The sugar will eventually be exported transporters (SWEET) family is an important group of transport carriers for carbon partitioning in plants and has important functions in growth, development, and abiotic stress tolerance. Although the SWEET family is an important sugar transporter, little is known of the functions of the SWEET family in maize (Zea mays), especially in response to abiotic stresses. To further explore the response pattern of maize SWEET to abiotic stress, a bioinformatics-based approach was used to predict and identify the maize SWEET gene (ZmSWEET) family. Twenty-four ZmSWEET genes were identified using the MaizeGDB database. Phylogenetic analysis resolved these twenty-four genes into four clades. One tandem and five segmental duplication events were identified, which played a major role in ZmSWEET family expansion. Synteny analysis provided insight into the evolutionary characteristics of the ZmSWEET genes with those of three graminaceous crop species. A heatmap showed that most ZmSWEET genes responded to at least one type of abiotic stress. By an abscisic acid signaling pathway, among which five genes were significantly induced under NaCl treatment, eight were obviously up-regulated under PEG treatment and five were up-regulated under Cd stress, revealing their potential functions in response to abiotic stress. These findings will help to explain the evolutionary links of the ZmSWEET family and contribute to future studies on the functional characteristics of ZmSWEET genes, and then improve abiotic stress tolerance in maize through molecular breeding.

Cadmium (Cd) contamination severely threatens crop productivity and food safety, particularly in maize (Zea mays L.), which exhibits relatively high capacities for metal uptake and translocation. Metal tolerance proteins (MTPs) play essential roles in metal homeostasis and detoxification; however, the functions of maize MTP under Cd stress remain poorly understood. In this study, a comprehensive expression analysis of the maize MTP gene family revealed that two Zn-CDF members, ZmMTP1-1 and ZmMTP1-2, displayed the strongest and most consistent transcriptional induction in response to Cd stress, especially in roots. Phylogenetic and structural analyses confirmed that both genes are closely related to MTP1 homologs from other plant species, while exhibiting distinct gene structures and regulatory features. Functional characterization in transgenic Arabidopsis thaliana demonstrated that overexpression of ZmMTP1-1 or ZmMTP1-2 significantly enhanced tolerance to Cd and Zn stress, as reflected by improved seed germination, root growth, survival, and biomass accumulation. Enhanced metal tolerance was associated with elevated antioxidant enzyme activities, reduced oxidative damage, and coordinated upregulation of endogenous metal transporter genes. Moreover, heterologous expression of ZmMTP1-1 in yeast further supported its conserved role in Cd tolerance. Collectively, these findings indicate that ZmMTP1-1 and ZmMTP1-2 contribute to Cd detoxification through coordinated metal transport and stress-response pathways, providing potential genetic resources for improving heavy metal tolerance in maize.

Cadmium (Cd) contamination poses a severe ecological risk to ecosystems. Trehalose (TR) is a non-reducing disaccharide which can mitigate the adverse effects of heavy metals. The physiological responses and transcriptomic characteristics underlying TR-mediated heavy metal tolerance remain unclear in maize. In this study, maize seedlings were exposed to 200 mg L⁻¹ CdCl₂·2.5H₂O with or without 23 mM exogenous TR for 5 days. By phenotypic observation, although TR supplementation could not fully restore maize growth under Cd stress, it significantly alleviated Cd-induced inhibition, increasing shoot and root dry weight by 33.80% and 36.67%, respectively, compared with Cd treatment alone. Exogenous TR also improved the photosynthesis under Cd stress. Cd stress triggered excessive ROS accumulation and membrane lipid peroxidation, whereas trehalose application alleviated oxidative damage by significantly reducing ${\mathrm{O}}_2^{-}$, H₂O₂, and MDA contents while further enhancing SOD and CAT activities. Compared with Cd treatment, cell-wall fractionation revealed a 20.53% increase in root cellulose under Cd+TR combined treatment. Further, exogenous TR reduced Cd concentrations in roots and shoots by 19% and 33%, respectively. RNA-seq identified enriched GO categories related to cell communication, signal transduction, amino acid transmembrane transport, and membrane components, suggesting possible involvement of these processes in the TR response. These findings collectively demonstrate that exogenous trehalose enhances maize cadmium tolerance through coordinated physiological responses and transcriptional adjustments.