Skip to main content

Diffrential expression of Nostoc PCC7120 psbC gene family

Final Activity Report Summary - NOSTOC S PSBCS (Diffrential expression of Nostoc PCC7120 psbC gene family)

Cyanobacteria are one of oldest known organisms on earth, dating back at least 2.7 billion years. Cyanobacteria were not only responsible for the rise of oxygen that enabled the development of multicellular organisms, but are still responsible, to date, for the production of significant portion of the oxygen we breath and removal of the carbon dioxide we produce. Cyanobacteria (and plants) harvest light energy and convert it to chemical energy by the combined action of 3 multi protein, membranous complexes, photosystem II (PSII), b6f complex and photosystem I (PSI). PSII accumulates light energy in the form of oxidized Mn ions and then uses it to split two water molecules to protons, electrons and molecular oxygen, transferring the electrons to PSI via the cytochrom b6f complex, were protons are pumped to generate ATP. Oxidized PSI accepts the electrons and uses the light energy to raise the redox potential of the electrons, allowing them to be transferred to NADPH used to fix carbon deoxide and nitrogen as well as other redox reactions. Light needed for the above process is harvested by the light-harvesting complexes, the phycobilisomes, a protein-pigment composite in cyanobacteria and red algae. Cyanobacteria can respond to a variety of conditions by adaptation of their light harvesting systems. Thus, the phycobilisomes complex can move between PSII and PSI , a process called 'state-transition' (in plants LHCII move in a similar way). Cyanobacterial state transition was also seen in connection to some metabolic states such as nitrogen-fixation.

In the last decade, the full genome sequence of a number of cyanobacteria became available. While these efforts have rewarded us with a lot of information, they also open the question: 'What do all those genes do?' This especially true in the case of multi gene families were multiple genes code for similar but not identical proteins.

The genome of one of those cyanobacteria, Nostoc PCC 7120 (aka Anabaena PCC 7120) was published in 2001, and found to contain multiple gene families. Among those 5 copies of the psbA genes (coding for the main scaffold PSII protein D1), and 5 psbC like genes (coding for the PSII CP43 subunit) were found. The different D1s have been found to express in response to UV light, light intensity and recently low oxygen levels, although the (bio)logic behind this expression pattern is not totally clear. The different CP43's expression pattern is basically unknown, and could hold information of importance on the way PSII is working, helping us understand this very important protein complex with implication in many fields from (bio) hydrogen production to carbon scavenging and global warming.

Of the 5 different psbC-like genes 2 show high similarity to the known (from other cyanobacteria) psbC and isiA respectively. The other 3 show intermediate homology to both isiA and psbCs. We are looking at the expression of the these 5 genes and the exitonic structure of the photosynthetic apparatus of the 7120, under different conditions, to better understand the role of these genes and their coding protein in the life scheme and photosynthetic apparatus of the Anbaena sp. PCC7120.