Figure 2.

Functional divergence of plant regulatory genes in haustorium formation and function. Quinone molecules released from plants are perceived by CARD1 to regulate stomatal closure and plant immunity through cellular Ca²⁺ elevation in Arabidopsis. CARD1 orthologs (CADLs) are potentially involved in prehaustorium initiation through Ca²⁺ elevation. Ethylene (ET) signaling mediated by ethylene receptors, including ETR1, and ethylene signaling component EIN2, mediate organ development and biotic interactions in autotrophic plants. Both ETR1 and EIN2 are employed by P. japonicum to terminate prehaustorium growth in the absence of a host and to promote tissue penetration upon host attachment