Exploring quinoa’s plant growth-promoting bacteria: a Pseudomonas seed endophyte promotes salinity tolerance and modifies root architecture in Arabidopsis thaliana

Quinoa (Chenopodium quinoa Willd) is a halophytic crop species native to the Andes. Its salt tolerance mechanisms have been widely studied but less is known about the beneficial microorganisms that potentially contribute to its resilience. Seed endophytes are the least investigated plant-associated microbes, despite their importance in supporting germination, seedling establishment, and in priming the plant for stress tolerance. In this work fifteen strains of culturable endophytic bacteria were isolated from surface-sterilised quinoa seeds and identified by MALDI-TOF. All strains were halotolerant and exhibited one or more plant growth-promoting (PGP) activity, viz. phosphate and potassium solubilization, indole-acetic acid, organic acid, exopolysaccharide, and siderophore production, ACC deaminase activity, and nitrogen fixation. A Pseudomonas strain (code A7) with the most PGP features was identified by 16S rDNA as Pseudomonas putida. To investigate the stress-mitigating potential of isolate A7, the model plant Arabidopsis was grown with 0 or 100 mM NaCl. After 12 days under salt stress, A7 restored fresh biomass and chlorophyll content to control levels. Inoculation with A7 enhanced the number of lateral roots on saline and non-saline medium. Transcript levels of genes belonging to several functional categories, analysed by quantitative real-time-PCR, were affected by salt or by inoculation with A7 alone; in several cases (AtCYCD2, AtANR1, AtNTR2.1, AtHEMA, AtGRX3 and 4, AtSOS1), salt-induced downregulation was reverted to control levels (or more) by A7.