Molecular characterization of phycobilisome regulatory mutants of Fremyella diplosiphon

Abstract

Three classes of pigment mutants were generated in Fremyella diplosiphon in the course of electroporation experiments. The red mutant class had high levels of phycoerythrin in both red and green light and no inducible phycocyanin in red light. Thus, this mutant behaved as if it were always in green light, regardless of light conditions. Blue mutants exhibited normal phycoerythrin photoregulation, whereas the inducible phycocyanin was present at high levels in both red- and green-light-grown cells. Furthermore, the absolute amount of allophycocyanin was increased threefold in comparison with our wild-type strain. Green mutants lost the capacity to accumulate phycoerythrin in green light but showed normal photoregulation of phycocyanin. Analyses of transcript abundance in these mutants demonstrated that changes in the levels of the different phycobilisome components correlated with changes in the levels of mRNAs encoding those components. The characterization of these mutants supports hypotheses previously discussed concerning molecular mechanisms involved in the regulation of the phycobiliprotein gene sets during chromatic adaptation.

Characterization of the light-regulated operon encoding the phycoerythrin-associated linker proteins from the cyanobacterium Fremyella diplosiphon

“…Phycobilisome preparation and analysis. F. diplosiphon 33 (a strain of Calothrix sp., PCC 7601; a subculture of UTEX 481) was grown at 30°C in BG-11 medium with 50 mM HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) (pH 8.0) in an atmosphere of 5% CO2 in air) in red or green light at 15 microeinsteins/cm2 as described by Bruns et al (8). Phycobilisomes were isolated from red light-and green light-grown cells as previously described (2).…”

Tracking the Light Environment by Cyanobacteria and the Dynamic Nature of Light Harvesting

“…FdR mutants are red under all conditions of illumination and constitutively synthesize PE whereas PC i is never synthesized. These mutants are fixed in a response normally exhibited only in GL, with aberrant regulation of both the cpeBA and cpcB2A2 operons (22). FdB strains are bluer than wild-type cells in RL and require more GL to suppress PC i synthesis (25).…”

“…Furthermore, an FdR phenotype can result from lesions in at least three distinct genes (rcaC, rcaE, and rcaF). The lesions that caused the mutant phenotype in these strains were the result of gene disruption by in vivo transposition (22). Each of the FdBk (rcaE-FdBk) and FdR (rcaE-FdR, rcaF-FdR) mutants characterized contained insertion sequences in the rcaE/rcaF operon (29).…”

“…Several classes of CCA mutants have been isolated (5,(22)(23)(24), including the red (FdR), blue (FdB), green (FdG), and black (FdBk) strains. FdR mutants are red under all conditions of illumination and constitutively synthesize PE whereas PC i is never synthesized.…”

A molecular understanding of complementary chromatic adaptation

“…A variety of CCA mutants were identified in several laboratories (Cobley and Miranda 1983;Tandeau de Marsac 1983;Bruns et al 1989;Chiang et al 1992;Casey et al 1997;Kehoe and Grossman 1996) and categorized into red (FdR), blue (FdB), green (FdG) and black (FdBk) mutant classes. The FdR mutants appear red under all conditions of illumination and they constitutively synthesize PE while PC is never synthesized.…”