Quorum sensing and the LysR-type transcriptional activator ToxR regulate toxoflavin biosynthesis and transport in Burkholderia glumae.
Burkholderia glumae BGR1 produces a broad-host range phytotoxin, called toxoflavin, which is a key pathogenicity factor in rice grain rot and wilt in many field crops. Our molecular and genetic analyses of toxoflavin-deficient mutants demonstrated that gene clusters for toxoflavin production consist of four transcriptional units. The toxoflavin biosynthesis genes were composed of five genes, toxA to toxE, as Suzuki et al. (2004) reported previously. Genes toxF to toxI, which are responsible for toxoflavin transport, were polycistronic and similar to the genes for resistance-nodulation-division (RND) efflux systems. Using Tn3-gusA reporter fusions, we found that ToxR, a LysR-type regulator, regulates both the toxABCDE and toxFGHI operons in the presence of toxoflavin as a coinducer. In addition, the expression of both operons required a transcriptional activator, ToxJ, whose expression is regulated by quorum sensing. TofI, a LuxI homologue, was responsible for the biosynthesis of both N-hexanoyl homoserine lactone and N-octanoyl homoserine lactone (C8-HSL). C8-HSL and its cognate receptor TofR, a LuxR homologue, activated toxJ expression. This is the first report that quorum sensing is involved in pathogenicity by the regulation of phytotoxin biosynthesis and its transport in plant pathogenic bacteria.
Kim
Jinwoo
J
School of Agricultural Biotechnology, Seoul National University, Seoul 151-742, Korea.
Kim
Jung-Gun
JG
Kang
Yongsung
Y
Jang
Ji Youn
JY
Jog
Geetanjali J
GJ
Lim
Jae Yun
JY
Kim
Suhyun
S
Suga
Hiroaki
H
Nagamatsu
Tomohisa
T
Hwang
Ingyu
I
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D019117:Burkholderia / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D046912:Multiprotein Complexes; D009876:Operon; D012275:Oryza / Q000033:anatomy & histology / Q000382:microbiology; D011744:Pyrimidinones / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014227:Triazines / Q000378:metabolism*
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; D011744:Pyrimidinones; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D014227:Triazines; C066719:toxR protein, bacteria; C009570:toxoflavin; C073470:LysR protein, Bacteria