Overexpression of a Novel ERF-X-Type Transcription Factor, OsERF106MZ, Reduces Shoot Growth and Tolerance to Salinity Stress in Rice

Genome-Wide Analysis of BBX Gene Family in Three Medicago Species Provides Insights into Expression Patterns under Hormonal and Salt Stresses

BBX protein is a class of zinc finger transcription factors that have B-box domains at the N-terminus, and some of these proteins contain a CCT domain at the C-terminus. It plays an important role in plant growth, development, and metabolism. However, the expression pattern of BBX genes in alfalfa under hormonal and salt stresses is still unclear. In this study, we identified a total of 125 BBX gene family members by the available Medicago reference genome in diploid alfalfa (Medicago sativa spp. Caerulea), a model plant (M. truncatula), and tetraploid alfalfa (M. sativa), and divided these members into five subfamilies. We found that the conserved motifs of BBXs of the same subfamily reveal similarities. We analyzed the collinearity relationship and duplication mode of these BBX genes and found that the expression pattern of BBX genes is specific in different tissues. Analysis of the available transcriptome data suggests that some members of the BBX gene family are involved in multiple abiotic stress responses, and the highly expressed genes are often clustered together. Furthermore, we identified different expression patterns of some BBX genes under salt, ethylene, salt and ethylene, salicylic acid, and salt and salicylic acid treatments, verified by qRT-PCR, and analyzed the subcellular localization of MsBBX2, MsBBX17, and MsBBX32 using transient expression in tobacco. The results showed that BBX genes were localized in the nucleus. This study systematically analyzed the BBX gene family in Medicago plants, which provides a basis for the study of BBX gene family tolerance to abiotic stresses.

Understanding AP2/ERF Transcription Factor Responses and Tolerance to Various Abiotic Stresses in Plants: A Comprehensive Review

Abiotic stress is an adverse environmental factor that severely affects plant growth and development, and plants have developed complex regulatory mechanisms to adapt to these unfavourable conditions through long-term evolution. In recent years, many transcription factor families of genes have been identified to regulate the ability of plants to respond to abiotic stresses. Among them, the AP2/ERF (APETALA2/ethylene responsive factor) family is a large class of plant-specific proteins that regulate plant response to abiotic stresses and can also play a role in regulating plant growth and development. This paper reviews the structural features and classification of AP2/ERF transcription factors that are involved in transcriptional regulation, reciprocal proteins, downstream genes, and hormone-dependent signalling and hormone-independent signalling pathways in response to abiotic stress. The AP2/ERF transcription factors can synergise with hormone signalling to form cross-regulatory networks in response to and tolerance of abiotic stresses. Many of the AP2/ERF transcription factors activate the expression of abiotic stress-responsive genes that are dependent or independent of abscisic acid and ethylene in response to abscisic acid and ethylene. In addition, the AP2/ERF transcription factors are involved in gibberellin, auxin, brassinosteroid, and cytokinin-mediated abiotic stress responses. The study of AP2/ERF transcription factors and interacting proteins, as well as the identification of their downstream target genes, can provide us with a more comprehensive understanding of the mechanism of plant action in response to abiotic stress, which can improve plants' ability to tolerate abiotic stress and provide a more theoretical basis for increasing plant yield under abiotic stress.

Molecular switches in plant stress adaptation

Climate change poses a significant threat to the global ecosystem, prompting plants to use various adaptive mechanisms via molecular switches to combat biotic and abiotic stress factors. These switches activate stress-induced pathways by altering their configuration between stable states. In this review, we investigated the regulation of molecular switches in different plant species in response to stress, including the stress-regulated response of multiple switches in Arabidopsis thaliana. We also discussed techniques for developing stress-resilient crops using molecular switches through advanced biotechnological tools. The literature search, conducted using databases such as PubMed, Google Scholar, Web of Science, and SCOPUS, utilized keywords such as molecular switch, plant adaptation, biotic and abiotic stresses, transcription factors, Arabidopsis thaliana, and crop improvement. Recent studies have shown that a single molecular switch can regulate multiple stress networks, and multiple switches can regulate a single stress condition. This multifactorial understanding provides clarity to the switch regulatory network and highlights the interrelationships of different molecular switches. Advanced breeding techniques, along with genomic and biotechnological tools, have paved the way for further research on molecular switches in crop improvement. The use of synthetic biology in molecular switches will lead to a better understanding of plant stress biology and potentially bring forth a new era of stress-resilient, climate-smart crops worldwide.

A comprehensive investigation of the regulatory roles of OsERF096, an AP2/ERF transcription factor, in rice cold stress response

KEY MESSAGE

OsERF096 negatively regulates rice cold tolerance and mediates IAA biosynthesis and signaling under cold stress. The APETALA2/ethylene-responsive factor (AP2/ERF) transcription factors play important roles in regulating plant tolerance to abiotic stress. OsERF096 was previously identified as a direct target of miR1320, and was suggested to negatively regulate rice cold tolerance. In this study, we performed RNA-sequencing and targeted metabolomics assays to reveal the regulatory roles of OsERF096 in cold stress response. GO and KEGG analysis of differentially expressed genes showed that the starch and sucrose metabolism, plant-pathogen interaction, and plant hormone signal transduction pathways were significantly enriched. Quantification analysis confirmed a significant difference in sugar contents among WT and OsERF096 transgenic lines under cold treatment. Targeted metabolomics analysis uncovered that IAA accumulation and signaling were modified by OsERF096 in response to cold stress. Expectedly, qRT-PCR assays confirmed significant OsIAAs and OsARFs expression changes in OsERF096 transgenic lines. Finally, we identified three targets of OsERF096 based on RNA-seq, qRT-PCR, and dual-LUC assays. In summary, these results revealed the multiple regulatory roles of OsERF096 in cold stress response.

Overexpression of OsHAD3, a Member of HAD Superfamily, Decreases Drought Tolerance of Rice

Haloacid dehalogenase-like hydrolase (HAD) superfamily have been shown to get involved in plant growth and abiotic stress response. Although the various functions and regulatory mechanism of HAD superfamily have been well demonstrated, we know little about the function of this family in conferring abiotic stress tolerance to rice. Here, we report OsHAD3, a HAD superfamily member, could affect drought tolerance of rice. Under drought stress, overexpression of OsHAD3 increases the accumulation of reactive oxygen species and malondialdehyde than wild type. OsHAD3-overexpression lines decreased but antisense-expression lines increased the roots length under drought stress and the transcription levels of many well-known stress-related genes were also changed in plants with different genotypes. Furthermore, overexpression of OsHAD3 also decreases the oxidative tolerance. Our results suggest that overexpression of OsHAD3 could decrease the drought tolerance of rice and provide a new strategy for improving drought tolerance in rice.

Overexpression of OsERF106MZ promotes parental root growth in rice seedlings by relieving the ABA-mediated inhibition of root growth under salinity stress conditions

BACKGROUND

Roots are essential for plant growth and have a variety of functions, such as anchoring the plant to the ground, absorbing water and nutrients from the soil, and sensing abiotic stresses, among others. OsERF106MZ is a salinity-induced gene that is expressed in germinating seeds and rice seedling roots. However, the roles of OsERF106MZ in root growth remain poorly understood.

RESULTS

Histochemical staining to examine β-glucuronidase (GUS) activity in transgenic rice seedlings harboring OsERF106MZp::GUS indicated that OsERF106MZ is mainly expressed in the root exodermis, sclerenchyma layer, and vascular system. OsERF106MZ overexpression in rice seedlings leads to an increase in primary root (PR) length. The phytohormone abscisic acid (ABA) is thought to act as a hidden architect of root system structure. The expression of the ABA biosynthetic gene OsAO3 is downregulated in OsERF106MZ-overexpressing roots under normal conditions, while the expression of OsNPC3, an AtNPC4 homolog involved in ABA sensitivity, is reduced in OsERF106MZ-overexpressing roots under both normal and NaCl-treated conditions. Under normal conditions, OsERF106MZ-overexpressing roots show a significantly reduced ABA level; moreover, exogenous application of 1.0 µM ABA can suppress OsERF106MZ-mediated root growth promotion. Additionally, OsERF106MZ-overexpressing roots display less sensitivity to ABA-mediated root growth inhibition when treated with 5.0 µM ABA under normal conditions or exposed to NaCl-treated conditions. Furthermore, chromatin immunoprecipitation (ChIP)-qPCR and luciferase (LUC) reporter assays showed that OsERF106MZ can bind directly to the sequence containing the GCC box in the promoter region of the OsAO3 gene and repress the expression of OsAO3.

CONCLUSIONS

OsERF106MZ may play a role in maintaining root growth for resource uptake when rice seeds germinate under salinity stress by alleviating ABA-mediated root growth inhibition.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

Modulating physiological and transcriptional regulatory mechanisms for enhanced climate resilience in cereal crops

Climate change adversely affects the yield and productivity of cereal crops, which consequently impacts food security. Therefore, studying stress acclimation, particularly transcriptional patterns and morpho-physiological responses of cereal crops to different stresses, will provide insights into the molecular determinants underlying climate resilience. The availability of advanced tools and approaches has enabled the characterization of plants at morphological, physiological, biochemical, and molecular levels, which will lead to the identification of genomic regions regulating the stress responses at these levels. This will further facilitate using transgenic, breeding, or genome editing approaches to manipulate the identified regions (genes, alleles, or QTLs) to enhance stress resilience. Next-generation sequencing approaches have advanced the identification of causal genes and markers in the genomes through forward or reverse genetics. In this context, the review enumerates the progress of dissecting the molecular mechanisms underlying transcriptional and physiological responses of major cereals to climate-induced stresses. The review systematically discusses different tools and approaches available to study the response of plants to various stresses and identify the molecular determinants regulating stress-resilience. Further, the application of genomics-assisted breeding, transgene-, and targeted editing-based approaches for modulating the genetic determinants for enhanced climate resilience has been elaborated.

Molecular tools, potential frontiers for enhancing salinity tolerance in rice: A critical review and future prospective

Improvement of salinity tolerance in rice can minimize the stress-induced yield losses. Rice (Oryza sativa) is one of Asia's most widely consumed crops, native to the subtropical regions, and is generally associated with sensitivity to salinity stress episodes. Salt-tolerant rice genotypes have been developed using conventional breeding methods; however, the success ratio is limited because of the complex nature of the trait and the high cost of development. The narrow genetic base of rice limited the success of conventional breeding methods. Hence, it is critical to launch the molecular tools for screening rice novel germplasm for salt-tolerant genes. In this regard, the latest molecular techniques like quantitative trait loci (QTL) mapping, genetic engineering (GE), transcription factors (TFs) analysis, and clustered regularly interspaced short palindromic repeats (CRISPR) are reliable for incorporating the salt tolerance in rice at the molecular level. Large-scale use of these potent genetic approaches leads to identifying and editing several genes/alleles, and QTL/genes are accountable for holding the genetic mechanism of salinity tolerance in rice. Continuous breeding practices resulted in a huge decline in rice genetic diversity, which is a great worry for global food security. However, molecular breeding tools are the only way to conserve genetic diversity by exploring wild germplasm for desired genes in salt tolerance breeding programs. In this review, we have compiled the logical evidences of successful applications of potent molecular tools for boosting salinity tolerance in rice, their limitations, and future prospects. This well-organized information would assist future researchers in understanding the genetic improvement of salinity tolerance in rice.

TCP Transcription Factors Involved in Shoot Development of Ma Bamboo (Dendrocalamus latiflorus Munro)

Ma bamboo (Dendrocalamus latiflorus Munro) is the most widely cultivated clumping bamboo in Southern China and is valuable for both consumption and wood production. The development of bamboo shoots involving the occurrence of lateral buds is unique, and it affects both shoot yield and the resulting timber. Plant-specific TCP transcription factors are involved in plant growth and development, particularly in lateral bud outgrowth and morphogenesis. However, the comprehensive information of the TCP genes in Ma bamboo remains poorly understood. In this study, 66 TCP transcription factors were identified in Ma bamboo at the genome-wide level. Members of the same subfamily had conservative gene structures and conserved motifs. The collinear analysis demonstrated that segmental duplication occurred widely in the TCP transcription factors of Ma bamboo, which mainly led to the expansion of a gene family. Cis-acting elements related to growth and development and stress response were found in the promoter regions of DlTCPs. Expression patterns revealed that DlTCPs have tissue expression specificity, which is usually highly expressed in shoots and leaves. Subcellular localization and transcriptional self-activation experiments demonstrated that the five candidate TCP proteins were typical self-activating nuclear-localized transcription factors. Additionally, the transcriptome analysis of the bamboo shoot buds at different developmental stages helped to clarify the underlying functions of the TCP members during the growth of bamboo shoots. DlTCP12-C, significantly downregulated as the bamboo shoots developed, was selected to further verify its molecular function in Arabidopsis. The DlTCP12-C overexpressing lines exhibited a marked reduction in the number of rosettes and branches compared with the wild type in Arabidopsis, suggesting that DlTCP12-C conservatively inhibits lateral bud outgrowth and branching in plants. This study provides useful insights into the evolutionary patterns and molecular functions of the TCP transcription factors in Ma bamboo and provides a valuable reference for further research on the regulatory mechanism of bamboo shoot development and lateral bud growth.

Function Analysis of the ERF and DREB Subfamilies in Tomato Fruit Development and Ripening

APETALA2/ethylene responsive factors (AP2/ERF) are unique regulators in the plant kingdom and are involved in the whole life activity processes such as development, ripening, and biotic and abiotic stresses. In tomato (Solanum lycopersicum), there are 140 AP2/ERF genes; however, their functionality remains poorly understood. In this work, the 14th and 19th amino acid differences in the AP2 domain were used to distinguish DREB and ERF subfamily members. Even when the AP2 domain of 68 ERF proteins from 20 plant species and motifs in tomato DREB and ERF proteins were compared, the binding ability of DREB and ERF proteins with DRE/CRT and/or GCC boxes remained unknown. During fruit development and ripening, the expressions of 13 DREB and 19 ERF subfamily genes showed some regular changes, and the promoters of most genes had ARF, DRE/CRT, and/or GCC boxes. This suggests that these genes directly or indirectly respond to IAA and/or ethylene (ET) signals during fruit development and ripening. Moreover, some of these may feedback regulate IAA or ET biosynthesis. In addition, 16 EAR motif-containing ERF genes in tomato were expressed in many organs and their total transcripts per million (TPM) values exceeded those of other ERF genes in most organs. To determine whether the EAR motif in EAR motif-containing ERF proteins has repression function, their EAR motifs were retained or deleted in a yeast one-hybrid (YIH) assay. The results indicate that most of EAR motif-containing ERF proteins lost repression activity after deleting the EAR motif. Moreover, some of these were expressed during ripening. Thus, these EAR motif-containing ERF proteins play vital roles in balancing the regulatory functions of other ERF proteins by completing the DRE/CRT and/or GCC box sites of target genes to ensure normal growth and development in tomato.

ERF Transcription Factor OsBIERF3 Positively Contributes to Immunity against Fungal and Bacterial Diseases but Negatively Regulates Cold Tolerance in Rice

We previously showed that overexpression of the rice ERF transcription factor gene OsBIERF3 in tobacco increased resistance against different pathogens. Here, we report the function of OsBIERF3 in rice immunity and abiotic stress tolerance. Expression of OsBIERF3 was induced by Xanthomonas oryzae pv. oryzae, hormones (e.g., salicylic acid, methyl jasmonate, 1-aminocyclopropane-1-carboxylic acid, and abscisic acid), and abiotic stress (e.g., drought, salt and cold stress). OsBIERF3 has transcriptional activation activity that depends on its C-terminal region. The OsBIERF3-overexpressing (OsBIERF3-OE) plants exhibited increased resistance while OsBIERF3-suppressed (OsBIERF3-Ri) plants displayed decreased resistance to Magnaporthe oryzae and X. oryzae pv. oryzae. A set of genes including those for PRs and MAPK kinases were up-regulated in OsBIERF3-OE plants. Cell wall biosynthetic enzyme genes were up-regulated in OsBIERF3-OE plants but down-regulated in OsBIERF3-Ri plants; accordingly, cell walls became thicker in OsBIERF3-OE plants but thinner in OsBIERF3-Ri plants than WT plants. The OsBIERF3-OE plants attenuated while OsBIERF3-Ri plants enhanced cold tolerance, accompanied by altered expression of cold-responsive genes and proline accumulation. Exogenous abscisic acid and 1-aminocyclopropane-1-carboxylic acid, a precursor of ethylene biosynthesis, restored the attenuated cold tolerance in OsBIERF3-OE plants while exogenous AgNO₃, an inhibitor of ethylene action, significantly suppressed the enhanced cold tolerance in OsBIERF3-Ri plants. These data demonstrate that OsBIERF3 positively contributes to immunity against M. oryzae and X. oryzae pv. oryzae but negatively regulates cold stress tolerance in rice.