The Non-Flagellar Type III Secretion System Evolved from the Bacterial Flagellum and Diversified into Host-Cell Adapted Systems
(A) Phylogeny of the secretin family. The numbers represent bootstrap support values for branches separating the different types of secretins found in NF-T3SSs (highlighted by colored bars). Gray boxes indicate the main secretin groups. The two genes encoding the Rhizo secretin are indicated in orange and yellow boxes (see panel B). NF-T3SS types are named as in Figure 4. (B) Domain architecture of the secretins related to NF-T3SS secretins. PFAM domains were identified using InterProScan , except for the Chlamy-specific N-terminal domain of the NF-T3SS secretin CdsC (burgundy box), and the dashed box “N-domain”, which were identified by sequence similarity with the other secretins using Blast. Signal peptides were detected with InterProScan and PsortB . Dotted lines correspond to the boundaries of the alignments of Blast hits. See Text S4 for more analyses of Rhizo secretins. (C) Analysis of the genetic organization of the Rhizo loci mapped on their phylogeny. The phylogeny was inferred from the concatenation of the eight NF-T3SS core genes (Figure 4, Figure S4). Conventions are the same as in Figure 5. Numbers in white boxes correspond to the number of genes separating the block of genes with conserved order (light green box) from the RhcC2 secretin (outside the box), or to the number of consecutive genes not annotated in this study (inside the box).