Overexpression of a multiple stress-responsive gene, ZmMPK4, enhances tolerance to low temperature in transgenic tobacco

Synthesis of CaWO4 as a Photocatalyst for Degradation of Methylene Blue and Carmine under Ultraviolet Light Irradiation

Photocatalysis is considered a promising method for wastewater treatment; however, most synthesized photocatalysts have complex structures and are costly. Thus, in this study, a novel CaWO4 sample was synthesized by a co-precipitation method in one step. The characteristic results show that CaWO4 has good dispersibility, a large specific surface area, and good photoresponse under UV light. The synthesized CaWO4 can be used to degrade methylene blue (MB) and carmine (CR) under UV light without the addition of oxidants. The effects of a water matrix, including pH value, solid–liquid ratio, light intensity, and initial concentration of pollutants on photocatalytic degradation were studied. According to the optimization of these factors, the optimal photocatalytic degradation condition was found under the catalyst concentration of 1.0 g/L and ultraviolet light intensity of 80 W. The optimal pH is 8.2 for the MB system and 6.0 for the CR system. The optimal photocatalytic degradation of MB and CR at 100 mg/L can be achieved as 100%. According to the results of scavenger experiments, holes and hydroxyl radicals dominate the degradation of MB while hydroxyl radicals and superoxide anions are mainly responsible for the degradation of CR. Further analyses showed that photogenerated electrons generated on the surface of the CaWO4 can form electron–hole pairs, thereby producing hydroxyl radicals and superoxide anions to degrade dyes. In addition, the CaWO4 has a good cycling performance in the process of degrading MB (more than 80% after five cycles). It provides a new idea for the photocatalytic degradation of dyes using mineral-like materials.

Comparative Transcriptome and Interaction Protein Analysis Reveals the Mechanism of IbMPK3-Overexpressing Transgenic Sweet Potato Response to Low-Temperature Stress

The sweet potato is very sensitive to low temperature. Our previous study revealed that IbMPK3-overexpressing transgenic sweet potato (M3) plants showed stronger low-temperature stress tolerance than wild-type plants (WT). However, the mechanism of M3 plants in response to low-temperature stress is unclear. To further analyze how IbMPK3 mediates low-temperature stress in sweet potato, WT and M3 plants were exposed to low-temperature stress for 2 h and 12 h for RNA-seq analysis, whereas normal conditions were used as a control (CK). In total, 3436 and 8718 differentially expressed genes (DEGs) were identified in WT at 2 h (vs. CK) and 12 h (vs. CK) under low-temperature stress, respectively, whereas 1450 and 9291 DEGs were detected in M3 plants, respectively. Many common and unique DEGs were analyzed in WT and M3 plants. DEGs related to low temperature were involved in Ca²⁺ signaling, MAPK cascades, the reactive oxygen species (ROS) signaling pathway, hormone transduction pathway, encoding transcription factor families (bHLH, NAC, and WRKY), and downstream stress-related genes. Additionally, more upregulated genes were associated with the MAPK pathway in M3 plants during short-term low-temperature stress (CK vs. 2 h), and more upregulated genes were involved in secondary metabolic synthesis in M3 plants than in the WT during the long-time low-temperature stress treatment (CK vs. 12 h), such as fatty acid biosynthesis and elongation, glutathione metabolism, flavonoid biosynthesis, carotenoid biosynthesis, and zeatin biosynthesis. Moreover, the interaction proteins of IbMPK3 related to photosynthesis, or encoding CaM, NAC, and ribosomal proteins, were identified using yeast two-hybrid (Y2H). This study may provide a valuable resource for elucidating the sweet potato low-temperature stress resistance mechanism, as well as data to support molecular-assisted breeding with the IbMPK3 gene.

Molecular cloning, characterization and expression analysis of CbPLDδ gene from Chorispora bungeana in low temperature

Chorispora bungeana (C. bungeana) is a rare alpine subnival species that is highly tolerant to low temperature stress. Phospholipase D (PLD) is a key enzyme involved in membrane phospholipid catabolism during plant growth and the stress response. In this study, one member of CbPLD gene family, CbPLDδ, was cloned from C. bungeana and was introduced into tobacco. This gene encodes an 864-amino acid protein with two catalytic HxKxxxxD motifs which are essential for phospholipase D activity. After the CbPLDδ gene is fused with the vector containing the GFP tag, subcellular localization showed that CbPLDδ was predominately located in the cell membrane. RT-qPCR and histochemical GUS assays showed that CbPLDδ gene was induced by low temperature and expressed predominantly in leaf and root. Compared with wild-type tobacco, CbPLDδ transgenic tobacco showed higher activities of antioxidant enzymes, and lower levels of malonidiadehyde and electrolyte leakage under low temperature stress. These results reflected that CbPLDδ is involved in the response to low temperature stress, and has the potential to improve the low temperature tolerance of plants.

Comparative effects of glycinebetaine on the thermotolerance in codA- and BADH-transgenic tomato plants under high temperature stress

We propose that codA tomato plants exhibited higher degrees of enhanced thermotolerance than BADH tomato plants, and H₂O₂ as a signaling molecule also plays an important role in heat resistance. Betaine aldehyde dehydrogenase (BADH) and choline oxidase (COD) are key enzymes in glycinebetaine (GB) synthesis. In this study, two kinds of transgenic tomato plants, which were transformed with BADH gene and codA gene, respectively, were used to explore their thermotolerance. Our results showed that the levels of GB in leaves of the fourteen independent transgenic lines ranged from 1.9 μmol g^-1 fresh weight to 3.4 μmol g^-1 fresh weight, while GB was almost undetectable in leaves of WT plants. CO₂ assimilation and photosystem II (PSII) photochemical activity in transgenic plants were more thermotolerant than WT plants, especially the codA-transgenic plants showed the most. Significant accumulation of hydrogen peroxide (H₂O₂), superoxide anion radical (O₂·^-), and malondialdehyde (MDA) were more in WT plants than transgenic plants, while this accumulation in codA-transgenic plant was the least. Furthermore, the expression of the heat response genes and the accumulation of heat shock protein 70 (HSP70) were found to be more in transgenic plants than that in WT plants during heat stress, as well as showing the most expression and accumulation of HSP70 in the codA-transgenic plants. Taken together, our results suggest that the enhanced thermotolerance in transgenic plants is due to the positive role of GB in response to heat stress. And interestingly, in addition to the major role of GB in codA-transgenic plants, H₂O₂ as a signaling molecule may also play an important role in heat resistance, leading to higher thermotolerance compared to BADH-transgenic plants.

MusaMPK5, a mitogen activated protein kinase is involved in regulation of cold tolerance in banana

Mitogen activated protein kinases (MAPKs) are known to play important functions in stress responses of plants. We have functionally characterized a MAPK, MusaMPK5 from banana and demonstrated its function in cold tolerance response of banana plants. Expression of MusaMPK5 showed positive response to cold, methyl-jasmonate and salicylic acid treatment. Transgenic banana plants harbouring P_MusaMPK5::GUS after exposure to cold stress (8 °C) showed strong induction of GUS in cells surrounding central vascular cylinder of corm and cortical cells of pseudostem. Transgenic banana lines overexpressing MusaMPK5 were regenerated and four different transgenic lines were confirmed for T-DNA insertions by Southern blot and PCR analysis. In an in-vitro growth assay transgenic lines gained better shoot length and fresh weight during recovery from cold stress indicating improved cold tolerance ability of transgenic lines than control plants. Leaf discs of transgenic lines bleached less and retain lower MDA content than leaf discs of control plants after cold stress (4 °C and 8 °C). Cold stress tolerance analysis using two month old plants suggested that improved cold tolerance ability of transgenic lines might be associated with increased level of proline and reduced MDA content. MusaMPK5 gets localized in cytoplasm as observed in onion epidermal cells transiently overexpressing either MusaMPK5-GFP or MusaMPK5-GUS fusion protein. MusaMPK5 is a functional kinase as it autophosphorylate itself and phosphorylate myelin basic protein (MBP) in an in vitro reaction. Purified MusaMPK5 can phosphorylate NAC042 and SNAC67 transcription factors of banana which are important regulators of stress tolerance in banana plants.

Cadmium activates ZmMPK3-1 and ZmMPK6-1 via induction of reactive oxygen species in maize roots

Both mitogen-activated protein kinase (MAPK) cascades and reactive oxygen species (ROS) are critical to signaling in eukaryotes. Cadmium induces MAPK activation and ROS production in plants. This study aims to identify specific MAPKs activated by CdCl₂ in maize roots, and examine the relationship between MAPK activation and ROS production under CdCl₂ treatment. Using in-gel kinase assays, immunoprecipitation, and immunoblot analysis, we identified 43 and 45 kDa ERK-like MAPKs in response to CdCl₂. Further analysis revealed that ZmMPK3-1 and ZmMPK6-1 correspond to the 43 and 45 kDa MAPKs, respectively. In addition, CdCl₂ induced ROS production prior to the activation of ZmMPK3-1 and ZmMPK6-1. Inhibition of ROS attenuated Cd-activation of ZmMPK3-1 and ZmMPK6-1, whereas inhibition of MAPK signaling did not disturb Cd-induced ROS production. Collectively, these results indicate that, in maize roots, cadmium stress activates ZmMPK3-1 and ZmMPK6-1 via ROS induction.

Analysis of MAP kinase MPK4/MEKK1/MKK genes of Carica papaya L. comparative to other plant homologues

Mitogen-activated protein kinase 4 (MPK4) interacts with the (Mitogen-activated protein kinase kinase kinase 1) MEKK1/ Mitogenactivated protein kinase kinase 1 (MKK1)/ Mitogen-activated protein kinase kinase 2 (MKK2) complex to affect its function in plant development or against pathogen attacks. The KEGG (Kyoto Encyclopedia of Genes and Genomes) network analysis of Arabidopsis thaliana revealed close interactions between those four genes in the same plant-pathogen interaction pathway, which warrants further study of these genes due to their evolutionary conservation in different plant species. Through targeting the signature sequence in MPK4 of papaya using orthologs from Arabidopsis, the predicted sequence of MPK4 was studied using a comparative in silico approach between different plant species and the MAP cascade complex of MEKK1/MKK1/MKK2. This paper reported that MPK4 was highly conserved in papaya with 93% identical across more than 500 bases compared in each species predicted. Slight variations found in the MEKK1/MKK1/MKK2 complex nevertheless still illustrated sequence similarities between most of the species. Localization of each gene in the cascade network was also predicted, potentiating future functional verification of these genes interactions using knock out or/and gene silencing tactics.

Genome-Wide Identification and Expression Analysis of the Mitogen-Activated Protein Kinase Gene Family in Cassava

Mitogen-activated protein kinases (MAPKs) play central roles in plant developmental processes, hormone signaling transduction, and responses to abiotic stress. However, no data are currently available about the MAPK family in cassava, an important tropical crop. Herein, 21 MeMAPK genes were identified from cassava. Phylogenetic analysis indicated that MeMAPKs could be classified into four subfamilies. Gene structure analysis demonstrated that the number of introns in MeMAPK genes ranged from 1 to 10, suggesting large variation among cassava MAPK genes. Conserved motif analysis indicated that all MeMAPKs had typical protein kinase domains. Transcriptomic analysis suggested that MeMAPK genes showed differential expression patterns in distinct tissues and in response to drought stress between wild subspecies and cultivated varieties. Interaction networks and co-expression analyses revealed that crucial pathways controlled by MeMAPK networks may be involved in the differential response to drought stress in different accessions of cassava. Expression of nine selected MAPK genes showed that these genes could comprehensively respond to osmotic, salt, cold, oxidative stressors, and abscisic acid (ABA) signaling. These findings yield new insights into the transcriptional control of MAPK gene expression, provide an improved understanding of abiotic stress responses and signaling transduction in cassava, and lead to potential applications in the genetic improvement of cassava cultivars.

The Comparatively Proteomic Analysis in Response to Cold Stress in Cassava Plantlets

Cassava (Manihot esculenta Crantz) is a tropical root crop and sensitive to low temperature. However, it is poorly to know how cassava can modify its metabolism and growth to adapt to cold stress. An investigation aimed at a better understanding of cold-tolerant mechanism of cassava plantlets was carried out with the approaches of physiology and proteomics in the present study. The principal component analysis of seven physiological characteristics showed that electrolyte leakage (EL), chlorophyll content, and malondialdehyde (MDA) may be the most important physiological indexes for determining cold-resistant abilities of cassava. The genome-wide proteomic analysis showed that 20 differential proteins had the same patterns in the apical expanded leaves of cassava SC8 and Col1046. They were mainly related to photosynthesis, carbon metabolism and energy metabolism, defense, protein synthesis, amino acid metabolism, signal transduction, structure, detoxifying and antioxidant, chaperones, and DNA-binding proteins, in which 40 % were related with photosynthesis. The remarkable variation in photosynthetic activity and expression level of peroxiredoxin is closely linked with expression levels of proteomic profiles. Moreover, analysis of differentially expressed proteins under cold stress is an important step toward further elucidation of mechanisms of cold stress resistance.

Overexpression of ZmMAPK1 enhances drought and heat stress in transgenic Arabidopsis thaliana

Mitogen-activated protein kinase (MAPK) signal transduction cascades play a crucial role in the response to extracellular stimuli in eukaryotes. A number of MAPK family genes have been isolated in plants, but the maize MAPK genes have been little studied. Here, we studied the role of maize MAP kinase 1 (ZmMAPK1) using gene expression, protein subcellular localization, transformation in Arabidopsis, expression patterns of the stress-responsive genes and physiological parameter analysis. Our physiological parameter analysis suggested that over-expression ZmMAPK1 can increase proline content and decrease malondialdehyde content under drought, and prevent chlorophyll loss and the production of scavenger reactive oxygen species under heat stress. The resistance characteristics of the over-expression of ZmMAPK1 were associated with a significant increase in survival rate. These results suggest that ZmMAPK1 plays a positive role in response to drought and heat stress in Arabidopsis, and provide new insights into the mechanisms of action of MAPK in response to abiotic stress in plants.

Genome-wide identification and analysis of expression profiles of maize mitogen-activated protein kinase kinase kinase

Mitogen-activated protein kinase (MAPK) cascades are highly conserved signal transduction model in animals, yeast and plants. Plant MAPK cascades have been implicated in development and stress responses. Although MAPKKKs have been investigated in several plant species including Arabidopsis and rice, no systematic analysis has been conducted in maize. In this study, we performed a bioinformatics analysis of the entire maize genome and identified 74 MAPKKK genes. Phylogenetic analyses of MAPKKKs from maize, rice and Arabidopsis have classified them into three subgroups, which included Raf, ZIK and MEKK. Evolutionary relationships within subfamilies were also supported by exon-intron organizations and the conserved protein motifs. Further expression analysis of the MAPKKKs in microarray databases revealed that MAPKKKs were involved in important signaling pathways in maize different organs and developmental stages. Our genomics analysis of maize MAPKKK genes provides important information for evolutionary and functional characterization of this family in maize.