Dark septate endophyte enhances maize cadmium (Cd) tolerance by the remodeled host cell walls and the altered Cd subcellular distribution

Abstract

Evidence accumulated in recent years supports the crucial role of remodeled cell walls (CWs) in enabling plants to adapt to environmental challenges. However, the metal tolerance and alleviation mechanisms involving the CWs by endophyte-plant interactions to toxic metals have not yet been elucidated. In the present study, these mechanisms are tested by exploring the maize (Zea mays) Cd tolerance by modifying its root CW structure via inoculation with a dark septate endophyte (DSE) fungus Exophiala pisciphila. Our present study demonstrates that the root CWs were the primary site for Cd accumulation, functioning as a sink for toxic Cd ions. Interestingly, E. pisciphila colonization significantly bioaugmented subcellular compartmentalization of maize roots and increased the Cd content of various CW subfractions through a significantly increased enzyme activity, e.g., pectin methylesterase, as well as an upregulated expression of genes involved in CW biosynthesis and changes in the contents of functional groups in pectin and hemicellulose 1 in response to Cd stress. Consequently, the enhanced Cd compartmentation in plant CWs by DSE lowers the entry of trace metals in the protoplast, thereby conferring the tolerant races of plants that can survive and thrive on metal-contaminated soils.