Date of Award

6-2017

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Dr. Yan Lu

Second Advisor

Dr. Tod Barkman

Third Advisor

Dr. Silvia Rossbach

Fourth Advisor

Dr. Jian Yao

Access Setting

Masters Thesis-Abstract Only

Restricted to Campus until

6-2027

Abstract

Photosynthesis is essential to all life on Earth. In photosynthetic organisms, the level of light intensity determines the activity of the photosystem II (PSII) repair process. Land plants do not have the ability to avoid excess photon energy, as do most cyanobacteria and algae, so they have evolved proteins, such as Low Quantum Yield of PSII 1 (LQY1), to aid in the PSII repair process. It was thought that LQY1 had no homologs in algae or cyanobacteria, until the recent discovery of CsLQY1 in Coccomyxa subellipsoidea, a sessile, terrestrial, polar arctic algae exposed to long summers of all light. The CsLQY1 protein has a similar number of amino acid residues, identical domain composition and protein disulfide isomerase activity that is essential to the PSII repair cycle.

In addition, the cyanobacterium Synechocystis sp. PCC 6803 expressing the AtLQY11-154 (Arabidopsis thaliana homolog) polypeptide shows increased light tolerance, when compared to the empty vector control. Chlorophyll fluorescence kinetics data reveal that the AtLQY11-154 transformant has increased dark-adapted photochemical efficiency (Fv/Fm), PSII electron transport rate (ETR) and reduced nonphotochemical quenching (NPQ) and photoinhibition (qI) under elevated light intensity. These data suggest that introducing AtLQY1 into cyanobacteria may increase their photosynthetic efficiency and light tolerance, potentially due to an increase in PSII repair.

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