Genotype-Specific Enrichment of 1-Aminocyclopropane-1-Carboxylic Acid Deaminase-Positive Bacteria in Winter Wheat Rhizospheres

Abstract

Core Ideas 1-Aminocyclopropane-1-carboxylic acid (ACC) deaminase-positive (ACC+) bacteria were studied in field soils planted to winter wheat. The relative abundance of ACC+ bacteria increased in wheat rhizospheres as soil water availability decreased. ACC+ bacterial abundance, composition, and deaminase activity were influenced by wheat genotype. The ability of ACC+ bacteria to promote drought resistance may be dependent on wheat genotype. Bacteria that produce 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase can promote plant growth under abiotic stress by lowering stress ethylene levels through deamination of ACC, the immediate precursor of ethylene. Unfortunately, little is known regarding the natural abundance and diversity of ACC deaminase-positive (ACC+) bacteria in soils or how ACC+ bacteria are influenced by plant genotype. Two field studies were conducted to assess the abundance, composition, and ACC deaminase activity of ACC+ bacteria in plots planted to different winter wheat (Triticum aestivum L.) genotypes under different irrigation regimes. In the first study, the relative abundance of ACC+ bacteria in wheat rhizospheres increased over time as soil water availability decreased. Relative abundance was also affected by genotype, with the greatest percentage of ACC+ bacteria in the rhizosphere of ‘RonL’ grown with limited or no irrigation (up to 54% at mid-grain filling). Species composition also varied by wheat genotype regardless of irrigation treatment. In the second study, the RonL rhizosphere had the greatest ACC deaminase activity and greatest predicted abundance of ACC+ bacteria, on the basis of Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis of 16S rDNA sequences, compared with other genotypes. In conclusion, the relative abundance, composition, and activity of culturable and predicted communities of ACC+ bacteria differed according to winter wheat genotype; therefore, the potential for ACC+ bacteria to promote drought resistance in winter wheat may be genotype-dependent.