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 <i>Phtheirospermum japonicum</i>, 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 <i>spontaneous prehaustorium 1</i> (<i>spoh1</i>) mutant, which forms prehaustoria without external host signals. <i>spoh1</i> 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 <i>Arabidopsis</i>. Introduction of PjUGT72B1 into <i>Arabidopsis</i> 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.