Characterization on TaMPK14, an MAPK family gene of wheat, in modulating N-starvation response through regulating N uptake and ROS homeostasis

Genome-Wide Identification of the MPK Gene Family and Expression Analysis under Low-Temperature Stress in the Banana

Mitogen-activated protein kinases (MAPKs and MPKs) are important in the process of resisting plant stress. In this study, 21, 12, 18, 16, and 10 MPKs were identified from Musa acuminata, Musa balbisiana, Musa itinerans, Musa schizocarpa, and Musa textilis, respectively. These MPKs were divided into Group A, B, C, and D. Phylogenetic analysis revealed that this difference in number was due to the gene shrinkage of the Group B subfamily of Musa balbisiana and Musa textilis. KEGG annotations revealed that K14512, which is involved in plant hormone signal transduction and the plant-pathogen interaction, was the most conserved pathway of the MPKs. The results of promoter cis-acting element prediction and focTR4 (Fusarium oxysporum f. sp. cubense tropical race 4) transcriptome expression analysis preliminarily confirmed that MPKs were relevant to plant hormone and biotic stress, respectively. The expression of MPKs in Group A was significantly upregulated at 4 °C, and dramatically, the MPKs in the root were affected by low temperature. miR172, miR319, miR395, miR398, and miR399 may be the miRNAs that regulate MPKs during low-temperature stress, with miR172 being the most critical. miRNA prediction and qRT-PCR results indicated that miR172 may negatively regulate MPKs. Therefore, we deduced that MPKs might coordinate with miR172 to participate in the process of the resistance to low-temperature stress in the roots of the banana. This study will provide a theoretical basis for further analysis of the mechanism of MPKs under low-temperature stress of bananas, and this study could be applied to molecular breeding of bananas in the future.

The efficacy of Azotobacter chroococcum in altering maize plant-defense responses to armyworm at elevated CO2 concentration

Elevated atmospheric carbon dioxide (eCO₂) concentrations can alter the carbon:nitrogen ratio and palatability of host plants for herbivorous insects, but rhizobacteria likely mitigate the alteration and influence physiological adaptation of insects. In this study, we conducted transcriptomic analysis of maize (Zea mays) response to Azotobacter chroococcum (AC) inoculation under eCO₂ conditions in contrast to ambient CO₂ (aCO₂), and studied the effects of plant-defense change of maize under eCO₂ on the oriental armyworm, Mythimna separata. Results showed that there were 16, 14, 16 and 135 differentially expressed genes that were associated with plant-defense response in maize leaves between aCO₂-CK and aCO₂-AC, eCO₂-CK and eCO₂-AC, aCO₂-CK and eCO₂-CK, aCO₂-AC and eCO₂-AC, respectively. Moreover, A. chroococcum inoculation and eCO₂ influenced plant hormone signal transduction of maize. Interestingly, A. chroococcum inoculation significantly decreased the contents of JA (jasmonic acid) and JA-Ile (isoleucine conjugate of JA) in leaves, but eCO₂ markedly increased contents of JA-Ile, JA and SA (salicylic acid). Compared to aCO₂, eCO₂ significantly decreased activity of protective enzyme (catalase), and increased activities of digestive (lipase and protease), protective (peroxidase) and detoxifying enzymes (carboxylesterase, Mixed-functional oxidase and glutathione s-transferase), prolonged developmental time, and decreased survival rate and body weight of larvae (P < 0.05). A. chroococcum inoculation significantly increased the activity of protective enzyme (catalase), and decreased the activities of detoxifying enzymes (carboxylesterase, glutathione s-transferase and mixed-functional oxidase), thus increased the growth rate and body weight of larvae in comparison with no-inoculation of A. chroococcum (P < 0.05). The indices of M. separata were significantly correlated with the foliar contents of JA, JA-Ile and SA (|r| = 0.44-0.85, P < 0.05), indicating that A. chroococcum inoculation altered the physiological adaptation of M. separata under eCO₂ by disturbing defense substances in maize. Our results in understanding effects of A. chroococcum inoculation on maize resistance to herbivorous insects will be valuable for agricultural pest control in the future at eCO₂ conditions.

MITOGEN-ACTIVATED PROTEIN KINASE PHOSPHATASE 1 mediates root sensing of serotonin through jasmonic acid signaling and modulating reactive oxygen species

Serotonin (5-hydroxytryptamine) acts as a neurotransmitter in mammals and is widely distributed in the plant kingdom, where it influences root growth and defense. Mitogen-Activated Protein Kinases (MAPKs) and MAPK phosphatases (MKPs) play critical functions in decoding hormonal signalling, but their possible roles in mediating serotonin responses await investigation. In this report, we unveiled positive roles for the MITOGEN-ACTIVATED PROTEIN KINASE PHOSPHATASE1 (MKP1) in the inhibition of the primary root growth, cell division, meristem structure, and differentiation events in Arabidopsis seedlings. mkp1 mutants were less sensitive to jasmonic acid applications that halted primary root growth in wild-type (WT) plants, and consistently, the neurotransmitter activated the expression of the JASMONATE ZIM-domain (JAZ) proteins JAZ1 and JAZ10, two critical proteins orchestrating jasmonic acid signalling. This effect correlated with exacerbated production of endogenous reactive oxygen species (ROS) in the WT, a process constitutively manifested in mkp1 mutants. These data help to clarify the relationship between serotonin and growth/defense trade-offs, and reveal the importance of the MAPK pathway in root development through ROS production.

A dominant gene Ihrl1 is tightly linked to and inhibits the gene Ndhrl1 mediating nitrogen-dependent hypersensitive reaction-like phenotype in wheat

Identification and mapping of an inhibitor of Ndhrl1 mediating nitrogen-dependent hypersensitive reaction-like phenotype in wheat. Hypersensitive reaction-like (HRL) traits are characteristic of spontaneous lesions including yellowish spots, brown spots or white-stripe that appeared randomly and dispersedly on all the leaves in the absence of plant pathogens. Our previous studies have shown that the wheat line P7001 showed an HRL trait at low nitrogen supply, and this trait was controlled by the gene Ndhrl1 (Nitrogen-dependent hypersensitive reaction-like 1). In order to investigate the robustness of the trait expression mediated by Ndhrl1 under different genetic backgrounds, seven genetic populations, with P7001 being the common female parent, were constructed and analyzed. F₁ plants from six of the seven combinations showed HRL trait and Ndhrl1 segregated in a dominant way of HRL: non-HRL = 3:1 in the six populations (F₂). Exceptionally, the F₁ plants of P7001/Fielder combination showed non-HRL trait and HRL trait in the F₂ population showed a contrasting recessive segregation ratio of HRL: non-HRL = 1:3, suggesting Fielder may have another HRL-related gene. Using 55 K SNP array and PCR-based markers, the HRL-related gene in Fielder was mapped to an interval of 5.63-12.91 Mb on the short arm of chromosome 2B with the flanking markers Yzu660R075552 and Yzu660F075941. A recombinant with genomic region of Fielder at Ndhrl1 locus showing HRL trait demonstrated that Fielder also harbored Ndhrl1 same as P7001. Thus, Fielder carries a single dominant suppressor of Ndhrl1, designated as Ihrl1 (Inhibitor of hypersensitive reaction-like). Interestingly, Ihrl1 is tightly linked to Ndhrl1 and may be also involved in nitrogen metabolic and (or) signaling pathways.

Mitogen-Activated Protein Kinase and Substrate Identification in Plant Growth and Development

Mitogen-activated protein kinases (MAPKs) form tightly controlled signaling cascades that play essential roles in plant growth, development, and defense response. However, the molecular mechanisms underlying MAPK cascades are still very elusive, largely because of our poor understanding of how they relay the signals. The MAPK cascade is composed of MAPK, MAPKK, and MAPKKK. They transfer signals through the phosphorylation of MAPKKK, MAPKK, and MAPK in turn. MAPKs are organized into a complex network for efficient transmission of specific stimuli. This review summarizes the research progress in recent years on the classification and functions of MAPK cascades under various conditions in plants, especially the research status and general methods available for identifying MAPK substrates, and provides suggestions for future research directions.

Transcriptome Differences in Response Mechanisms to Low-Nitrogen Stress in Two Wheat Varieties

Nitrogen plays a crucial role in wheat growth and development. Here, we analyzed the tolerance of wheat strains XM26 and LM23 to low-nitrogen stress using a chlorate sensitivity experiment. Subsequently, we performed transcriptome analyses of both varieties exposed to low-nitrogen (LN) and normal (CK) treatments. Compared with those under CK treatment, 3534 differentially expressed genes (DEGs) were detected in XM26 in roots and shoots under LN treatment (p < 0.05, and |log2FC| > 1). A total of 3584 DEGs were detected in LM23. A total of 3306 DEGs, including 863 DEGs in roots and 2443 DEGs in shoots, were specifically expressed in XM26 or showed huge differences between XM26 and LM23 (log2FC ratio > 3). These were selected for gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. The calcium-mediated plant–pathogen interaction, MAPK signaling, and phosphatidylinositol signaling pathways were enriched in XM26 but not in LM23. We also verified the expression of important genes involved in these pathways in the two varieties using qRT-PCR. A total of 156 transcription factors were identified among the DEGs, and their expression patterns were different between the two varieties. Our findings suggest that calcium-related pathways play different roles in the two varieties, eliciting different tolerances to low-nitrogen stress.

Transcriptome Analysis Reveals Different Responsive Patterns to Nitrogen Deficiency in Two Wheat Near-Isogenic Lines Contrasting for Nitrogen Use Efficiency

Simple Summary

Nitrogen (N) limitation is the key factor for wheat production worldwide. Therefore, the development of genotypes with improved nitrogen use efficiency (NUE) is a prerequisite for sustainable and productive agriculture. Exploring the molecular mechanisms of low N stress tolerance is significant for breeding wheat cultivars with high NUE. To clarify the underlying molecular mechanisms of enhanced resilience to low N in high-NUE wheat, we performed an RNA sequencing (RNA-seq) analysis. In the current research, two wheat near-isogenic lines (NILs) differing dramatically in NUE were used to measure gene expression differences under different N treatments. There was a dramatic difference between two wheat NILs in response to N deficiency at the transcriptional level, and the classification of identified candidate genes may provide new valuable insights into the resilience mechanism of wheat.

Abstract

The development of crop cultivars with high nitrogen use efficiency (NUE) under low-N fertilizer inputs is imperative for sustainable agriculture. However, there has been little research on the molecular mechanisms underlying enhanced resilience to low N in high-NUE plants. The comparison of the transcriptional responses of genotypes contrasting for NUE will facilitate an understanding of the key molecular mechanism of wheat resilience to low-N stress. In the current study, the RNA sequencing (RNA-seq) technique was employed to investigate the genotypic difference in response to N deficiency between two wheat NILs (1Y, high-NUE, and 1W, low-NUE). In our research, high- and low-NUE wheat NILs showed different patterns of gene expression under N-deficient conditions, and these N-responsive genes were classified into two major classes, including “frontloaded genes” and “relatively upregulated genes”. In total, 103 and 45 genes were identified as frontloaded genes in high-NUE and low-NUE wheat, respectively. In summary, our study might provide potential directions for further understanding the molecular mechanism of high-NUE genotypes adapting to low-N stress.

Transcriptome Analysis of Two Near-Isogenic Lines with Different NUE under Normal Nitrogen Conditions in Wheat

Simple Summary

High nitrogen use efficiency (NUE) in wheat (Triticum aestivum L.) is the key to ensure high yield and reduce pollution. Understanding the physiological and molecular changes that regulate NUE is important for the breeding of high-NUE wheat varieties. Carbon and nitrogen metabolism are the basic metabolic pathways in plants. It becomes important to reveal the underlying molecular mechanisms related to carbon and nitrogen metabolism, which may be helpful to improve NUE. In this paper, two wheat near-isogenic lines (NILs) with contrasting NUE were performed RNA-Sequencing (RNA-Seq) to identify candidate genes associated with carbon/nitrogen metabolism under normal nitrogen conditions. Our research may provide new insights into the comprehensive understanding of the molecular mechanism underlying NUE.

Abstract

Nitrogen (N) is an essential nutrient element for crop productivity. Unfortunately, the nitrogen use efficiency (NUE) of crop plants gradually decreases with the increase of the N application rate. Nevertheless, little has been known about the molecular mechanisms of differences in NUE among genotypes of wheat. In this study, we used RNA-Sequencing (RNA-Seq) to compare the transcriptome profiling of flag leaves at the stage of anthesis in wheat NILs (1Y, high-NUE, and 1W, low-NUE) under normal nitrogen conditions (300 kg N ha⁻¹, corresponding to 1.6 g N pot⁻¹). We identified 7023 DEGs (4738 upregulated and 2285 downregulated) in the comparison between lines 1Y and 1W. The responses of 1Y and 1W to normal N differed in the transcriptional regulatory mechanisms. Several genes belonging to the GS and GOGAT gene families were upregulated in 1Y compared with 1W, and the enhanced carbon metabolism might lead 1Y to produce more C skeletons, metabolic energy, and reductants for nitrogen metabolism. A subset of transcription factors (TFs) family members, such as ERF, WRKY, NAC, and MYB, were also identified. Collectively, these identified candidate genes provided new information for a further understanding of the genotypic difference in NUE.

Signaling Responses to N Starvation: Focusing on Wheat and Filling the Putative Gaps With Findings Obtained in Other Plants. A Review

Wheat is one of the most important food crops worldwide. In recent decades, fertilizers, especially nitrogen (N), have been increasingly utilized to maximize wheat productivity. However, a large proportion of N is not used by plants and is in fact lost into the environment and causes serious environmental pollution. Therefore, achieving a low N optimum via efficient physiological and biochemical processes in wheat grown under low-N conditions is highly important for agricultural sustainability. Although N stress-related N capture in wheat has become a heavily researched subject, how this plant adapts and responds to N starvation has not been fully elucidated. This review summarizes the current knowledge on the signaling mechanisms activated in wheat plants in response to N starvation. Furthermore, we filled the putative gaps on this subject with findings obtained in other plants, primarily rice, maize, and Arabidopsis. Phytohormones have been determined to play essential roles in sensing environmental N starvation and transducing this signal into an adjustment of N transporters and phenotypic adaptation. The critical roles played by protein kinases and critical kinases and phosphatases, such as MAPK and PP2C, as well as the multifaceted functions of transcription factors, such as NF-Y, MYB, DOF, and WRKY, in regulating the expression levels of their target genes (proteins) for low-N tolerance are also discussed. Optimization of root system architecture (RSA) via root branching and thinning, improvement of N acquisition and assimilation, and fine-tuned autophagy are pivotal strategies by which plants respond to N starvation. In light of these findings, we attempted to construct regulatory networks for RSA modification and N uptake, transport, assimilation, and remobilization.