期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2009
卷号：106
期号：14
页码：5990-5995
DOI：10.1073/pnas.0812885106
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The CO2-concentrating mechanism (CCM) of Chlamydomonas reinhardtii and other microalgal species is essential for photosynthetic growth in most natural settings. A great deal has been learned regarding the CCM in cyanobacteria, including identification of inorganic carbon (Ci; CO2 and HCO[IMG]f1.gif" ALT="Formula" BORDER="0">) transporters; however, specific knowledge of analogous transporters has remained elusive in eukaryotic microalgae such as C. reinhardtii. Here we investigated whether the limiting-CO2-inducible, putative ABC-type transporter HLA3 might function as a HCO[IMG]f1.gif" ALT="Formula" BORDER="0"> transporter by evaluating the effect of pH on growth, photosynthetic Ci affinity, and [14C]-Ci uptake in very low CO2 conditions following RNA interference (RNAi) knockdown of HLA3 mRNA levels in wild-type and mutant cells. Although knockdown of HLA3 mRNA alone resulted in only modest but high-pH-dependent decreases in photosynthetic Ci affinity and Ci uptake, the combination of nearly complete knockdown of HLA3 mRNA with mutations in LCIB (which encodes limiting-Ci-inducible plastid-localized protein required for normal Ci uptake or accumulation in low-CO2 conditions) and/or simultaneous, apparently off-target knockdown of LCIA mRNA (which encodes limiting-Ci-inducible plastid envelope protein reported to transport HCO[IMG]f1.gif" ALT="Formula" BORDER="0">) resulted in dramatic decreases in growth, Ci uptake, and photosynthetic Ci affinity, especially at pH 9, at which HCO[IMG]f1.gif" ALT="Formula" BORDER="0"> is the predominant form of available Ci. Collectively, the data presented here provide compelling evidence that HLA3 is directly or indirectly involved in HCO[IMG]f1.gif" ALT="Formula" BORDER="0"> transport, along with additional evidence supporting a role for LCIA in chloroplast envelope HCO[IMG]f1.gif" ALT="Formula" BORDER="0"> transport and a role for LCIB in chloroplast Ci accumulation.
