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Conjugal transfer of the S inorhizobium meliloti 1021 symbiotic plasmid is governed through the concerted action of one‐ and two‐component signal transduction regulators
Author(s) -
Nogales Joaquina,
BlancaOrdóñez Helena,
Olivares José,
Sanjuán Juan
Publication year - 2013
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.12073
Subject(s) - biology , derepression , plasmid , gene , psychological repression , transcription (linguistics) , mutant , transcription factor , regulator , signal transduction , genetics , response regulator , gene expression , linguistics , philosophy
Summary Conjugal transfer of S inorhizobium meliloti and R hizobium etli symbiotic plasmids are repressed by the transcriptional regulator RctA . Here we report on new key players in the signal transduction cascade towards S . meliloti pSym conjugation. We have identified S . meliloti pSymA gene SM a0974 as an orthologue of the R . etli rctB gene which is required to antagonize repression by RctA . In S . meliloti two additional genes, rctR and rctC participate in control of rctB expression. rctR ( SM a0955) encodes a protein of the GntR family of transcriptional regulators involved in repression of rctB . A rctR mutant promotes pSymA conjugal transfer and displays increased transcription of tra , virB and rctB genes even in presence of wild‐type rctA gene. Among genes repressed by RctR , rctC ( SM a0961) encodes a response regulator required to activate rctB transcription and therefore for derepression of plasmid conjugative functions. We conclude that in both R . etli and S . meliloti pSym conjugal transfer is derepressed via rctB , however the regulatory cascades to achieve activation of rctB are probably different. Upstream of rctB , the S . meliloti pSym conjugal transfer is regulated through the concerted action of genes representing one‐ ( rctR ) and two‐component ( rctC ) signal transduction systems in response to yet unidentified signals.