Fructan exohydrolases (FEHs) are upregulated by salicylic acid together with defense-related genes in non-fructan accumulating plants.

The identification of several fructan exohydrolases (FEHs, EC 3.2.1.80) in non-fructan accumulating plants raised the question of their roles. FEHs may be defense-related proteins involved in the interactions with fructan-accumulating microorganisms. Since known defense-related proteins are upregulated by defense-related phytohormones, we tested the hypothesis that FEHs of non-fructan accumulating plants are upregulated by salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) using the model plant Arabidopsis thaliana and the agronomically relevant and genetically related species Brassica napus. By sequence homologies with the two known FEH genes of A. thaliana, At6-FEH, and At6&1-FEH, the genes coding for the putative B. napus FEHs, Bn6-FEH and Bn6&1-FEH, were identified. Plants were treated at root level with SA, methyl jasmonate (MeJA) or 1-aminocyclopropane-1-carboxylic acid (ACC). The transcript levels of defense-related and FEH genes were measured after treatments. MeJA and ACC did not upregulate FEHs, while HEL (HEVEIN-LIKE PREPROTEIN) expression was enhanced by both phytohormones. In both species, the expression of AOS, encoding a JA biosynthesis enzyme, was enhanced by MeJA and that of the defensine PDF1.2 and the ET signaling transcription factor ERF1/2 by ACC. In contrast, SA not only increased the expression of genes encoding antimicrobial proteins (PR1 and HEL) and the defense-related transcription factor WRKY70 but also that of FEH genes, in particular 6&1-FEH genes. This result supports the putative role of FEHs as defense-related proteins. Genotypic variability of SA-mediated FEH regulation (transcript level and activities) was observed among five varieties of B. napus, suggesting different susceptibilities toward fructan-accumulating pathogens.