Metabolic profiling of two maize (Zea mays L.) inbred lines inoculated with the nitrogen fixing plant-interacting bacteria Herbaspirillum seropedicae and Azospirillum brasilense

Abstract

Maize roots can be colonized by free-living atmospheric nitrogen (N2)-fixing bacteria (diazotrophs). However, the agronomic potential of non-symbiotic N2-fixation in such an economically important species as maize, has still not been fully exploited. A preliminary approach to improve our understanding of the mechanisms controlling the establishment of such N2-fixing associations has been developed, using two maize inbred lines exhibiting different physiological characteristics. The bacterial-plant interaction has been characterized by means of a metabolomic approach. Two established model strains of Nif+ diazotrophic bacteria, Herbaspirillum seropedicae and Azospirillum brasilense and their Nif- couterparts defficient in nitrogenase activity, were used to evaluate the impact of the bacterial inoculation and of N2 fixation on the root and leaf metabolic profiles. The two N2-fixing bacteria have been used to inoculate two genetically distant maize lines (FV252 and FV2), already characterized for their contrasting physiological properties. Using a well-controlled gnotobiotic experimental system that allows inoculation of maize plants with the two diazotrophs in a N-free medium, we demonstrated that both maize lines were efficiently colonized by the two bacterial species. We also showed that in the early stages of plant development, both bacterial strains were able to reduce acetylene, suggesting that they contain functional nitrogenase activity and are able to efficiently fix atmospheric N2 (Fix+). The metabolomic approach allowed the identification of metabolites in the two maize lines that were representative of the N2 fixing plant-bacterial interaction, these included mannitol and to a lesser extend trehalose and isocitrate. Whilst other metabolites such as asparagine, although only exhibiting a small increase in maize roots following bacterial infection, were specific for the two Fix+ bacterial strains, in comparison to their Fix- counterparts. Moreover, a number of metabolites exhibited a maize-genotype specific pattern of accumulation, suggesting that the highly diverse maize genetic resources could be further exploited in terms of beneficial plant-bacterial interactions for optimizing maize growth, with reduced N fertilization inputs.

Agricultural practices to improve nitrogen use efficiency through the use of arbuscular mycorrhizae: Basic and agronomic aspects

“…This research should be carried out before glasshouse or field studies using natural soils, when interaction with the microbiome 9 and the neighboring plants are much more complex. Such investigations could be first conducted using microcosms [34] and well-controlled gnotobiotic systems similar to those recently developed for non-symbiotic N2-fixing associations [35], (Figure 1). These two experimental systems could then be adapted to study the interaction between a mixture of several plant species and multiple fungal partners both at the molecular and physiological levels, thus gradually increasing the complexity of the plant/AMF symbiotic association.…”

“…Therefore, the type of N fertilization is an important factor that controls both AMF colonization and biological activity in terms of N uptake efficiency [34]. Using the controlled experimental systems described in Figure 1 [34,35], it will be interesting, to study the physiological and regulatory mechanisms that control N uptake by the fungi and its transfer to the host plant when the mineral N is low, or when there are high concentrations of amino acids or carbohydrates present in the growth medium.…”

“…Studies need to be first conducted in an appropriate microcosm and well-controlled experimental systems involving one fungal species and one plant partner, such as those presented in section 2 (Fig. 1), [34,35] using increasing N concentrations in order to understand the mechanisms of C/N exchange in AMF [100]. Using such a kind of experimental systems, it will be possible to assess the benefit of a given plant/fungal symbiotic association and then to select and study the best ones by means of holistic, physiological and systems biology approaches including modeling studies [99].…”

Evaluating maize phenotypic variance, heritability, and yield relationships at multiple biological scales across agronomically relevant environments

“…There have been some analyses that explore a maize plant's response to specific environmental conditions such as salinity, heat, and drought (Sun, Li, et al, 2016b;Witt et al, 2012), nitrogen (Amiour et al, 2012;Brusamarello-Santos et al, 2017;Simons et al, 2014) and low phosphorus (Ganie et al, 2015) by monitoring the relationships of these environmental factors to those of metabolites and transcripts. Further examinations have begun to characterize the breadth of diversity of various inbreds and hybrids across typical agronomic environments particularly emphasizing these effectors on grain and forage composition (Asiago, Hazebroek, Harp, & Zhong, 2012;Baniasadi, Vlahakis, Hazebroek, Zhong, & Asiago, 2014;Benevenuto et al, 2017;Hall et al, 2016;Tang et al, 2017;Venkatesh et al, 2016).…”

Metabolite profiling and genome‐wide association studies reveal response mechanisms of phosphorus deficiency in maize seedling

“…The comprehensive high‐throughput analysis technologies, such as ultra‐high performance liquid chromatography–quadrupole time‐of‐flight mass spectrometry (UPLC‐QTOF‐MS) and gas chromatography–mass spectrometry (GC‐MS), allow us to accurately measure vast metabolite profiles (the metabolome), which in turn facilitates the study of complex trait regulation via the ‘gene–metabolism–phenotype’ research model. In the case of Zea mays (maize), metabolomics has been used for the characterization of responses to abiotic stress and inoculation with nitrogen‐fixing plant‐interacting bacteria (Ganie et al ., ; Obata et al ., ; Brusamarello‐Santos et al ., ), the association of leaf physiology with kernel yield, the complex metabolism of the maize kernel (Wen et al ., , ; Cañas et al ., ) and the mechanism for the induction of genotype‐dependent embryonic callus (Ge et al ., ). Additionally, previous studies on the metabolic variations under low‐Pi conditions have been conducted in Arabidopsis and white lupin (Müller et al ., ; Pant et al ., ).…”