DIFFERENTIAL GENE-EXPRESSION IN NEMATODE-INDUCED FEEDING STRUCTURES OF TRANSGENIC PLANTS HARBORING PROMOTER GUSA FUSION CONSTRUCTS

Sedentary plant-parasitic nematodes are able to induce specialized fee ding structures in the root system of their host plants by triggering a series of dramatic cellular responses. These changes presumably are accompanied by a reprogramming of gene expression. To monitor such cha nges, a variety of promoter-gusA fusion constructs were introduced int o Arabidopsis and tobacco. Transgenic plants were analysed histochemic ally for GUS activity in the nematode feeding structures after infecti on with either Heterodera schachtii or Meloidogyne incognita. Promoter s of the Cauliflower Mosaic Virus 35S gene, the bacterial nopaline syn thase, rooting loci (rol) and T-cyt genes and the plant-derived phenyl alanine ammonia-lyase I gene, which are highly active in non-infected roots, were all downregulated in the feeding structures as indicated b y the strong decrease of GUS activity inside these structures. Less st ringent down-regulation was observed with chimeric gusA fusion constru cts harbouring truncated rolB and rolC promoter sequences. Similar obs ervations were made with transgenic Arabidopsis lines that carried ran domly integrated promoterless gusA constructs to identify regulatory s equences in the plant genome. Most of the lines that were selected for expression in the root vascular cylinder demonstrated local down-regu lation in feeding structures after infection with H. schachtii. The re verse pattern of GUS activity, a blue feeding structure amidst unstain ed root cells, was also found in several lines. However, GUS activity that was entirely specific for the feeding structures was not observed . Our data show that the expression of a large number of genes is infl uenced during the development of the nematode feeding structures.