A Bacillus velezensis strain improves growth and root system development in Arabidopsis thaliana through cytokinin signaling

Abstract

Bacillus velezensis 83 (Bv 83) is the bio-active component of a Mexican biotechnological product marketed as Fungifree AB™, showing both antagonistic activity against fungal phyto-pathogens and plant growth promotion properties. Here, we employed an in vitro system to characterize phytohormone signaling in growth promotion of Arabidopsis thaliana (L.) Heynh. [A. thaliana] driven by the strain Bv 83. Inoculation at the front of the growing root system or allowing the bacteria to spread along the root, produced a strong and long-lasting biostimulant effect that changes root architecture and drives root and shoot biomass production, which correlates with enhanced mitosis in meristems. Noteworthy, the bacterial growth promotion capacity depends on cytokinin signaling since Bv 83, although unable to alter the expression pattern of reporter genes for auxins, jasmonic acid and salicylic acid, it induced the expression of cytokinin-related genes ARR5 and LBD3. Consistently, the bacterium neither enhanced root nor shoot biomass production or root branching in A. thaliana mutants harboring double mutant combinations of all three canonical cytokinin receptors CRE1/AHK4, AHK2 and AHK3. Our data extend what is known about the properties of Bv 83, highlighting its promise not only as a biological control agent but also as plant growth promoter to improve productivity.