A Genetic and Metabolomic Perspective on the Production of Indole-3-Acetic Acid by Pantoea agglomerans and Use of Their Metabolites as Biostimulants in Plant Nurseries

Abstract

Pantoea-Based Biostimulants and 1,080 plantlets of Corylus avellana L. showed that metabolites from strain C1 improved percentage of rooted-explant, number of adventitious root formation, plant survival, and quality of plant as vigor, with an increase in the leaf area between 17.5 and 42.7% compared to IBA-K (indole-3-butyric acid potassium salt)-treated plants.

Metabolites Secreted by a Plant-Growth-Promoting Pantoea agglomerans Strain Improved Rooting of Pyrus communis L. cv Dar Gazi Cuttings

“…In previous work, we demonstrated that the production of IAA and IAA-related compounds by P. agglomerans strain C1 is tryptophan dependent and is affected by several parameters, including the medium composition, the carbon source, the physiological state of the cells, and the induction timing ( Luziatelli et al, 2020b ). Usually, standard experiments with PGP bacteria are designed to obtain the maximum auxin production, and to avoid inhibitory effects on the plant growth, culture filtrates containing a higher IAA equ titer are extensively diluted before use as plant biostimulants.…”

“…Usually, standard experiments with PGP bacteria are designed to obtain the maximum auxin production, and to avoid inhibitory effects on the plant growth, culture filtrates containing a higher IAA equ titer are extensively diluted before use as plant biostimulants. Although, in general, bacterial strains exhibiting higher volumetric productivity of a specific metabolite are preferred for large-scale production, in this context, extensive dilution of the culture filtrate can be detrimental to evaluating the synergistic effects that metabolites secreted by IAA/auxin-producing bacteria can have on transport and turnover of exogenous and endogenous auxin in plants ( Luziatelli et al, 2020b ). In this study, we demonstrated that the auxin production by P. agglomerans strain C1 can be modulated (until one-third of the maximum) by lowering the growth temperature and the aeration of the liquid culture.…”

“…A growing body of research demonstrated that cells and metabolites from plant-growth-promoting (PGP) bacteria and fungi can be successfully used as biostimulants to promote plant growth, enhancing nutrient uptake and photosynthetic activity, as well as to increase crop quality and plant resistance to both biotic and abiotic stresses ( Wu and Zou, 2009 ; Glick, 2014 ; Ruzzi and Aroca, 2015 ; Colla et al, 2017 ; Rouphael and Colla, 2018 ; Woo and Pepe, 2018 ). Due to the increasing demand of high-quality planting materials through agamic propagation and, in particular, tissue culture techniques ( Twaij et al, 2020 ), there is rising interest in the use of microbial and nonmicrobial biostimulants in the improvement of micropropagation methods for industrial, ornamental, and food vegetable and fruit crops ( Campobenedetto et al, 2020 ; Cardarelli et al, 2020 ; Cirillo et al, 2020 ; de Azevedo et al, 2020 ; Dong et al, 2020 ; Gulzar et al 2020 ; Luziatelli et al 2020b ; Umanzor et al, 2020 ). In this respect, beneficial microorganisms able to synthesize or metabolize plant hormones are of particular importance because they can modulate the balance between plant growth and defense against stresses and pathogens, by changing the concentration of specific phytohormones ( Tsukanova et al, 2017 ; Saia et al, 2019 , 2020 ; Rouphael et al, 2020 ).…”

“…P. agglomerans is a rod-shaped, non-spore-forming, Gram-negative bacterium that is found in soil and is adapted to live in association with plants ( Walterson and Stavrinides, 2015 ; Zhang and Qiu, 2015 ). Certain strains belonging to this species are agronomically relevant for their PGP traits and biocontrol activity ( Dutkiewicz et al, 2016 ) and for their ability to produce IAA through a highly conserved indole-3-pyruvic acid (IPyA) pathway ( Luziatelli et al, 2020b ). P. agglomerans strain C1 was previously isolated from the phyllosphere of lettuce plants ( Lactuca sativa L.) treated with plant-derived protein hydrolysates ( Luziatelli et al, 2016 ).…”

“…Recently, the whole genome of P. agglomerans C1 was sequenced, providing insights into heavy metal resistance and metabolic capacities of this strain ( Luziatelli et al, 2019b , 2020a ). In addition, it was demonstrated that inoculation with C1 cells improved the growth in pots of tomato ( Solanum lycopersicum L.) and corn ( Zea mays L.) fertilized with rock phosphates ( Saia et al, 2020 ) and, also, that metabolites secreted by this strain can be utilized as biostimulants to improve the root surface area in cuttings of tomato ( Luziatelli et al, 2020a ), Prunus rootstocks GF/677, and Corylus avellana L. ( Luziatelli et al, 2020b ).…”