Gene Activities in Nematode-Induced Feeding Structures

Summary

Sedentary plant-parasitic nematodes induce elaborate feeding structures in the roots of their host plants. This is probably the result of an interaction between nematode secretions that interfere, after injection in the host cell, with the expression pattern of plant genes. A number of promoters have been identified that are both up-and down regulated during the development of the feeding structure. Sequence analysis of characterized promoters revealed the presence of a recognition sequence for the transcription factor ASF1 in most down-regulated promoters (e.g. CaMV 35S [1]). The recognition sequence was conspicuously absent in a nematode-responsive element of the TobRB7 promoter [2]. To analyze the significance of the ASF1 binding site for down-regulation, we mutated or replaced the as-1 sequence of the CaMV 35S promoter and transformed Arabidopsis with the new promoter/gusA fusion constructs. Transgenic plants were subsequently infected with nematodes and analyzed for GUS activity during the development of the feeding structure. After infection with the root-knot nematode Meloidogyne incognita, the mutated promoters did not result in an alteration of GUS expression in the feeding structure. After infection with the cyst nematode Heterodera schachtii, the mutations did not affect the GUS expression pattern to a large extend although the down-regulation of the mutated 35S promoter was no longer as stringent as with the WT promoter. We conclude from these results that the nematode-induced down-regulation of promoters is not directly related to the presence of an ASF1 binding site.