A novel zinc transporter essential for Arabidopsis zinc and iron-dependent growth

StZIP2 promotes root growth by improving the transport efficiency of zinc in potato(Solanum tuberosum L.)

Zinc is an essential trace element for plant growth and development. Zinc transporters play an important role in regulating zinc homeostasis in plants. In this study, the potato cultivar 'Atlantic' was used as experimental material to analyze the expression characteristics of the StZIP2 gene in different potato tissues under zinc deficiency stress. Transgenic plants with overexpression and interference expression of the StZIP2 gene were obtained by genetic transformation and treated with zinc deficiency stress. Chlorophyll content, antioxidant enzyme activity, proline (Pro) and malonic dialdehyde (MDA) content, zinc content in aboveground parts and roots, and root indices were determined. The results showed that the expression level of the StZIP2 gene in roots, stems and leaves under zinc deficiency stress was significantly higher than that of the control, and the expression level of the StZIP2 gene in roots under zinc deficiency stress was the highest. After zinc deficiency treatment, the content of chlorophyll and Pro, the activity of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), root-to-shoot ratio, root length and root fresh weight of overexpressed plants were significantly increased, while the MDA content was significantly decreased. The ratio of zinc content between the above-ground part and the root of the overexpressed plants was significantly higher than that of the non-transgenic plants, and the transport efficiency from the root to the above-ground part was significantly increased in the overexpressed plants, whereas it was just the opposite in the interference expressing plants. The result provides basic data to further elucidate the StZIP2 gene function.

Global transcriptional modulation and nutritional status of soybean plants following foliar application of zinc borate as a suspension concentrate fertilizer

The management of micronutrients, such as boron (B) and zinc (Zn), is critical for plant growth and crop yields. One method of rapid intervention crop management to mitigate nutritional deficiency is the foliar supply of B and Zn. Our study investigates the effect of foliar-supplied B and Zn availability on the global transcriptional modulation in soybean (Glycine max). The transcriptional response to B was more widespread compared to Zn. RNA-Seq of leaves under different B levels revealed modulated genes with potential roles in nutritional homeostasis and stress response that may be key to controlling B status in the plant. We also identified putative B transporters whose expression levels were significantly affected by B supplementation with foliar fertilization of plants growing under low B conditions. Furthermore, a gene lacking functional annotation (Glyma.03G180300) emerged as a novel potential marker of B status. Two genes (Glyma.16G118000, Glyma.16G199000) were consistently induced by Zn availability, highlighting their potential as biomarkers for assessing its status in soybean plants. This work advances our understanding of nutritional homeostasis in soybean plants and identifies target genes and potential molecular mechanisms involved in nutritional response. Our study informs fertilizer design targeting specific nutrient transporters, thereby enhancing nutrient efficiency in crops.

Transit of NEAT1 and MTP11 to the plasma membrane and co-localization to vesicles support a role for exocytosis-mediated export in metal homeostasis

Understanding the role and mode of action of nutrient transporters requires information about their dynamic associations with plant membranes. Historically, apoplastic nutrient export has been associated with proteins localized at the plasma membrane (PM), while the role of endomembrane localization has been less explored. However, recent work on the PHOSPHATE 1 (PHO1) inorganic phosphate (Pi) exporter demonstrated that, although primarily localized at the Golgi and trans-Golgi network (TGN) vesicles, PHO1 does associate with the PM when clathrin-mediated endocytosis (CME) was inhibited, supporting a mechanism for Pi homeostasis involving exocytosis. We explored whether CME inhibition can identify other transporters that, although primarily localized at Golgi/TGN at steady-state level, also transit via the PM and are potentially involved in export via exocytosis. We found that, similar to PHO1, Golgi-localized transporters NA EFFLUX TRANSPORTER1 (NAET1) and METAL TOLERANCE PROTEIN11 (MTP11) relocate to the PM when CME is inhibited, both transiently in Nicotiana benthamiana and conditionally in Arabidopsis thaliana. Such PM re-localization of transporters upon CME inhibition is specific, since it does not occur with several other Golgi-associated transporters, including MTP5 and BIVALENT CATION TRANSPORTER 3 (BICAT3), as well as resident Golgi/TGN membrane proteins, such as α-1,2-MANNOSIDASE I (Man1) and VESICLE TRANSPORT V-SNARE 12 (VTI12). Additionally, we observed that NAET1, MTP11 and PHO1 all partially co-localize to vesicles. Overall, our study supports a role for synaptic-like vesicle-mediated exocytosis for both NEAT1 and MTP11 in nutrient transport in plants and highlights the importance of assessing the transient localization of Golgi/TGN proteins to the PM.

The role of the Arabidopsis tandem zinc-finger C3H15 protein in metal homeostasis

Living organisms have developed finely regulated homeostatic networks to mitigate the effects of environmental fluctuations in transition metal micronutrients, including iron, zinc, and copper. In Saccharomyces cerevisiae, the tandem zinc-finger protein Cth2 post-transcriptionally regulates gene expression under conditions of iron deficiency by controlling the levels of mRNAs that code for non-essential ferroproteins. The molecular mechanism involves Cth2 binding to AU-rich elements present in the 3' untranslated region of target mRNAs, negatively affecting their stability and translation. Arabidopsis thaliana has two TZF proteins homologous to yeast Cth2, C3H14 and C3H15, which participate in cell wall remodelling. The present work examines the expression of representative metal homeostasis genes with putative AREs in plants with altered levels of C3H14 and C3H15 grown under varying metal availabilities. The results suggest that C3H15 may act as a post-transcriptional plant modulator of metal adequacy, as evidenced by the expression of SPL7, the main transcriptional regulator under copper deficiency, and PETE2, which encodes plastocyanin. In contrast to S. cerevisiae, the plant C3H15 affects copper and zinc homeostasis rather than iron. When grown under copper-deficient conditions, adult C3H15OE plants exhibit lower chlorophyll content and photosynthetic efficiency compared to control plants, suggesting accelerated senescence. Likewise, metal content in C3H15OE plants under copper deficiency shows altered mobilization of copper and zinc to seeds. These data suggest that the C3H15 protein plays a role in modulating both cell wall remodelling and metal homeostasis. The interaction between these processes may be the cause of altered metal translocation.

The Role of Membrane Transporters in the Biofortification of Zinc and Iron in Plants

Over three billion people suffer from various health issues due to the low supply of zinc (Zn) and iron (Fe) in their food. Low supply of micronutrients is the main cause of malnutrition and biofortification could help to solve this issue. Understanding the molecular mechanisms of biofortification is challenging. The membrane transporters are involved in the uptake, transport, storage, and redistribution of Zn and Fe in plants. These transporters are also involved in biofortification and help to load the Zn and Fe into the endosperm of the seeds. Very little knowledge is available on the role and functions of membrane transporters involved in seed biofortification. Understanding the mechanism and role of membrane transporters could be helpful to improve biofortification. In this review, we provide the details on membrane transporters involved in the uptake, transport, storage, and redistribution of Zn and Fe. We also discuss available information on transporters involved in seed biofortification. This review will help plant breeders and molecular biologists understand the importance and implications of membrane transporters for seed biofortification.

Photosynthetic, Molecular and Ultrastructural Characterization of Toxic Effects of Zinc in Caulerpa racemosa Indicate Promising Bioremediation Potentiality

Caulerpaceae are unconventional green algae composed of multinucleated, single siphonous cells. The species of Caulerpa are acquiring major scientific interest for both their invasion in the Mediterranean ecological niche and for the production of valuable natural metabolites. Furthermore, the abilities of Caulerpa spp. in the biorecovery of polluted waters were recently investigated. Among heavy metal contaminants in marine systems, zinc (Zn) is considered a critical pollutant, progressively accumulating from plastic leachates. In this study, the responses of Caulerpa racemosa to different levels (5-10 mg L^-1) of Zn were studied for 14 days under laboratory-controlled conditions. Effects of Zn were monitored by measuring the growth rate, photosynthetic efficiency and gene expression. Moreover, the ability of Caulerpa to remove Zn from seawater was monitored. Zn induced detrimental effects by decreasing the relative growth rate (RGR) and maximal PSII photochemical efficiency (F_v/F_m). Moreover, C. racemosa, grown in contaminated seawater, reduced the levels of Zn to a final concentration of 1.026 and 1.932 mg L^-1 after 14 days, thus demonstrating efficient uptake. Therefore, our results characterized the effects of zinc on C. racemosa and the possible role of this alga as being effective in the bioremediation of marine seawater.

Zinc Transporter ZmLAZ1-4 Modulates Zinc Homeostasis on Plasma and Vacuolar Membrane in Maize

Zinc is an essential micronutrient for plant growth and development, and functions as a cofactor for hundreds of transcription factors and enzymes in numerous biological processes. Zinc deficiency is common abiotic stress resulting in yield loss and quality deterioration of crops, but zinc excess causes toxicity for biological systems. In plants, zinc homeostasis is tightly modulated by zinc transporters and binding compounds that uptake/release, transport, localize, and store zinc, as well as their upstream regulators. Lazarus 1 (LAZ1), a member of DUF300 protein family, functions as transmembrane organic solute transporter in vertebrates. However, the function of LAZ1 in plants is still obscure. In the present study, the ZmLAZ1-4 protein was confirmed to bind to zinc ions by bioinformatic prediction and thermal shift assay. Heterologous expression of ZmLAZ1-4 in the zinc-sensitive yeast mutant, Arabidopsis, and maize significantly facilitated the accumulation of Zn2+ in transgenic lines, respectively. The result of subcellular localization exhibited that ZmLAZ1-4 was localized on the plasma and vacuolar membrane, as well as chloroplast. Moreover, the ZmLAZ1-4 gene was negatively co-expressed with ZmBES1/BZR1-11 gene through co-expression and real-time quantitative PCR analysis. The results of yeast one-hybrid and dual-luciferase assay suggested that ZmBES1/BZR1-11 could bind to ZmLAZ1-4 promoter to inhibit its transcription. All results indicated that ZmLAZ1-4 was a novel zinc transporter on plasma and vacuolar membrane, and transported zinc under negative regulation of the ZmBES1/BZR1-11 transcription factor. The study provides insights into further underlying the mechanism of ZmLAZ1-4 regulating zinc homeostasis.

Zinc in plants: Integrating homeostasis and biofortification

Zinc plays many essential roles in life. As a strong Lewis acid that lacks redox activity under environmental and cellular conditions, the Zn²⁺ cation is central in determining protein structure and catalytic function of nearly 10% of most eukaryotic proteomes. While specific functions of zinc have been elucidated at a molecular level in a number of plant proteins, wider issues abound with respect to the acquisition and distribution of zinc by plants. An important challenge is to understand how plants balance between Zn supply in soil and their own nutritional requirement for zinc, particularly where edaphic factors lead to a lack of bioavailable zinc or, conversely, an excess of zinc that bears a major risk of phytotoxicity. Plants are the ultimate source of zinc in the human diet, and human Zn deficiency accounts for over 400 000 deaths annually. Here, we review the current understanding of zinc homeostasis in plants from the molecular and physiological perspectives. We provide an overview of approaches pursued so far in Zn biofortification of crops. Finally, we outline a "push-pull" model of zinc nutrition in plants as a simplifying concept. In summary, this review discusses avenues that can potentially deliver wider benefits for both plant and human Zn nutrition.

Molecular regulation of zinc deficiency responses in plants

Zinc (Zn) is an essential micronutrient for plants and animals. Because of its low availability in arable soils worldwide, Zn deficiency is becoming a serious agricultural problem resulting in decreases of crop yield and nutritional quality. Plants have evolved multiple responses to adapt to low levels of soil Zn supply, involving biochemical and physiological changes to improve Zn acquisition and utilization, and defend against Zn deficiency stress. In this review, we summarize the physiological and biochemical adaptations of plants to Zn deficiency, the roles of transporters and metal-binding compounds in Zn homeostasis regulation, and the recent progresses in understanding the sophisticated regulatory mechanisms of Zn deficiency responses that have been made by molecular and genetic analyses, as well as diverse 'omics' studies. Zn deficiency responses are tightly controlled by multiple layers of regulation, such as transcriptional regulation that is mediated by transcription factors like F-group bZIP proteins, epigenetic regulation at the level of chromatin, and post-transcriptional regulation mediated by small RNAs and alternative splicing. The insights into the regulatory network underlying Zn deficiency responses and the perspective for further understandings of molecular regulation of Zn deficiency responses have been discussed. The understandings of the regulatory mechanisms will be important for improving Zn deficiency tolerance, Zn use efficiency, and Zn biofortification in plants.

Zinc toxicity in plants: a review

This review highlights the most recent updated information available about Zn phytotoxicity at physiological, biochemical and molecular levels, uptake mechanisms as well as excess Zn homeostasis in plants. Zinc (Zn) is a natural component of soil in terrestrial environments and is a vital element for plant growth, as it performs imperative functions in numerous metabolic pathways. However, potentially noxious levels of Zn in soils can result in various alterations in plants like reduced growth, photosynthetic and respiratory rate, imbalanced mineral nutrition and enhanced generation of reactive oxygen species. Zn enters into soils through various sources, such as weathering of rocks, forest fires, volcanoes, mining and smelting activities, manure, sewage sludge and phosphatic fertilizers. The rising alarm in environmental facet, as well as, the narrow gap between Zn essentiality and toxicity in plants has drawn the attention of the scientific community to its effects on plants and crucial role in agricultural sustainability. Hence, this review focuses on the most recent updates about various physiological and biochemical functions perturbed by high levels of Zn, its mechanisms of uptake and transport as well as molecular aspects of surplus Zn homeostasis in plants. Moreover, this review attempts to understand the mechanisms of Zn toxicity in plants and to present novel perspectives intended to drive future investigations on the topic. The findings will further throw light on various mechanisms adopted by plants to cope with Zn stress which will be of great significance to breeders for enhancing tolerance to Zn contamination.