Characterization of complementary chromatic adaptation in Gloeotrichia UTEX 583 and identification of a transposon-like insertion in the cpeBA operon

Many cyanobacteria are able to alter the pigment composition of the phycobilisome in a process called complementary chromatic adaptation (CCA). The regulatory mechanisms of CCA have been identified in Fremyella diplosiphon, which regulates both phycoerythrin and phycocyanin levels, and Nostoc punctiforme, which regulates only phycoerythrin production. Recent studies show that these species use different regulatory proteins for CCA. We chose to study the CCA response of Gloeotrichia UTEX 583 in an effort to expand our knowledge about CCA and its regulation. We found that Gloeotrichia 583 has a CCA pigment response more similar to that of N. punctiforme rather than F. diplosiphon and exhibits none of the CCA-regulated morphological responses seen in F. diplosiphon. Preliminary experiments suggest that Gloeotrichia 583 contains a homolog to the CCA photoreceptor from N. punctiforme but not the CCA photoreceptor from F. diplosiphon. Additionally, two spontaneous mutants lacking phycoerythrin production were identified. Analysis has shown that these mutants contain a transposon-like insertion in the cpeA gene, which encodes the α subunit of phycoerythrin. These results suggest that CCA in Gloeotrichia UTEX 583 is more similar to that of N. punctiforme than it is to F. diplosiphon, a closely related species.     

Phosphorelay control of phycobilisome biogenesis during complementary chromatic adaptation

For some cyanobacteria, the spectral distribution of light in the environment regulates the synthesis of specific polypeptides of the phycobilisome or light harvesting antenna complex. This process, called complementary chromatic adaptation, is controlled by a complex type of two component regulatory system. In such pathways, phosphorelay typically occurs through two histidine and two aspartate residues. Generation and complementation of mutants in CCA have uncovered three elements of this pathway, a putative sensor, RcaE, and two response regulators, RcaC and RcaF. RcaC, a large response regulator, contains two input domains, a DNA binding motif and a putative histidine phosphoacceptor domain. RcaF is a small response regulator and apparently lacks an output domain. Ordering of the pathway components has placed RcaE before RcaF, and RcaF before RcaC. This phosphorelay circuitry is novel because it has, instead of four, at least five potential phosphoacceptor domains for signal transduction.     

Chromatic adaptation and the events involved in phycobilisome biosynthesis

Abstract. The major light-harvesting complex in cyanobacteria and red algae is the phycobilisome, a macromolecular complex that is attached to the surface of the photosynthetic membranes. The phycobilisome is composed of a number of different chromophoric polypeptides called phycobiliproteins and nonchromophoric polypeptides called linker proteins. Several environmental parameters modulate the synthesis, assembly and degradation of phycobilisome components. In many cyanobacteria, the composition of the phycobilisome can change to accommodate the prevalent wavelengths of light in the environment. This phenomenon is called complementary chromatic adaptation. Organisms that exhibit complementary chromatic adaptation must perceive the wavelengths of light in the environment and transduce the light signals into a sequence of biochemical events that result in altering the activities of genes encoding specific phycobiliprotein and linker polypeptides. Other environmental parameters such as light intensity and nutrient status can also have marked effects on both the number and composition of the phycobilisomes. The major concern of this article is the molecular events involved in chromatic adaptation. Most of the information concerning this process has been gained from studies involving the filamentous cyanobacterium Fremyella diplosiphon . However, also briefly considered are some of the complexities involved in phycobilisome biosynthesis and degradation; they include post-translational modification of phycobilisome polypeptides, the coordinate expression of chromophore and apobiliprotein, the specific degradation of phycobilisomes when cyanobacteria are deprived of macronutrients such as nitrogen, sulphur and phosphorus, and the assembly of the individual phycobilisome components into substructures of the light harvesting complex.     

Light-driven translocation of signaling proteins in vertebrate photoreceptors

The dynamic localization of proteins within cells is often determined by environmental stimuli. In retinal photoreceptors, light exposure results in the massive translocation of three key signal transduction proteins, transducin, arrestin and recoverin, into and out of the outer segment compartment where phototransduction takes place. This phenomenon has rapidly taken the center stage of photoreceptor cell biology, thanks to the introduction of new quantitative and transgenic approaches. Here, we discuss evidence that intracellular protein translocation contributes to adaptation of photoreceptors to diurnal changes in ambient light intensity and summarize the current debate on whether it is driven by diffusion or molecular motors.     

Genomic DNA microarray analysis: identification of new genes regulated by light color in the cyanobacterium Fremyella diplosiphon

Many cyanobacteria use complementary chromatic adaptation to efficiently utilize energy from both green and red regions of the light spectrum during photosynthesis. Although previous studies have shown that acclimation to changing light wavelengths involves many physiological responses, research to date has focused primarily on the expression and regulation of genes that encode proteins of the major photosynthetic light-harvesting antennae, the phycobilisomes. We have used two-dimensional gel electrophoresis and genomic DNA microarrays to expand our understanding of the physiology of acclimation to light color in the cyanobacterium Fremyella diplosiphon. We found that the levels of nearly 80 proteins are altered in cells growing in green versus red light and have cloned and positively identified 17 genes not previously known to be regulated by light color in any species. Among these are homologs of genes present in many bacteria that encode well-studied proteins lacking clearly defined functions, such as tspO, which encodes a tryptophan-rich sensory protein, and homologs of genes encoding proteins of clearly defined function in many species, such as nblA and chlL, encoding phycobilisome degradation and chlorophyll biosynthesis proteins, respectively. Our results suggest novel roles for several of these gene products and highly specialized, unique uses for others.     

Emerging Roles and New Paradigms in Signaling Mechanisms of Plant Cryptochromes

Analogous to the opsin-based receptors in animals, plants contain a diverse and elaborate set of photoreceptors to perceive a much wider spectrum of light and adapt to varying light conditions. Cryptochromes (CRYs), the blue/UV-A light sensing receptors, represent one such class of photoreceptors found ubiquitously in plants. Although structurally similar to DNA photolyases which could repair UV-induced DNA damage, photoactivated CRYs, instead, initiate signal transduction pathways, which lead to gene expression changes and eventually more overt photomorphogenic responses. Apart from the well-established roles of CRYs in regulating seedling de-etiolation, flowering time, and circadian clock, recent reports have highlighted their roles in controlling other aspects of plant development as well. This review attempts to describe the novel/atypical roles of CRYs that have emerged in the past few years, and also present an account of the various signaling components involved in CRY signal transduction pathway.     

Regulation of cyanobacterial photosynthesis determined from variable fluorescence yields of photosystem II

Abstract The cyanobacteria Fremyella diplosiphon 7601 and Synechocystis 6701 were grown in continuous cultures with monochromatic red light (680 nm). The distribution of light energy over photosystem I and II was determined from changes in PS II fluorescence at 685 nm. In both organisms, wavelengths absorbed primarily by chlorophyll a caused the high fluorescent state of PS II (State 1), while wavelengths absorbed by the phycobilisome led to low PS II fluorescence (State 2). Superimposing continuous light 2 on the excitation light yielded State 2 fluorescence patterns for Synechocystis 6701, while F. diplosiphon 7601 showed fluorescence patterns similar to state 1 → 2 transitions and changes in fluorescence yield were related to the intensity of the background light. Some ecological implications of energy (re)distribution in cyanobacterial photosynthesis are discussed.     

How do cyanobacteria sense and respond to light?

Cyanobacteria exhibit numerous responses to changes in the intensity and spectral quality of light. What sensors do cyanobacteria use to detect light and what are the mechanisms of signal transduction? The publication in 1996 of the complete genome sequence of the cyanobacterium Synechocystis 6803 provided a tremendous stimulus for research in this field, and many light‐sensors and signal transducers have now been identified. However, our knowledge of cyanobacterial light‐signal transduction remains fragmentary. This review summarizes what we know about the ways in which cyanobacteria perceive light, some of the ways which they respond to light signals and some recent achievements in elucidating the signal transduction mechanisms. Some problems in characterizing cyanobacterial signal transduction pathways are outlined and alternative experimental strategies are discussed.     

Shedding new light on the regulation of complementary chromatic adaptation

Complementary chromatic adaptation (CCA) is a light-dependent acclimation process that occurs in cyanobacteria and likely is related to increased fitness of these organisms in natural environments. Although CCA has been studied for over 40 years, significant advances in our understanding of the molecular foundations of CCA are still emerging. In this minireview, I explore recently reported developments that include novel insights into the molecular mechanisms utilized in the photoregulation of pigmentation and the molecular basis of light-dependent changes in cellular morphology, which are central elements of the process of CCA. I also discuss future avenues of study that are expected to lead to additional progress in our understanding of CCA and our general appreciation of light sensing and photomorphogenesis in cyanobacteria.     

A molecular understanding of complementary chromatic adaptation

Photosynthetic activity and the composition of the photosynthetic apparatus are strongly regulated by environmental conditions. Some visually dramatic changes in pigmentation of cyanobacterial cells that occur during changing nutrient and light conditions reflect marked alterations in components of the major light-harvesting complex in these organisms, the phycobilisome. As noted well over 100 years ago, the pigment composition of some cyanobacteria is very sensitive to ambient wavelengths of light; this sensitivity reflects molecular changes in polypeptide constituents of the phycobilisome. The levels of different pigmented polypeptides or phycobiliproteins that become associated with the phycobilisome are adjusted to optimize absorption of excitation energy present in the environment. This process, called complementary chromatic adaptation, is controlled by a bilin-binding photoreceptor related to phytochrome of vascular plants; however, many other regulatory elements also play a role in chromatic adaptation. My perspectives and biases on the history and significance of this process are presented in this essay. This revised version was published online in August 2006 with corrections to the Cover Date.     

Light signals in leaf and chloroplast development: photoreceptors and downstream responses in search of a transduction pathway

Light affects both the development and the metabolism of plants. In addition to the role of light in providing energy for photosynthesis, light signals cause profound changes in the morphology of the developing young seedling, including cotyledon expansion, leaf development, inhibition of stem growth, and production of chlorophyll in the photosynthetically competent chloroplast. The light-dependent development of plants (photomorphogenesis) is a complex process resulting from the combined action of several photoreceptors. This review summarizes what is known of the red- and blue-light photoreceptors that regulate dicotyledonous seedling development and the complexity of the downstream responses. Special emphasis is placed on the recent progress made toward genetic and biochemical dissection of the signal transduction pathways.