A monomeric G-protein of the Rab family is required for root hair formation and pre- infection stages in the common bean-rhizobium symbiotic association

BLANCO, F.A; PELTZER MESCHINI, E; ZANETTI, M.E; O. M. AGUILAR

PLANT CELL

AMER SOC PLANT BIOLOGISTS

Año: 2009 vol. 21 p. 2797 - 2810

1040-4651

Legume plants are able to establish a symbiotic relationship with soil bacteria from the genus Rhizobium, leading tothe formation of nitrogen-fixing root nodules. Successful nodulation requires both the formation of infection threads (ITs) inthe root epidermis and the activation of cell division in the cortex to form the nodule primordium. This study describes thecharacterization of RabA2, a common bean (Phaseolus vulgaris) cDNA previously isolated as differentially expressed in roothairs infected with Rhizobium etli, which encodes a protein highly similar to small GTPases of the RabA2 subfamily. Thisgene is expressed in roots, particularly in root hairs, where the protein was found to be associated with vesicles that movealong the cell. The role of this gene during nodulation has been studied in common bean transgenic roots using a reversegenetic approach. Examination of root morphology in RabA2 RNA interference (RNAi) plants revealed that the number andlength of the root hairs were severely reduced in these plants. Upon inoculation with R. etli, nodulation was completelyimpaired and no induction of early nodulation genes (ENODs), such as ERN1, ENOD40, and Hap5, was detected in silencedhairy roots. Moreover, RabA2 RNAi plants failed to induce root hair deformation and to initiate ITs, indicating thatmorphological changes that precede bacterial infection are compromised in these plants. We propose that RabA2 acts inpolar growth of root hairs and is required for reorientation of the root hair growth axis during bacterial infection.