Biology subjects

Jardinaud, M.-F.

Publications and source records attributed to Jardinaud, M.-F..

7 recordsLinked to original sources

bioRxiv2025

Artificial symbiont replacement in a vertically-transmitted plant-bacterium association provides insights into the basis for specificity

Some plants engage in permanent, vertically transmitted symbioses with bacteria. Often, these bacteria are hosted extracellularly in specific structures on the leaves, where they produce specialized bioactive metabolites that benefit their host. These associations are highly specific, with one plant species associating with a single bacterial species, but little is known about how these symbioses originate and how specificity is maintained. In this study, we show that the symbiotic association between a wild yam and a bacterium can be manipulated experimentally, and that bacteria-free plants are open to colonization by environmental bacteria. Through metabolic profiling, we show that the endophytic niche is rich in organic acids and intermediates of the TCA cycle. Environmental bacteria capable of utilizing these acids, such as the soil bacterium Pseudomonas putida, readily colonize aposymbiotic plants. However, successful colonization is contingent upon the absence of the vertically-transmitted symbiont and an active type VI secretion system. Unexpectedly for a vertically-transmitted symbiosis, these findings suggest that microbe-microbe interactions, including antagonism, may play a crucial role in maintaining the specificity of an association. However, low transmission rates of synthetic symbionts provide evidence that transmission barriers or bottlenecks may still occur, further enforcing partner fidelity. Together, these results highlight the complexity of mechanisms underlying mutualistic associations, and provide insights into the evolution of bacterial leaf symbiosis.

microbiology↗

bioRxiv2024

Comparative transcriptomics reveal a highly polymorphic Xanthomonas HrpG virulence regulon

Bacteria of the genus Xanthomonas cause economically significant diseases in various crops. Their virulence is dependent on the translocation of type III effectors (T3Es) into plant cells by the type III secretion system (T3SS), a process regulated by the master response regulator HrpG. Although HrpG has been studied for over two decades, its regulon across diverse Xanthomonas species, particularly beyond type III secretion, remains understudied. In this study, we conducted transcriptome sequencing to explore the HrpG regulons of 17 Xanthomonas strains, encompassing six species and nine pathovars, each exhibiting distinct host and tissue specificities. We employed constitutive expression of plasmid-borne hrpG*, which encodes a constitutively active form of HrpG, to induce the regulon. Our findings reveal substantial inter- and intra-specific diversity in the HrpG* regulons across the strains. Besides 21 genes directly involved in the biosynthesis of the T3SS, the core HrpG* regulon is limited to only five additional genes encoding the transcriptional activator HrpX, the two T3E proteins XopR and XopL, a major facility superfamily (MFS) transporter, and the phosphatase PhoC. Interestingly, genes involved in chemotaxis and genes encoding enzymes with carbohydrate-active and proteolytic activities are variably regulated by HrpG*. The diversity in the HrpG* regulon suggests that HrpG-dependent virulence in Xanthomonas might be achieved through several distinct strain-specific strategies, potentially reflecting adaptation to diverse ecological niches. These findings enhance our understanding of the complex role of HrpG in regulating various virulence and adaptive pathways, extending beyond T3Es and the T3SS. IMPORTANCEIn the decades since its discovery, HrpG and its role in the regulation of the type III secretion system (T3SS) and its associated type III effectors (T3Es) in Xanthomonas has been the subject of extensive research. Despite notable progress in understanding its molecular regulatory mechanisms, the full spectrum of processes under control of HrpG, particularly beyond the T3SS and T3Es, and the degree of regulatory conservation across plant-pathogenic Xanthomonas species, remained unclear. To address this knowledge gap, we systematically compared the transcriptomes of 17 Xanthomonas strains, expressing a constitutively active form of HrpG, called HrpG*. We showed that HrpG* regulates different physiological processes other than the T3SS and T3Es and that this regulation shows substantial variation across the different strains. Taken together, our results provide new insights into Xanthomonas-plant interactions through the regulation of different metabolic and virulence pathways by the master response regulator HrpG.

microbiology↗

bioRxiv2023

The association between Dioscorea sansibarensis and Orrella dioscoreae as a model for hereditary leaf symbiosis

Hereditary, or vertically-transmitted, symbioses affect a large number of animal species and some plants. The precise mechanisms underlying transmission of functions of these associations are often difficult to describe, due to the difficulty in separating the symbiotic partners. This is especially the case for plant-bacteria hereditary symbioses, which lack experimentally tractable model systems. Here, we demonstrate the potential of the leaf symbiosis between the wild yam Dioscorea sansibarensis and the bacterium Orrella dioscoreae (O. dioscoreae) as a model system for hereditary symbiosis. O. dioscoreae is easy to grow and genetically manipulate, which is unusual for hereditary symbionts. These properties allowed us to design an effective antimicrobial treatment to rid plants of bacteria and generate whole aposymbiotic plants, which can later be re-inoculated with bacterial cultures. Aposymbiotic plants did not differ morphologically from symbiotic plants and the leaf forerunner tip containing the symbiotic glands formed normally even in the absence of bacteria, but microscopic differences between symbiotic and aposymbiotic glands highlight the influence of bacteria on the development of trichomes and secretion of mucilage. This is to our knowledge the first leaf symbiosis where both host and symbiont can be grown separately and where the symbiont can be genetically altered and reintroduced to the host.

plant biology↗

bioRxiv2022

Arabidopsis hydathodes are sites of intense auxin metabolism and nutrient scavenging

Hydathodes are small organs located on the leaf margins of all vascular plants. They release excess xylem sap through guttation when stomata are closed or when the humidity level is high. Many promoter analyses have suggested other hydathode functions in metabolite transport and auxin metabolism, but experimental demonstration is still lacking. Here, we compared the transcriptomic and metabolomic features of mature Arabidopsis hydathodes to the leaf blade. 1460 differentially-expressed genes were identified revealing that genes related to auxin metabolism, transport, stress, DNA, plant cell wall, RNA or wax were on average more expressed in hydathodes. On the other hand, genes involved in glucosinolate metabolism, sulfation pathway, metal handling or photosynthesis were downregulated in hydathodes. In hydathodes, there are an increased expression of auxin transcriptional regulators and biosynthetic genes, a lower expression of auxin transport genes and a differential expression of genes related to its vacuolar storage that is consistent with increased contents of free and conjugated auxin. We also found that ca. 78% of the total content of 52 xylem sap metabolites were removed from guttation fluid at the hydathode level. Using reverse genetics, we showed that the capture of nitrate and phosphate in the guttation fluid relies on the NRT2.1 and PHT1;4 transporters, respectively. Thus, hydathodes absorb a significant part of xylem sap nutrients, limiting the loss of valuable chemicals during guttation. Our transcriptomic and metabolomic analyses reveal an organ with its own transcriptomic and physiological identity and highlight hydathode biological processes that may impact the whole plant. One sentence summaryTranscriptome and physiological analysis of mature and healthy hydathodes of Arabidopsis demonstrates that those organs are sites of intense auxin metabolism and nutrient scavenging

plant biology↗

bioRxiv2022

Genome-wide identification of fitness determinants in the Xanthomonas campestris bacterial pathogen during early stages of plant infection

Plant diseases are an important threat to food production. While major pathogenicity determinants required for disease have been extensively studied, less is known on how pathogens thrive during host colonization especially at early infection stages. Here, we used randomly barcoded-transposon insertion site sequencing (RB-TnSeq) to perform a genome-wide screen and identify key bacterial fitness determinants of the vascular pathogen Xanthomonas campestris pv. campestris (Xcc) during infection of the cauliflower host plant (Brassica oleracea). This high-throughput analysis was conducted in hydathodes, the natural entry site of Xcc, in xylem sap and in synthetic media. Xcc did not face a strong bottleneck during hydathode infection. 183 genes important for fitness were identified in plant-associated environments with functional enrichment in genes involved in metabolism when only few genes known to be involved in virulence were found to be affected. The biological relevance of 13 genes was independently confirmed by phenotyping single mutants. Notably, we show that the XC_3388, a protein with no known function (DUF1631), plays a key role in the adaptation and virulence of Xcc possibly through c-di-GMP-mediated regulation. This study thus revealed yet unsuspected social behaviors adopted by Xcc individuals when confined inside hydathodes at early infection stages.

microbiology↗

bioRxiv2021

Autoregulation dependent and independent mechanisms are responsible for the systemic control of nodule formation by the plant N demand

In legumes interacting with rhizobia the formation of symbiotic organs responsible for the acquisition of atmospheric nitrogen is depending of the plant nitrogen (N) demand. We discriminated between local and systemic impact of nitrogen on nodule formation using Medicago truncatula plants cultivated in split-root systems. We obtained evidence of the control of nodule formation by whole plant systemic N-satisfaction signaling but obtained little evidence of a local control by mineral nitrogen. We characterized the impact of systemic N signaling on the root transcriptome reprogramming associated to nodule formation. We identified, large genes clusters displaying common expression profiles in response to systemic N signaling enriched in particular fonctions required during these biological processes. We found evidence of a strong effect of SUNN in the control by systemic N signaling of many genes involved in the early interaction with rhizobium as well as organogenesis supporting a role of autoregulation pathway in systemic N signaling. However, we also found evidence that major SUNN independent systemic N signaling controls were maintained in the mutant. This study shed light on the unexpected high complexity of the control of nodule formation by systemic N signaling, that probably involves multiple pathways.

plant biology↗

bioRxiv2021

Xanthomonas transcriptome inside cauliflower hydathodes reveals bacterial virulencestrategies and physiological adaptation at early infection stages

Xanthomonas campestris pv. campestris (Xcc) bacterium is a seed-transmitted vascular pathogen causing black rot disease on cultivated and wild Brassicaceae. Xcc enters the plant tissues preferentially via hydathodes which are organs localized at leaf margins. In order to decipher both physiological and virulence strategies deployed by Xcc during early stages of infection, the transcriptomic profile of Xcc was analyzed three days after entry into cauliflower hydathodes. Despite the absence of visible plant tissue alterations and a bacterial biotrophic lifestyle, 18% of Xcc genes undergo a transcriptional reprogramming, including a striking repression of chemotaxis and motility functions. Xcc full repertoire of virulence factors was not yet activated but the expression of the 95-gene HrpG regulon, including genes coding for the type three secretion machinery important for suppression of plant immunity, was induced. The expression of genes involved in metabolic adaptations such as catabolism of plant compounds, transport functions, sulfur and phosphate metabolism was upregulated while limited stress responses were observed three days post infection. These transcriptomic observations give information about the nutritional and stress status of bacteria during the early biotrophic infection stages and help to decipher the adaptive strategy of Xcc to the hydathode environment.

microbiology↗