Effect Of Overexpression Of Arabidopsis Thaliana Lhca5 On Its PSI-LHCI Structural And Spectroscopic Features

Photosynthesis,which provides organic matter,energy and oxygen for almost all life activities on Earth,consists of two independent and closely related processes,the light and dark reactions.In cyanobacteria,algae and higher plants,the light reaction is driven by two photosystems,Photosystem I(PSI)and Photosystem II(PSII).In algae and higher plants,PSI consists of a core complex and a peripheral light-harvesting antenna system(Light-harvesting complex I(LHCI)).In higher plants,LHCI has four light-trapping antenna binding sites.During the transition from aquatic to terrestrial plants,the second site of LHCI was replaced by Lhca4 to Lhca5,so Lhca4 and Lhca5 may be related to the evolution of plants.Current research on Lhca5 has focused on its localization and function in higher plants,but it is still controversial.By investigating the effect of Lhca4 or Lhca5 binding in the PSI-LHCI supercomplex on the photosynthetic properties of plants,it can help to analyze the potential role of Lhca4 or Lhca5 in plant landing process.In this study,A.thaliana(Arabidopsis thaliana,At)was used as experimental material to obtain A.thaliana Lhca5 overexpression plants with wild-type(WT),lhca1 and lhca4 mutants as background.The photosynthetic capacity,pigment composition and fluorescence emission spectra of these Lhca5 transgenic plants were also determined.Subsequently,the PSI-LHCI complexes of these Lhca5 transgenic plants were further isolated and analyzed for spectroscopic features to explore the position of Lhca5 in the PSI-LHCI complexes of A.thaliana.The above results provide new insights into the effect of Lhca4 or Lhca5,binding in the PSI-LHCI supercomplex on the photosynthetic properties of plants.The findings of this thesis are as follows:(1)The Lhca5 overexpression vector was constructed to transform A.thaliana of different backgrounds,and Lhca5 overexpression plants with A.thaliana WT,lhca1 mutant and lhca4 mutant backgrounds were successfully obtained.(2)There are little difference in phenotype,pigment composition and chlorophyll fluorescence parameters between the transgenic A.thaliana and their corresponding background materials(WT,lhca1 and lhca4).35S:LHCA5f/WT-13 and 35S:LHCA5f/WT-28 on WT background behaved similarly to WT in terms of phenotype,pigment composition and chlorophyll fluorescence parameters;35S:LHCA5f/lhca4-3,35S:LHCA5f/lhca4-22 and 35S:LHCA5f/lhca4-24 showed almost no differences in phenotype,pigment composition and chlorophyll fluorescence parameters compared with lhca4;35S:LHCA5f/lhca1-36,also with lhca1 as background,showed insignificant differences in phenotype,pigment composition and chlorophyll fluorescence parameters compared with lhca1.(3)The PSI-LHCI supercomplex obtained by sucrose density gradient centrifugation contained only a small amount of Lhca5,the Lhca5 included PSI-LHCI supercomplex can be obtained by extracting samples incubated with anti-FLAG M2 Affinity Gel,in which Lhca5 is found to substitute for Lhca4 as analyzed by immunoblotting analysis.(4)The replacement of Lhca4 with Lhca5 within PSI-LHCI super-complex leads to a blue shift in low temperature fluorescence emission,suggesting a decrease in far-red absorbance.These results provide new clues to understand the position and function of Lhca4 and Lhca5 during the evolution of green plants from aquatic to terrestrial lifestyles.