Induction Patterns of an Extensin Gene in Tobacco upon Nematode Infection.

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Abstract
When sedentary endoparasitic nematodes infect plants, they induce complex feeding sites within the root tissues of their host. To characterize cell wall changes induced within these structures at a molecular level, we studied the expression of an extensin gene (coding for a major structural cell wall protein) in nematode-infected tobacco roots. Extensin gene expression was observed to be induced very early upon infection. This induction was weak, transient, and probably due to wounding during penetration and migration of the tobacco cyst nematode Globodera tabacum ssp solanacea-rum. In contrast, high extensin gene expression was observed during the whole second larval stage (an ~2-week-long phase of establishment of the feeding site) of the root knot nematode Meloidogyne javanica. During later stages of this interaction, expression gradually decreased. Extensin gene expression was found in at least three different tissues of the gall. We propose that distinct mechanisms lead to induced expression in these different cell types. The significance of these results for the understanding of plant-nematode interactions as well as the function of structural cell wall proteins, such as extensin, is discussed.