Glucosylation of endogenous haustorium-inducing factors underpins kin avoidance in parasitic plants

Parasitic plants rarely attack themselves, suggesting the existence of a kin-avoidance mechanism. In the root parasitic plant Phtheirospermum japonicum, prehaustorium formation is triggered by host-secreted haustorium-inducing factors (HIFs), but it is unresponsive to its own exudates. Here we report the identification of the spontaneous prehaustorium 1 (spoh1) mutant, which forms prehaustoria without external host signals. spoh1 harbors a point mutation in the gene encoding uridine diphosphate–glucosyltransferase UGt72b1, an enzyme that glucosylates and thereby inactivates phenolic HIFs. PjUGt72b1 has a different substrate specificity than its ortholog of the host Arabidopsis. Introduction of PjUGt72b1 into Arabidopsis reduced prehaustorium induction activity, indicating that UGt72b1 regulates haustorium induction by hosts. Our findings suggest that Orobanchaceae hemiparasitic plants have evolved kin-avoidance mechanisms through the glucosylation of endogenous HIFs.