Spore associated bacteria regulates maize root K(+)/Na(+) ion homeostasis to promote salinity tolerance during arbuscular mycorrhizal symbiosis

BACKGROUND: The interaction between arbuscular mycorrhizal fungi (AMF) and AMF spore associated bacteria (SAB) were previously found to improve mycorrhizal symbiotic efficiency under saline stress, however, the information about the molecular basis of this interaction remain unknown. Therefore, the present study aimed to investigate the response of maize plants to co-inoculation of AMF and SAB under salinity stress. RESULTS: The co-inoculation of AMF and SAB significantly improved plant dry weight, nutrient content of shoot and root tissues under 25 or 50 mM NaCl. Importantly, co-inoculation significantly reduced the accumulation of proline in shoots and Na(+) in roots. Co-inoculated maize plants also exhibited high K(+)/Na(+) ratios in roots at 25 mM NaCl concentration. Mycorrhizal colonization significantly positively altered the expression of ZmAKT2, ZmSOS1, and ZmSKOR genes, to maintain K(+) and Na(+) ion homeostasis. Confocal laser scanning microscope (CLSM) view showed that SAB were able to move and localize into inter- and intracellular spaces of maize roots and were closely associated with the spore outer hyaline layer. CONCLUSION: These new findings indicate that co-inoculation of AMF and SAB effectively alleviates the detrimental effects of salinity through regulation of SOS pathway gene expression and K(+)/Na(+) homeostasis to improve maize plant growth. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12870-018-1317-2) contains supplementary material, which is available to authorized users.