Molecular characterization and in silico analysis of the malate dehydrogenase (MDH) gene family in wheat (Triticum aestivum L.) with expression profiling under heavy metal stresses.

内容摘要

Malate dehydrogenase (MDH) catalyzes the reversible conversion of malate to oxaloacetate and plays essential roles in plant metabolism, redox balance, and stress adaptation. However, comprehensive characterization of TaMDH genes in wheat (Triticum aestivum L.), including their evolutionary features and stress-responsive expression patterns, remains limited. In this study, 18 TaMDH genes were systematically identified and characterized using integrated computational and transcriptomic approaches. Phylogenetic analysis grouped TaMDH proteins into three distinct sub-clades, while chromosomal mapping revealed their distribution across chromosomes 1, 3, 5, and 7 of the A, B, and D subgenomes. Gene structure, conserved motif, and duplication analyses indicated both evolutionary conservation and functional diversification within the TaMDH family. Functional annotation and protein-protein interaction network analysis suggested their involvement in the tricarboxylic acid cycle, malate metabolism, and carbon-nitrogen metabolic pathways. Promoter analysis identified multiple stress, hormone, and light-responsive cis-elements, whereas nine putative miRNAs were predicted to regulate TaMDH gene expression. Tissue-specific expression profiling showed that TaMDH4 and TaMDH5 were highly expressed across multiple tissues and developmental stages, whereas TaMDH1, TaMDH8, and TaMDH9 exhibited moderate to high expression. Under abscisic acid (ABA) treatment as well as cold, heat, and salt stresses, TaMDH genes displayed relatively stable and minimal transcriptional variation in shoots, indicating limited responsiveness to these general abiotic stresses. In contrast, exposure to heavy metals, including cobalt (Co), nickel (Ni), zinc (Zn), and cadmium (Cd), triggered pronounced, metal-specific, and time-dependent expression changes in both shoots and roots. Notably, TaMDH2, TaMDH4, TaMDH5, TaMDH7, TaMDH10, TaMDH15, and TaMDH17 showed strong upregulation at early (6-12 h) and/or late (24 h) stages, with distinct tissue-specific expression patterns between shoots and roots, particularly under Cd and Ni stress. Overall, these findings indicate that TaMDH genes exhibit stronger transcriptional responsiveness to heavy metal exposure, highlighting their potential roles in metal detoxification, redox regulation, and stress adaptation in wheat. This study provides a valuable foundation for future functional investigations and for improving wheat resilience to heavy metal-contaminated environments.