Population density-dependent regulation of the Bradyrhizobium japonicum nodulation genes

Citation
Jt. Loh et al., Population density-dependent regulation of the Bradyrhizobium japonicum nodulation genes, MOL MICROB, 42(1), 2001, pp. 37-46
Citations number
53
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Microbiology
Journal title
MOLECULAR MICROBIOLOGY
ISSN journal
0950-382X → ACNP
Volume
42
Issue
1
Year of publication
2001
Pages
37 - 46
Database
ISI
SICI code
0950-382X(200110)42:1<37:PDROTB>2.0.ZU;2-H
Abstract
The nodulation genes of Bradyrhizobium japonicum are essential for infectio n and establishment of a nitrogen-fixing symbiosis. Here, we demonstrate th at plant-produced isoflavones induce nodulation gene expression in a popula tion density-dependent fashion. Nodulation gene induction is highest at a l ow population density and significantly reduced in more dense cultures. A q uorum signal molecule in the conditioned medium of B. japonicum cultures me diates this repression. Repression in response to the quorum signal results from the induction of NolA which, in turn, induces NodD2 leading to inhibi tion of nod gene expression. Consistent with this, nolA-lacZ and nodD2-lacZ expression increased with increasing population density. Unlike the wild t ype, the ability to induce nodY-lacZ expression did not decline with popula tion density in a NolA mutant. Normally, nod gene expression is repressed i n planta (i.e. within nodules). However, expression of a nodY-GUS fusion wa s not repressed in a NolA mutant, suggesting that quorum-sensing control ma y mediate in planta repression of the nod genes. Addition of conditioned me dium to cultures significantly reduced nod gene expression. Treatment of in oculant cultures with conditioned medium also reduced the ability of B. jap onicum to nodulate soybean plants.