The monomeric GTPase RabA2 is required for progression and maintenance of membrane integrity of infection threads during root nodule symbiosis

Abstract

Progression of the infection canal that conducts rhizobia to the nodule primordium requires a functional Rab GTPase located in Golgi/trans-Golgi that also participate in root hair polar growth. Common bean (Phaseolus vulgaris) symbiotically associates with its partner Rhizobium etli, resulting in the formation of root nitrogen-fixing nodules. Compatible bacteria can reach cortical cells in a tightly regulated infection process, in which the specific recognition of signal molecules is a key step to select the symbiotic partner. In this work, we show that RabA2, a monomeric GTPase from common bean, is required for the progression of the infection canal, referred to as the infection thread (IT), toward the cortical cells. Expression of miss-regulated mutant variants of RabA2 resulted in an increased number of abortive infection events, including bursting of ITs and a reduction in the number of nodules. Nodules formed in these plants were small and contained infected cells with disrupted symbiosome membranes, indicating either early senescence of these cells or defects in the formation of the symbiosome membrane during bacterial release. RabA2 localized to mobile vesicles around the IT, but mutations that affect GTP hydrolysis or GTP/GDP exchange modified this localization. Colocalization of RabA2 with ArfA1 and a Golgi marker indicates that RabA2 localizes in Golgi stacks and the trans-Golgi network. Our results suggest that RabA2 is part of the vesicle transport events required to maintain the integrity of the membrane during IT progression.

Differential tetraspanin genes expression and subcellular localization during mutualistic interactions in Phaseolus vulgaris

“…The monomeric GTPase PvRabA2 is a good marker of the different developmental stages of root hairs due to its key role in root hair tip growth (S4 Fig), although it is also expressed in root tissue [53, 54]. We observed that RabA2 transcript accumulated in root hairs; as expected, the transcript accumulation was higher in zones II and III, where the cells are rapidly expanding or reaching full length, compared with zone I, where root hairs are just bulging out (S4 Fig).…”

EhRabB mobilises the EhCPADH complex through the actin cytoskeleton during phagocytosis of Entamoeba histolytica

“…They act as molecular switches during the vesicle fusion and fission to facilitate the transport of cargo molecules (Hutagalung & Novick, ) and are involved in protein recycling after endocytosis. In E. histolytica trophozoites, several authors have demonstrated that Rab‐GTPases also participate in maintaining membranes integrity and remodeling (Dalla Via et al, ; Nakayama, ). These events are fundamental for tissue invasion and phagocytosis by trophozoites (Nozaki & Nakada‐Tsukui, ).…”

Spatio-temporal control of post-Golgi exocytic trafficking in plants

“…However, Rab-A2 members are associated with the establishment and maintenance of beneficial microbial interactions in plants (reviewed by Rivero et al, 2019). For instance, a Phaseus vulgarus Rab-A2 protein mediates polarised trafficking in the context of cell wall remodelling during colonisation by the symbiotic nitrogen-fixer Rhizobium etli (Blanco et al, 2009;Dalla Via et al, 2017). Expression of a dominant-negative Rab-A2 variant results in defects during infection thread formation, indicating that Rab-A2 is also required at later stages of infection (Dalla Via et al, 2017).…”

“…For instance, a Phaseus vulgarus Rab-A2 protein mediates polarised trafficking in the context of cell wall remodelling during colonisation by the symbiotic nitrogen-fixer Rhizobium etli (Blanco et al, 2009;Dalla Via et al, 2017). Expression of a dominant-negative Rab-A2 variant results in defects during infection thread formation, indicating that Rab-A2 is also required at later stages of infection (Dalla Via et al, 2017). In addition to its role in FLS2 endocytosis, RAB-A4c is also implicated in cell wall remodelling during infection with the powdery mildew Golovinomyces cichoracearum ( Fig.…”