Pseudomonas syringae Type III Effector HopZ1 Targets a Host Enzyme to Suppress Isoflavone Biosynthesis and Promote Infection in Soybean

Type III secreted effectors (T3SEs), such as Pseudomonas syringae HopZ1, are essential bacterial virulence proteins injected into the host cytosol to facilitate infection. However, few direct targets of T3SEs are known. Investigating the target(s) of HopZ1 in soybean, a natural P. syringae host, we find that HopZ1 physically interacts with the isoflavone biosynthesis enzyme, 2-hydroxyisoflavanone dehydratase (GmHID1). P. syringae infection induces gmhid1 expression and production of daidzein, a major soybean isoflavone. Silencing gmhid1 increases susceptibility to P. syringae infection, supporting a role for GmHID1 in innate immunity. P. syringae expressing active but not the catalytic mutant of HopZ1 inhibits daidzein induction and promotes bacterial multiplication in soybean. HopZ1-enhanced P. syringae multiplication is at least partially dependent on GmHID1. Thus, GmHID1 is a virulence target of HopZ1 to promote P. syringae infection of soybean. This work highlights the isoflavonoid biosynthesis pathway as an antibacterial defense mechanism and a direct T3SE target.