Abiotic stresses such as drought and salinity are major environmental factors that limit crop yields. Unraveling the molecular mechanisms underlying abiotic stress resistance is crucial for improving crop performance and increasing productivity under adverse environmental conditions. Zinc finger proteins, comprising one of the largest transcription factor families, are known for their finger-like structure and their ability to bind Zn 2+ . Zinc finger proteins are categorized into nine subfamilies based on their conserved Cys and His motifs, including the Cys2/His2-type (C2H2), C3H, C3HC4, C2HC5, C4HC3, C2HC, C4, C6, and C8 subfamilies. Over the past two decades, much progress has been made in understanding the roles of C2H2 zinc finger proteins in plant growth, development, and stress signal transduction. In this review, we focus on recent progress in elucidating the structures, functions, and classifications of plant C2H2 zinc finger proteins and their roles in abiotic stress responses. FIGURE 1 | Structure of C2H2 zinc finger proteins. Structural model of the Arabidopsis C2H2 zinc finger protein STZ produced using the Protein Model Portal tool. Han et al.

The effect of NaCl on reproductive development was investigated in euhalophyte Suaeda salsa L. under controlled conditions. Results showed that NaCl promoted the reproductive growth of S. salsa and 200 mM NaCl was optimal. This was reflected in the increases of seed yield, seed number, flower number per plant and leaf axil, 1000 seed weight, as well as a decrease in flower abortion percentage with supply of NaCl. NaCl reduced the flower abortion percentage by increasing stigma receptivity instead of pollen viability. The Na+ and Cl– concentration in petals, stems and leaves were increased significantly but slightly in stamen and pistil. In contrast, the K+ concentration decreased markedly in leaves, stems and petals but a little in stamen and pistil. The Na+ and Cl– concentrations also increased significantly in seed from mother plants exposed to NaCl, whereas K+ decreased. However, seed quality was not influenced. Our results showed that high concentration of NaCl markedly increases the seed number and quality of S. salsa primarily via increasing flower number and fertility and S. salsa develops strategy to maintain ion homeostasis in reproductive organs for the generation. These factors play a pivotal role in setting up plant populations in saline environment.

Salinity is a major and complex abiotic stress that inhibits plant growth and reduces crop yield. Given the global increase in soil salinity, there is a need to develop salt-tolerant species. Brassica napus L. is an important oilseed crop with some level of salt tolerance. However, few studies have evaluated its salt tolerance thoroughly or screened for traits that can be reliably evaluated for salt tolerance. Here, we evaluated salt tolerance in 549 B. napus inbred lines with different genetic backgrounds using the membership function value (MFV) of certain traits, including the germination rate, root and shoot length, root and shoot fresh weight, and total fresh weight. According to the evaluation criteria-mean MFV, 50 highly salt-tolerant, 115 salt-tolerant, 71 moderately salt-tolerant, 202 salt-sensitive, and 111 highly salt-sensitive inbred lines were screened at the germination stage. We also developed a mathematical evaluation model and identified that the salt tolerance index of shoot fresh weight is a single trait that reliably represents the salt tolerance of B. napus germplasm at the germination stage. These results are useful for evaluating and breeding salt-tolerant B. napus germplasm.

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Suaeda salsa is an annual herbaceous euhalophyte in the family Chenopodiaceae that produces dimorphic seeds on the same plant under natural conditions. In order to determine the effect of salinity on seed quality traits during seed formation, seeds from plants grown under control conditions and on 200 mM NaCl were used to investigate the effect of NaCl on seed production and seed germination. Results showed that size and weight of both black and brown seeds generated from 200 mM NaCl-treated plants were markedly greater than those from controls. The germination percentage of brown seeds from both control and NaCl-treated plants was higher than that of black seeds. Furthermore, the germination percentage of the black seeds generated from 200 mM NaCl-treated plants was significantly higher than that of the control at different concentrations of NaCl, although germination percentage declined with the increase NaCl concentration. Surprisingly, NaCl did not affect germination of the brown seeds. The germination index and vigour index of both black and brown seeds from the control plants were significantly lower than those of seeds from the different NaCl treatments. Seed starch, soluble sugar, protein and lipid content of both black and brown seeds generated from the 200 mM NaCl-treated plants were significantly higher than those from the control. These results suggest that a certain concentration of NaCl plays a pivotal role in seed vitality of the euhalophyte S. salsa through increasing seed weight and contents of storage compounds such as protein, starch and fatty acids.

Cys2His2-like fold group (C2H2)-type zinc finger proteins promote root hair growth and development by regulating their target genes. However, little is known about their potential negative roles in root hair initiation and elongation. Here, we show that the C2H2-type zinc finger protein named ZINC FINGER PROTEIN1 (AtZP1), which contains an ERF-associated amphiphilic repression (EAR) motif, negatively regulates Arabidopsis (Arabidopsis thaliana) root hair initiation and elongation. Our results demonstrate that AtZP1 is highly expressed in root hairs and that AtZP1 inhibits transcriptional activity during root hair development. Plants overexpressing AtZP1 lacked root hairs, while loss-of-function mutants had longer and more numerous root hairs than the wild type. Transcriptome analysis indicated that AtZP1 downregulates genes encoding basic helix-loop-helix (bHLH) transcription factors associated with root hair cell differentiation and elongation. Mutation or deletion of the EAR motif substantially reduced the inhibitory activity of AtZP1. Chromatin immunoprecipitation assays, AtZP1:glucocorticoid receptor (GR) induction experiments, electrophoretic mobility shift assays, and yeast one-hybrid assays showed that AtZP1 directly targets the promoters of bHLH transcription factor genes, including the key root hair initiation gene ROOT HAIR DEFECTIVE6 (RHD6) and root hair elongation genes ROOT HAIR DEFECTIVE 6-LIKE 2 (RSL2) and RSL4, and suppresses root hair development. Our findings suggest that AtZP1 functions downstream of GL2 and negatively regulates root hair initiation and elongation, by suppressing RHD6, RSL4, and RSL2 transcription via the GL2/ZP1/ RSL pathway.

Background: Halophytes possess efficient salt-tolerance mechanisms and can complete their life cycles in naturally saline soils with NaCl contents exceeding 200 mM. While a significant progress have been made in recent decades elucidating underlying salt-tolerance mechanisms, these studies have been mostly confined to the vegetative growth stage. At the same time, the capacity to generate high-quality seeds and to survive early developmental stages under saline conditions, are both critically important for plants. Halophytes perform well in both regards, whereas non-halophytes cannot normally complete their life cycles under saline conditions.Scope: Research into the effects of salinity on plant reproductive biology has gained momentum in recent years. However, it remains unclear whether the reproductive biology of halophytes differs from that of non-halophytes, and whether their reproductive processes benefit, like their vegetative growth, from the presence of salt in the rhizosphere. Here, we summarize current knowledge of the mechanisms underlying the superior reproductive biology of halophytes, focusing on critical aspects including control of flowering time, changes in plant hormonal status and their impact on anther and pollen development and viability, plant carbohydrate status and seed formation, mechanisms behind the early germination of halophyte seeds, and the role of seed polymorphism.Conclusion: Salt has beneficial effects on halophyte reproductive growth that include late flowering, increased flower numbers and pollen vitality, and high seed yield. This improved performance is due to optimal nutrition during vegetative growth, alterations in plant hormonal status, and regulation of flowering genes. In addition, the seeds of halophytes harvested under saline conditions show higher salt tolerance than those obtained under non-saline condition, largely due to increased osmolyte accumulation, more optimal hormonal composition (e.g., high gibberellic acid and low abcisic acid content) and, in some species, seed dimorphism. In the near future, identifying key genes involved in halophyte reproductive physiology and using them to transform crops could be a promising approach to developing saline agriculture.

Named for the characteristic basic helix-loop-helix (bHLH) region in their protein structure, bHLH proteins are a widespread transcription factor class in eukaryotes. bHLHs transcriptionally regulate their target genes by binding to specific positions on their promoters and thereby direct a variety of plant developmental and metabolic processes, such as photomorphogenesis, flowering induction, shade avoidance, and secondary metabolite biosynthesis, which are important for promoting plant tolerance or adaptation to adverse environments. In this review, we discuss the vital roles of bHLHs in plant responses to abiotic stresses, such as drought, salinity, cold, and iron deficiency. We suggest directions for future studies into the roles of bHLH genes in plant and discuss their potential applications in crop breeding.