in intertidal macroalgae, we produced chloroplast-localized βCA1 knockdown mutants of P. yezoensis through RNA interference, and Pyβca1i mutants (hereinafter referred to as ca1i) showed a notable decrease in leaf area and overall biomass, as well as decreased soluble protein and unsaturated fatty acid content under different DIC conditions. However, ca1i mutants showed relatively higher starch content compared to the wild-type. The activity of enzymes involved in the Calvin cycle, photorespiration, Pentose-phosphate pathway, and floridean starch synthesis of P. yezoensis indicated an effective starch accumulation pathway after the interference of βCA1. All results suggest that the decreased activity of PyβCA1 impaired the CCM and development of thalli of P. yezoensis, but stimulated starch accumulation in the cytoplasm through feedback to the photorespiration pathway and pentose phosphate pathway to replenish intermediates for the Calvin cycle. This study is the first to explore the specific function of chloroplast CA in intertidal macroalgae using genomic technology. The results provide valuable insights into the adaption mechanisms of intertidal macroalgae to their environment.