Grain cadmium (Cd) is translocated from source to sink tissues exclusively via phloem, though the phloem Cd unloading transporter has not been identified yet. Here, we isolated and functionally characterized a defensin-like gene DEFENSIN 8 (DEF8) highly expressed in rice (Oryza sativa) grains and induced by Cd exposure in seedling roots. Histochemical analysis and subcellular localization detected DEF8 expression preferentially in pericycle cells and phloem of seedling roots, as well as in phloem of grain vasculatures. Further analysis demonstrated that DEF8 is secreted into extracellular spaces possibly by vesicle trafficking. DEF8 bound to Cd in vitro, and Cd efflux from protoplasts as well as loading into xylem vessels decreased in the def8 mutant seedlings compared with the wild type. At maturity, significantly less Cd accumulation was observed in the mutant grains. These results suggest that DEF8 is a dual function protein that facilitates Cd loading into xylem and unloading from phloem, thus mediating Cd translocation from roots to shoots and further allocation to grains, representing a phloem Cd unloading regulator. Moreover, essential mineral nutrient accumulation as well as important agronomic traits were not affected in the def8 mutants, suggesting DEF8 is an ideal target for breeding low grain Cd rice.

Zinc (Zn) is an essential micronutrient required for plants to perform various metabolic functions, and plant responses to Zn deficiency have been extensively studied. However, excessive levels of Zn in soil can induce toxic effects in plants, posing a substantial challenge to global agricultural productivity. Consequently, elucidating the response mechanisms of crop plants to excessive Zn toxicity is currently of great significance. In this study, seedlings of maize inbred line B73 were exposed to excessive Zn treatment, and transcriptomic profiling of the roots was conducted at 0, 2, 6, 12, 24, and 48 h post-treatment. In addition to changes in the expression of genes encoding zinc-regulated, iron-regulated transporter-like protein (ZIP), metal tolerance protein (MTP), and yellow stripe-like (YSL) transporter family members involved in Zn transport, we observed that differentially expressed genes (DEGs) were significantly enriched in the phenylpropanoid–lignin metabolic pathway across all treatment stages, including the early (2 and 6 h), middle (12 and 24 h), and late (48 h) stages of Zn treatment. Among the 11 core structural enzyme-encoding genes involved in monolignols biosynthesis from phenylalanine in this pathway, the expression of eight of them was altered by Zn treatment. Additionally, genes encoding peroxidase (POD), which are responsible for the polymerization of monolignols into lignin, demonstrated extensive changes across all treatment stages, particularly at the late stage. The expression levels of these key enzyme genes were further validated using quantitative real-time PCR. Correspondingly, the activity of POD enzymes and the lignin content both significantly increased in Zn treated roots. These findings suggest that the phenylpropanoid–lignin metabolic pathway plays a crucial role in maize root responses to excessive Zn stress.

Stresses caused by deficiency/excess of mineral nutrients or of pollution of toxic metals have already become a primary factor in limiting crop production worldwide. Genes involved in minerals and toxic metals accumulation/tolerance could be potential candidates for improving crop plants with enhanced nutritional efficiency and environmental adaptability. In this study, we first generated a high-quality yeast expression cDNA library of Brassica napus (Westar), and 46 genes mediating excess micronutrients and toxic metals detoxification were screened using the yeast genetic complementation system, including 11, 5, 6, 14, 6, 5 genes involved in cadmium (Cd), zinc (Zn), iron (Fe), manganese (Mn), boron (B), copper (Cu) tolerance respectively. Characterization of genes mediating excess ions stress resistance in this study is beneficial for us to further understand ions homeostasis in B. napus.

Cadmium (Cd) is a highly toxic non-essential heavy metal that severely impairs plant growth, compromises crop yield and quality, and threatens food safety and human health. Jasmonic acid (JA) and salicylic acid (SA) are well-characterized endogenous phytohormones that serve as central regulators in modulating plant adaptive responses to Cd stress. This review comprehensively synthesizes current knowledge on the involvement of JA and SA in regulating Cd accumulation and tolerance in plants, including their Cd-induced biosynthetic dynamics and signaling transduction pathways, as well as their functions in restricting Cd uptake and translocation, modulating chelation and sequestration, reinforcing antioxidant defense systems and protecting photosynthetic apparatus. Moreover, we analyze the antagonistic and synergistic crosstalk between JA and SA, and discuss how this interplay shapes Cd resilience in plants. Finally, the application potential of JA and SA in developing Cd-safe crops and phytoremediation in Cd-contaminated farmland is explored. This review provides a systematic analysis of the regulatory roles of JA and SA in plant responses to Cd stress, along with an in-depth discussion of their crosstalk. These insights contribute to the rational development of hormone-based breeding strategies for Cd-safe crops and the optimization of agronomic management practices.

SWEET (Sugars Will Eventually be Exported Transporter) proteins constitute a conserved family of sugar transporters that play pivotal roles in carbohydrate allocation and stress responses. In this study, we systematically identified 14 SWEET homologs in the genome of sacred lotus (Nelumbo nucifera) and validated their transport activity for both hexoses and sucrose. Subsequent analysis revealed that stress-responsive elements are the most enriched promoter sequences of NnSWEET genes. Quantitative expression profiling of the members found that NnSWEET4a was strongly upregulated under salt stress. NnSWEET4a was localized at the plasma membrane; its expression conferred salt sensitivity in both yeast and Arabidopsis thaliana. Transgenic Arabidopsis lines overexpressing NnSWEET4a exhibited substantial downregulation of the SOS3–SOS2–SOS1 signaling module and concomitant alterations in cellular sugar homeostasis. Further analysis revealed that exogenous sugar application aggravated salt sensitivity and SOS pathway inhibition in NnSWEET4a transgenic plants, and NnSWEET15-overexpressing Arabidopsis recapitulated identical phenotypic and molecular responses, including salt sensitivity and repression of SOS genes. These findings indicate that NnSWEET4a impairs salt tolerance through disruption of sugar homeostasis. The results establish a mechanistic framework for future investigations into SWEET-dependent regulation of sugar homeostasis and salt stress adaptation.