Striga hermonthica induces lignin deposition at the root tip to facilitate prehaustorium formation and obligate parasitism

Striga hermonthica, an obligate parasitic plant that causes severe agricultural damage, recognizes its hosts by sensing haustorium-inducing factors (HIFs). Perception of HIFs induces the rapid transformation of S. hermonthica radicles into prehaustoria, structures that enable host invasion and mature into haustoria. HIFs consist of various aromatic compounds, including quinones, lignin monomers, and flavonoids. However, the downstream molecular pathways that orchestrate these developmental events are largely unknown. Here, we report that S. hermonthica root-tip cells rapidly deposit lignin, a major cell wall component, in response to HIFs. In addition to enhancing lignin levels, HIFs strongly induce genes involved in lignin monomer biosynthesis and polymerization, including several respiratory burst oxidase homologs (RBOHs) and class III peroxidases. Disruption of lignin monomer biosynthesis compromises prehaustorium formation, whereas HIF-induced class III peroxidases facilitate the process by promoting lignification. Our study demonstrates that cell wall lignification is a converged cellular process downstream of various HIFs that guides root meristematic cells in prehaustorium development.