Metabolomics, biomass and lignocellulosic total sugars analysis in foxtail millet (Setaria italica) inoculated with different combinations of plant growth promoting bacteria and mycorrhiza

Abstract

Foxtail millet (Setaria italica) is the second most widely produced millet with potential as a biofuel source. Employment of plant growth promoting bacteria (PGPB) and mycorrhiza could serve as environment-friendly alternatives for the use of excessive NPK fertilizers and producing biofuel. The highest increase of biomass was associated with endomycorrhiza combined with PGPB in comparison to control. Nuclear magnetic resonance (NMR) analysis detected 28 metabolites in foxtail shoot with most of them upregulated in ecto/endomycorrhiza group and combined with PGPB. The upregulation of metabolites associated with synthesis of amino acids correlated positively with biomass. The inoculation with both PGPB and endomycorrhiza gave the best results with reference to total sugar yield. Our study indicates that PGPB and endomycorrhiza combination is well suited for enhancing biomass and boosting sugar yield, which are useful attributes for utilizing foxtail millet as a biofuel source. Highlighted Conclusions1. Effect of PGPB and mycorrhiza on foxtail millet biomass, metabolites and total sugars was studied. 2. Biomass and total sugars increased by combined PGPB and endomycorrhiza treatment. 3. Higher biomass correlated positively with metabolites associated with amino acid biosynthesis.Foxtail millet (Setaria italica) is a diploid C4 grass with a relatively small genome (~515 Mb) (Li and Brutnell 2011). Foxtail millet is an annual grass that is widely used for both food and livestock feed and grown in arid and semi-arid regions of the world (Pandey et al. 2017). Being a close relative of an important biofuel crop switchgrass, it is also a potential biofuel source. The early maturity of foxtail in 60-70 days makes it a good model for experimental studies. Several recent studies have explored the molecular responses of foxtail millet under abiotic stress. Colonization of arbuscular mycorrhizal (AM) fungus Glomus mosseae and its effect on phosphate transport was reported previously, where a significant increase in the expression of plant phosphate transporters belonging to PHT1 family in low phosphate environment was reported in the presence of AM fungi (Ceasar et al. 2014). PHT1 transporter gene family of foxtail millet consists of 12 members with varying levels of expression depending on the availability of phosphate and AM colonization, which helps in enhancing phosphate availability.The plant growth promoting bacteria used in this study was isolated from Torch Lake sediments rich in copper deposits and was shown to enhance maize growth and metal uptake (Li and Ramakrishna 2011). Previously, we reported higher biomass and element uptake in sorghum and maize and upregulation of stress tolerance associated proteins in sorghum as a result of root colonization of PGPB and AM fungi (Dhawi et al. 2015(Dhawi et al. , 2016

Plant Growth Promoting Rhizobacteria (PGPR) Regulated Phyto and Microbial Beneficial Protein Interactions

“…The successful use of Plant-Growth-Promoting Rhizobacteria (PGPR) in agriculture is correlated with reciprocal gene regulation between bacteria and plants during plant colonization. This gene regulation exerts phytobeneficial results on biomass, nutrient uptake and metabolite upregulation [1][2][3][4][5] on proteins and biological pathways [6], as well as on gene expression [7]. In the current study, the PGPR-Pseudomonas sp.…”

“…Roots were washed with distilled water to remove soil then frozen in liquid nitrogen. Protein was extracted from frozen roots; three samples for each group followed the procedure described in Dhawi et al [6] and modified from Fukao et al [8].…”

What Did We Learn From Plant Growth-Promoting Rhizobacteria (PGPR)-Grass Associations Studies Through Proteomic and Metabolomic Approaches?

“…The same was determined for plants inoculated with the ectomycorrhizal consortium, composed by Rhizopogon villosullus, R. luteolus, R. amylogpogon, R. fulvigleba, Pisolithus tinctorius, Scleroderma cepa, and S. citrinum. In inoculated plants, the fructose and glucose concentrations were decreased, having a negative or no correlation with the S. italica biomass amount, while gallate, gluconate, and malate increased positively correlated with plant height and chlorophyll amount (Dhawi et al, 2018).…”

“…Both proteomics and metabolomics employ the previous extraction with solvents to obtain the analytes, which will be identified and quantified by mass spectrometers. Metabolomic studies also can use Nuclear Magnetic Resonance (NMR) spectroscopy, as in the study of the interaction between plant growth-promoting bacteria and mycorrhiza with Setaria italica, a livestock grass and a potential source of carbon for biofuel production as well (Dhawi et al, 2018). In this study, the endomycorrhizal consortium alone, composed by Glomus intraradices, G. mosseae, G. aggregatum, and G. etunicatum, or combined with the PGPR Pseudomonas TLC6-6-5.4, showed a positive effect on biomass, plant height and chlorophyll content compared to non-inoculated plants.…”

“…Except for the metabolomic analysis performed with HPLC in the work of Mishra et al (2006) and with NMR by Dhawi et al (2018), the other metabolomic studies employed LC-MS or GC-MS. Agtuca et al (2020) studied the metabolome of Setaria viridis roots colonized by Herbaspirillum seropedicae SmR1 (Fix + ) and the SmR54 mutant (Fix − ) using laser-ablation electrospray ionization (LAESI) (Agtuca et al, 2020). LAESI employs a midinfrared to ablate material from a sample surface, and then, the ablated material is ionized by an electrospray source (Etalo et al, 2018).…”