Identification and characterization of yellow stripe-like genes in maize suggest their roles in the uptake and transport of zinc and iron

Iron sensing, signalling and acquisition by microbes and plants under environmental stress: Use of iron-solubilizing bacteria in crop biofortification for sustainable agriculture

Iron is very crucial micronutrient prerequisite for growth of all cellular organisms including plants, microbes, animals and humans. Though iron (Fe) is present in abundance in earth's crust, but most of its forms present in soil are biologically unavailable, thus putting a constraint to utilize it. Plants and microorganisms maintain iron homeostasis to balance the supply of enough Fe for metabolism from their surrounding environments and to avoid excessive toxic levels. Microorganisms and plants employ different strategies for sensing, signaling, transportation and uptake of Fe under different types of stressed environments. Microbial communities present in soil and vicinity of roots contribute in biogeochemical cycling and uptake of different nutrients including Fe resulting into improved soil fertility and plant health. In this review, the regulation of iron uptake and transport under different kinds of biotic and abiotic stresses is described. In addition, the insights have been provided for enhancing bioavailability of Fe in sustainable agriculture practices. The inoculation of different crop plants with iron solubilizing microbes improved bioavailablilty of Fe in soil and increased plant growth and crop yield. Insights were provided about possible role of recent bioengineering techniques to improve Fe availability and uptake by plants. However, well-planned and large-scale field trials are required before recommending particular iron solubilizing microbes as biofertilizers for increasing Fe availability, improving plant development and crop yields in sustainable agriculture.

ZmPRR37-ZmYSL14 module enhances salt stress tolerance in maize

KEY MESSAGE

Maize YSL gene ZmYSL14 enhances salt tolerance in maize. Our findings demonstrate that ZmPRR37-ZmYSL14 module promotes salt stress tolerance in maize. Environmental challenges, particularly soil salinity, have severely impacted maize production worldwide. Yellow Stripe-Like (YSL) is a subfamily of oligopeptide transporter, and there is limited reporting on its role in salt stress response. In this study, we screened an Ac/Ds mutant library and identified a salt-sensitive line, K17-16H876. Further characterization revealed that the Ds element was inserted into the coding region of Zm00001d054041 (ZmYSL14), which encodes a YSL protein. The zmysl14 mutant exhibited increased salt sensitivity, while ZmYSL14 overexpression lines displayed enhanced salt tolerance. Yeast one-hybrid screening identified a PRR transcription factor, ZmPRR37, which has previously been reported to enhance salt stress tolerance in maize. Dual-luciferase assays and RT-qPCR analysis indicated that ZmPRR37 promotes the expression of ZmYSL14. Our findings suggest the ZmPRR37-ZmYSL14 module enhances salt tolerance in maize. This research enriches the functional understanding of YSL family genes and provides valuable genetic resources for breeding new salt-tolerant maize varieties.

Dissecting the genetic architecture of polygenic nutritional traits in maize through meta-QTL analysis

Maize, as a staple crop, contributes significantly to global nutritional security. However, improving its nutritional quality, including grain zinc (GZn), grain iron (GFe), kernel oil (KO), protein quality (PQ), and content (PC), is difficult due to the complex and polygenic nature of these traits. In traditional quantitative trait loci (QTLs) mapping, different populations tested across variable environments have resulted in heterogeneous findings, highlighting the challenge of QTL instability. Therefore, we tested whether Meta-QTL (MQTL) analysis enables the identification of stable QTLs with broader allelic coverage and higher mapping resolution for effective marker-assisted selection (MAS) of complex traits. A comprehensive literature search revealed 29 mapping studies encompassing 308 QTLs for the targeted traits. A total of 34 stable MQTLs were identified, with an average CI of 4.59 cM. These MQTLs were located on all ten maize chromosomes, with phenotypic variance explained (PVE %) ranging from 7.3 % (MQTL1_2) to 49.0 % (MQTL3_2). Furthermore, the analysis revealed six MAS-friendly and five hotspot MQTLs. Besides, 591 CGs were identified underlying these MQTLs, of which 14 have known roles in grain filling, metal homeostasis, and fatty acid biosynthesis in maize. In silico analysis confirmed the tissue-specific expression of these 14 CGs. MQTL analysis effectively refined the genomic regions (4.86 folds) linked with nutritional quality and identified stable MQTLs and CGs. These findings will be useful for developing nutritionally enriched varieties through MAS and genetic engineering.

Type 4 plant metallothioneins - players in zinc biofortification?

Food security is defined as uninterrupted access to food that meets people's dietary needs. One essential trace element of a complete diet is zinc, which is vital for various processes, including growth, development, and the immune response. The estimated global prevalence of zinc deficiency is around 30%. Meat and meat products provide an abundant and also bioavailable source of zinc. However, in developing countries, access to meat is restricted, and in developed countries, meat consumption has declined for ethical and environmental reasons. The potential for zinc deficiency arises from (i) low concentrations of this element in plant-based diets, (ii) poor zinc absorption from plant-based food in the human intestine, and (iii) the risk of uptake of toxic metals together with essential ones. This review summarises the current knowledge concerning type 4 metallothioneins, which represent promising targets for zinc biofortification. We describe their place in the zinc route from soil to seed, their expression patterns, their role in plants, and their three-dimensional protein structure and how this affects their selectivity towards zinc. This review aims to provide a comprehensive theoretical basis for the potential use of type 4 plant metallothioneins to create zinc-biofortified crops.

The multifaceted role of YSL proteins: Iron transport and emerging functions in plant metal homeostasis

Understanding metal transport in plants has always been critical. Several gene families have been identified in the last two decades that have aided in the understanding of channelized metal transport, including their uptake, distribution, and storage in plants. Identifying Yellow Stripe-like (YSL) genes has contributed to an improved understanding of metal homeostasis in plants, especially monocots. Several studies have demonstrated that these genes play a role in transporting metals complexed with phytosiderophores (PS) and/or nicotianamine (NA). In the current review, we have discussed and opinionated the signalling role of YSL protein in maintaining inter and intracellular metal homeostasis in plants. Although the genes are known to have a broader range of metal substrate specificity, these are primary iron (Fe) transporters, and a detailed Fe transport in plants is discussed. Furthermore, based on recent findings, alternative functions of these genes are also discussed. Overall, we provide a broader overview of YSL protein in modulating the Fe mobilization and provides evidence of the expanding functions in plants.

ZmYSL2 affects the physiological function of iron deficiency in maize

MAIN CONCLUSION

Iron deficiency resulted in reduced sensitivity of the enhanced iron tolerance in maize o213 mutants, affecting pigment synthesis, photosynthesis parameters, sugar content, and iron distribution, with variable expression of the YSL gene. Iron (Fe) is a vital trace element for the growth and development of plants. A deficiency of this element results in the formation of yellow leaves. The present study demonstrated that a mutation in the ZmYSL2 gene resulted in reduced sensitivity of o213 mutant maize seedlings to Fe deficiency. The mutation resulted in a reduction in the content of photosynthetic pigments in the leaves, particularly carotenoids, and a decline in photosynthetic parameters. However, it is noteworthy that the soluble sugar content was increased. The mutant displayed increased iron accumulation in the roots and decreased accumulation in the shoots, accompanied by elevated iron content in the sap of the phloem. The expression pattern of the ZmYSL2 gene demonstrated a correlation between its expression level and the iron deficiency phenotype. In conclusion, the results of this study demonstrate that the ZmYSL2 gene plays a crucial physiological role in enabling maize to adapt to an iron-deficient environment.

Genome-wide identification and expression analysis of ferric reductase oxidase (FRO) genes in Gossypium spp. reveal their crucial role in iron homeostasis under abiotic and biotic stress

Ferric Reductase Oxidase (FRO) genes are pivotal in iron uptake and homeostasis in plants, yet they are not studied in cotton. Here, we identify and analyze 65 FRO homologs (21 GhFRO, 21 GbFRO, 11 GaFRO, 12 GrFRO) across four Gossypium species (G. hirsutum, G. barbadense, G. arboreum, G. raimondii). FRO exhibit conserved ferric reductase activity and conserved domain structures; Ferric_reduct (PF01794), FAD_binding_8 (PF08022), and NAD_binding_6 (PF08030) across species. Physicochemical properties and subcellular localization analysis provided insights into FRO proteins' functional characteristics, mainly localized to the plasma membrane. Phylogenetic analysis delineates 11 groups, indicating both conserved and divergent evolutionary patterns. Gene structure analysis unveils varying exon-intron compositions. Chromosomal localization shows distribution across A and D genomes, suggesting evolutionary dynamics. Synteny analysis reveals paralogous and orthologous gene pairs subjected to purifying selection. The cis-regulatory elements analysis implicates diverse regulatory mechanisms. Expression profiling highlights dynamic regulation across developmental stages, abiotic and biotic stress conditions. GhFRO interacts with Ca++-dependent protein kinases-10/28-like (CDPKs10/28-like) and metal transporter Natural resistance-associated macrophage protein 6 (Nramp6) to regulate metal ion transport and iron homeostasis. The three-dimensional protein structure prediction suggests potential ligand-binding sites in FRO proteins. Moreover, qRT-PCR analysis of selected eight GhFROs in leaves treated with stress elicitors, MeJA, SA, NaCl, and PEG for 1h, 2h, 4h, and 6h revealed significant downregulation. Overall, this comprehensive study provides insights into FRO gene diversity, evolution, structure, regulation, and function in cotton, with implications for understanding plant iron homeostasis and stress responses.

Genome-Wide Identification of the Maize Chitinase Gene Family and Analysis of Its Response to Biotic and Abiotic Stresses

BACKGROUND/OBJECTIVES

Chitinases, enzymes belonging to the glycoside hydrolase family, play a crucial role in plant growth and stress response by hydrolyzing chitin, a natural polymer found in fungal cell walls. This study aimed to identify and analyze the maize chitinase gene family, assessing their response to various biotic and abiotic stresses to understand their potential role in plant defense mechanisms and stress tolerance.

METHODS

We employed bioinformatics tools to identify 43 chitinase genes in the maize B73_V5 genome. These genes were characterized for their chromosomal positions, gene and protein structures, phylogenetic relationships, functional enrichment, and collinearity. Based on previous RNA-seq data, the analysis assessed the expression patterns of these genes at different developmental stages and under multiple stress conditions.

RESULTS

The identified chitinase genes were unevenly distributed across maize chromosomes with a history of tandem duplications contributing to their divergence. The ZmChi protein family was predominantly hydrophilic and localized mainly in chloroplasts. Expression analysis revealed that certain chitinase genes were highly expressed at specific developmental stages and in response to various stresses, with ZmChi31 showing significant responsiveness to 11 different abiotic and biotic stresses.

CONCLUSIONS

This study provides new insights into the role of chitinase genes in maize stress response, establishing a theoretical framework for exploring the molecular basis of maize stress tolerance. The identification of stress-responsive chitinase genes, particularly ZmChi31, offers potential candidates for further study in enhancing maize resistance to environmental challenges.

Types of Membrane Transporters and the Mechanisms of Interaction between Them and Reactive Oxygen Species in Plants

Membrane transporters are proteins that mediate the entry and exit of substances through the plasma membrane and organellar membranes and are capable of recognizing and binding to specific substances, thereby facilitating substance transport. Membrane transporters are divided into different types, e.g., ion transporters, sugar transporters, amino acid transporters, and aquaporins, based on the substances they transport. These membrane transporters inhibit reactive oxygen species (ROS) generation through ion regulation, sugar and amino acid transport, hormone induction, and other mechanisms. They can also promote enzymatic and nonenzymatic reactions in plants, activate antioxidant enzyme activity, and promote ROS scavenging. Moreover, membrane transporters can transport plant growth regulators, solute proteins, redox potential regulators, and other substances involved in ROS metabolism through corresponding metabolic pathways, ultimately achieving ROS homeostasis in plants. In turn, ROS, as signaling molecules, can affect the activity of membrane transporters under abiotic stress through collaboration with ions and involvement in hormone metabolic pathways. The research described in this review provides a theoretical basis for improving plant stress resistance, promoting plant growth and development, and breeding high-quality plant varieties.