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

VIRGINIA DALLA VÍA, VIRGINIA SAVY, MARÍA E. ZANETTI, MARIO AGUILAR, FLAVIO A. BLANCO.

Austin

Congreso; Plant Biology 2012; 2012

American Society of Plant Biology

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, we obtained constitutively active (CA) and dominant negative (ND) forms of PvRabA2 by site-directed mutagenesis. Overexpression of ND PvRabA2 showed a reduction on root hair length, whereas PvRabA2 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 PvRabA2 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 PvRabA2 CA is associated with infection threads(IT). Concomitantly, overexpression of PvRabA2 CA and ND affected formation of IT, producing an increase of abortive infection events. These results support that PvRabA2 participates in vesicle transport events during IT formation.