When sedentary endoparasitic nematodes infect plants, they induce comp
lex feeding sites within the root tissues of their host. To characteri
ze cell wall changes induced within these structures at a molecular le
vel, we Studied the expression of an extensin gene (coding for a major
structural cell wall protein) in nematode-infected tobacco roots. Ext
ensin gene expression was observed to be induced very early upon infec
tion. This induction was weak, transient, and probably due to wounding
during penetration and migration of the tobacco cyst nematode Globode
ra tabacum ssp solanacea rum. In contrast, high extensin gene expressi
on was observed during the whole second larval stage (an similar to 2-
week-long phase of establishment of the feeding site) of the root knot
nematode Meloidogyne javanica. During later stages of this interactio
n, expression gradually decreased. Extensin gene expression was found
in at least three different tissues of the gall. We propose that disti
nct mechanisms lead to induced expression in these different cell type
s. The significance of these results for the understanding of plant-ne
matode interactions as well as the function of structural cell wall pr
oteins, such as extensin, is discussed.