F. diplosiphon has a fascinating response to sulfur starvation.  PC and PE expression changes during sulfur deplete conditions.  PC1 is constitutively expressed regardless of light color in sulfur replete conditions and is found in the interior of the light harvesting antennae.  PC2, located in the outer portion of the antennae, increases when cells chromatically acclimate to red light in sulfur replete conditions.  PC3 expression increases only in low sulfur conditions in both red and green light.  The relationship between PC1, PC2, and PC3 expression is interesting because PC3 lacks all of the sulfur containing amino acids that PC1 and PC2 contains, with the exception of a few functionally important cysteines.  PC1 and PC2 do not accumulate in sulfur deplete conditions and are replaced by PC3.  This presumably allows the use of the sulfur from the sulfur containing amino acids within PC1 and PC2.  
We are interested in expanding our understanding of the mechanisms through which F. diplosiphon regulates its response to sulfur limiting conditions. We already know through previous work in our lab that the down regulation of PC2 mRNA in low sulfur conditions is posttranscriptional, while the up-regulation of PC3 mRNA is transcriptionally controlled.  Currently, I am focusing on a set of genes already known to play a role in the general response to sulfur limiting conditions Synechococcus elongatus PCC 7942 and E. coli to see if they play a similar role in F. diplosiphon.  These include three genes encoding putative sulfur-binding proteins.  The mRNA levels of the F. diplosiphon homologs of these putative sulfur-binding protein encoding genes were examined by qPCR to determine the fold change of mRNA transcripts between low and high sulfur conditions.  All three of these genes have significantly up regulated mRNA levels in sulfur limiting conditions.
In the future I plan to identify more F. diplosiphon genes that are differentially regulated in low sulfur conditions.  Microarrays will be used to identify additional genes that are up regulated in low sulfur conditions in F. diplosiphon.  The F. diplosiphon genome is sequenced, so microarrays can be designed that will allow me to analyze most of the possible reading frames.  I plan to do microarrays comparing sulfur starvation conditions and standard sulfur conditions.  I also intend to do microarrays comparing low and standard sulfur conditions in wild-type cells and in cell lines containing specifically selected gene knockouts.