Are roots special? Nematodes have their say

Nematodes are ubiquitous and cosmopolitan parasites of vascular plants, causing substantial crop damage. Although various species exploit all parts of the plant, roots are the major target. Nematodes deploy a broad spectrum of feeding strategies, ranging from simple grazing to the establishment of complex cellular structures (including galls) in host tissues. Various models of feeding site formation have been proposed. and a role for phytohormones has long been speculated. Based on recent molecular evidence we present several scenarios involving phytohormones in the induction of giant cells by root-knot nematodes. The origin of parasitism by nematodes, and the role of horizontal gene transfer from microbes is discussed. Throughout, parallels with aphid-plant interactions are emphasized. (C) 2003 Elsevier Science Ltd. All rights reserved.