Auxin-producing bacteria promote barley rhizosheath formation

Abstract

The rhizosheath, or the layer of soil closely adhering to roots, can help plants to tolerate drought under moderate soil drying conditions. Rhizosheath formation is the result of poorly understood interactions between root exudates, microbes, and soil conditions. Here, we study the roles played by the soil microbiota in rhizosheath formation in barley (a dry crop). We show that barley rhizosheath formation is greater in acid soil than in alkaline soil, and inoculation with microbiota from acid soil enhances rhizosheath formation in alkaline soil. The rhizosheath-promoting activity is associated with the presence of Flavobacteriaceae and Paenibacillaceae bacteria that express genes for biosynthesis of indole-3-acetic acid (IAA, a common auxin), as determined by metagenomics and metatranscriptomics. Two bacterial strains isolated from rhizosheath (Chryseobacterium culicis and Paenibacillus polymyxa) produce IAA and enhance barley rhizosheath formation, while their IAA-defective mutants are unable to promote rhizosheath formation. Co-inoculation with the IAA-producing strains enhances barley grain yield in field experiments through an increase in spike number. Our findings contribute to our understanding of barley rhizosheath formation, and suggest potential strategies for crop improvement.

Potential Biofertilizers for Alkaline Soil: Bacteria Isolated from the Rhizosphere of Potatoes

“…PGPR can promote plant growth by directly secreting plant hormones or by influencing the hormone synthesis process of plants [5]. The production of IAA has been recognized as an important factor in direct plant growth-promoting abilities of rhizosphere bacteria.…”

“…As the second genome of plants, the rhizosphere microbiome plays an important role in promoting plant growth and disease resistance [4]. In particular, plant growth-promoting rhizobacteria (PGPR), which can benefit plants by producing plant growth hormones [5], convert many plant-unavailable essential nutrients, such as nitrogen, phosphorous, zinc and iron, into available forms, synthesize antibiotics or enhance induced systemic resistance (ISR) to help plants against pathogenic bacteria and fungi [6].…”

Influence and Role of Fungi, Bacteria, and Mixed Microbial Populations on Phosphorus Acquisition in Plants

“…Two bacterial strains isolated from rhizosheath (Chryseobacterium culicis and Paenibacillus polymyxa) were found to affect rhizosheath development, which appeared to be directly related to the ability of Flavobacterium sp. and Chryseobacterium culicis to produce growth hormones, while barley root sheaths inoculated with auxin-mutant strains were significantly stunted [176]. Studies have shown that the metabolic synthesis of growth hormones in plants is affected by the concentration of growth hormone in the soil, which appears to be linked to the bacterial production of the hormone [177].…”

The Plant-Associated Flavobacterium: A Hidden Helper for Improving Plant Health

“…The amount of auxin that plant-associated Flavobacterium produces is about 4.88 μg/ml ( Lin et al, 2023 ). Flavobacterium species associated with plants might synthesize auxin through the tryptophan-dependent pathway rather than the tryptophan-independent pathway ( Tillmann et al, 2021 ; Tsavkelova et al, 2007 ; Xu et al, 2023 ; Wang et al, 2015 ). For example, Flavobacterium sp.…”

“…For example, Flavobacterium sp. 11 showed tryptophan-dependent IAA production regulated by the indole-3-glycerol phosphate synthase gene ( trpC ), which converts 1-( o -ecarboxyphenylamino)-1-deoxyribulose-5-phosphate to indole-3-glycerol-phosphate ( Kagan et al, 2008 ; Xu et al, 2023 ). In addition to auxin, the treatment of Flavobacterium sp.…”