The F-bZIP-regulated Zn deficiency response in land plants

The transcription factor OsbZIP48 governs rice responses to zinc deficiency

Zinc (Zn) deficiency is the most prevalent micronutrient disorder in rice and leads to delayed development and decreased yield. Nevertheless, despite its primary importance, how rice responds to Zn deficiency remains poorly understood. This study presents genetic evidence supporting the crucial role of OsbZIP48 in regulating rice's response to Zn deficiency, consistent with earlier findings in the model plant Arabidopsis. Genetic inactivation of OsbZIP48 in rice seedlings resulted in heightened sensitivity to Zn deficiency and reduced Zn translocation from roots to shoots. Consistently, OsbZIP48 was constitutively expressed in roots, slightly induced by Zn deficiency in shoots and localized into nuclei induced by Zn deficiency. Comparative transcriptome analysis of the wild-type plants and osbzip48 mutant grown under Zn deficiency enabled the identification of OsbZIP48 target genes, including key Zn transporter genes (OsZIP4 and OsZIP8). We demonstrated that OsbZIP48 controlled the expressions of these genes by directly binding to their promoters, specifically to the Zn deficiency response element motif. This study establishes OsbZIP48 as a critical transcription factor in rice's response to Zn deficiency, offering valuable insights for developing Zn-biofortified rice varieties to combat global Zn limitation.

Reactive oxygen species- and nitric oxide-dependent regulation of ion and metal homeostasis in plants

Deterioration and impoverishment of soil, caused by environmental pollution and climate change, result in reduced crop productivity. To adapt to hostile soils, plants have developed a complex network of factors involved in stress sensing, signal transduction, and adaptive responses. The chemical properties of reactive oxygen species (ROS) and reactive nitrogen species (RNS) allow them to participate in integrating the perception of external signals by fine-tuning protein redox regulation and signal transduction, triggering specific gene expression. Here, we update and summarize progress in understanding the mechanistic basis of ROS and RNS production at the subcellular level in plants and their role in the regulation of ion channels/transporters at both transcriptional and post-translational levels. We have also carried out an in silico analysis of different redox-dependent modifications of ion channels/transporters and identified cysteine and tyrosine targets of nitric oxide in metal transporters. Further, we summarize possible ROS- and RNS-dependent sensors involved in metal stress sensing, such as kinases and phosphatases, as well as some ROS/RNS-regulated transcription factors that could be involved in metal homeostasis. Understanding ROS- and RNS-dependent signaling events is crucial to designing new strategies to fortify crops and improve plant tolerance of nutritional imbalance and metal toxicity.

Combined transcriptome and proteome analysis revealed the molecular regulation mechanisms of zinc homeostasis and antioxidant machinery in tobacco in response to different zinc supplies

Zinc (Zn) is an essential micronutrient for plants. Adequate regulation of Zn uptake, transport and distribution, and adaptation to Zn-deficiency stress or Zn-excess toxicity are crucial for plant growth and development. However, little has been done to understand the molecular responses of plants toward different Zn supply levels. In the present study, we investigated the growth and physiological responses of tobacco seedlings grown under Zn-completely deficient, Zn-limiting, Zn-normal, and Zn-4-fold sufficient conditions, respectively, and demonstrated that Zn deficiency/limitation caused oxidative stress and impaired growth of tobacco plants. Combined transcriptome and proteome analysis revealed up-regulation of genes/proteins associated with Zn uptake and distribution, including ZIPs, NAS3s, and HMA1s, and up-regulation of genes/proteins involved in regulation of oxidative stress, including SODs, APX1s, GPX6, and GSTs in tobacco seedlings in response to Zn deficiency/limitation, suggesting that tobacco possessed mechanisms to regulate Zn homeostasis primarily through up-regulation of the ZIPs-NAS3s module, and to alleviate Zn deficiency/limitation-induced oxidative stress through activation of the antioxidant machinery. Our results provide novel insights into the adaptive mechanisms of tobacco in response to different Zn supplies, and would lay a theoretical foundation for development of varieties of tobacco or its relatives with high tolerance to Zn-deficiency.

Nicotianamine: A Key Player in Metal Homeostasis and Hyperaccumulation in Plants

Nicotianamine (NA) is a low-molecular-weight N-containing metal-binding ligand, whose accumulation in plant organs changes under metal deficiency or excess. Although NA biosynthesis can be induced in vivo by various metals, this non-proteinogenic amino acid is mainly involved in the detoxification and transport of iron, zinc, nickel, copper and manganese. This review summarizes the current knowledge on NA biosynthesis and its regulation, considers the mechanisms of NA secretion by plant roots, as well as the mechanisms of intracellular transport of NA and its complexes with metals, and its role in radial and long-distance metal transport. Its role in metal tolerance is also discussed. The NA contents in excluders, storing metals primarily in roots, and in hyperaccumulators, accumulating metals mainly in shoots, are compared. The available data suggest that NA plays an important role in maintaining metal homeostasis and hyperaccumulation mechanisms. The study of metal-binding compounds is of interdisciplinary significance, not only regarding their effects on metal toxicity in plants, but also in connection with the development of biofortification approaches to increase the metal contents, primarily of iron and zinc, in agricultural plants, since the deficiency of these elements in food crops seriously affects human health.