Characterization of phycobiliprotein and linker polypeptide genes in Fremyella diplosiphon and their regulated expression during complementary chromatic adaptation

Abstract

Phycobilisomes, comprised of both chromophoric (phycobiliproteins) and non-chromophoric (linker polypeptides) proteins, are light-harvesting complexes present in the prokaryotic cyanobacteria and the eukaryotic red algae. Many cyanobacteria exhibit complementary chromatic adaptation, a process which enables these organisms to optimize absorption of prevalent wavelengths of light by altering the composition of the phycobilisome. To examine the mechanisms involved in adjusting the levels of phycobilisome components during complementary chromatic adaptation, we have isolated and sequenced genes encoding phycobiliprotein and linker polypeptides in the cyanobacterium Fremyella diplosiphon, analyzed their transcriptional characteristics (transcript sizes and abundance when F. diplosiphon is grown in different light qualities) and mapped transcript initiation and termination sites. Our results demonstrate that genes encoding phycobilisome components are often cotranscribed as polycistronic messenger RNAs. Light quality regulates the composition of the phycobilisome by causing changes in the abundance of transcripts encoding specific components, suggesting that regulation is at the level of transcription (although not eliminating the possibility of changes in mRNA stability). The work presented here sets the foundation for analyzing the evolution of the different phycobilisome components and exploring signal transduction from photoperception to activation of specific genes using in vivo and in vitro genetic technology.

Changes in Accumulation and Synthesis of Transcripts Encoding Phycobilisome Components during Acclimation of Fremyella diplosiphon to Different Light Qualities

“…3, 22, 23, 45, and 46 for reviews of pertinent literature). Both light quality (3, 22,23,46) and quantity (27,41,50) can influence the composition of the phycobilisome. Generally, high light fluence rates result in reduced numbers of chromophoric proteins in the complex (50) and a decrease in the number of phycobilisomes per cell (27,34).…”

“…Some cyanobacteria, such as Fremyella diplosiphon, alter the components of their phycobilisomes in response to changes in the wavelengths of light in the environment, a phenomenon termed complementary chromatic adaptation (3). Red light (R) promotes PC synthesis while green light (G) promotes PE synthesis (2,14,15,17 (22,23). In F. diplosiphon high levels of PE mRNA are detectable in Gacclimated cells while low levels are present in R-acclimated cells (22,23,39 from the beginning of the coding region of apcC and ending 55 nucleotides downstream of the termination codon was used to quantitate transcripts encoding the core linker protein (PG Lemaux, AR Grossman, unpublished data).…”

“…Red light (R) promotes PC synthesis while green light (G) promotes PE synthesis (2,14,15,17 (22,23). In F. diplosiphon high levels of PE mRNA are detectable in Gacclimated cells while low levels are present in R-acclimated cells (22,23,39 from the beginning of the coding region of apcC and ending 55 nucleotides downstream of the termination codon was used to quantitate transcripts encoding the core linker protein (PG Lemaux, AR Grossman, unpublished data). The cpcB2A2 and cpeBA fragments were purified from an agarose gel after digestion of pUC8 (containing appropriate inserts) with HindIII and XbaI, respectively.…”

“…In addition to the 400-base transcript, an 1800-base transcript (23) (apparent in Fig. 2, C and D) which is a polycistronic mRNA, encodes the core linker polypeptide plus AP"',' (23). The abundance of both the 400-and 1800-base transcripts are similar in R and G. Recently, low abundance mRNAs of 5200 and 5900 bases (not detectable in these autoradiograms) have also been shown to encode the AP subunits and core linker polypeptide (PG Lemaux, AR Grossman, unpublished data).…”

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

“…These proteins constitute -85% of the mass of the complex, with the remainder comprising nonpigmented "linker" proteins (48). Both the pigmented and nonpigmented constituents of the phycobilisome rods can vary depending on growth conditions, such as temperature, light quality and quantity, and the nutritional status of the growth medium (2,5,25,35,38,47,49).…”