The Psb28 Proteins of Oxygenic Photosynthesis

This project focused on the Photosystem II (PS II) extrinsic proteins Psb28 and Psb28-2 and reports, for the first time, results using a mutant deficient in Psb28-2. The psb28 and psb28-2 genes were interrupted with antibiotic-resistance cassettes both singularly and in combination together. The resulting strains: Dpsb28, DPsb28-2 and Dpsb28:DPsb28-2 along with a wild-type control strain were physiologically tested to determine photoautotrophic growth rates; oxygen evolution rates; vulnerability to, and ability to recover from, photoinhibition; relative quantities of PSII; fluorescence characteristics at liquid nitrogen temperatures; and the expression of psb28 and psb28-2. The two single mutants (Dpsb28 and DPsb28-2) were found to grow slightly slower than wild type and the double mutant (Dpsb28:DPsb28-2) was found to grow slower again. No substantial differences were found in oxygen evolution rates, ability to recover from and susceptibility to photoinhibition or the relative quantities of PSIIbetween mutants and wild type. The use of 77 K fluorescence was developed during this project and was subsequently used to demonstrate that the mutants lacking Psb28-2 have deficient energy transfer between the phycobilisomes and the photosystems, thus providing the first indication of separate functions of the Psb28 and Psb28-2 proteins. This project has laid the groundwork for further research into Psb28 and Psb28-2, and the Dpsb28, DPsb28-2 and Dpsb28:DPsb28-2 strains created in this project will provide the tools for further research into these proteins