Differential growth responses of Brachypodium distachyon genotypes to inoculation with plant growth promoting rhizobacteria

Abstract

Plant growth promoting rhizobacteria (PGPR) can associate and enhance the growth of important crop grasses. However, in most cases, the molecular mechanisms responsible for growth promotion are not known. Such research could benefit by the adoption of a grass model species that showed a positive response to bacterial inoculation and was amenable to genetic and molecular research methods. In this work we inoculated different genotypes of the model grass Brachypodium distachyon with two, well-characterized PGPR bacteria, Azospirillum brasilense and Herbaspirillum seropedicae, and evaluated the growth response. Plants were grown in soil under no nitrogen or with low nitrogen (i.e., 0.5 mM KNO3). A variety of growth parameters (e.g., shoot height, root length, number of lateral roots, fresh and dry weight) were measured 35 days after inoculation. The data indicate that plant genotype plays a very important role in determining the plant response to PGPR inoculation. A positive growth response was observed with only four genotypes grown under no nitrogen and three genotypes tested under low nitrogen. However, in contrast, relatively good root colonization was seen with most genotypes, as measured by drop plate counting and direct, microscopic examination of roots. In particular, the endophytic bacteria H. seropedicae showed strong epiphytic and endophytic colonization of roots.

The Variation in the Rhizosphere Microbiome of Cotton with Soil Type, Genotype and Developmental Stage

“…The rhizosphere microbiome affects plant growth, development, biotic and abiotic stress resistance through altering the absorption of nutrients into plant cells, the exchange of chemical signals, and affects enzyme activity during metabolic processes 5–8 . For example, plant growth-promoting rhizobacteria (PGPR) directly or indirectly provide nitrogen and phosphorus to plants 9–13 , promoting plant growth and development 14, 15 , preventing pathogen colonization and adjusting the resistance of plants to biotic and abiotic stresses 12, 16–19 . Similarly, the plants can regulate the rhizosphere through adjusting the input of material, energy and signals in the soil, thereby changing the community structure of the rhizosphere microbiome 20 .…”

Microbiome and Exudates of the Root and Rhizosphere of Brachypodium distachyon, a Model for Wheat

“…Brachypodium serves as a functional genomics model in elucidating cereal genomes [ 4 ] as well as for studying small noncoding RNAs such as microRNAs [ 5 , 6 ]. This species has also been studied for flowering time variation [ 7 ], plant-pathogen relations [ 8 – 10 ], plant microbe relations [ 11 , 12 ], and for root architecture and genetics [ 13 – 15 ]. Brachypodium provides a convenient model for studying cereal root systems because its mature roots are less than a third of the size of cereal crops such as wheat, maize and rice, and therefore are more amenable to laboratory and glasshouse studies [ 14 ].…”

“…Rhizosphere microorganisms benefit plant growth by increasing nutrient supply to plants, suppressing pathogens, and by carrying out other less studied roles [ 18 ]. Plant growth promoting (PGP) strains of Azospirillum and Herbaspirillum have been reported to colonize Brachypodium roots and enhance growth of some Brachypodium genotypes under low or no nitrogen conditions [ 11 ]. Inoculation with the PGP strain Bacillus subtilis B26 increased Brachypodium biomass and also enhanced plant drought resistance [ 12 ].…”

Effects of Tobacco Pathogens and Their Antagonistic Bacteria on Tobacco Root Exudates

“…For example, inoculation with Bacillus subtilis B26 not only increased the yield of rape (B. distachyon), but also increased drought resistance [20], even in the absence of nitrogen source. Both (Azospirillum) and (Herbaspirillum) of Vibrio herbaceus could promote the growth of Brassica napus [21]. These studies suggest that rhizosphere microbes play a potential role in plant root exudates.…”