Yan Gao

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.

To investigate the coordinated role of RALF1 and eIF4E1 within the FER signaling module in regulating root hair elongation and stress responses in Arabidopsis thaliana, we constructed a ralf1/eif4e1 double mutant via conventional hybridization. Although the roles of the RALF1 and eIF4E1 genes are well known, the simultaneous absence of them remains poorly characterized. The double mutant exhibited significantly reduced root hair numbers and elongation and heightened sensitivity to ABA, Cd²⁺, and NaCl stress. The ralf1/eif4e1 double mutant exhibited delayed flowering time and higher numbers of rosette leaves. Fluorescence quantitative PCR analyses revealed that several key genes involved in regulating flowering such as FT, LFY and SOC reached maximum levels in wild-type plants. However, other genes that regulated floral meristem exhibited higher expression levels in the ralf1 mutant, followed by in wild-type plants. This work provides new insight into the RALF1-FERONIA-eIF4E1 module, demonstrating that it converges environmental cues to coordinately regulate root hair elongation, stress responses, and flowering time in Arabidopsis.

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.

Ferroptosis is an iron-dependent cell death that was discovered recently. For beneficial microbes to establish mutualistic relationships with hosts, precisely controlled cell death in plant cells is necessary. However, whether ferroptosis is involved in the endophyte‒plant system is poorly understood. Here, we reported that endophytic Streptomyces hygroscopicus OsiSh-2, which established a sophisticated and beneficial interaction with host rice plants, caused ferroptotic cell death in rice characterized by ferroptosis- and immune-related markers. Treatments with ferroptosis inhibitors and inducers, different doses of OsiSh-2, and the siderophore synthesis-deficient mutant ΔcchH revealed that only moderate ferroptosis induced by endophytes is essential for the establishment of an optimal symbiont to enhance plant growth. Additionally, ferroptosis involved in a defence-primed state in rice, which contributed to improved resistance against rice blast disease. Overall, our study provides new insights into the mechanisms of endophyte‒plant interactions mediated by ferroptosis and suggests new directions for crop yield promotion.

Lignocellulolytic bacteria have revealed to be a promising source for biofuel production, yet the underlying mechanisms are still worth exploring. Our previous study inferred that the highly efficient lignocellulose degradation by bacterium Pantoea ananatis Sd-1 might involve Fenton chemistry (Fe2+ + H2O2 + H+ → Fe3+ + OH· + H2O), similar to that of white-rot and brown-rot fungi. The aim of this work is to investigate the existence of this Fenton-based oxidation mechanism in the rice straw degradation process of P. ananatis Sd-1. After 3 days incubation of unpretreated rice straw with P. ananatis Sd-1, the percentage in weight reduction of rice straw as well as its cellulose, hemicellulose, and lignin components reached 46.7, 43.1, 42.9, and 37.9 %, respectively. The addition of different hydroxyl radical scavengers resulted in a significant decline (P < 0.001) in rice straw degradation. Pyrolysis gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy analysis revealed the consistency of chemical changes of rice straw components that exists between P. ananatis Sd-1 and Fenton reagent treatment. In addition to the increased total iron ion concentration throughout the rice straw decomposition process, the Fe3+-reducing capacity of P. ananatis Sd-1 was induced by rice straw and predominantly contributed by aromatic compounds metabolites. The transcript levels of the glucose-methanol-choline oxidoreductase gene related to hydrogen peroxide production were significantly up-regulated (at least P < 0.01) in rice straw cultures. Higher activities of GMC oxidoreductase and less hydrogen peroxide concentration in rice straw cultures relative to glucose cultures may be responsible for increasing rice straw degradation, which includes Fenton-like reactions. Our results confirmed the Fenton chemistry-assisted degradation model in P. ananatis Sd-1. We are among the first to show that a Fenton-based oxidation mechanism exists in a bacteria degradation system, which provides a new perspective for how natural plant biomass is decomposed by bacteria. This degradative system may offer an alternative approach to the fungi system for lignocellulosic biofuels production.