SPI1 and infection: The human pathogen Salmonella uses two types of T3SS (SPI-1 and SPI-2) at different stages of host infection (Valdez et al., 2009), while nitrogen-fixing Rhizobiales use a particular T3SS (Rhizobiales type) to establish symbiotic interactions with host plants (Dai et al., 2008; Kambara et al., 2009).