Author : Ming Ho
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (15 download)
Book Synopsis Characterization of Far-red Light Photoacclimation in Cyanobacteria by : Ming Ho
Download or read book Characterization of Far-red Light Photoacclimation in Cyanobacteria written by Ming Ho and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation discusses a mechanism that allows some cyanobacteria to utilize far-red light for oxygenic photosynthesis. Although visible light is the major source of energy for oxygenic photosynthesis, the availability of visible light is limiting in some environments, such as the shade of canopies, soils, microbial mats, and stromatolites. Cyanobacteria that grow in such environments have developed an acclimation process called as Far-Red Light Photoacclimation (FaRLiP) to harvest far-red light for oxygenic photosynthesis. In visible light, these cyanobacteria behave like canonical cyanobacteria, harvesting visible light by using phycobilisomes (PBS), and chlorophyll (Chl) a-associated photosystem I (PSI) and photosystem II (PSII). However, in far-red light (FRL; wavelength > 700 nm), in response to the change of light quality, they synthesize Chl d and Chl f, and remodel PBS, PSII, and PSI to harvest FRL for photosynthesis. This capability mostly comes from a conserved FaRLiP gene cluster comprising 20 genes used to remodel the photosynthetic apparatus. These genes include a knotless phytochrome (RfpA), two response regulators (RfpB and RfpC), and genes encoding seventeen proteins that are homologous subunits found in the PBS, PSII, and PSI complexes that occur in white light. More than 15 cyanobacteria encompassing all five taxonomic sections having this FaRLiP gene cluster.The FaRLiP mechanism was further elucidated in this dissertation. Chapter 2 of this thesis describes the establishment of a conjugative method for producing gene deletions and replacements in one of the cyanobacterial strains, Synechococcus sp. PCC 7335, that can perform FaRLiP. The genes encoding the phytochrome (rfpA) and the two response regulators (rfpB and rfpC) were individually deleted in this strain, which showed that each of them is essential for FaRLiP. Using the conjugative system, in Chapter 3, I describe the remarkable discovery that Chl f synthase is a paralog of the D1 subunit of PSII, which is encoded in the FaRLiP gene cluster. Like the photochemistry in PSII, the Chl f biosynthetic reaction is also light-dependent. Chapter 4 describes transcriptomic analyses performed to analyze transcriptional responses to growth in FRL. These studies showed that the phytochrome and response regulators specifically control the expression of all the genes in the FaRLiP gene cluster as well as the gene(s) required for the synthesis of Chl d. The characterization of the remodeling of PBS in FRL is discussed in Chapter 5. In Synechococcus sp. PCC 7335, the hemidiscoidal PBS assembled in red light have a tricylindrical core and six peripheral rods. However, in FRL, an additional type of phycobiliprotein complex, bicylindrical cores, are produced. They contain the products of five paralogous genes from the FaRLiP gene cluster, which are allophycocyanin subunits that absorb FRL. A model was developed for the composition and structure of the bicylindrical core complexes produced in FRL. The characterization of remodeled PSI, PSII, and the kinetics of energy transfer from PBS to PSII and PSI in red light and FRL are summarized in Chapter 6 (and to some extent in Chapter 5). In FRL, Chl a is still the major Chl associated with PSI and PSII; additionally, PSI binds Chl f, and PSII binds Chl d and Chl f. The kinetics of energy transfer support the presence of PBS-PSII-PSI megacomplexes and showed that energy is transferred from PBPs to PSII and PSI, and eventually mostly to PSI, in FRL. Overall, this dissertation describes highly detailed information concerning diverse mechanistic aspects of FRL light harvesting for oxygenic photosynthesis. This information will be invaluable for introducing the ability to use FRL into plants in the future.
