is a facultative parasitic plant in the Orobanchaceae that parasitizes the roots of a wide range of host plants including , , rice and maize. The important exception to this broad host range is that rarely parasitize other . We explored self and kin recognition in and showed that exudates collected from roots of host species, and , induced haustorium development when applied to the roots of seedlings while those collected from did not. In mixed exudate experiments, exudates did not inhibit the haustorium-inducing activity of those from host roots. Interestingly, when roots of a seedlings were treated with either horseradish peroxidase or fungal laccase, the extracts showed haustorium-inducing factor (HIF... More
is a facultative parasitic plant in the Orobanchaceae that parasitizes the roots of a wide range of host plants including , , rice and maize. The important exception to this broad host range is that rarely parasitize other . We explored self and kin recognition in and showed that exudates collected from roots of host species, and , induced haustorium development when applied to the roots of seedlings while those collected from did not. In mixed exudate experiments, exudates did not inhibit the haustorium-inducing activity of those from host roots. Interestingly, when roots of a seedlings were treated with either horseradish peroxidase or fungal laccase, the extracts showed haustorium-inducing factor (HIF) activity, suggesting that roots contain the proper substrates for producing HIFs. Transgenic Triphysaria roots overexpressing a fungal laccase gene showed an increased responsiveness to a known HIF, 2,6-dimethoxy benzoquinone (DMBQ), in developing haustoria. Our results indicate kin recognition in is associated with the lack of active HIFs in root exudates. Treatment of roots with enzymatic oxidases activates or releases molecules that are HIFs. This study shows that exogenously applied oxidases can activate HIFs in roots that had no previous HIF activity. Further studies are necessary to determine if differential oxidase activities in host and parasite roots account for the kin recognition in haustorium development.
