Résumé
Apart from their antifungal role, plant defensins have recently been shown to be involved in abiotic stress tolerance or in inhibition of root growth when added in plant culture medium. We studied the subcellular localization of these proteins, which may account for these different roles. Stable and transient expression of AhPDFI. 1:: GFP (green fluorescent protein) fusion proteins were analysed in yeast and plants. Functional tests established that the GFP tag did not alter the action of the defensin. Subcellular localization of AhPDFI. 1 was characterized: by imaging AhPDFI. 1:: GFP together with organelle markers; and by immunolabelling AhPDFI. 1 in Arabidopsis hallen' and Arabidopsis thaliana leaves using a polyclonal serum. All our independent approaches demonstrated that AhPDFI. 1 is retained in intracellular compartments on the way to the lytic vacuole, instead of being addressed to the apoplasm. These findings challenge the commonly accepted idea of secretion of defensins.The subcellular localization highlighted in this study could partly explain the dual role of plant defensins on plant cells and is of major importance to unravel the mechanisms of action of theseproteins at the cellular level.