Genetics of Heterocyst Differentiation and Patterning

University Of Hawaii, Honolulu

Investigators

Abstract

The development of a pattern of differentiated cell types from a group of equivalent cells is a fundamental paradigm in biology. In bacteria, the differentiation of nitrogen-fixing heterocysts from a filament of vegetative cells by some cyanobacteria represents one of the few examples of a developmental pattern that can be maintained indefinitely given the appropriate environmental conditions. It represents a simple model system for elucidation of the minimal set of genetic elements that are necessary for pattern generation and maintenance by an organism. Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium that can be induced to differentiate a pattern of nitrogen-fixing heterocysts from a chain of undifferentiated vegetative cells. Heterocysts occur, on average, at 10 cell intervals, are terminally differentiated, and differ from vegetative cells morphologically, metabolically, and genetically. The first objective of the project is the identification and characterization of genetic elements that are involved in development. A mutagenic approach will be pursued using a genetically engineered strain of Anabaena 7120 that can be induced to form close to 100% heterocysts under conditions that do not require differentiation for growth. The second objective of the project is to test two hypotheses that relate to inhibition of differentiation by the gene hetN. The third objective is the identification and characterization of additional genes that are necessary for inhibition of differentiation by hetN. This project is narrowly focused on the genetics of heterocyst differentiation in cyanobacteria, but the broader biological impact will be on differentiation and pattern formation in general.