Ethylene signaling mediates host invasion by parasitic plants

Parasitic plants form a specialized organ, a haustorium, to invade host
tissues and acquire water and nutrients. To understand the molecular
mechanism of haustorium development, we performed a forward genetics
screening to isolate mutants exhibiting haustorial defects in the model
parasitic plant Phtheirospermum japonicum. We isolated
two mutants that show prolonged and sometimes aberrant
meristematic activity in the haustorium apex, resulting in severe defects
on host invasion. Whole genome sequencing revealed that the two
mutants respectively have point mutations in homologs of ETHYLENE
RECEPTOR 1 (ETR1) and ETHYLENE INSENSITIVE
2 (EIN2), signaling components in response to the gaseous
phytohormone ethylene. Application of the ethylene signaling inhibitors
also caused similar haustorial defects, indicating that ethylene
signaling regulates cell proliferation and differentiation of parasite
cells. Importantly, genetic disruption of host ethylene
production also perturbs parasite invasion. We propose that parasitic
plants utilize ethylene as a signal to invade host roots.