The Arabidopsis extensin gene is developmentally regulated, is induced by wounding, methyl jasmonate, abscisic and salicylic acid, and codes for a protein with unusual motifs.

A single-copy extensin gene (atExt1) has been isolated from Arabidopsis thaliana (L.) Heynh. The deduced amino acid sequence consists of 374 amino acids which are organised into highly ordered repeating blocks in which Ser(Pro)4 and Ser(Pro)3 motifs alternate. Two copies of the Tyr-X-Tyr-Lys motif and 13 copies of the Val-Tyr-Lys motif are present, showing that this extensin may be highly cross-linked, possessing the capacity for both intra and inter-molecular bond formation. The gene atExt1 is normally expressed in the root and is silent in the leaf; wounding reverses this pattern, turning on the gene in the leaf and repressing it in the root. The promoter contains motifs which have been found to activate plant defence genes in response to salicylic acid, abscisic acid and methyl jasmonate; when these compounds are applied to the roots, the atExt1 gene is activated in the leaf.