Parasitic plants initiate haustorium formation—a critical step in parasitism and nutrient acquisition—by recognizing haustorium inducing factors (HIFs) from their hosts. However, the mechanisms by which these plants sense and transduce host-derived signals during early development remain poorly understood. Previous research has identified lignin monomers and their precursors, notably G- and S-type monolignols produced during lignin biosynthesis, as HIFs that trigger the formation of prehaustoria, early haustorial structures arising from the transformation of root apical meristem tissue. Additional compounds, such as quinones and flavonoids, have also been implicated as HIFs.
In this study, we explored the molecular basis of HIF signal transduction using a combination of fluorescently labeled monolignol probes, inhibitor assays, transcriptomic analysis, and heterologous gene expression in Striga hermonthica. Our results demonstrate that HIFs induce rapid lignin deposition at the root tip by activating class III peroxidases, which facilitate prehaustorium development. Peroxidases, previously shown to be essential for haustorium formation, are significantly upregulated across multiple stages of haustorial development in various Orobanchaceae species. This suggests that peroxidase-mediated local lignification may be a conserved mechanism within this family of parasitic plants. Lignin, a highly recalcitrant biopolymer, is typically scarce in root tips except under specific stress conditions. We propose that its rapid accumulation enhances cell wall rigidity and alters the cellular physical environment, promoting the swift fate transition of root apical meristem cells into haustorial cells. This finding highlights a dual role for monolignols in haustorium development: serving as direct signaling molecules while also contributing structurally to support haustorial induction.
Future studies will investigate the recognition mechanisms of phenolic signals, including lignin monomers, in parasitic plants and examine the dynamics of lignin polymerization and degradation during host invasion. These efforts aim to elucidate how parasitic plants optimize their infection strategies through cell wall remodeling, potentially providing novel approaches for managing agricultural parasitic weeds.
Research article: Cui S, Takeda-Kimura Y, Wakatake T, Luo J, Tobimatsu Y, Yoshida S (2025) Striga hermonthica induces lignin deposition at the root tip to facilitate prehaustorium formation and obligate parasitism. Plant Communications: 101294 (DOI: 10.1016/j.xplc.2025.101294)
Link for the article: https://www.cell.com/plant-communications/fulltext/S2590-3462(25)00056-2