Promoter of a salinity and cold stress-induced MCM6 DNA helicase from pea

Structural and functional analysis of stress-inducible genes and their promoters selected from young oil palm (Elaeis guineensis) under salt stress

Background

Soil salinity is a problem in more than 100 countries across all continents. It is one of the abiotic stress that threatens agriculture the most, negatively affecting crops and reducing productivity. Transcriptomics is a technology applied to characterize the transcriptome in a cell, tissue, or organism at a given time via RNA-Seq, also known as full-transcriptome shotgun sequencing. This technology allows the identification of most genes expressed at a particular stage, and different isoforms are separated and transcript expression levels measured. Once determined by this technology, the expression profile of a gene must undergo validation by another, such as quantitative real-time PCR (qRT-PCR). This study aimed to select, annotate, and validate stress-inducible genes—and their promoters—differentially expressed in the leaves of oil palm (Elaeis guineensis) plants under saline stress.

Results

The transcriptome analysis led to the selection of 14 genes that underwent structural and functional annotation, besides having their expression validated using the qRT-PCR technique. When compared, the RNA-Seq and qRT-PCR profiles of those genes resulted in some inconsistencies. The structural and functional annotation analysis of proteins coded by the selected genes showed that some of them are orthologs of genes reported as conferring resistance to salinity in other species. There were those coding for proteins related to the transport of salt into and out of cells, transcriptional regulatory activity, and opening and closing of stomata. The annotation analysis performed on the promoter sequence revealed 22 distinct types of cis-acting elements, and 14 of them are known to be involved in abiotic stress.

Conclusion

This study has helped validate the process of an accurate selection of genes responsive to salt stress with a specific and predefined expression profile and their promoter sequence. Its results also can be used in molecular-genetics-assisted breeding programs. In addition, using the identified genes is a window of opportunity for strategies trying to relieve the damages arising from the salt stress in many glycophyte crops with economic importance.

The Minichromosome Maintenance Complex Component 2 (MjMCM2) of Meloidogyne javanica is a potential effector regulating the cell cycle in nematode-induced galls

Root-knot nematodes Meloidogyne spp. induce enlarged multinucleate feeding cells—galls—in host plant roots. Although core cell-cycle components in galls follow a conserved track, they can also be usurped and manipulated by nematodes. We identified a candidate effector in Meloidogyne javanica that is directly involved in cell-cycle manipulation—Minichromosome Maintenance Complex Component 2 (MCM2), part of MCM complex licensing factor involved in DNA replication. MjMCM2, which is induced by plant oxilipin 9-HOT, was expressed in nematode esophageal glands, upregulated during parasitic stages, and was localized to plant cell nucleus and plasma membrane. Infected tomato hairy roots overexpressing MjMCM2 showed significantly more galls and egg-mass-producing females than wild-type roots, and feeding cells showed more nuclei. Phylogenetic analysis suggested seven homologues of MjMCM2 with unknown association to parasitism. Sequence mining revealed two RxLR-like motifs followed by SEED domains in all Meloidogyne spp. MCM2 protein sequences. The unique second RxLR-like motif was absent in other Tylenchida species. Molecular homology modeling of MjMCM2 suggested that second RxLR2-like domain is positioned on a surface loop structure, supporting its function in polar interactions. Our findings reveal a first candidate cell-cycle gene effector in M. javanica—MjMCM2—that is likely secreted into plant host to mimic function of endogenous MCM2.

Comparative genomic analysis reveals evolutionary and structural attributes of MCM gene family in Arabidopsis thaliana and Oryza sativa

The mini-chromosome maintenance (MCM) family, a large and functionally diverse protein family belonging to the AAA+ superfamily, is essential for DNA replication in all eukaryotic organisms. The MCM 2-7 form a hetero-hexameric complex which serves as licensing factor necessary to ensure the proper genomic DNA replication during the S phase of cell cycle. MCM 8-10 are also associated with the DNA replication process though their roles are particularly unclear. In this study, we report an extensive in silico analysis of MCM gene family (MCM 2-10) in Arabidopsis and rice. Comparative analysis of genomic distribution across eukaryotes revealed conservation of core MCMs 2-7 while MCMs 8-10 are absent in some taxa. Domain architecture analysis underlined MCM 2-10 subfamily specific features. Phylogenetic analyses clustered MCMs into 9 clades as per their subfamily. Duplication events are prominent in plant MCM family, however no duplications are observed in Arabidopsis and rice MCMs. Synteny analysis among Arabidopsis thaliana, Oryza sativa, Glycine max and Zea mays MCMs demonstrated orthologous relationships and duplication events. Further, estimation of synonymous and non-synonymous substitution rates illustrated evolution of MCM family under strong constraints. Expression profiling using available microarray data and qRT-PCR revealed differential expression under various stress conditions, hinting at their potential use to develop stress resilient crops. Homology modeling of Arabidopsis and rice MCM 2-7 and detailed comparison with yeast MCMs identified conservation of eukaryotic specific insertions and extensions as compared to archeal MCMs. Protein-protein interaction analysis revealed an extensive network of putative interacting partners mainly involved in DNA replication and repair. The present study provides novel insights into the MCM family in Arabidopsis and rice and identifies unique features, thus opening new perspectives for further targeted analyses.

De novo RNA sequencing analysis of Aeluropus littoralis halophyte plant under salinity stress

The study of salt tolerance mechanisms in halophyte plants can provide valuable information for crop breeding and plant engineering programs. The aim of the present study was to investigate whole transcriptome analysis of Aeluropus littoralis in response to salinity stress (200 and 400 mM NaCl) by de novo RNA-sequencing. To assemble the transcriptome, Trinity v2.4.0 and Bridger tools, were comparatively used with two k-mer sizes (25 and 32 bp). The de novo assembled transcriptome by Bridger (k-mer 32) was chosen as final assembly for subsequent analysis. In general, 103290 transcripts were obtained. The differential expression analysis (log₂^FC > 1 and FDR < 0.01) showed that 1861 transcripts expressed differentially, including169 up and 316 down-regulated transcripts in 200 mM NaCl treatment and 1035 up and 430 down-regulated transcripts in 400 mM NaCl treatment compared to control. In addition, 89 transcripts were common in both treatments. The most important over-represented terms in the GO analysis of differentially expressed genes (FDR < 0.05) were chitin response, response to abscisic acid, and regulation of jasmonic acid mediated signaling pathway under 400 mM NaCl treatment and cell cycle, cell division, and mitotic cell cycle process under 200 mM treatment. In addition, the phosphatidylcholine biosynthetic process term was common in both salt treatments. Interestingly, under 400 mM salt treatment, the PRC1 complex that contributes to chromatin remodeling was also enriched along with vacuole as a general salinity stress responsive cell component. Among enriched pathways, the MAPK signaling pathway (ko04016) and phytohormone signal transduction (ko04075) were significantly enriched in 400 mM NaCl treatment, whereas DNA replication (ko03032) was the only pathway that significantly enriched in 200 mM NaCl treatment. Finally, our findings indicate the salt-concentration depended responses of A. littoralis, which well-known salinity stress-related pathways are induced in 400 mM NaCl, while less considered pathways, e.g. cell cycle and DNA replication, are highlighted under 200 mM NaCl treatment.

Auxin Response Factors (ARFs) are potential mediators of auxin action in tomato response to biotic and abiotic stress (Solanum lycopersicum)

Survival biomass production and crop yield are heavily constrained by a wide range of environmental stresses. Several phytohormones among which abscisic acid (ABA), ethylene and salicylic acid (SA) are known to mediate plant responses to these stresses. By contrast, the role of the plant hormone auxin in stress responses remains so far poorly studied. Auxin controls many aspects of plant growth and development, and Auxin Response Factors play a key role in the transcriptional activation or repression of auxin-responsive genes through direct binding to their promoters. As a mean to gain more insight on auxin involvement in a set of biotic and abiotic stress responses in tomato, the present study uncovers the expression pattern of SlARF genes in tomato plants subjected to biotic and abiotic stresses. In silico mining of the RNAseq data available through the public TomExpress web platform, identified several SlARFs as responsive to various pathogen infections induced by bacteria and viruses. Accordingly, sequence analysis revealed that 5' regulatory regions of these SlARFs are enriched in biotic and abiotic stress-responsive cis-elements. Moreover, quantitative qPCR expression analysis revealed that many SlARFs were differentially expressed in tomato leaves and roots under salt, drought and flooding stress conditions. Further pointing to the putative role of SlARFs in stress responses, quantitative qPCR expression studies identified some miRNA precursors as potentially involved in the regulation of their SlARF target genes in roots exposed to salt and drought stresses. These data suggest an active regulation of SlARFs at the post-transcriptional level under stress conditions. Based on the substantial change in the transcript accumulation of several SlARF genes, the data presented in this work strongly support the involvement of auxin in stress responses thus enabling to identify a set of candidate SlARFs as potential mediators of biotic and abiotic stress responses.

The plant cell cycle: Pre-Replication complex formation and controls

The multiplication of cells in all living organisms requires a tight regulation of DNA replication. Several mechanisms take place to ensure that the DNA is replicated faithfully and just once per cell cycle in order to originate through mitoses two new daughter cells that contain exactly the same information from the previous one. A key control mechanism that occurs before cells enter S phase is the formation of a pre-replication complex (pre-RC) that is assembled at replication origins by the sequential association of the origin recognition complex, followed by Cdt1, Cdc6 and finally MCMs, licensing DNA to start replication. The identification of pre-RC members in all animal and plant species shows that this complex is conserved in eukaryotes and, more importantly, the differences between kingdoms might reflect their divergence in strategies on cell cycle regulation, as it must be integrated and adapted to the niche, ecosystem, and the organism peculiarities. Here, we provide an overview of the knowledge generated so far on the formation and the developmental controls of the pre-RC mechanism in plants, analyzing some particular aspects in comparison to other eukaryotes.

Emerging Importance of Helicases in Plant Stress Tolerance: Characterization of Oryza sativa Repair Helicase XPB2 Promoter and Its Functional Validation in Tobacco under Multiple Stresses

Genetic material always remains at the risk of spontaneous or induced damage which challenges the normal functioning of DNA molecule, thus, DNA repair is vital to protect the organisms against genetic damage. Helicases, the unique molecular motors, are emerged as prospective molecules to engineer stress tolerance in plants and are involved in nucleic acid metabolism including DNA repair. The repair helicase, XPB is an evolutionary conserved protein present in different organisms, including plants. Availability of few efficient promoters for gene expression in plants provoked us to study the promoter of XPB for better understanding of gene regulation under stress conditions. Here, we report the in silico analysis of novel stress inducible promoter of Oryza sativa XPB2 (OsXPB2). The in vivo validation of functionality/activity of OsXPB2 promoter under abiotic and hormonal stress conditions was performed by Agrobacterium-mediated transient assay in tobacco leaves using OsXPB2::GUS chimeric construct. The present research revealed that OsXPB2 promoter contains cis-elements accounting for various abiotic stresses (salt, dehydration, or cold) and hormone (Auxin, ABA, or MeJA) induced GUS expression/activity in the promoter-reporter assay. The promoter region of OsXPB2 contains CACG, GTAACG, CACGTG, CGTCA CCGCCGCGCT cis acting-elements which are reported to be salt, dehydration, cold, MeJA, or ABA responsive, respectively. Functional analysis was done by Agrobacterium-mediated transient assay using agroinfiltration in tobacco leaves, followed by GUS staining and fluorescence quantitative analyses. The results revealed high induction of GUS activity under multiple abiotic stresses as compared to mock treated control. The present findings suggest that OsXPB2 promoter is a multi-stress inducible promoter and has potential applications in sustainable crop production under abiotic stresses by regulating desirable pattern of gene expression.

Identification of candidate genes involved in early iron deficiency chlorosis signaling in soybean (Glycine max) roots and leaves

BACKGROUND

Iron is an essential micronutrient for all living things, required in plants for photosynthesis, respiration and metabolism. A lack of bioavailable iron in soil leads to iron deficiency chlorosis (IDC), causing a reduction in photosynthesis and interveinal yellowing of leaves. Soybeans (Glycine max (L.) Merr.) grown in high pH soils often suffer from IDC, resulting in substantial yield losses. Iron efficient soybean cultivars maintain photosynthesis and have higher yields under IDC-promoting conditions than inefficient cultivars.

RESULTS

To capture signaling between roots and leaves and identify genes acting early in the iron efficient cultivar Clark, we conducted a RNA-Seq study at one and six hours after replacing iron sufficient hydroponic media (100 μM iron(III) nitrate nonahydrate) with iron deficient media (50 μM iron(III) nitrate nonahydrate). At one hour of iron stress, few genes were differentially expressed in leaves but many were already changing expression in roots. By six hours, more genes were differentially expressed in the leaves, and a massive shift was observed in the direction of gene expression in both roots and leaves. Further, there was little overlap in differentially expressed genes identified in each tissue and time point.

CONCLUSIONS

Genes involved in hormone signaling, regulation of DNA replication and iron uptake utilization are key aspects of the early iron-efficiency response. We observed dynamic gene expression differences between roots and leaves, suggesting the involvement of many transcription factors in eliciting rapid changes in gene expression. In roots, genes involved iron uptake and development of Casparian strips were induced one hour after iron stress. In leaves, genes involved in DNA replication and sugar signaling responded to iron deficiency. The differentially expressed genes (DEGs) and signaling components identified here represent new targets for soybean improvement.

Isolation and functional characterization of the promoter of a DEAD-box helicase Psp68 using Agrobacterium-mediated transient assay

Helicases are molecular motor proteins that perform a variety of cellular functions including transcription, translation, DNA replication and repair, RNA maturation, ribosome synthesis, nuclear export and splicing processes. The p68 is an evolutionarily conserved protein which plays pivotal roles in all aspect RNA metabolism processes. It is well established that helicases provides abiotic stress adaptation in plants but analysis of cis-regulatory elements present in the upstream regions is still infancy. Here we report isolation and functional characterization of the promoter of a DEAD-box helicase Psp68 in response to abiotic stress and hormonal regulation. The promoter of Psp68 was isolated by gene walking PCR from pea genomic DNA library constructed in BD genome walker kit. In silico analysis revealed that promoter of Psp68 contained a TATA, a CAAT motif and also harbors some important stress and hormone associated cis regulatory elements, including E-box, AGAAA, GATA-box, ACGT, GAAAA and GTCTC. Functional analyses were performed by Agrobacterium-mediated transient assay in tobacco leaves. Very high level of GUS activity was observed in agroinfiltrated tobacco leaves by the construct carrying the Psp68 promoter::GUS, subjected to abiotic stress and exogenous hormonal treatments. Stress-inducible nature of Psp68 promoter opens possibility for the study of the gene regulation under stress condition. Therefore, may be useful in the field of agriculture and biotechnology.

Isolation and functional characterization of the promoter of a DEAD-box helicase Psp68 using Agrobacterium-mediated transient assay

Helicases are molecular motor proteins that perform a variety of cellular functions including transcription, translation, DNA replication and repair, RNA maturation, ribosome synthesis, nuclear export and splicing processes. The p68 is an evolutionarily conserved protein which plays pivotal roles in all aspect RNA metabolism processes. It is well established that helicases provides abiotic stress adaptation in plants but analysis of cis-regulatory elements present in the upstream regions is still infancy. Here we report isolation and functional characterization of the promoter of a DEAD-box helicase Psp68 in response to abiotic stress and hormonal regulation. The promoter of Psp68 was isolated by gene walking PCR from pea genomic DNA library constructed in BD genome walker kit. In silico analysis revealed that promoter of Psp68 contained a TATA, a CAAT motif and also harbors some important stress and hormone associated cis regulatory elements, including E-box, AGAAA, GATA-box, ACGT, GAAAA and GTCTC. Functional analyses were performed by Agrobacterium-mediated transient assay in tobacco leaves. Very high level of GUS activity was observed in agroinfiltrated tobacco leaves by the construct carrying the Psp68 promoter::GUS, subjected to abiotic stress and exogenous hormonal treatments. Stress-inducible nature of Psp68 promoter opens possibility for the study of the gene regulation under stress condition. Therefore, may be useful in the field of agriculture and biotechnology.

Isolation and in silico analysis of promoter of a high salinity stress-regulated pea DNA helicase 45

Helicases are motor proteins that can transiently catalyze the unwinding of energetically stable duplex DNA or RNA molecules by using ATP hydrolysis as the source of energy. Many helicases share a core region of highly conserved sequence motifs, and belong to the rapidly growing DEAD-box protein family. Pea DNA helicase 45 (PDH45), that exhibits striking homology with eukaryotic translation initiation factor 4A (eIF4A), contains ATP-dependent DNA and RNA helicase, DNA-dependent ATPase, and ATP-binding activities. The transcript of the PDH45 gene was reported to be upregulated in pea plant in response to high salinity, cold stress, abscisic acid (ABA), dehydration and early wounding. The first direct evidence that overexpression of PDH45 confers salinity stress tolerance without yield loss has also been reported. A promoter analysis of PDH45 gene has not been studied. The cis-regulatory elements present on promoter region of the gene act as binding sites for RNA polymerase and transcription factors and control the regulation of gene expression. Here we report the promoter of the PDH45 gene that contains stress-responsive cis-regulatory elements which may be responsible for regulating the expression of PDH45 under abiotic stress conditions.