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 arbuscular mycorrhizal fungi Glomus mosseae and Glomus intraradices. Here we show by in situ hybridization techniques that Mtchitinase III‐3 is only expressed in cortical root cells containing arbuscules formed by either of the fungi. Transcripts of Mtchitinase III‐3 were detected in cells containing developing as well as mature arbuscules. They were absent from cells adjacent to arbuscule‐containing cells, from cells in contact with intraradical hyphae and from cortical cells in non‐colonized areas of the root. These results indicate that the product of the Mtchitinase III‐3 gene has a role within individual cortical cells during formation and functioning of arbuscules.