Identification Of S86 And Its Functional Analysis During Acclimation Of Synechocystis Sp.Strain PCC 6803 To Iron Deficiency

Although iron is the fourth largest element in the earth's crust,the bivalent iron,which originally existed in the oceans and had high bio-availability,was oxidized into trivalent iron,due to the fact that the earth's environment has long been oxidized,making the bio-availability of iron gradually decreased.However,iron is a key control of cyanobacterial community composition and ecological distribution,and the iron requirement of cyanobacteria is one order of magnitude more than that of non-photosynthetic organisms based on the same size.Among them,the photosystem I(PSI)complex contained more than 25% of total intracellular iron.As a consequence,the damage to PSI under long-term iron deficiency is extremely serious.To reduce the damage of the PSI under iron deficiency,cyanobacteria have evolved a variety of protective strategies,among which Isi A is the most well-known one.Isi A can combine with PSI to form super complex,on the one hand,maintain the structural integrity of PSI,on the other hand,dissipate the excess energy,so as to protect PSI.However,up to now,the specific mechanism underlying the cyanobacterial isi A regulation remains poorly understood.Under the background of deleting the iron transport gene s56 in Synechocystis sp.strain PCC 6803(heareafter Synechocystis 6803),this thesis constructed a system to screen genes involved in photosystem protection under iron deficiency,and an unknown function gene s86,which is unique in cyanobacteria,was successfully screened and identified,and its function was investigated.The main research results are summarized as follows:(1)In the cyanobacterium Synechocystis 6803,s56 encodes an iron transporter specific to photosynthetic organisms.Under high light conditions,the deletion of s56 can cause a significant increase in the expression of isi A at the transcription level,and at the same time,other known genes related to iron-deficiency stress in cyanobacteria are also significantly increased at the transcription level.These results indicate that under high light,the absence of s56 causes the cyanobacteria to be in an iron-deficient environment.(2)By analyzing the existing transcriptomic data in the existing literature,we screened the genes that might play a role in iron deficiency stress,and further over-expressed them into the(35)s56 mutant to obtain the over-expressed strains.Through the growth phenotype analysis under high light,we screened and identified an unknown functional gene s86,which could recover the high light-sensitive phenotype caused by s56 deletion,after over-expression in(35)s56.(3)By analyzing and comparing the difference in transcription level between(35)s56 and(35)s56+s86,we found that the expression of isi A increased significantly in(35)s56+s86.Meanwhile,other known genes related to iron deficiency in cyanobacteria are also significantly increased to varying degrees.Since Isi A is involved in maintaining the stability of PSI and thus protecting PSI under iron deficiency stress,the above results suggest that the increase of isi A expression may protect PSI activity and thus restore the high light-sensitive phenotype of(35)s56.(4)By analyzing the photosynthetic activity of(35)s56 and(35)s56+s86,it was found that the loss of s56 resulted in a significant decrease in PSI activity in normal growth conditions,and the damage of PSI was more serious under high light.However,the lose had little,if any,effect on the PSII activity.By contrast,over-expression of s86 in(35)s56 restored the PSI activity to wild type level,even under high light condition.In conclusion,we successfully constructed a system to screen for genes involved in PSI protection under iron deficiency stress,and successfully screened the gene s86 unique in cyanobacteria.In the absence of s56,the over-expression of s86 significantly increased the expression of isi A,which is necessary for maintaining PSI activity and growth under high light.We hypothesized that s86 may involved in isi A regulation,and protecting the activity of PSI under iron deficient.However,how s86 regulates the expression of isi A still need further study.This paper further deepens the understanding of the mechanism of isi A transcription regulation in cyanobacteria,and provides a new idea and direction for further research on the iron deficiency adaptation mechanism of photosynthetic organisms.