Rhizobium symbiotic efficiency meets CEP signaling peptides.

C-terminally encoded peptides (CEP) signaling peptides are drivers of systemic pathways regulating nitrogen (N) acquisition in different plants, from Arabidopsis to legumes, depending on mineral N availability (e.g. nitrate) and on the whole plant N demand. Recent studies in the Medicago truncatula model legume revealed how root-produced CEP peptides control the root competence for endosymbiosis with N fixing rhizobia soil bacteria through the activity of the Compact Root Architecture 2 (CRA2) CEP receptor in shoots. Among CEP genes, MtCEP7 was shown to be tightly linked to nodulation, and the dynamic temporal regulation of its expression reflects the plant ability to maintain a different symbiotic root competence window depending on the symbiotic efficiency of the rhizobium strain, as well as to reinitiate a new window of root competence for nodulation.

Acceptability of interventional materials: public participation in public health interventional research / Acceptabilité d'une intervention : exemple de participation des publics en recherche interventionnelle en santé publique

Introduction: The uptake rate of colorectal cancer screening remains insufficient in France and decreases as the level of deprivation increases. Participants' health literacy appears to be an important determinant of screening uptake. Aim of the study: The aim of this study, nested in our multicenter-randomized controlled trial, was to present the development and acceptability of interventional material (training and a pictorial brochure) for general practitioners and healthcare users in disadvantaged geographical areas using a participatory involvement approach. Methods: The development of the brochure and the training was carried out in three stages, two for the development, usability, and acceptability testing and a third for its evaluation with the target audience. We used a qualitative approach based on focus groups and cognitive interviews. The qualitative analysis was based on Morville's "Honeycomb" conceptual model and the COREQ checklist. Results: The development and test of the acceptability of the material enabled us to adjust the content of the training by proposing examples that were more rooted in professional reality, and to produce a brochure that was easy to read, understand, acceptable and adapted to the intervention's targeted audience. Conclusions: This experience illustrates in a concrete way the feasibility of public participation and its value in the context of interventional research, and more generally in the creation of interventional material.

Introduction: Le taux de participation au dépistage du cancer colorectal reste insuffisant en France et diminue à mesure que le niveau de précarité augmente. La littératie en santé est un déterminant important du recours au dépistage. But de l'étude: Cette étude, nichée dans notre essai randomisé multicentrique, a pour but de présenter la procédure d'élaboration (procédé itératif de test d'utilisabilité et d'acceptabilité) et de vérification de l'acceptabilité de l'intervention (formation et brochure imagée) ciblant les médecins généralistes et usagers du soin dans des zones géographiques défavorisées, selon une approche participative. Méthodes: Le développement de la brochure et de la formation a été réalisé en trois étapes : deux pour l'élaboration et tests itératifs d'utilisabilité et acceptabilité et une troisième pour vérifier l'acceptabilité auprès des publics cibles. Nous avons utilisé une approche qualitative par focus group et entretiens individuels cognitifs dont l'analyse repose sur le « nid d'abeille ¼ de Morville et la grille COREQ. Résultats: Le développement itératif et la vérification de l'acceptabilité du matériel nous ont permis, d'une part, de réaliser des ajustements quant au contenu de la formation, en proposant des exemples plus ancrés dans la réalité professionnelle et, d'autre part, de produire une brochure imagée facile à lire et à comprendre, acceptable et adaptée au public ciblé par l'intervention. Conclusions: Cette expérience illustre, de manière concrète, la faisabilité de cette modalité de participation des publics concernés et son intérêt dans le cadre de la recherche interventionnelle et, plus généralement, dans le matériel interventionnel.

The Medicago SymCEP7 hormone increases nodule number via shoots without compromising lateral root number.

Legumes acquire soil nutrients through nitrogen-fixing root nodules and lateral roots. To balance the costs and benefits of nodulation, legumes negatively control root nodule number by autoregulatory and hormonal pathways. How legumes simultaneously coordinate root nodule and lateral root development to procure nutrients remains poorly understood. In Medicago (Medicago truncatula), a subset of mature C-TERMINALLY ENCODED PEPTIDE (CEP) hormones can systemically promote nodule number, but all CEP hormones tested to date negatively regulate lateral root number. Here we showed that Medicago CEP7 produces a mature peptide, SymCEP7, that promotes nodulation from the shoot without compromising lateral root number. Rhizobial inoculation induced CEP7 in the susceptible root nodulation zone in a Nod factor-dependent manner, and, in contrast to other CEP genes, its transcription level was elevated in the ethylene signaling mutant sickle. Using mass spectrometry, fluorescence microscopy and expression analysis, we demonstrated that SymCEP7 activity requires the COMPACT ROOT ARCHITECTURE 2 receptor and activates the shoot-to-root systemic effector, miR2111. Shoot-applied SymCEP7 rapidly promoted nodule number in the pM to nM range at concentrations up to five orders of magnitude lower than effects mediated by root-applied SymCEP7. Shoot-applied SymCEP7 also promoted nodule number in White Clover (Trifolium repens) and Lotus (Lotus japonicus), which suggests that this biological function may be evolutionarily conserved. We propose that SymCEP7 acts in the Medicago shoot to counter balance the autoregulation pathways induced rapidly by rhizobia to enable nodulation without compromising lateral root growth, thus promoting the acquisition of nutrients other than nitrogen to support their growth.

The NIN transcription factor coordinates CEP and CLE signaling peptides that regulate nodulation antagonistically.

Legumes tightly regulate nodule number to balance the cost of supporting symbiotic rhizobia with the benefits of nitrogen fixation. C-terminally Encoded Peptides (CEPs) and CLAVATA3-like (CLE) peptides positively and negatively regulate nodulation, respectively, through independent systemic pathways, but how these regulations are coordinated remains unknown. Here, we show that rhizobia, Nod Factors, and cytokinins induce a symbiosis-specific CEP gene, MtCEP7, which positively regulates rhizobial infection. Via grafting and split root studies, we reveal that MtCEP7 increases nodule number systemically through the MtCRA2 receptor. MtCEP7 and MtCLE13 expression in rhizobia-inoculated roots rely on the MtCRE1 cytokinin receptor and on the MtNIN transcription factor. MtNIN binds and transactivates MtCEP7 and MtCLE13, and a NIN Binding Site (NBS) identified within the proximal MtCEP7 promoter is required for its symbiotic activation. Overall, these results demonstrate that a cytokinin-MtCRE1-MtNIN regulatory module coordinates the expression of two antagonistic, symbiosis-related, peptide hormones from different families to fine-tune nodule number.

Transcriptional and post-transcriptional regulation of a NAC1 transcription factor in Medicago truncatula roots.

• Legume roots develop two types of lateral organs, lateral roots and nodules. Nodules develop as a result of a symbiotic interaction with rhizobia and provide a niche for the bacteria to fix atmospheric nitrogen for the plant. • The Arabidopsis NAC1 transcription factor is involved in lateral root formation, and is regulated post-transcriptionally by miRNA164 and by SINAT5-dependent ubiquitination. We analyzed in Medicago truncatula the role of the closest NAC1 homolog in lateral root formation and in nodulation. • MtNAC1 shows a different expression pattern in response to auxin than its Arabidopsis homolog and no changes in lateral root number or nodulation were observed in plants affected in MtNAC1 expression. In addition, no interaction was found with SINA E3 ligases, suggesting that post-translational regulation of MtNAC1 does not occur in M. truncatula. Similar to what was found in Arabidopsis, a conserved miR164 target site was retrieved in MtNAC1, which reduced protein accumulation of a GFP-miR164 sensor. Furthermore, miR164 and MtNAC1 show an overlapping expression pattern in symbiotic nodules, and overexpression of this miRNA led to a reduction in nodule number. • This work suggests that regulatory pathways controlling a conserved transcription factor are complex and divergent between M. truncatula and Arabidopsis.