RtERF1-activated RtXTH2 enhances aluminum tolerance in Rhodomyrtus tomentosa via modifying cell wall components

Acidic soils trigger a surge of soluble aluminum (Al), thereby causing Al³⁺ toxicity that inhibits plant growth and limits crop yields. Rhodomyrtus tomentosa, a shrub distributed in tropical and subtropical regions with acid soil, is an important genetic source for exploring the mechanism of Al tolerance. The xyloglucan endotransglucosylase/hydrolase (XTH) cleaves and rejoins xyloglucan polymers, which is important for plants to adapt to Al³⁺ stress. In the present study, a total of 29 RtXTHs were identified in R. tomentosa. These RtXTHs showed distinct tissue-specific expression patterns. Al³⁺ stress significantly upregulated several RtXTH genes in the roots, among which RtXTH2 showed the most prominent responsiveness. The subcellular localization assay determined that RtXTH2 encoded a cell wall-localized XTH protein. Overexpression of RtXTH2 enhanced Al tolerance in Arabidopsis by reducing hemicellulose and pectin contents in the cell wall. RtERF1, an Al³⁺-induced AP2/ERF transcription factor, directly activated RtXTH2 by binding to the CRT elements in its promoter. Silencing either RtXTH2 or RtERF1 reduced Al tolerance in R. tomentosa seedlings, as evidenced by increased Al accumulation, enhanced membrane damage, and more severe inhibition of root elongation under Al³⁺ stress. In summary, our results indicate that RtERF1 activates RtXTH2 to modify cell wall composition, thereby enhancing Al tolerance in R. tomentosa.