FIGURE 1.

Schematic representation of specific features of class IA and class IB T3Cs in plant pathogenic bacteria. (A) List of known T3Cs in Hrp1 T3SS bacteria (left panel). All are class IA T3Cs. A model depicting the role of the T3C ShcM is shown as a representative example (right panel). ShcM is co-transcribed with its cognate T3E HopM1. ShcM specifically interacts with HopM1, prevents its degradation by Lon proteases in the bacterial cytoplasm and promotes its secretion/translocation via the T3SS. (B) List of known T3Cs in Hrp2 T3SS bacteria (left panel). All are class IB T3Cs. A schematic representation of known binding partners of HpaB in X. campestris pv. vesicatoria is shown (right panel). HpaB is encoded within the hrp cluster and without any T3E in the vicinity. HpaB interacts with itself and with multiple T3SS-related proteins, comprising the secretion regulators HpaC and HpaA (see also Figure 2), the inner membrane components HrcU and HrcV, the cytoplasmic ATPase HrcN and T3Es. HpaB is required for efficient secretion of T3Es.