Acclimative remodeling of the photosynthetic apparatus in response to light and iron limitation in Leptolyngbya sp. JSC-1

Open Access
Gan, Fei
Graduate Program:
Biochemistry, Microbiology, and Molecular Biology
Doctor of Philosophy
Document Type:
Date of Defense:
October 06, 2014
Committee Members:
  • Donald Bryant, Dissertation Advisor
  • Ying Gu, Committee Member
  • Jennifer Macalady, Committee Member
  • John H Golbeck, Committee Member
  • B Tracy Nixon, Committee Member
  • cyanobacteria
  • photosynthesis
  • acclimation
  • far-red light
  • iron stress
Cyanobacteria are widely distributed in diverse ecosystems on Earth, and are unique among chlorophototrophic bacteria in performing oxygenic photosynthesis. To survive and flourish in natural environments with fluctuant physiochemical properties and nutrient availabilities, cyanobacteria have evolved multiple strategies to regulate their photosynthetic apparatus that contains three large, multisubunit complexes: photosystem (PS) I, PS II, and phycobilisomes (PBS). In this work, the acclimative remodeling of cyanobacterial photosynthetic apparatus in response to far-red light and iron deficiency was studied. A previously unknown, acclimative response, far-red light photoacclimation (FaRLiP), was discovered for the first time in cyanobacterium Leptolyngbya sp. JSC-1 (hereafter JSC-1). The FaRLiP response includes synthesis of red-shifted Chls d and f in addition to Chl a and substitution of core subunits of PS I, PS II, and PBS with products of gene variants from a 21-gene cluster, which confers upon strain JSC-1 the ability to grow photoautotrophically in far-red light. The key components controlling FaRLiP have been proposed to be a red/far-red knotless phytochrome and two response regulators that are expressed from an apparent operon within the 21-gene cluster. Comparative genome analysis identified gene clusters similar to the 21-gene cluster of JSC-1 in twelve additional strains that belong to all five taxonomic sections of the phylum Cyanobacteria. Synechococcus sp. PCC 7335 was experimentally confirmed to perform FaRLiP, and both Chls d and f were detected in four additional strains after cells were grown in far-red light. Therefore, FaRLiP occurs in a group of cyanobacteria that inhabit niches enriched in far-red light, and these cyanobacteria contain specific, common features in their genomes. Additionally, under iron-limitation stress, JSC-1 cells up-regulate the expression of multiple Chlbinding IsiA proteins and a novel IsiC protein (a fusion of domains similar to IsiA and PsaL), and assemble a PS I-IsiA-IsiC supercomplex that has enlarged chlorophyll-based, light-harvesting antenna. The studies in this thesis demonstrate the remarkable versatility of cyanobacteria forremodeling their photosynthetic apparatus to acclimate to specific environmental challenges. The FaRLiP response should be very important for cyanobacteria that grow in terrestrial environments (soil, microbial mat communities, shade, and blooms), which are enriched in far-red light wavelengths due to filtering by Chl a and Chl b or by wavelength-dependent light scattering effects.