Host responses to haustorium invasion of the stem parasitic plant, <i>Cuscuta campestris</i>, differ from responses to wounding

The parasitic mechanism employed by the stem parasitic plant, Cuscuta campestris, involves degradation of the host epidermis and intrusion of the cortical tissue of the host stem by a specialized organ called the haustorium. In host plants, the mechanical stimuli associated with this degradation and intrusion of host tissues is considered to be comparable to wounding. However, it has not yet been clarified whether parasitic invasion and wounding induce equivalent responses in host plants. In this study, we demonstrated that parasitic intrusion-induced responses that were comparable to wounding in the host plant, Arabidopsis thaliana, including upregulation of Arabidopsis NAC DOMAIN-CONTAINING PROTEIN 71 (ANAC071), which is a key transcription factor associated with wound repair, cell division, and vascular development. Despite these similarities, we found that the mechanism regulating the induction of cell division- and vascular development-related genes at the host-parasite interface differed from that associated with wound repair. Specifically, ANAC071 was not required for the induction of cell division-related genes, as their upregulation was observed in anac071/096/011 triple mutants as well as in wild-type host plants. We also found that neither auxin nor ethylene plays a significant role in inducing the expression of vascular development-related genes. Thus, the findings show that the mechanisms responsible for upregulating cell division- and vascular development-related genes differ between parasitic and wound repair responses.