Local induction of a mycorrhiza-specific class III chitinase gene in cortical root cells of Medicago truncatula containing developing or mature arbuscules

A class III chitinase gene. Mtchitinase III-3, has been found to be induced in roots of Medicago truncatula specifically upon colonization by the arbu scular mycorrhizal fungi Glomus mosseae and Glomus intraradices. Here we sh ow by in situ hybridization techniques that Mtchitinase III-3 is only expre ssed in cortical root cells containing arbuscules formed by either of the f ungi. Transcripts of Mtchitinase III-3 were detected in cells containing de veloping as well as mature arbuscules. They were absent from cells adjacent to arbuscule-containing cells, from cells in contact with intraradical hyp hae and from cortical cells in non-colonized areas of the root. These resul ts indicate that the product of the Mtchitinase III-3 gene has a role withi n individual cortical cells during formation and functioning of arbuscules.