Functional Coupling Between L-Shaped NDH-1 And CO₂ Uptake In Cyanobacteria

Cyanobacteria and eukaryotic algae provide more than 50 percent of global carbon dioxide fixation.Among them,cyanobacteria have become a research hotspot in recent years because of its highly efficient CO₂ concentration mechanism?CCM?.In cyanobacteria,this CCM consists of bicarbonate absorption transporters in the plasma membrane,NDH-1MS/NDH-1MS in the thylakoid membrane,and carboxysome.It operates through NDH-1MS/NDH-1MS' converting freely diffused CO₂ into bicarbonate,which is then transferred and converted back into CO₂ by carbonic anhydrase in the carboxysome as the substrate of Ru Bis Co.Through this mechanism,the concentration difference of CO₂ in and out of cell is maintained,as a consequence,cyanobacteria can maintain a higher concentration of CO₂ in the low-carbon environment,which is very important for the survival of cyanobacteria in changing CO₂ conditions.It is well known that two U-typed NDH-1 complexes are involved in CO₂ uptake,one of which is the NDH-1MS complex containing Ndh D3,NdhF3,Cup A and Cup S that involved in the high affinity CO₂ uptake,and another is the NDH-1MS complex containing Ndh D4,Ndh F4 and Cup B that is involved in the constitutional low affinity CO₂ uptake.We observed from previous study that compared to the wild type,ndh D1/D2 mutant strains also have an impaired CO₂ uptake,and Ndh D1 and Ndh D2 is L-typed NDH-1 complex specific subunits.Therefore,in addition to the U-typed NDH-1MS/NDH-1MS complex plays a significant role in CO₂ uptake,the L-typed NDH-1 complex may be involved in CO₂ uptake.To test this possibility,this thesis has carried out by selecting ?ndh F1 as the experimental material representing the L-typed NDH-1 complex,and the main results are as follows:?1?In order to determine whether L-typed NDH-1 affect CO₂ uptake,we conduct experiments and found that the growth of ?ndh F1 is impaired under low carbon and low p H conditions.Meanwhile,by using a membrane inlet massspectrometer?MIMS?to detect CO₂ uptake in wild-type and mutant strains,it was found that the deletion of ndh F1 resulting in damaging the CO₂ uptake function.?2?In order to explore how L-typed NDH-1 complex affects the CO₂ uptake activity,the P515 module of chlorophyll fluorescence was used to detect the ?p H in wild type and ?ndh F1.We found that the ?p H in the mutant strain is impaired when compared with wild type.At the same time,the blocked electron transfer of the?ndh F1 was detected by the Dual-PAM-100 machine.?3?In order to understand whether the ?p H and electron transfer affect the transcriptional level of the relevant CCM genes further.The RT-PCR results showed that the transcriptional level of carbonic anhydrase gene eca B is impaired.As a consequence,activity of CA in ?ndh F1 is also impaired.In summary,we found that the L-typed NDH-1 complex is very important for sufficient CO₂ uptake in cyanobacteria.Its defect results in a fact that ?p H is impaired and consequently electron transfer is also partly blocked,coupling to impaired activities of CA and CO₂ uptake.