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Review
. 2009 Aug;150(4):1656-64.
doi: 10.1104/pp.109.139089. Epub 2009 May 20.

Type III protein secretion in plant pathogenic bacteria

Daniela Büttner  1 , Sheng Yang He
Affiliations
Review

Type III protein secretion in plant pathogenic bacteria

Daniela Büttner et al. Plant Physiol. 2009 Aug.
No abstract available

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Figures

Figure 1.
Figure 1.
Schematic representation of the T3SS from plant (A) and animal (B) pathogenic bacteria. The secretion apparatus spans both bacterial membranes and is associated with a cytoplasmic ATPase. The T3SS from plant pathogenic bacteria is connected to an extracellular pilus that presumably spans the plant cell wall. The T3SS system from animal pathogenic bacteria is associated with a short extracellular needle, which serves as a transport channel for secreted proteins. The needle is linked via the so-called tip complex to the translocon, which forms a proteinaceous channel in the host plasma membrane and allows transport of effector proteins into the host cell cytosol. Evidence for the presence of a tip complex in plant pathogenic bacteria is still missing. IM, Inner membrane; OM, outer membrane; PM, plasma membrane.
Figure 2.
Figure 2.
Protein identities among selected putative translocators and T3S4 proteins, respectively, from plant pathogenic bacteria and the animal pathogen Yersinia enterocolitica. Full-length protein sequences were compared using the BLASTP program (http://blast.ncbi.nlm.nih.gov). Numbers refer to the percentage of protein identity. Boxes with protein identities of 75% to 100% are shaded in dark gray, and boxes with protein identities of 25% to 50% are in light gray. The following protein sequences were used: HrpF (X. campestris pv vesicatoria strain 85-10, AAB86527), PopF1 (R. solanacearum GMI1000, CAD18706), PopF2 (R. solanacearum GMI1000, CAD18051), HrpK1 (P. syringae pv tomato DC3000, AAO54927), HrpK (E. amylovora, AAX39435), YopB (Y. enterocolitica, AAK69211), HpaC (X. campestris pv vesicatoria strain 85-10, CAJ22055), HpaP (R. solanacearum GMI1000, CAB58249), HrpP (P. syringae pv tomato DC3000, AAG33881), and YscP (Y. enterocolitica, AAK69225). n.s., Not significant (protein identity among full-length proteins was defined as not significant when regions with identical residues were smaller than 100 amino acids); Eam, E. amylovora; Psyr, P. syringae pv tomato DC3000; Rsol, R. solanacearum GMI1000; Xcv, X. campestris pv vesicatoria strain 85-10; Xoo, X. oryzae pv oryzae PXO99A; Yent, Y. enterocolitica. a, The region with 32% protein identity is restricted to 137 amino acids; b, the region with 24% protein identity is restricted to 205 amino acids; c, the region with 26% protein identity is restricted to 105 amino acids; d, the region with 27% protein identity is restricted to 147 amino acids.
Figure 3.
Figure 3.
Model of T3S in the plant pathogenic bacterium X. campestris pv vesicatoria. The secretion apparatus consists of approximately 20 components, nine of which, labeled with single letters here, are designated Hrc (Hrp conserved) because they are conserved among plant and animal pathogenic bacteria. The pilus protein HrpE and the putative inner rod protein HrpB2 are the first substrates that travel the T3SS. A yet unidentified signal activates a switch in the T3S substrate specificity that depends on the cytoplasmic T3S4 protein HpaC and an inner membrane component of the T3SS, HrcU. HrcU consists of four transmembrane helices and a C-terminal cytoplasmic domain (UC), which is proteolytically cleaved. HpaC presumably induces a conformational change in the C-terminal cytoplasmic domain of HrcU and activates secretion of translocon and effector proteins. Targeting of effector proteins to the secretion apparatus depends on the global T3S chaperone HpaB, which binds to multiple effector proteins. The activity of HpaB is normally inhibited by HpaA, which binds to HpaB in the bacterial cytoplasm. Secretion and translocation of HpaA after assembly of the T3SS liberates HpaB and is thus a prerequisite for the efficient translocation of effector proteins (Lorenz et al., 2008a). Secretion of all known T3S substrates depends on the ATPase HrcN, which was shown to disassemble HpaB-effector complexes. IM, Inner membrane; OM, outer membrane; PM, plasma membrane.
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