Silicon enhances potassium uptake and leaf growth in Avicennia marina, a silicon-accumulating mangrove plant with silicon transporters

Abstract

Silicon (Si) is an essential fertilizer that enhances plant growth and stress resilience. Mangroves thrive in high-salinity, oxygen-deficient soils with high productivity, rapid decomposition, and fast elemental cycling. However, the physiological effects of Si on mangrove plants, as well as their mechanisms for Si uptake, transport, and function, remain unclear. In this study, we identified Avicennia marina as a Si-accumulating mangrove species and elucidated its Si transport pathways and associated physiological benefits. Through bioinformatics and heterologous expression in yeast, we demonstrated that the Si transporters AmLsi1 and AmSIET4 are localized to cellular membranes and mediate Si transport. RT-qPCR and RNA-seq analyses revealed that AmLsi1 and AmSIET4 are predominantly expressed in roots and leaves, respectively, with comparable expression levels. Both genes showed similar responses to salt, flooding, and Si treatments, indicating their coordinated roles in Si transport. AmLsi1 acts as a bidirectional transporter of Si and As(III) in roots, also facilitating H₂O and H₂O₂ transport, while AmSIET4 functions as an efflux transporter for Si and As(III) in leaves. Si absorption by roots and secretion through salt glands were further confirmed using SEM-EDX and ICP-MS. Si treatment enhanced leaf area, upregulated K⁺ channel gene expression, enhanced K⁺ uptake, and reduced Na⁺ concentration in the roots, improving the K⁺/Na⁺ ratio and restoring F_v/F_m under saline conditions. This study provides new insights into Si uptake, transport, and its physiological significance in mangroves, deepening our understanding of Si’s role in A. marina and its contribution to mangrove ecosystem productivity.