Genetic Analysis of Chromatically Adapting Nostoc sp.

University Of Missouri-Kansas City, Columbia MO

Investigators

Abstract

Light is a critical environmental parameter for photosynthetic organisms. In addition to driving photosynthesis, it provides the information necessary for acclimation to changes in ambient conditions. Most photosynthetic organisms at all levels of biological complexity can modulate their photosynthetic capacity to accommodate native fluctuations in light availability. Most often, genes that encode the components of the photosynthetic apparatus are controlled by wavelength-specific photoreceptors that initiate light-responsive signaling pathways. Although photoregulated gene expression is well documented for prokaryotic and eukaryotic phototrophs, little is known about the associate signaling and gene regulatory mechanisms. Cyanobacteria classified as Group III chromatic adaptors respond to spectral changes in light quality by altering the phycobiliprotein composition of the light-harvesting phycobilisome. Green light promotes synthesis of phycobilisomes enriched for phycoerythrin, whereas red light promotes the synthesis of phycobilisomes enriched for phycocyanin. This acclimation response, termed complementary chromatic adaptation (CCA), provides for optimal harvesting of the incident light energy by modulating the bilin composition of the phycobilisome rods. CCA has been most extensively studied in the filamentous cyanobacterium Fremyella diplosiphon (also referred to as Calothrix sp. strain PCC 7601). Recent work has revealed that CCA involves a multi-component phosphorelay signaling pathway that links the activity of a photoreceptor to regulated expression of specific phycobiliprotein gene sets. However, the molecular genetic dissection of the CCA regulatory mechanism in F. diplosiphon remains compromised by the lack of a standard genetic system for the strain. The goal of this project is to develop a transposon-tagging system for identifying the molecular components of the CCA regulatory mechanism in two Group III chromatically adapting Nostoc sp. Using a conjugation-based protocol established for Anabaena sp., both Nostoc strains will be subjected to Tn5-1058 mutagenesis with the objective of isolating phycobilisome regulatory mutants. Such mutants will provide for rapid identification of new phycobilisome regulatory genes and facilitate the molecular dissection of the CCA regulatory mechanism.