Project 1. Light Sensing and Signaling in Extremophilic Cyanobacteria Photosynthetic organisms optimize their photosynthetic performance in response to ever changing light environments by virtue of a range of photosensory and signaling systems. Sensing of light cues is mediated by various photoreceptors including bilin type phytochromes. Light sensing and signaling machinery is barely known in cyanobacteria from extreme environments such as saline lagoons and soda lakes. Such habitats feature high content of carbonates and high levels of pH and contain unicellular (Rhabdoderma, Euhalothece and Synechococcus) and multicellular filamentous (Microcoleus, Phormidium and Mastigocladus) cyanobacteria. Recently, we sequenced a dozen genomes of extremophilic cyanobacteria including Microcoleus, Rhabdoderma, and Euhalothece that was diverged between 0.67 ~ 1.5 BYA. Along with genome information, systematic approaches are undertaken to explore biochemical and biological functions of bilin based photoreceptors primarily aiming for our understanding of ancient photosensory networks and accordingly evolution of the photosensory modules.
Fig. 1. Images of circular genome (left), domain structures of phytochrome superfamily (middle) and absorption spectra of bilin photoreceptors (right) from Microcoleus sp.
Project 2. Oiling designer cyanobacteria Photosynthetic biofuel production is one of alternative forms of energy supply to fossil fuels since its use is controversially considered as a main reason for high oil prices and global warming. However, natural algal strains should be redesigned to increase their low lipid productivities for the sake of biofuel production. Additionally, cell harvesting and post harvesting steps should become more cost-effective. Recently, oiling algae concept has been introduced to overcome this limitation. To manipulate carbon partitioning and skip algae harvesting and breakage steps, spatio-temporal inducible rather than constitutive gene expression system is required. We are working on light-inducible switches, which are potentially useful in genetically manipulating cyanobacteria for designer oiling algae. For this purpose, we take advantage of a model cyanobacterim Synechocystis sp. PCC 6803 that has been extensively exploited as bioreactors for production of useful materials including a variety of proteins and biofuels.
Fig. 2. GFP (left) and YFP (middle) images for PilT and LsiR localization and proposed near-UV light sensing and signaling leading to negative phototaxis (right) in the unicellular cyanobacterium Synechocystis sp. PCC 6803.
Project 3. Sugar-Hormone Cross-Talk in Anthocyanin Biosynthesis
Anthocyanins, a class of flavonoids, are recognized for their diverse functions in plant development and beneficial effects on human health. Anthocyanin biosynthesis regulatory proteins including HY5, PAP1 and MYBL2 are differentially modulated by environmental and biological factors such as light, temperature, sugar and hormones. Recent studies hint the presence of tissue specific mesophyll-derived redox signals in the intercellular signaling between cyanic and acyanic cells, though as to the redox sensing and downstream signaling components remains obscure. Currently, we are characterizing the biological functions of regulatory factors that were screened by reverse genetics approaches using Arabidopsis pap1D gain-of-function mutants, hoping to fill in some blank leading to transcriptional activation of PAP1 expression.
Fig. 3. Preferential accumulation of anthocyanins in epidermis and vascular bundles (left), proposed model for redox mediated signaling between acyanic and cyanic cells (middle) and schematic illustration of PAP1 as a convergent point of various factors modulating anthocyanin accumulation (right)