Earthworms and arbuscular mycorrhizal fungi improve salt tolerance in maize through symplastic pathways

Symplastic pathways involving plasma membrane H+-ATPases and Na+/H+ antiporters maintain Na+ homeostasis in the symplastic pathways and protect plant functions under salt stress. In this study, we characterized the effects of earthworms and arbuscular mycorrhizal fungi (AMF) on Na+ absorption and transport in roots. Measurements of root Na+ content, plasma membrane H+-ATPase, and Na+/H+ antiporter and antioxidant enzyme activities were performed together with transcriptome analysis. The addition of earthworms and AMF under saline conditions decreased the accumulation of Na+ in maize roots and significantly increased root K:Na ratios, as well as increasing the levels of transcripts encoding plasma membrane H+-ATPases, Na+/H+ antiporters, antioxidant enzymes, and proteins involved in nitrogen and phosphorus uptake under saline conditions. The transcript changes induced by earthworms and AMF suggest that abscisic acid mediates the effects on salt tolerance. Taken together, these findings indicate that earthworms and AMF improve the salt tolerance of maize seedlings through improved symplastic pathways.