Molecular characterization of the AtCXE8 gene, which promotes resistance to Botrytis cinerea infection

The relationships of sterase- and lipase-like proteins with three signaling molecules (salicylic acid, jasmonic acid, and ethylene) expressed during plant–pathogen interactions were studied. We isolated two carboxylesterase (AtCXE) genes, AtCXE8 and AtCXE9, from Arabidopsis thaliana. The AtCXE8 and AtCXE9 proteins possess carboxylesterase motifs (-GXSXG-) and catalytic triads (Ser, Asp, and His). We demonstrated that recombinant AtCXE8 and AtCXE9 proteins have both enzymatic activity and specific activity for p-nitrophenyl butyrate (C₄) in vitro. Moreover, the enzymatic activity of recombinant AtCXE8 was twofold higher than that of AtCXE9. To gain a better understanding of the endogenous role of the AtCXE8 gene in Arabidopsis, we identified an enhancer trap T-DNA mutant (AtCXE8_KO) and used it to show that the AtCXE8 gene was induced in response to fungal infection. AtCXE8_KO plants were also more susceptible to infections than wild-type Col-0 plants. Moreover, overexpression of the AtCXE8 gene in transgenic Arabidopsis plants led to enhanced disease resistance against B. cinerea. Taken together, our data indicate that AtCXE8 plays a role in promoting resistance to fungal invasion.