The monomeric GTPase PvRabA2 is involved in infection thread formation and the strain-specific response to rhizobia

VIRGINIA DALLA VIA, VIRGINIA SAVY, MARÍA EUGENIA ZANETTI, O. MARIO AGUILAR AND FLAVIO BLANCO

Austin, Texas

Congreso; Plant Biology 2012 The annual meeting of the American Society of Plant Biologists; 2012

American Society of Plant Biologists

Common bean (Phaseolus vulgaris) associates with its partner Rhizobium etli, resulting in the formation of root nitrogen-fixing nodules. We have previously shown that a transcription factor of the NF-Y family of common bean is required for the preferential association with efficient strains of R. etli and that a GTPase of the Rab family (PvRabA2) acts upstream of this transcription factor. An RNAi silencing strategy showed that PvRabA2 is involved in the polar growth of root hairs and is required for early responses during nodulation. On the other hand, overexpression had no effect on the phenotype. In order to evaluate the role of Rab proteins in the strain-specific response and considering post translational regulation of Rab proteins, we obtained constitutively active (CA) and dominant negative (ND) forms of PvRabA2 by site-directed mutagenesis. Overexpression of the ND form showed a reduction on root hair length, whereas CA roots presented a decrease of the root hair density. However, no differences were found on roots hair deformation in response to rhizobia. The number of nodules was significantly reduced in composite plants overexpressing the CA or ND forms when they were inoculated with the most efficient R. etli strain SC15, but not with the less efficient strain 55N1. Furthermore, nodules formed with R. etli SC15 were smaller in transgenic roots overexpressing ND or CA forms. This result suggests that PvRABA2 might participate in the strain-specific response together with NF-YC. Localization experiments using GFP fusions showed that the CA form is associated to infection structures, known as infection threads (IT). Concomitantly, overexpression of CA affected formation of IT, producing an increase of abortive infection events. These results suggest that PvRabA2 participates in vesicle transport events during IT formation.