Characterization of novel F-box proteins in plants induced by biotic and abiotic stress.

Plants protect against pathogen infections by a combination of constitutive and induced strategies. The induction of plant defense involves the recognition of compounds derived from the pathogen or the plant itself, called elicitors. Looking for new genes involved in plant defense responses, we isolated a cDNA clone corresponding to an elicitor-induced mRNA from Phaseolus vulgaris cell suspension cultures. This clone, PvFBS1, encodes a protein with an F-box, therefore a putative component of an SCF ubiquitin ligase complex. PvFBS1 mRNA accumulates in leaves of whole plants in response to wounding or osmotic stress, as well as, following the application of methyl jasmonate (MeJA). salicylic acid (SA) or abscisic acid (ABA). Several sequences related to PvFBS1 were found in the GenBank. In Arabidopsis thaliana there are 4 genomic sequences coding for proteins with similarity to PvFBS1. One of them, AtFBS1, displays a pattern of induction analogous to the one observed for PvFBS1. A yeast two-hybrid assay proved that AtFBS1 was able to interact with ASK1, the component of the SCF complex that binds the F-box. A deletion of the F-box in AtFBS1 abolishes the ability of this protein to interact with ASK1. This demonstrates the functionality of the F-box contained in AtFBS1. Gene fusions to the GUS reporter gene revealed a complex regulation for AtFBS1 expression.