Systems Biology at Washington University

FIBR


Response of Synechocystis 6803 to PS-II and PS-I Specific Light :

Photosynthetic organisms constantly balance excitation between photosystem II (PS II) and photosystem I (PS I) to avoid the damaging effect and optimize photosynthetic electron transport. Specific excitation of either photosystem would differentially change the redox chemistry of components involved in the photosynthetic transport chain. To comprehend the responses of Synechocystis 6803 under these circumstances, we have utilized DNA microarray to identify the molecular events occurring following the excitation of either PS II ( Red ) or PS I ( Blue ).

Key Findings: Synechocystis 6803 responds to specific light by manipulating the relative fluorescence intensity of two photosystems . Light-dependent expression of genes coding for proteins involved in photosynthetic process is a key adaptive mechanism (table) Expression of large number of genes coding for proteins involved in metabolic pathways and redox homeostasis are controlled by the selective excitation of two photosystems. (table). Gene regulatory network has identified key regulatory genes that respond to specific light quality. Effect of excess carbon and nitrogen source on response to red and blue light (Figure) Bicarbonate transport are affected by red and blue light (Figure) Future Goals: Identify the role of key regulatory genes in light-specific gene expression identified from the gene regulatory network using the gene expression datasets. construction of gene specific mutant strain and analysis of global changes in the expression patterns during excitation of photosystems.

Microarray Experiments : Design and Data



Excitation of PS II ( Red ) and PS I ( Blue )

by Abhay Singh
Schematic representation of energy transfer following excitation of PS II with red light and PS I with blue light. The direction of arrows indicate the energy spillover following excitation. The color of oxidized and reduced PQ represents status during exitation with red or blue light.
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Relative Fluorescence Intensity of Two Photosystems

by Abhay Singh
Synechocystis 6803 cells grown under normal condition (30⁰C; 20 µEm^-2s^-1) were exposed to either blue light (10 µEm^-2s^-1) or red light (10 µEm^-2s^-1). Red and blue light were provided by light emitting diode. Cells were collected at various time points and 77K emission spectra of chlorophyll fluorescence was measured following excitation at 435 nm absorbed by chlorophyll a. Three peaks (685, 695, and 725 nm) were observed. The peaks at 685 and 695 nm arise from PS II whereas the 725-nm peak arises from PS I. Curves were normalized to the fluorescence intensity at 695 nm. It is clear from above figures that exposure of cells to red light resulted in greater relative fluorescence intensity of PSI suggesting that energy transfer from phycobilisome to PSI was enhanced. Interestingly this transfer of energy was observed till 90 min of red light and further exposure did not result in further increase suggesting a homeostatic response. On the other hand, exposure to blue light resulted in lesser relative fluorescence intensity of PSI suggesting that energy transfer to PSI was decreased. Similar to red light, we observed this phenomenon till 90 min of blue light and further exposure did not result in further increase suggesting a homeostatic response
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Gene regulatory network - Key regulatory genes that respond to specific light quality

by Rangesh Kunnavakkam
The topology of 559-node coexpression network: The core sub-network consists of 559 nodes and 11645 edges.
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Microarray Experiments : Design and Data