Neofunctionalized RGF pathways drive haustorial organogenesis in parasitic plants

Parasitic plants will initiate rapid de novo organogenesis of a specialized feeding structure called a haustorium upon contact with their hosts. Currently, little is known about the internal signals regulating haustorium development. Here, we identify root meristem growth factor (RGF) peptides in Phtheirospermum japonicum as endogenous inducers of prehaustorium formation. Treatment with specific RGF peptides in the absence of hosts triggered prehaustoria and induced expression of PjYUC3, a gene required for auxin biosynthesis and prehaustorium formation. CRISPR-mediated knockouts showed that PjRGFR1 and PjRGFR3, receptors activated by the haustorium-specific RGF peptides PjRGF2 and PjRGF5, are essential for prehaustorium formation, revealing functional redundancy. Phylogenetic analyses indicate that PjRGF2 is broadly conserved among Orobanchaceae, whereas PjRGF5 appears to have recently evolved through segmental tandem multiplication. Our findings establish RGF peptides and their corresponding receptors as critical components of haustorium developmental signaling and provide insights into the evolutionary trajectories that shape plant parasitism.