Exposure of harvested grapefruit to UV-C (254 nm) irradiation was previously found to induce resistance against the green mold decay caused by Penicillium digitatum. In order to gain insight into the mechanism of this UV-induced resistance we initiated a study for isolation of genes induced during this process. Using the differential display method we cloned cDNA representing an mRNA which is accumulated in grapefruit peel upon UV irradiation. Sequence analysis revealed that this cDNA represents a gene encoding for an isoflavone reductase-like protein and was termed IRL (isoflavone reductase-like). The grapefruit IRL protein sequence has high homology also to a novel family of other isoflavone reductase-like proteins present in few non-legume plants and whose function is not clear yet. The UV dose, and time following it, which lead to maximal accumulation of the IRL transcript were found to be similar to those leading to maximal induced resistance. The expression of the IRL gene was demonstrated to be induced also by wounding and pathogen infection.