SummaryArabidopsis thaliana is a host for the sugar beet cyst nematode Heterodera schachtii. Juvenile nematodes invade the roots and induce the development of a syncytium, which functions as a feeding site for the nematode. Here, we report on the transcriptome of syncytia induced in the roots of Arabidopsis. Microaspiration was employed to harvest pure syncytium material, which was then used to prepare RNA for hybridization to Affymetrix GeneChips. Initial data analysis showed that the gene expression in syncytia at 5 and 15 days post-infection did not differ greatly, and so both time points were compared together with control roots. Out of a total of 21 138 genes, 18.4% (3893) had a higher expression level and 15.8% (3338) had a lower expression level in syncytia, as compared with control roots, using a multipletesting corrected false discovery rate of below 5%. A gene ontology (GO) analysis of up-and downregulated genes showed that categories related to high metabolic activity were preferentially upregulated. A principal component analysis was applied to compare the transcriptome of syncytia with the transcriptome of different Arabidopsis organs (obtained by the AtGenExpress project), and with specific root tissues. This analysis revealed that syncytia are transcriptionally clearly different from roots (and all other organs), as well as from other root tissues.

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The dsRNA-binding protein Staufen was the first RNA-binding protein proven to play a role in RNA localization in Drosophila. A mammalian homolog, Staufen1 (Stau1), has been implicated in dendritic RNA localization in neurons, translational control, and mRNA decay. However, the precise mechanisms by which it fulfills these specific roles are only partially understood. To determine its physiological functions, the murine Stau1 gene was disrupted by homologous recombination. Homozygous stau1 tm1Apa mutant mice express a truncated Stau1 protein lacking the functional RNA-binding domain 3. The level of the truncated protein is significantly reduced. Cultured hippocampal neurons derived from stau1 tm1Apa homozygous mice display deficits in dendritic delivery of Stau1-EYFP and ␤-actin mRNA-containing ribonucleoprotein particles (RNPs). Furthermore, these neurons have a significantly reduced dendritic tree and develop fewer synapses. Homozygous stau1 tm1Apa mutant mice are viable and show no obvious deficits in development, fertility, health, overall brain morphology, and a variety of behavioral assays, e.g., hippocampus-dependent learning. However, we did detect deficits in locomotor activity. Our data suggest that Stau1 is crucial for synapse development in vitro but not critical for normal behavioral function.dendrite ͉ RNA transport ͉ ribonucleoprotein particles ͉ double-stranded RNA-binding protein

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.