An integrated transcriptome, metabolomic, and physiological investigation uncovered the underlying tolerance mechanisms of Monochoria korsakowii in response to acute/chronic cadmium exposure

Abstract

Identifying the physiological response and tolerance mechanism of wetland plants to heavy metal exposure can provide theoretical guidance for an early warning for acute metal pollution and metal-contaminated water phytoremediation. A hydroponic experiment was employed to investigate variations in the antioxidant enzyme activity, chlorophyll content, and photosynthesis in leaves of Monochoria korsakowii under 0.12 mM cadmium ion (Cd²⁺) acute (4 d) and chronic (21 d) exposure. Transcriptome and metabolome were analyzed to elucidate the underlying defensive strategies. The acute/chronic Cd²⁺ exposure decreased chlorophyll a and b contents, and disturbed photosynthesis in the leaves. The acute Cd²⁺ exposure increased catalase activity by 36.42%, while the chronic Cd²⁺ exposure markedly increased ascorbate peroxidase, superoxide dismutase, and glutathione peroxidase activities in the leaves. A total of 2 685 differentially expressed genes (DEGs) in the leaves were identified with the plants exposed to the acute/chronic Cd²⁺ contamination. In the acute Cd²⁺ exposure treatment, DEGs were preferentially enriched in the plant hormone transduction pathway, followed by phenylrpopanoid biosynthesis. However, the chronic Cd²⁺ exposure induced DEGs enriched in the biosynthesis of secondary metabolites pathway as priority. With acute/chronic Cd²⁺ exposure, a total of 157 and 227 differentially expressed metabolites were identified in the leaves. Conjoint transcriptome and metabolome analysis indicated the plant hormone signal transduction pathway and biosynthesis of secondary metabolites was preferentially activated by the acute and chronic Cd²⁺ exposure, respectively. The phenylpropanoid pathway functioned as a chemical defense, and the positive role of deoxyxylulose phosphate pathway in leaves against acute/chronic Cd²⁺ exposure was impaired.

Keywords: Antioxidant strategies; Monochoria korsakowii; Pevalonate pathway; Phenylpropanoid pathway; Plant hormone signal transduction.