A gene cluster that regulates both heterocyst differentiation and pattern formation in Anabaena sp. strain PCC 7120

Abstract

SummaryWild-type Anabaena sp. strain PCC 7120, a filamentous nitrogen-fixing cyanobacterium, produces single heterocysts at semi-regular intervals. asr0100 (patU5) and alr0101 (patU3) are homologous to the 5Ј and 3Ј portions of patU of Nostoc punctiforme. alr0099 (hetZ) overlaps the 5Ј end of patU5. hetZ, patU5 and patU3 were all upregulated, or expressed specifically, in proheterocysts and heterocysts. Mutants of hetZ showed delayed or no heterocyst differentiation. In contrast, a patU3 mutation produced a multiple contiguous heterocyst (Mch) phenotype and restored the formation of otherwise lost intercalary heterocysts in a patA background. Decreasing the expression of patU3 greatly increased the frequency of heterocysts in a mini-patS strain. Two promoter regions and two principal, corresponding transcripts were detected in the hetZ-patU5-patU3 region. Transcription of hetZ was upregulated in a hetZ mutant and downregulated in a patU3 mutant. When mutants hetZ::C.K2 and hetZ::Tn5-1087b were nitrogen-deprived, P hetC-gfp was very weakly expressed, and in hetZ::Tn5-1087b, PhetR-gfp was relatively strongly expressed in cells that had neither a regular pattern nor altered morphology. We conclude that the hetZ-patU5-patU3 cluster plays an important role in co-ordination of heterocyst differentiation and pattern formation. The presence of homologous clusters in filamentous genera without heterocysts is suggestive of a more general role.

Identification of the HetR Recognition Sequence Upstream of hetZ in Anabaena sp. Strain PCC 7120

“…The transcriptional start point of all0097 was determined by rapid amplification of cDNA ends (RACE) as described by Zhang et al (39), but primers all0097-1 and all0097-2 (see Table S1 in the supplemental material) were used in the first and second rounds of PCR, respectively.…”

“…patU5 and patU3 in Anabaena 7120 correspond to the 5= and 3= portions of patU in Nostoc punctiforme. The hetZ-patU cluster, hetR, and patS-like genes have been found in all filamentous cyanobacteria whose genomes have been analyzed (no genomic sequence is yet available for an organism in subsection V) (29,39). Because hetZ and hetR are both among the core set genes of filamentous cyanobacteria (29) and involved in heterocyst differentiation in Anabaena 7120, the two genes may be related in function and associated in evolution.…”

“…Located in the hetZ-patU5-patU3 cluster, patU3 is involved in pattern formation, whereas hetZ is required for heterocyst formation (39). hetZ and patU5-patU3 are independently transcribed but also cotranscribed.…”

CalA, a cyAbrB protein, binds to the upstream region of ftsZ and is down-regulated in heterocysts in Anabaena sp. PCC 7120

“…EU346690; Elhai and Wolk 1988b) and cloned into the BamHI site upstream of P petE in plasmid pHB1487 (Zhang et al 2007), resulting in pHB2294. The kanamycin-resistance gene was cloned in the opposite direction relative to P petE .…”

The HetR-binding site that activates expression of patA in vegetative cells is required for normal heterocyst patterning in Anabaena sp. PCC 7120

“…Heterocyst patterning is affected by numerous genes, such as patS [2], hetN [3], patU3 [4], patA [5], patL [6], etc. Whereas inactivation of patS, hetN or patU3 leads to formation of multiple contiguous heterocysts, inactivation of patA or patL leads to formation of heterocysts almost exclusively at terminal positions.…”