Study Of Far-red Light Photoacclimation Of Phycobiliprotein And Its Application In Cyanobacteria And Tobacco

Cyanobacteria use a huge light-harvesting complex:phycobilisomes,attached to the thylakoid membrane by multidomain core-membrane linker,to capture light and transfer the energy to light reaction center.Many species of algae on the earth can adapt to extreme conditions,such as Chroococcidiopsis species which can grow on rocky surfaces and other places where white light is weak.They can undergo extensive remodeling and perform photosynthesis under far-red light conditions.Two mechanisms were known by which components of the phycobilisome core can be adapted to such light conditions.One is non-covalent binding of the chromophore of protein variants lacking the conventional cysteine that form a thioether bond to the chromophore.An even larger red-shift has been identified with variants of the bulk allophycocyanin subunits.It would be a huge advantage for the development of fluorescence probe to find red-shifted fluorescent protein.This work studied?-and?-subunits of Chroococcidiopsis thermalis sp.PCC 7203.The cells with combination of ApcA2 and ApcB2 catalyzed by CpcS1 showed two emission peaks,one at 647 nm and the other one 722 nm.ApcA,ApcB in Synechocystis sp.PCC 6803 was replaced by ApcA2,ApcB2 to investigate whether Synechocystis sp.PCC 6803 could acclimate under far-red light conditions with the expression of ApcA2,ApcB2.The results show that the mutant failed to undergo far-red light photoacclimation with little variation of OD_{730 nm},chlorophyll and phycocyanin content.Plants mainly utilize blue-violet light and red-orange light for photosynthesis.So with these red-shifted proteins,plants may be able to carry out photosynthesis when the light is weak,and thus to broaden the range of light that plants bring into use,or increase the photosynthetic efficiency.We tried different Linker of variant length to fuse the excellent mutant BDFP1.1 screened before with mCherry to enable it to perform the optimal F?rster resonance energy transfer?FRET?.The spectral characteristics of mCherry:12 aa Linker:BDFP1.1 are realistic.It was transfered into plants to study its effect on plant's physiological functions.The biological data shows that there is no significant change in chlorophyll fluorescence,maximum photosynthetic rate,and electron transfer rate compared to wild type.It is well-known that the red-shifted proteins have significant potential for the development of fluorescent probes with higher transmission rate and lower damage in tissues.It is also a hotspot in fluorescent protein research.The algae which can undergo far-red light acclimation are the important resource for this study.Although the ApcA2and ApcB2 require the catalysis of the lyase CpcS1 to bind phycobilin,the red-shifted fluorescence of 722 nm is still of great interest.By means of random mutation and other molecular evolutionary methods,finding the self-catalyzed phycobiliprotein with more red-shifted fluorescent spectrum will be the main lead for future research.Therefore,this study sets a foundation for screening more optimized fluorescent proteins.Through the FRET effect of the fusion protein,the photosynthetic light absorption range of the plant can be broadened,thereby enhancing the photosynthesis efficiency of the plant.Although the research in this article has not yet achieved the expected results,it also provides new ideas for the research of plant photosynthesis.The application of the fusion protein to crops is beneficial to improve the light adaptability of crops under extreme environmental conditions,and has important significance for increasing crop yield.