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Actin Monoubiquitylation Is Induced in Plants in Response to Pathogens and Symbionts

¹Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, UNAM, Apartado Postal 510-3, Cuernavaca Morelos 62271, México; ²Departamento de Genética y Fisiología Molecular, Instituto de Biotecnología, UNAM, Apartado Postal 510-3, Cuernavaca Morelos 62271, México

Most dramatic examples of actin reorganization have been described during host-microbe interactions. Plasticity of actin is, in part, due to posttranslational modifications such as phosphorylation or ubiquitylation. Here, we show for the first time that actins found in root nodules of Phaseolus vulgaris are modified transiently during nodule development by monoubiquitylation. This finding was extended to root nodules of other legumes and to other plants infected with mycorrhiza or plant pathogens such as members of the genera Pseudomonas and Phytophthora. However, neither viral infections nor diverse stressful conditions (heat shock, wounding, or osmotic stress) induced this response. Additionally, this phenomenon was mimicked by the addition of a yeast elicitor or H₂O₂ to Phaseolus vulgaris suspension culture cells. This modification seems to provide increased stability of the microfilaments to proteolytic degradation and seems to be found in fractions in which the actin cytoskeleton is associated with membranes. All together, these data suggest that actin monoubiquitylation may be considered an effector mechanism of a general plant response against microbes.

Additional keywords: cortical cytoskeleton, microfilaments stabilization, oxidative burst.