Introduction
Fig.1 A schematic illustration of mechanism of the two-component signal transduction system. The direction of phosphoryl-group transfer is depicted by solid line and the direction of signal transduction is depicted by a dashed line. P in the circular frames represents the phosphoryl group. H, N, G1, F and G2 represent typical conserved motifs in the histidine kinase sensor. D1, D2, and K represent typical conserved motifs in the response regulator. Definition of these motifs is according to a previous study (Parkinson and Kofoid, 1992). |
Overview of TCSTSs in the genomes of Xanthomonas
Tab.1 Histidine kinases and response regulators encoded by the genomes of Xanthomonas |
genome | genome size/mb | orthodox histidine kinase | hybrid histidine kinase | response regulator | total |
---|---|---|---|---|---|
Xcc 8004 | 5.15 | 32 | 20 | 54 | 106 |
Xcc ATCC 33913 | 5.08 | 32 | 20 | 54 | 106 |
Xcc B100 | 5.08 | 32 | 20 | 54 | 106 |
Xoo PXO99 | 5.24 | 32 | 13 | 58 | 104 |
Xoo KACC10331 | 4.94 | 28 | 12 | 52 | 92 |
Xoo MAFF311013 | 4.94 | 28 | 15 | 50 | 93 |
Xcv 85-10 | 5.18 | 37 | 23 | 61 | 121 |
Xac 306 | 5.18 | 35 | 21 | 58 | 114 |
TCSTSs regulating expression of virulence factors in Xanthomonas spp.
Fig.2 Domain organization of the virulence and avriulence regulatory histidine kinases and response regulators in BoldItalic spp.. The names of the domains are according to those of the pfam database. HK (HisKA, pfam acc. No.: PF07730); HA (HATPase_c, PF02518); REC (Response_reg, PF00072); HPT (PF01672); HD (PF1966); Trans (Trans_reg, PF00486); PAS (PF00989); GGDEF (PF00990); EAL (PF00563) and HAMP (PF00672). |
The RpfC-RpfG system: sensing the quorum sensing signal (DSF) to regulate the virulence gene expression
RavS-RavR system: controlling c-di-GMP turnover to regulate virulence gene expression
HrpG system: a core regulator of virulence factor secretion through T3SS and T2SS
VgrS-VgrR and VemR systems: two novel identified virulence-associated TCSTSs
RaxH-RaxR and PhoQ-PhoP systems: modulating the activity of the avirulence factor Ax21
Concluding remarks and perspective
Fig.3 Network of the two-component signal transduction systems in regulating virulence and avirulence factor expressions in BoldItalic spp.. Different colors are applied to different signaling cascades. The RpfC-RpfG system (yellow) positively controls extracellular enzyme and exocellular polysaccharides (EPS) biosynthesis, and negatively regulates diffusible signal factor (DSF) synthesis. The RavS-RavR system (brown) controls EPS biosynthesis by affecting c-di-GMP turnover. VemR (light blue) is probably associated with FleQ. VgrS-VgrR system (pink) regulates EPS biosynthesis and transcription of the hrp genes. HrpG (blue) is the central regulator of type III secretion system (T3SS) and has relationship to the type II secretion system (T2SS). The RaxH-RaxR (light brown) and PhoQ-PhoP (green) systems are involved in expression and modification of the avirulence factor Ax21. OM: outer-membrane; IM: inner-membrane; T1SS: type I secretion system. P in the circular frame indicates the phosphoryl group. Names of the proteins and genes are according to the main text. |