Optimizing heavy metal phytoextraction in king grass through Serendipita indica symbiosis: insights into core root exudates and GABA signaling in rhizoremediation

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This study investigated the symbiosis between Serendipita indica (SI) and king grass (KG) to optimize the phytoextraction of cadmium (Cd) and chromium (Cr) from contaminated agriculture soils, focusing on root exudate profile dynamics and GABA signaling in rhizoremediation. We examined the mechanisms linking heavy metals (HMs), microbial symbiosis, and root exudates in the rhizosphere during remediation. First, SI promoted plant growth, increasing biomass by 10.2%–17.7% and significantly enhancing fine root development. It also boosted antioxidant enzyme activities (SOD, APX, GR) by 11.5%, 27.7%, and 15.0%, respectively, while reducing MDA and H2O2 levels, thereby alleviating HMs-induced stress. Root uptake of Cd and Cr increased by 23.2%–30.0% and 20.8%–30.0%, respectively, while soil Cd and Cr removal increased by 27.5% and 28.7%. Second, under Cd/Cr stress, SI increased root vigor and regulated root exudates by KG, upregulating IAA, betaine, ascorbic acid, riboflavin, and notably γ-aminobutyric acid (GABA), which increased 4.0–14.0–fold, reaching 19.2 mmol mL-1 at the tillering stage. These exudates correlated with Cr concentration and growth-promotion. SI upregulated the Alanine-Aspartate-Glutamate and Arginine-Proline pathways, closely association with the TCA cycle. Third, exogenous GABA further enhanced oxidative stress responses, alleviated toxicity, increased biomass by 34.1%–41.6%, and boosted Cr uptake by 21.1%–25.1%, while inhibiting Cr translocation to aerial parts. This study highlights the metabolic interactions between GABA and other metabolites in the KGSI symbiosis. The growth-promoting properties of SI and GABA's ability to sequester HMs in roots support their potential in phytoremediation, offering new opportunities to optimize soil phytoremediation technologies.

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