The oligomeric states of elicitins affect the hypersensitive response and resistance in tobacco.

Successful plant defence against microbial pathogens is based on early recognition and fast activation of inducible responses. Key mechanisms include detection of microbe-associated molecular patterns by membrane-localized pattern recognition receptors that induce a basal resistance response. A well-described model of such responses to pathogens involves the interactions between Solanaceae plants and proteinaceous elicitors secreted by oomycetes, called elicitins. It has been hypothesized that the formation of oligomeric structures by elicitins could be involved in their recognition and activation of defensive transduction cascades. In this study, we tested this hypothesis using several approaches, and we observed differences in tobacco plant responses induced by the elicitin β-cryptogein (β-CRY) and its homodimer, β-CRYDIM. We also found that the C-terminal domain of elicitins of other ELI (true-elicitin) clades plays a significant role in stabilization of their oligomeric structure and restraint in the cell wall. In addition, covalently cross-linking β-CRYDIM impaired the formation of signalling complexes, thereby reducing its capacity to elicit the hypersensitive response and resistance in the host plant, with no significant changes in pathogenesis-related protein expression. By revealing the details of the effects of β-CRY dimerization on recognition and defence responses in tobacco, our results shed light on the poorly understood role of elicitins' oligomeric structures in the interactions between oomycetes and plants.