Identification Of The Function Of CYP120A1 In Light Acclimation Of Cyanobacterium Synechocystis Sp.PCC6803 By Gene Knockout

Cyanobacteria are the earliest photosynthetic organisms on earth,and it is very important primary producers in water.Synechocystis.sp.PCC6803 has a natural genetic transformation system,and S.sp.PCC6803 is one of the best patterns of molecular biology research in cyanobacteria.The fact that P450 monooxygenase CYP120A1 of S.sp.PCC6803 contributes to retinal analogues metabolism has been proved,but it,s not known whether or not the process can influence the biological function of cyanobacteria.A retinal-based proton pump helps cyanobacteria to utilize far-red light.In order to reveal the function of CYP120A1 in light acclimation of cyanobacterium S.sp.PCC6803.In this study,slr0574 gene in S.sp.PCC6803 has been knocked out,slr0574 mutations and complementary strains have been built.Compared with the wild type(WT),the different light intensity change treatment,ultraviolet stress and phototaxis expenence have been conducted,in which the growth of cyanobacteria,pigments,phycobiliprotein and photosynthetic activity have been measured.The results are as follows:1.After 7 days in the treatment of low light,high light and normal light,the growth,chlorophyll a(Chi a),carotenoid(CAR),phycobiliprotein(CPC),P-I curve and Fv/Fm of slr0574::C.K2 mutant strains have no significant difference with WT and slr0574-com(P>0,05).Under Low light to high light conditions(LL4d,HL3d),Chi a/cell,CAR/cell,CPC/cell,the pigment composition of slr0574::C.K2 is the same with WT and slr0574-com,but the growth of the slr0574::C.K2 has been inhibited obviously compared with WT and slr0574-com(P<0.05),and photosynthetic electron transport rate(rETR)response to light intensity(PAR)reduced obviously(P<0.05),the largest photochemical efficiency of PS ?(Fv/Fm)decrease obviously(P<0.05),the photosynthetic activity significantly suppressed.So CYP120A1 in S.sp.PCC6803 play an important role under low light changes to high light,through which retinal-based proton pump on the proteorhodopsin promotes the rate of photosynthetic electron transport on thylakoid membranes,NADPH is generated to provide energy for photosynthesis,so as to maintain its normal growth of photosynthesis.2.After 3 days under normal light,S.sp.PCC6803 was been treamented with UV-B 8 hours,the growth,chlorophyll a(Chi a),carotenoid(CAR),phycobiliprotein(CPC),P-I curve and Fv/Fm of slr0574::C.K2 mutant strains have no significant difference with WT and slr0574-com(P>0.05).So CYP120A1 is not involved in UV protection mechanism in cyanobacteria.3.Under the unidirectional light,WT,slr0574::CK2,slr0574-com of S.sp.PCC6803 showed obvious phototaxis,which explained that gene knockout of CYP120A1 has no influence on phototaxis in S.sp.PCC6803.