Epistatic Relationships of Two Regulatory Factors During Heterocyst Development

Abstract

The filamentous cyanobacterium Anabaena sp. Strain PCC 7120 produces a developmental pattern of single heterocystsseparated by approximately 10 vegetative cells. Heterocysts differentiate from vegetative cells and are specializedfor nitrogen fixation. The patS gene, which encodes a small peptide that inhibits heterocyst differentiation, isexpressed in proheterocysts and plays a critical role in establishing the heterocyst pattern. Another key regulator ofheterocyst development is the hetR gene. hetR mutants fail to produce heterocysts and extra copies of hetR on a plasmidcause a multiple contiguous heterocyst phenotype. To elucidate the relationship between these two counter actingfactors in the genetic regulatory pathway during heterocyst differentiation, the expression patterns of a patS-gfpand a hetR-gfp fusion were examined in a patS deletion and a hetR deletion strain. The results, in combination withthe result from a hetR and patS double deletion strain, suggest patS and hetR are mutually antagonistic and the balancebetween these two factors in two different cell types (heterocysts and vegetative cells) may be critical duringthe decision making process on their cell fates.