Identification of potential genetic components involved in the deviant quorum-sensing signaling pathways of Burkholderia glumae through a functional genomics approach

Abstract

Burkholderia glumae is the chief causal agent for bacterial panicle blight of rice. The acyl-homoserine lactone (AHL)-mediated quorum-sensing (QS) system dependent on a pair of luxI and luxR homologs, tofI and tofR, is the primary cell-to-cell signaling mechanism determining the virulence of this bacterium. Production of toxoflavin, a major virulence factor of B. glumae, is known to be dependent on the tofI/tofR QS system. In our previous study, however, it was observed that B. glumae mutants defective in tofI or tofR produced toxoflavin if they grew on the surface of a solid medium, suggesting that alternative signaling pathways independent of tofI or tofR are activated in that growth condition for the production of toxoflavin. In this study, potential genetic components involved in the tofI- and tofR-independent signaling pathways for toxoflavin production were sought through screening random mini-Tn5 mutants of B. glumae to better understand the intercellular signaling pathways of this pathogen. Fifteen and three genes were initially identified as the potential genetic elements of the tofI- and tofR-independent pathways, respectively. Especially, the ORF (bglu_2g06320) divergently transcribed from toxJ, which encodes an orphan LuxR protein and controls toxoflavin biosynthesis, was newly identified in this study as a gene required for the tofR-independent toxoflavin production and named as toxK. Among those genes, flhD, dgcB, and wzyB were further studied to validate their functions in the tofI-independent toxoflavin production, and similar studies were also conducted with qsmR and toxK for their functions in the tofR-independent toxoflavin production. This work provides a foundation for future comprehensive studies of the intercellular signaling systems of B. glumae and other related pathogenic bacteria.

Genes Required for the Anti-fungal Activity of a Bacterial Endophyte Isolated from a Corn Landrace Grown Continuously by Subsistence Farmers Since 1000 BC

“…Chitinase encoding genes were previously found to be upregulated by c-di-GMP ( Zogaj et al, 2012 ). Furthermore, binding of c-di-GMP resulted in transcriptional regulation of anti-pathogen genes required for biofilm formation, adhesion, motility and synthesis of bacterial virulence factors ( Landini et al, 2010 ; Srivastava and Waters, 2012 ; Römling et al, 2013 ; An et al, 2014 ; Chen et al, 2015 ; Fazli et al, 2015 ; Steinberg and Kolodkin-Gal, 2015 ). Here, for the first time, to the best of our knowledge, the YajQ/c-di-GMP signaling system has been shown to underlie a mutualistic endophyte-host interaction of critical importance to its host plant.…”

Editorial: LuxR Solos are Becoming Major Players in Cell–Cell Communication in Bacteria

“…Some solos respond to an endogenous, non-AHL, ligand. The LuxR-type receptor PluR of Photorhabdus luminescens responds to α-pyrones, while the related organism Photorhabdus asymbiotica responds to dialkylresorcinols using the LuxR homolog PauR (Brachmann et al, 2013 ; Brameyer et al, 2014 , 2015 ; Brameyer and Heermann, 2015 ; Chen et al, 2015 ). The synthases for these molecules were determined to be PpyS and DarABC, respectively.…”

Functional and genomic insights into the pathogenesis of Burkholderia species to rice

“…A role in regulation of toxoflavin production has been demonstrated. Although QS‐defective ( tofI, tofR ) mutants of B. glumae do not produce toxoflavin in lysogenic broth, they do produce high levels of the toxin when grown to high density on solid media (Chen et al ., ). This indicates the existence of QS‐independent regulation of toxoflavin synthesis.…”

“…This indicates the existence of QS‐independent regulation of toxoflavin synthesis. A mutational analysis to identify potential components of this alternative pathway identified a role for the REC‐GGDEF domain protein DgcB, and the IclR family regulatory protein QsmR (Chen et al ., ). Mutation of these genes in a wild‐type QS‐proficient background showed that QsmR was required for toxoflavin production in both QS‐dependent and QS‐independent pathways, whereas DgcB only has a role in the QS‐independent pathway(s).…”