Heterocyst Differentiation in Cylindrospermum licheniforme: Studies on the Role of Transcription

Abstract

Heterocysts of the cyanobacterium Cji/indrospermum licheniforme occur at the ends of the filaments. These cells, specialized for aerobic N fixation, synchronously differentiate after the fragmentation of filaments grown in a medium free of combined nitrogen. This study has examined the role of transcription during and after heterocyst differentiation. Autoradiography of intact filaments pre-labelled for 3 h with [3H]uracil revealed that R N A synthesis occurred at similar rates in vegetative cells, developing (pro)heterocysts and mature heterocysts. Since mature heterocysts no longer divide and contain a similar amount of DNA as vegetative cells, transcription must continue under conditions where replication no longer occurs. Rifdmpicin, when added to fragmented filaments at concentrations that reduced RNA synthesis by 95 % in all cell types, inhibited proheterocyst formation but not the final morphological step of differentiation (pore plug deposition). However, chloramphenicol blocked all stages of heterocyst differentiation. Since the average mRNA half-life was 29 min, and the rifdmpicininsensitive stage lasted 3-6 h, the later stages of differentiation may depend on long-lived mRNAs.

Changes in gene expression during nitrogen starvation in Anabaena variabilis ATCC 29413

“…Using inhibitors and pulse-labeling techniques, Van de Water and Simon (28) Expression of cpc and apc genes stopped rapidly during nitrogen starvation (Fig. 2) (26).…”

“…There have been comparatively few investigations of changes in gene expression at the RNA level during nitrogen starvation in cyanobacteria. Transcription is required for heterocyst development (28), and many heterocyst-specific transcripts are synthesized during development (23). We (17); pAN120, which is pBR322 with a 3.9-kb ClaI insert containing the A. variabilis cpcA and cpcB genes (18); and pAN121, which is pBR322 with a 1.5-kb NheI fragment containing the Anabaena variabilis apcA and apcB genes (18).…”

Dinitrogen Fixation Is Restricted to the Terminal Heterocysts in the Invasive Cyanobacterium Cylindrospermopsis raciborskii CS-505

“…However, some cyanobacteria differentiate heterocysts exclusively at the end of their trichomes (terminal heterocysts), such as cyanobacteria of the genera Cylindrospermum and Cylindrospermopsis . Few studies have addressed the physiology or mechanisms related to this terminal heterocyst phenotype [7], [8], [9]. Although their trichomes may be composed of more than 100 cells, these cyanobacteria differentiate at the most two heterocysts [7].…”