Plant growth‐promoting abilities of Methylobacterium sp. 2A involve auxin‐mediated regulation of the root architecture

Abstract

Methylobacterium sp. 2A, a plant growth‐promoting rhizobacteria (PGPR) able toproduce indole‐3‐acetic acid (IAA), significantly promoted the growth of Arabidopsisthaliana plants in vitro. We aimed to understand the determinants of Methylobacterium sp. 2A–A. thaliana interaction, the factors underlying plant growth‐promotion and the host range. Methylobacterium sp. 2A displayed chemotaxis tomethanol and formaldehyde and was able to utilise 1‐aminocyclopropane carboxylate as a nitrogen source. Confocal microscopy confirmed that fluorescent protein‐labelled Methylobacterium sp. 2A colonises the apoplast of A. thaliana primary rootcells and its inoculation increased jasmonic and salicylic acid in A. thaliana, while IAAlevels remained constant. However, inoculation increased DR5 promoter activity inroot tips of A. thaliana and tomato plants. Inoculation of this PGPR partially restoredthe agravitropic response in yucQ mutants and lateral root density was enhanced iniaa19, arf7, and arf19 mutant seedlings. Furthermore, Methylobacterium sp. 2Avolatile organic compounds (VOCs) had a dose‐dependent effect on the growth of A.thaliana. This PGPR is also able to interact with monocots eliciting positive responsesupon inoculation. Methylobacterium sp. 2A plant growth‐promoting effects can beachieved through the regulation of plant hormone levels and the emission of VOCsthat act either locally or at a distance.