Biology subjects

Frances, L.

Publications and source records attributed to Frances, L..

3 recordsLinked to original sources

bioRxiv2025

Rhizobial motility preference in root colonization of Medicago truncatula

O_LITunnel-like infection thread (IT) structures support root colonization by symbiotic nitrogen-fixing rhizobia bacteria in most legume species. These tip-grown structures are key to direct rhizobia from root hairs to developing nodules, where they are hosted to fix nitrogen. Rhizobia likely progress inside ITs by combining growth and motility, by modes not yet defined. Here, we tackled this question by combining mathematical modeling, live cell imaging, and bacterial mutant phenotyping in Medicago truncatula. C_LIO_LIModeling the motion of fluorescently-labeled Sinorhizobium meliloti inside early root hair IT compartments estimated slow movement (2 to 6 {micro}m/h), compatible with passive rather than active motility. Consistent with this model, flagella-less fliF and fliF-fliRdel S. meliloti mutants were impaired in active swimming motility in vitro, yet could colonize host roots and nodules in planta. In contrast, mutation in the rhizobactin 1021 siderophore rhbE biosynthesis gene affected both surface motility in vitro, and host root and nodule colonisation. This mutation also promoted the formation of branched ITs in root hairs, which ultimately resulted in impaired nodule development and infection. C_LIO_LIOur findings support the model estimation and suggest that S. meliloti prioritises flagella-independent surface translocation, partially by secreting rhizobactin 1021 surfactants to reach developing nodules in M. truncatula. C_LI

plant biology↗

bioRxiv2024

Identification of regulatory promoter sequences directing MtCP6 transcription at the onset of nodule senescence in Medicago truncatula.

O_LIThe symbiotic association of legumes with rhizobia results in the formation of new root organs called nodules. However, the lifespan of nodules is limited by the senescence process. Increased proteolytic activity is one of the hallmarks of nodule senescence. In Medicago truncatula, a papain cysteine protease encoding gene, MtCP6, is a marker for the onset of nodule senescence under both developmental and stress-induced pathways. C_LIO_LITo identify promoter regions conferring MtCP6 senescence-related expression, progressive MtCP6 promoter deletions were generated and the resulting sequences were fused with a reporter gene for promoter::GUS fusion analysis in transgenic M. truncatula roots. C_LIO_LIIn planta, a minimal promoter sequence of 67 bp was identified as sufficient for specific spatiotemporal transcriptional activation of MtCP6 in nodules. The functionality of this cis-regulatory sequence, thereafter named Nodule Senescence (NS), was validated by both gain- and loss-of-function approaches. C_LIO_LIERF091, an AP2/ERF family transcription factor, was identified in a yeast one-hybrid (Y1H) screen as an NS-box interacting factor, and shown to mediate transcription activation of a NS-box:GUS reporter in transactivation assays in Nicotiana benthamiana. C_LIO_LIThis work uncovered a new senescence-related nodule specific cis-regulatory region (NS-box) and provided evidence for the likely involvement of a stress-related ERF family member in the regulation of MtCP6, at the onset of nodule senescence. C_LI

plant biology↗

bioRxiv2024

Annexin and calcium-regulated priming of legume root cells for endosymbiotic infection

Legumes establish endosymbioses with arbuscular mycorrhizal (AM) fungi or rhizobia bacteria to improve mineral nutrition. Symbionts are hosted in privileged habitats, root cortex (for AM fungi) or nodules (for rhizobia) for efficient nutrient exchange. To reach these habitats, plants form cytoplasmic bridges, which are key to predicting and guiding the cellular route of entry of fungal hyphae or rhizobia-filled infection threads (ITs). However, the underlying mechanisms are poorly studied. Here we show that unique ultrastructural changes and Ca2+ spiking signatures, closely linked to MtAnn1 annexin accumulation, accompany rhizobia-associated bridge formation. Loss of MtAnn1 function in M. truncatula affects Ca2+ spike amplitude, cytoplasmic configuration and rhizobia infection efficiency, consistent with a role of MtAnn1 in regulating infection priming. MtAnn1, which evolved in species establishing intracellular symbioses, is also AM-symbiosis-induced and required for proper arbuscule formation. Together, we propose that MtAnn1 is part of an ancient Ca2+-regulatory module for transcellular endosymbiotic infection.

plant biology↗