The rhizosheath: from desert plants adaptation to crop breeding

International audienceBackground : First discovered on desert plants by Volkens 1887, rhizosheath formation, i.e. soil aggregation at the root surface, is now considered as a very promising adaptive trait to deal with abiotic stress. Indeed, the rhizosheath could help plants better cope with water stress, nitrogen and phosphorus deficiencies, and soil acidity.Scope : We have reviewed studies on the biological factors involved in rhizosheath formation, the methods used to quantify it, and its importance in plant nutrition. Thus, we have collected recent evidence that shows that the rhizosheath is an important trait arising from the morphology and physiology of plant root system, and the cooperation between plant root and its associated microbiota. In particular, the transformation of root exudates by exopolysaccharide-producing bacteria effectively contributes to soil aggregation and thus to increases the volume of the rhizosheath (i.e. root-adhering soil), thereby improving the absorption of minerals and water by plants. The growing interest for this process has led to the genetic mapping of potential plant QTLs controlling this trait in order to provide new tools for the selection of plant varieties with improved tolerance to abiotic stresses.Conclusion : Finally, we discussed some important issues that need to be addressed in order to develop an appropriate selection strategy focused on the rhizosheath, such as the relationship between the genes controlling rhizosheath formation and those controlling other root traits, but also the impact of rhizosheath formation on soil carbon sequestration, a potential strategy for mitigating climate change

Rhizodeposition efficiency of pearl millet genotypes assessed on a short growing period by carbon isotopes (<i>δ</i>¹³C and F¹⁴C)

International audienceRhizosheath size varies significantly with crop genotype, and root exudation is one among its driving factors. Unravelling the relationships between rhizosheath formation, root exudation and soil carbon dynamics may bring interesting perspectives in terms of crop breeding towards sustainable agriculture. Here we grew four pearl millet (C 4 plant type: δ 13 C of −12.8 ‰, F 14 C = 1.012) inbred lines showing contrasting rhizosheath sizes in a C 3 soil type (organic matter with δ 13 C of −22.3 ‰, F 14 C = 1.045). We sampled the root-adhering soil (RAS) and bulk soil after 28 d of growth under a semi-controlled condition. The soil organic carbon (SOC) content and δ 13 C and F 14 C of soil samples were measured and the plant-derived C amount and C lost / C new ratio in the RAS were calculated. The results showed a significant increase in δ 13 C in the RAS of the four pearl millet lines compared to the control soil, suggesting that this approach was able to detect plant C input into the soil at an early stage of pearl millet growth. The concentration of plant-derived C in the RAS did not vary significantly between pearl millet lines, but the absolute amount of plant-derived C varied significantly when we considered the RAS mass of these different lines. Using a conceptual model and data from the two carbon isotopes' measurements, we evidenced a priming effect for all pearl millet lines. Importantly, the priming effect amplitude (C lost / C new ratio) was higher for the small rhizosheath (low-aggregation) line than for the large rhizosheath (high-aggregation) ones, indicating a better C sequestration potential of the latter

Microbial catabolic activity: methods, pertinence, and potential interest for improving microbial inoculant efficiency

Microbial catabolic activity (MCA) defined as the degrading activity of microorganisms toward various organic compounds for their growth and energy is commonly used to assess soil microbial function potential. For its measure, several methods are available including multi-substrate-induced respiration (MSIR) measurement which allow to estimate functional diversity using selected carbon substrates targeting specific biochemical pathways. In this review, the techniques used to measure soil MCA are described and compared with respect to their accuracy and practical use. Particularly the efficiency of MSIR-based approaches as soil microbial function indicators was discussed by (i) showing their sensitivity to different agricultural practices including tillage, amendments, and cropping systems and (ii) by investigating their relationship with soil enzyme activities and some soil chemical properties (pH, soil organic carbon, cation exchange capacity). We highlighted the potential of these MSIR-based MCA measurements to improve microbial inoculant composition and to determine their potential effects on soil microbial functions. Finally, we have proposed ideas for improving MCA measurement notably through the use of molecular tools and stable isotope probing which can be combined with classic MSIR methods

Correlation between holobiont metabolomics and the interaction network of the pearl millet rhizosphere microbiota

Pearl millet is a cereal crop that is given a little attention by researchers despite its tremendous capabilities with respect to its pears (wheat, barley, ...). This plant cultivated in arid and semi-arid areas in Western Africa and Sahel resisting low rainfall and poor soil conditions is the main food and cheapest nutritive source for people living out there. When speaking about such stresses, we are directly involving the root traits (growth and exudation) that are responsible for water uptake and nutrient acquisition and their interaction with soil and inhabiting microbiota.As part of an ANR project*, 188 pearl millet inbred lines were selected based on the amount of root exudates produced and the architecture of the roots. Four different pearl millet lines with contrasting properties in term of root growth and exudation have been selected to decipherer the metabolic interactions and reveal the structure-function of root associated microbiota. The four selected inbred lines were grown whether in a hydroponic system or in soil in Bambey (Senegal). The metabolites were extracted from roots, shoots and rootadhering soil (RAS) for plants grown in Bambey soil (Senegal), and from roots, shoots and growth solution for plants grown under hydroponic conditions. The extracted metabolites were analyzed by the Fourier transform ion cyclotron resonance mass spectrophotometer (FTICR-MS). In parallel, RNA was extracted from bulk soil, RAS and from roots for 16S and ITS metabarcoding and metatranscriptomic analysis. Identification of the microbial populations most influenced by changes in pearl millet exudation and the correlation between these populations and specific metabolic pathways and compounds from roots, shoots and root exudates will be discussed

Correlation between holobiont metabolomics and the interaction network of the pearl millet rhizosphere microbiota

Pearl millet is a cereal crop that is given a little attention by researchers despite its tremendous capabilities with respect to its pears (wheat, barley, ...). This plant cultivated in arid and semi-arid areas in Western Africa and Sahel resisting low rainfall and poor soil conditions is the main food and cheapest nutritive source for people living out there. When speaking about such stresses, we are directly involving the root traits (growth and exudation) that are responsible for water uptake and nutrient acquisition and their interaction with soil and inhabiting microbiota.As part of an ANR project*, 188 pearl millet inbred lines were selected based on the amount of root exudates produced and the architecture of the roots. Four different pearl millet lines with contrasting properties in term of root growth and exudation have been selected to decipherer the metabolic interactions and reveal the structure-function of root associated microbiota. The four selected inbred lines were grown whether in a hydroponic system or in soil in Bambey (Senegal). The metabolites were extracted from roots, shoots and rootadhering soil (RAS) for plants grown in Bambey soil (Senegal), and from roots, shoots and growth solution for plants grown under hydroponic conditions. The extracted metabolites were analyzed by the Fourier transform ion cyclotron resonance mass spectrophotometer (FTICR-MS). In parallel, RNA was extracted from bulk soil, RAS and from roots for 16S and ITS metabarcoding and metatranscriptomic analysis. Identification of the microbial populations most influenced by changes in pearl millet exudation and the correlation between these populations and specific metabolic pathways and compounds from roots, shoots and root exudates will be discussed

Coorrelation between holobiont metabolomics and the pearl millet root-associated-microbiota

Plants and their associated microbiota have long interacted, forming an assemblage of species oftenreferred to as a holobiont. Microbiomes can greatly expand the genomic and metabolic capabilities oftheir plant hosts, providing or facilitating a range of essential life-supporting functions, including nutri-ent acquisition, immune modulation, growth promotion, biocontrol, and abiotic stress tolerance. Theseinteractions are mainly driven by root exudates, whose composition reflects contradictory attractive andrepulsive behaviors, as they are highly diverse and contain nutritional, antimicrobial and signaling mol-ecules. We characterized the assemblages and ecological network microbial populations most influenced bychanges in root exudation of four pearl millet inbred lines with contrasting rhizosphere aggregation pat-terns and the correlation of these populations with specific metabolic pathways and compounds fromroots, shoots, and root exudates. We provide plausible evidence for the importance of heritable plant traits carried by the inbred lines inmodulating plant-associated microbiomes by establishing diverse metabolic profiles in their tissue androot exudates and the strong correlation of these two interconnected aspects manifested by co-inertiaanalysis. Root exudates composition is revealed to be a major component of root-associated microbiome modu-lation of the pearl millet lines in correlation with their soil aggregation capacities

Correlation between holobiont metabolomics and the interaction network of the pearl millet rhizosphere microbiota

Pearl millet is a cereal crop that is given a little attention by researchers despite its tremendous capabilities with respect to its pears (wheat, barley, ...). This plant cultivated in arid and semi-arid areas in Western Africa and Sahel resisting low rainfall and poor soil conditions is the main food and cheapest nutritive source for people living out there. When speaking about such stresses, we are directly involving the root traits (growth and exudation) that are responsible for water uptake and nutrient acquisition and their interaction with soil and inhabiting microbiota.As part of an ANR project*, 188 pearl millet inbred lines were selected based on the amount of root exudates produced and the architecture of the roots. Four different pearl millet lines with contrasting properties in term of root growth and exudation have been selected to decipherer the metabolic interactions and reveal the structure-function of root associated microbiota. The four selected inbred lines were grown whether in a hydroponic system or in soil in Bambey (Senegal). The metabolites were extracted from roots, shoots and rootadhering soil (RAS) for plants grown in Bambey soil (Senegal), and from roots, shoots and growth solution for plants grown under hydroponic conditions. The extracted metabolites were analyzed by the Fourier transform ion cyclotron resonance mass spectrophotometer (FTICR-MS). In parallel, RNA was extracted from bulk soil, RAS and from roots for 16S and ITS metabarcoding and metatranscriptomic analysis. Identification of the microbial populations most influenced by changes in pearl millet exudation and the correlation between these populations and specific metabolic pathways and compounds from roots, shoots and root exudates will be discussed

Coorrelation between holobiont metabolomics and the pearl millet root-associated-microbiota

Plants and their associated microbiota have long interacted, forming an assemblage of species oftenreferred to as a holobiont. Microbiomes can greatly expand the genomic and metabolic capabilities oftheir plant hosts, providing or facilitating a range of essential life-supporting functions, including nutri-ent acquisition, immune modulation, growth promotion, biocontrol, and abiotic stress tolerance. Theseinteractions are mainly driven by root exudates, whose composition reflects contradictory attractive andrepulsive behaviors, as they are highly diverse and contain nutritional, antimicrobial and signaling mol-ecules. We characterized the assemblages and ecological network microbial populations most influenced bychanges in root exudation of four pearl millet inbred lines with contrasting rhizosphere aggregation pat-terns and the correlation of these populations with specific metabolic pathways and compounds fromroots, shoots, and root exudates. We provide plausible evidence for the importance of heritable plant traits carried by the inbred lines inmodulating plant-associated microbiomes by establishing diverse metabolic profiles in their tissue androot exudates and the strong correlation of these two interconnected aspects manifested by co-inertiaanalysis. Root exudates composition is revealed to be a major component of root-associated microbiome modu-lation of the pearl millet lines in correlation with their soil aggregation capacities

Coorrelation between holobiont metabolomics and the pearl millet root-associated-microbiota

Plants and their associated microbiota have long interacted, forming an assemblage of species oftenreferred to as a holobiont. Microbiomes can greatly expand the genomic and metabolic capabilities oftheir plant hosts, providing or facilitating a range of essential life-supporting functions, including nutri-ent acquisition, immune modulation, growth promotion, biocontrol, and abiotic stress tolerance. Theseinteractions are mainly driven by root exudates, whose composition reflects contradictory attractive andrepulsive behaviors, as they are highly diverse and contain nutritional, antimicrobial and signaling mol-ecules. We characterized the assemblages and ecological network microbial populations most influenced bychanges in root exudation of four pearl millet inbred lines with contrasting rhizosphere aggregation pat-terns and the correlation of these populations with specific metabolic pathways and compounds fromroots, shoots, and root exudates. We provide plausible evidence for the importance of heritable plant traits carried by the inbred lines inmodulating plant-associated microbiomes by establishing diverse metabolic profiles in their tissue androot exudates and the strong correlation of these two interconnected aspects manifested by co-inertiaanalysis. Root exudates composition is revealed to be a major component of root-associated microbiome modu-lation of the pearl millet lines in correlation with their soil aggregation capacities

Coorrelation between holobiont metabolomics and the pearl millet root-associated-microbiota

Plants and their associated microbiota have long interacted, forming an assemblage of species oftenreferred to as a holobiont. Microbiomes can greatly expand the genomic and metabolic capabilities oftheir plant hosts, providing or facilitating a range of essential life-supporting functions, including nutri-ent acquisition, immune modulation, growth promotion, biocontrol, and abiotic stress tolerance. Theseinteractions are mainly driven by root exudates, whose composition reflects contradictory attractive andrepulsive behaviors, as they are highly diverse and contain nutritional, antimicrobial and signaling mol-ecules. We characterized the assemblages and ecological network microbial populations most influenced bychanges in root exudation of four pearl millet inbred lines with contrasting rhizosphere aggregation pat-terns and the correlation of these populations with specific metabolic pathways and compounds fromroots, shoots, and root exudates. We provide plausible evidence for the importance of heritable plant traits carried by the inbred lines inmodulating plant-associated microbiomes by establishing diverse metabolic profiles in their tissue androot exudates and the strong correlation of these two interconnected aspects manifested by co-inertiaanalysis. Root exudates composition is revealed to be a major component of root-associated microbiome modu-lation of the pearl millet lines in correlation with their soil aggregation capacities