Functional auxin signaling and phosphorus acquisition triggered in planta by the extremophile bacterium Pseudomonas extremaustralis

Abstract

Pseudomonas extremaustralis 14-3b, a strain isolated from Antarctica, was evaluated forplant-growth-promoting traits under different oxygen conditions. Genomic analysisrevealed genes related to phosphorus solubilization and indole-3-acetic acid (IAA)biosynthesis. In vitro assays confirmed its ability to solubilize tricalcium phosphate andproduce gluconic acid. IAA production was higher under microaerobic conditionscompared to aerobic cultures. Using Arabidopsis thaliana DII-VENUS reporter lines, weconfirmed in vivo IAA perception in roots, with reduced VENUS fluorescence uponbacterial inoculation, regardless of prior oxygen conditions. Confocal microscopy showedroot surface colonization and internal localization in cotyledons, including sub-stomatalspaces. Morphological changes in A. thaliana included reduced primary root length andincreased root hair length. In wheat, P. extremaustralis exhibited chemotaxis toward rootexudates and colonized root tissues. After 30 days in pot experiments, inoculated wheatplants showed significantly higher stem dry weight and leaf phosphorus content thancontrol plants. These findings indicate that P. extremaustralis promotes plant growththrough multiple mechanisms, supporting its potential as a bioinoculant under variableenvironmental conditions, including low oxygen availability.