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During the interaction between sedentary plant-parasitic nematodes and their host, complex morphological and physiological changes occur in the infected plant tissue, finally resulting in the establishment of a nematode feeding site. This cellular transformation is the result of altered plant gene expression most likely induced by proteins injected in the plant cell by the nematode. Here, we report on the identification of a WRKY transcription factor expressed during nematode infection. Using both promoter-reporter gene fusions and in situ reverse transcription-polymerase chain reaction, we could show that AtWRKY23 is expressed during the early stages of feeding site establishment. Knocking down the expression of WRKY23 resulted in lower infection of the cyst nematode Heterodera schachtii. WRKY23 is an auxin-inducible gene and in uninfected plants WRKY23 acts downstream of the Aux/IAA protein SLR/IAA14. Although auxin is known to be involved in feeding site formation, our results suggest that, during early stages, auxin-independent signals might be at play to activate the initial expression of WRKY23.
Sedentary plant-parasitic nematodes (e.g. Heterodera and Meloidogyne ssp.) have developed a fascinating way to parasitize plants. After locating and migrating toward their host, they penetrate the root and find their way to the vascular tissue. There they manipulate plant root cells, resulting in the establishment of highly specialized nematode feeding sites (NFS). Depending on the nematode species, the initial feeding cell develops into either a syncytium (for cyst nematodes such as Heterodera spp.) or a system of giant cells (for the root-knot nematodes such as Meloidogyne spp.; Vanholme et al., 2004). The nematodes depend strictly on these feeding cells for food supply during their entire life cycle. Although it is not yet understood how nematodes establish syncytia or giant cells, glandular secretions produced by the nematode and injected into plant cells are suspected of interacting directly or indirectly with the plant nuclear genome, causing a whole cascade of altered gene expression that ultimately results in the complex NFS (Vanholme et al., 2004). To study how NFS become established, different molecular approaches were used to identify plant genes/promoters that are induced upon nematode infection. Previously, the promoter-tagging strategy was used, which led to the identification of six Arabidopsis (Arabidopsis thaliana) lines exhibiting GUS activity in nematode feeding structures (Barthels et al., 1997). A...