Rice DEP1, encoding a highly cysteine-rich G protein γ subunit, confers cadmium tolerance on yeast cells and plants

Pivotal role of heterotrimeric G protein in the crosstalk between sugar signaling and abiotic stress response in plants

Heterotrimeric G-proteins are key modulators of multiple signaling and developmental pathways in plants, in which they act as molecular switches to engage in transmitting various stimuli signals from outside into the cells. Substantial studies have identified G proteins as essential components of the organismal response to abiotic stress, leading to adaptation and survival in plants. Meanwhile, sugars are also well acknowledged key players in stress perception, signaling, and gene expression regulation. Connections between the two significant signaling pathways in stress response are of interest to a general audience in plant biology. In this article, advances unraveling a pivotal role of G proteins in the process of sugar signals outside the cells being translated into the operation of autophagy in cells during stress are reviewed. In addition, we have presented recent findings on G proteins regulating the response to drought, salt, alkali, cold, heat and other abiotic stresses. Perspectives on G-protein research are also provided in the end. Since G protein signaling regulates many agronomic traits, elucidation of detailed mechanism of the related pathways would provide useful insights for the breeding of abiotic stress resistant and high-yield crops.

Agronomic potential of plant-specific Gγ proteins

The vascular plant-specific type III Gγ proteins have emerged as important targets for biotechnological applications. These proteins are exemplified by Arabidopsis AGG3, rice Grain Size 3 (GS3), Dense and Erect Panicle 1 (DEP1), and GGC2 and regulate plant stature, seed size, weight and quality, nitrogen use efficiency, and multiple stress responses. These Gγ proteins are an integral component of the plant heterotrimeric G-protein complex and differ from the canonical Gγ proteins due to the presence of a long, cysteine-rich C-terminal region. Most cereal genomes encode three or more of these proteins, which have similar N-terminal Gγ domains but varying lengths of the C-terminal domain. The C-terminal domain is hypothesized to give specificity to the protein function. Intriguingly, many accessions of cultivated cereals have natural deletion of this region in one or more proteins, but the mechanistic details of protein function remain perplexing. Distinct, sometimes contrasting, effects of deletion of the C-terminal region have been reported in different crops or under varying environmental conditions. This review summarizes the known roles of type III Gγ proteins, the possible action mechanisms, and a perspective on what is needed to comprehend their full agronomic potential.

Rapid Visual Detection of Elite Erect Panicle Dense and Erect Panicle 1 Allele for Marker-Assisted Improvement in Rice (Oryza sativa L.) Using the Loop-Mediated Isothermal Amplification Method

Molecular-assisted breeding is an effective way to improve targeted agronomic traits. dep1 (dense and erect panicle 1) is a pleiotropic gene that regulates yield, quality, disease resistance, and stress tolerance, traits that are of great value in rice (Oryza sativa L.) breeding. In this study, a colorimetric LAMP (loop-mediated isothermal amplification) assay was developed for the detection of the dep1 allele and tested for the screening and selection of the heavy-panicle hybrid rice elite restorer line SHUHUI498, modified with the allele. InDel (Insertion and Deletion) primers (DEP1_F and DEP1_R) and LAMP primers (F3, B3, FIP, and BIP) for genotyping were designed using the Primer3 Plus (version 3.3.0) and PrimerExplore (version 5) software. Our results showed that both InDel and LAMP markers could be used for accurate genotyping. After incubation at a constant temperature of 65 °C for 60 min with hydroxynaphthol blue (HNB) as a color indicator, the color of the LAMP assay containing the dep1 allele changed to sky blue. The SHUHUI498 rice line that was detected in our LAMP assay displayed phenotypes consistent with the dep1 allele such as having a more compact plant architecture, straight stems and leaves, and a significant increase in the number of effective panicles and spikelets, demonstrating the effectiveness of our method in screening for the dep1 allele in rice breeding.

Overexpression of a Plant-Specific Gγ Protein, AGG3, in the Model Monocot Setaria viridis Confers Tolerance to Heat Stress

The vascular plant-specific, cysteine-rich type III Gγ proteins, which are integral components of the heterotrimeric G-protein complex, play crucial roles in regulating a multitude of plant processes, including those related to crop yield and responses to abiotic stresses. The presence of multiple copies of type III Gγ proteins in most plants and a propensity of the presence of specific truncated alleles in many cultivated crops present an ambiguous picture of their roles in modulating specific responses. AGG3 is a canonical type III Gγ protein of Arabidopsis, and its overexpression in additional model crops offers the opportunity to directly evaluate the effects of protein expression levels on plant phenotypes. We have shown that AGG3 overexpression in the monocot model Setaria viridis leads to an increase in seed yield. In this study, we have investigated the response of the S. viridis plants overexpressing AGG3 to heat stress (HS), one of the most important abiotic stresses affecting crops worldwide. We show that a short span of HS at a crucial developmental time point has a significant effect on plant yield in the later stages. We also show that plants with higher levels of AGG3 are more tolerant to HS. This is attributed to an altered regulation of stress-responsive genes and improved modulation of the photosynthetic efficiency during the stress. Overall, our results confirm that AGG3 plays a crucial role in regulating plant responses to unfavorable environmental conditions and may contribute positively to avoiding crop yield losses.

Fine Mapping and Candidate Gene Analysis of Rice Grain Length QTL qGL9.1

Grain length (GL) is one of the crucial determinants of rice yield and quality. However, there is still a shortage of knowledge on the major genes controlling the inheritance of GL in japonica rice, which severely limits the improvement of japonica rice yields. Here, we systemically measured the GL of 667 F₂ and 1570 BC₃F₃ individuals derived from two cultivated rice cultivars, Pin20 and Songjing15, in order to identify the major genomic regions associated with GL. A novel major QTL, qGL9.1, was mapped on chromosome 9, which is associated with the GL, using whole-genome re-sequencing with bulked segregant analysis. Local QTL linkage analysis with F₂ and fine mapping with the recombinant plant revealed a 93-kb core region on qGL9.1 encoding 15 protein-coding genes. Only the expression level of LOC_Os09g26970 was significantly different between the two parents at different stages of grain development. Moreover, haplotype analysis revealed that the alleles of Pin20 contribute to the optimal GL (9.36 mm) and GL/W (3.31), suggesting that Pin20 is a cultivated species carrying the optimal GL variation of LOC_Os09g26970. Furthermore, a functional-type mutation (16398989-bp, G>A) located on an exon of LOC_Os09g26970 could be used as a molecular marker to distinguish between long and short grains. Our experiments identified LOC_Os09g26970 as a novel gene associated with GL in japonica rice. This result is expected to further the exploration of the genetic mechanism of rice GL and improve GL in rice japonica varieties by marker-assisted selection.

RNA-Seq Transcriptome Analysis and Evolution of OsEBS, a Gene Involved in Enhanced Spikelet Number per Panicle in Rice

Spikelet number per panicle (SNP) is one of the most important yield components in rice. Rice ENHANCING BIOMASS AND SPIKELET NUMBER (OsEBS), a gene involved in improved SNP and yield, has been cloned from an accession of Dongxiang wild rice. However, the mechanism of OsEBS increasing rice SNP is poorly understood. In this study, the RNA-Seq technology was used to analyze the transcriptome of wildtype Guichao 2 and OsEBS over-expression line B102 at the heading stage, and analysis of the evolution of OsEBS was also conducted. A total of 5369 differentially expressed genes (DEGs) were identified between Guichao2 and B102, most of which were down-regulated in B102. Analysis of the expression of endogenous hormone-related genes revealed that 63 auxin-related genes were significantly down-regulated in B102. Gene Ontogeny (GO) enrichment analysis showed that the 63 DEGs were mainly enriched in eight GO terms, including auxin-activated signaling pathway, auxin polar transport, auxin transport, basipetal auxin transport, and amino acid transmembrane transport, most of which were directly or indirectly related to polar auxin transport. Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathway analysis further verified that the down-regulated genes related to polar auxin transport had important effects on increased SNP. Analysis of the evolution of OsEBS found that OsEBS was involved in the differentiation of indica and japonica, and the differentiation of OsEBS supported the multi-origin model of rice domestication. Indica (XI) subspecies harbored higher nucleotide diversity than japonica (GJ) subspecies in the OsEBS region, and XI experienced strong balancing selection during evolution, while selection in GJ was neutral. The degree of genetic differentiation between GJ and Bas subspecies was the smallest, while it was the highest between GJ and Aus. Phylogenetic analysis of the Hsp70 family in O. sativa, Brachypodium distachyon, and Arabidopsis thaliana indicated that changes in the sequences of OsEBS were accelerated during evolution. Accelerated evolution and domain loss in OsEBS resulted in neofunctionalization. The results obtained from this study provide an important theoretical basis for high-yield rice breeding.

Cadmium in Cereal Crops: Uptake and Transport Mechanisms and Minimizing Strategies

Cadmium (Cd) contamination in soils and accumulation in cereal grains have posed food security risks and serious health concerns worldwide. Understanding the Cd transport process and its management for minimizing Cd accumulation in cereals may help to improve crop growth and grain quality. In this review, we summarize Cd uptake, translocation, and accumulation mechanisms in cereal crops and discuss efficient measures to reduce Cd uptake as well as potential remediation strategies, including the applications of plant growth regulators, microbes, nanoparticles, and cropping systems and developing low-Cd grain cultivars by CRISPR/Cas9. In addition, miRNAs modulate Cd translocation, and accumulation in crops through the regulation of their target genes was revealed. Combined use of multiple remediation methods may successfully decrease Cd concentrations in cereals. The findings in this review provide some insights into innovative and applicable approaches for reducing Cd accumulation in cereal grains and sustainable management of Cd-contaminated paddy fields.

Heterotrimeric G Protein Signaling in Abiotic Stress

As sessile organisms, plants exhibit extraordinary plasticity and have evolved sophisticated mechanisms to adapt and mitigate the adverse effects of environmental fluctuations. Heterotrimeric G proteins (G proteins), composed of α, β, and γ subunits, are universal signaling molecules mediating the response to a myriad of internal and external signals. Numerous studies have identified G proteins as essential components of the organismal response to stress, leading to adaptation and ultimately survival in plants and animal systems. In plants, G proteins control multiple signaling pathways regulating the response to drought, salt, cold, and heat stresses. G proteins signal through two functional modules, the Gα subunit and the Gβγ dimer, each of which can start either independent or interdependent signaling pathways. Improving the understanding of the role of G proteins in stress reactions can lead to the development of more resilient crops through traditional breeding or biotechnological methods, ensuring global food security. In this review, we summarize and discuss the current knowledge on the roles of the different G protein subunits in response to abiotic stress and suggest future directions for research.

The multifaceted roles of heterotrimeric G-proteins: lessons from models and crops

The review summarizes our advanced understanding of the heterotrimeric G-protein research from model plants and their emerging roles in modulating various plant architecture and agronomical traits in crop species. Heterotrimeric G-proteins (hereafter G-proteins), consisting of G-alpha (Gα), G-beta (Gβ) and G-gamma (Gγ) subunits, are key signal transducers conserved across different forms of life. The discovery of plant lineage-specific G-protein components (extra-large G-proteins and type-C Gγ subunits), inherent polyploidy in angiosperms, and unique modes of G-protein cycle regulation in plants pointed out to a few fundamental differences of plant G-protein signaling from its animal counterpart. Over the last 2 decades, extensive studies in the model plant Arabidopsis thaliana have confirmed the involvement of G-proteins in a wide range of plant growth and development, and stress adaptation processes. The G-protein research in crop species, however, is still in its infancy, and a handful of studies suggest important roles of G-proteins in regulating plant architectural and key agronomical traits including plant's response to abiotic and biotic factors. We propose that the advancement made in plant G-proteins research will facilitate the development of novel approaches to manage plant yield and fitness in changing environments.

TT2 controls rice thermotolerance through SCT1-dependent alteration of wax biosynthesis

Global warming threatens crop production. G proteins mediate plant responses to multiple abiotic stresses. Here we identified a natural quantitative trait locus, TT2 (THEROMOTOLERANCE 2), encoding a Gγ subunit, that confers thermotolerance in rice during both vegetative and reproductive growth without a yield penalty. A natural allele with loss of TT2 function was associated with greater retention of wax at high temperatures and increased thermotolerance. Mechanistically, we found that a transcription factor, SCT1 (Sensing Ca²⁺ Transcription factor 1), functions to decode Ca²⁺ through Ca²⁺-enhanced interaction with calmodulin and acts as a negative regulator of its target genes (for example, Wax Synthesis Regulatory 2 (OsWR2)). The calmodulin-SCT1 interaction was attenuated by reduced heat-triggered Ca²⁺ caused by disrupted TT2, thus explaining the observed heat-induced changes in wax content. Beyond establishing a bridge linking G protein, Ca²⁺ sensing and wax metabolism, our study illustrates innovative approaches for developing potentially yield-penalty-free thermotolerant crop varieties.

Rice G protein γ subunit qPE9-1 modulates root elongation for phosphorus uptake by involving 14-3-3 protein OsGF14b and plasma membrane H+ -ATPase

Heterotrimeric G protein is involved in plant growth and development, while the role of rice (Oryza sativa) G protein γ subunit qPE9-1 in response to low-phosphorus (LP) conditions remains unclear. The gene expression of qPE9-1 was significantly induced in rice roots under LP conditions. Rice varieties carrying the qPE9-1 allele showed a stronger primary root response to LP than the varieties carrying the qpe9-1 allele (mutant of the qPE9-1 allele). Transgenic rice plants with the qPE9-1 allele had longer primary roots and higher P concentrations than those with the qpe9-1 allele under LP conditions. The plasma membrane (PM) H⁺ -ATPase was important for the qPE9-1-mediated response to LP. Furthermore, OsGF14b, a 14-3-3 protein that acts as a key component in activating PM H⁺ -ATPase for root elongation, is also involved in the qPE9-1 mediation. Moreover, the overexpression of OsGF14b in WYJ8 (carrying the qpe9-1 allele) partially increased primary root length under LP conditions. Experiments using R18 peptide (a 14-3-3 protein inhibitor) showed that qPE9-1 is important for primary root elongation and H⁺ efflux under LP conditions by involving the 14-3-3 protein. In addition, rhizosheath weight, total P content, and the rhizosheath soil Olsen-P concentration of qPE9-1 lines were higher than those of qpe9-1 lines under soil drying and LP conditions. These results suggest that the G protein γ subunit qPE9-1 in rice plants modulates root elongation for phosphorus uptake by involving the 14-3-3 protein OsGF14b and PM H⁺ -ATPase, which is required for rice P use.

Enhancing phytoremediation of hazardous metal(loid)s using genome engineering CRISPR-Cas9 technology

Rapid and drastic changes in the global climate today have given a strong impetus to developing newer climate-resilient phytoremediation approaches. These methods are of great public and scientific importance given the urgency of this environmental crisis. Climate change has adverse effects on the growth, outputs, phenology, and overall productivity of plants. Contamination of soil with metal(loid)s is a major worldwide problem. Some metal(loids) are carcinogenic pollutants that have a long half-life and are non-degradable in the environment. There are many instances of the potential link between chronic heavy metal exposure and human disease. The adaptation of plants in the changing environment is, however, a major concern in phytoremediation practice. The creation of climate-resistant metal hyperaccumulation plants using molecular techniques could provide new opportunities to mitigate these problems. Consequently, advancements in molecular science would accelerate our knowledge of adaptive plant remediation/resistance and plant production in the context of global warming. Genome modification using artificial nucleases has the potential to enhance phytoremediation by modifying genomes for a sustainable future. This review focuses on biotechnology to boost climate change tolerant metallicolous plants and the future prospects of such technology, particularly the CRISPR-Cas9 genome editing system, for enhancing phytoremediation of hazardous pollutants.

Heterotrimeric G protein signalling in plant biotic and abiotic stress response

Heterotrimeric G proteins act as molecular switches to participate in transmitting various stimuli signals from outside of cells. G proteins have three subunits, Gα, Gβ and Gγ, which function mutually to modulate many biological processes in plants, including plant growth and development, as well as biotic and abiotic stress responses. In plants, the number of Gγ subunits is larger than that of the α and β subunits. Based on recent breakthroughs in studies of plant G protein signal perception, transduction and downstream effectors, this review summarizes and analyses the connections between different subunits and the interactions of G proteins with other signalling pathways, especially in plant biotic and abiotic stress responses. Based on current progress and unresolved questions in the field, we also suggest future research directions on G proteins in plants.

Heterotrimeric G-protein γ subunits regulate ABA signaling in response to drought through interacting with PP2Cs and SnRK2s in mulberry (Morus alba L.)

ABA signaling plays a central role in regulating plants respond to drought. Although much progress has been made in understanding the functions of ABA signaling in drought response, very little information is available regarding woody plants. In this study, the components of ABA signaling pathway were identified in mulberry which has excellent adaptation to drought, including three PYLs, two PP2Cs, two SnRK2s, four ABFs, and an ABA responsive gene MaRD29B. The gene expression of ABA signaling components exhibited significant response to ABA and drought, and their roles in drought response were revealed using a transient transformation system in mulberry seedlings. We discovered the ABA signaling components, MaABI1/2 and MaSnRK2.1/2.4, could directly interact with G-protein γ subunits, MaGγ1 and MaGγ2, which indicated that G-protein γ subunits may mediate the signal crosstalk between G-proteins and ABA signaling. Transient activation assay in tobacco and RNAi silencing assay in mulberry further demonstrated that MaGγ1 and MaGγ2 regulated drought response by enhancing ABA signaling. This study expands the repertoire of ABA signaling controlling drought responses in plants and provides the direct evidence about the crosstalk between ABA signaling and G-proteins for the first time.

Molecular Insights into Inflorescence Meristem Specification for Yield Potential in Cereal Crops

Flowering plants develop new organs throughout their life cycle. The vegetative shoot apical meristem (SAM) generates leaf whorls, branches and stems, whereas the reproductive SAM, called the inflorescence meristem (IM), forms florets arranged on a stem or an axis. In cereal crops, the inflorescence producing grains from fertilized florets makes the major yield contribution, which is determined by the numbers and structures of branches, spikelets and florets within the inflorescence. The developmental progression largely depends on the activity of IM. The proper regulations of IM size, specification and termination are outcomes of complex interactions between promoting and restricting factors/signals. Here, we focus on recent advances in molecular mechanisms underlying potential pathways of IM identification, maintenance and differentiation in cereal crops, including rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), and barley (Hordeum vulgare), highlighting the researches that have facilitated grain yield by, for example, modifying the number of inflorescence branches. Combinatorial functions of key regulators and crosstalk in IM determinacy and specification are summarized. This review delivers the knowledge to crop breeding applications aiming to the improvements in yield performance and productivity.

Genetic Control Diversity Drives Differences Between Cadmium Distribution and Tolerance in Rice

Rice, a staple crop for nearly half the planet's population, tends to absorb and accumulate excessive cadmium (Cd) when grown in Cd-contaminated fields. Low levels of Cd can degrade the quality of rice grains, while high levels can inhibit the growth of rice plants. There is genotypic diversity in Cd distribution and Cd tolerance in different rice varieties, but their underlying genetic mechanisms are far from elucidated, which hinders genetic improvements. In this study, a joint study of phenotypic investigation with quantitative trait loci (QTLs) analyses of genetic patterns of Cd distribution and Cd tolerance was performed using a biparent population derived from japonica and indica rice varieties. We identified multiple QTLs for each trait and revealed that additive effects from various loci drive the inheritance of Cd distribution, while epistatic effects between various loci contribute to differences in Cd tolerance. One pleiotropic locus, qCddis8, was found to affect the Cd distribution from both roots to shoots and from leaf sheaths to leaf blades. The results expand our understanding of the diversity of genetic control over Cd distribution and Cd tolerance in rice. The findings provide information on potential QTLs for genetic improvement of Cd distribution in rice varieties.

Profiling of rice Cd-tolerant genes through yeast-based cDNA library survival screening

The bioaccumulation of cadmium (Cd) in crop and the subsequent food chain has aroused extensive concerns. However, the underlying molecular mechanisms of plant Cd tolerance remain to be clarified from the viewpoint of novel candidate genes. Here we described a highly efficient approach for preliminary identifying rice Cd-tolerant genes through the yeast-based cDNA library survival screening combined with high-throughput sequencing strategy. About 690 gene isoforms were identified as being Cd-tolerant candidates using this shotgun approach. Among the Cd-tolerant genes identified, several categories of genes such as BAX inhibitor (BI), NAC transcription factors and Rapid ALkalinization Factors (RALFs) were of particular interest, and their function of Cd tolerance was further validated via heterologous expression, which suggested that SNAC1, RALF12, OsBI-1 can confer Cd tolerance in yeast and tobacco leaves. Regarding the genes involved in ion transport, the validated Cd-tolerant heavy metal-associated domain (HMAD) isoprenylated protein HIPP42 was particularly noteworthy. Further elucidation of these genes associated with Cd tolerance in rice will benefit agricultural activities.

Transcription Factor GmWRKY142 Confers Cadmium Resistance by Up-Regulating the Cadmium Tolerance 1-Like Genes

Cadmium (Cd) is a widespread pollutant that is toxic to living organisms. Previous studies have identified certain WRKY transcription factors, which confer Cd tolerance in different plant species. In the present study, we have identified 29 Cd-responsive WRKY genes in Soybean [Glycine max (L.) Merr.], and confirmed that 26 of those GmWRKY genes were up-regulated, while 3 were down-regulated. We have also cloned the novel, positively regulated GmWRKY142 gene from soybean and investigated its regulatory mechanism in Cd tolerance. GmWRKY142 was highly expressed in the root, drastically up-regulated by Cd, localized in the nucleus, and displayed transcriptional activity. The overexpression of GmWRKY142 in Arabidopsis thaliana and soybean hairy roots significantly enhanced Cd tolerance and lead to extensive transcriptional reprogramming of stress-responsive genes. ATCDT1, GmCDT1-1, and GmCDT1-2 encoding cadmium tolerance 1 were induced in overexpression lines. Further analysis showed that GmWRKY142 activated the transcription of ATCDT1, GmCDT1-1, and GmCDT1-2 by directly binding to the W-box element in their promoters. In addition, the functions of GmCDT1-1 and GmCDT1-2, responsible for decreasing Cd uptake, were validated by heterologous expression in A. thaliana. Our combined results have determined GmWRKYs to be newly discovered participants in response to Cd stress, and have confirmed that GmWRKY142 directly targets ATCDT1, GmCDT1-1, and GmCDT1-2 to decrease Cd uptake and positively regulate Cd tolerance. The GmWRKY142-GmCDT1-1/2 cascade module provides a potential strategy to lower Cd accumulation in soybean.

Cloning, characterization of TaGS3 and identification of allelic variation associated with kernel traits in wheat (Triticum aestivum L.)

Background

Grain weight is an important yield component. Selection of advanced lines with heavy grains show high grain sink potentials and strong sink activity, which is an increasingly important objective in wheat breeding programs. Rice OsGS3 has been identified as a major quantitative trait locus for both grain weight and grain size. However, allelic variation of GS3 has not been characterized previously in hexaploid wheat.

Results

We cloned 2445, 2393, and 2409 bp sequences of the homologs TaGS3-4A, TaGS3-7A, and TaGS3-7D in wheat ‘Changzhi 6406’, a cultivar that shows high grain weight. The TaGS3 genes each contained five exons and four introns, and encoded a deduced protein of 170, 169, and 169 amino acids, respectively. Phylogenetic analysis of plant GS3 protein sequences revealed GS3 to be a monocotyledon-specific gene and the GS3 proteins were resolved into three classes. The length of the atypical Gγ domain and the cysteine-rich region was conserved within each class and not conserved between classes. A single-nucleotide polymorphism in the fifth exon (at position 1907) of TaGS3-7A leads to an amino acid change (ALA/THR) and showed different frequencies in two pools of Chinese wheat accessions representing extremes in grain weight. Association analysis indicated that the TaGS3-7A-A allele was associated with higher grain weight in the natural population. The TaGS3-7A-A allele was favoured in global modern wheat cultivars but the allelic frequency varied among different wheat-production regions of China, which indicated that this allele is of potential utility to improve wheat grain weight in certain wheat-production areas of China.

Conclusions

The novel molecular information on wheat GS3 homologs and the KASP functional marker designed in this study may be useful in marker-assisted breeding for genetic improvement of wheat.

Maize NAC-domain retained splice variants act as dominant negatives to interfere with the full-length NAC counterparts

The plant-specific NAC transcription factors play diverse roles in various stress signaling. Alternative splicing is particularly prevalent in plants under stress. However, the investigation of cadmium (Cd) on the differential expression of the splice variants of NACs is in its infancy. Here, we identified three Cd-induced intron retention splice NAC variants which only contained the canonical NAC domain, designated as nacDomains, derived from three Cd-upregulated maize NACs. Subcellular localization analysis indicated that both nacDomain and its full-length NAC counterpart co-localized in the nucleus as manifested in the BiFC assay, thus implied that nacDomains and their corresponding NACs form heterodimers through the identical NAC domain. Further chimeric reporter/effector transient expression assay and Cd-tolerance assay in tobacco leaves collectively indicated that nacDomain-NAC heterodimers were involved in the regulation of NAC function. The results obtained here were in accordance with the model of dominant negative, which suggested that nacDomain act as the dominant negative to antagonize the regulation of NAC on its target gene expression and the Cd-tolerance function performance of NAC transcription factor. These findings proposed a novel insight into understanding the molecular mechanisms of Cd response in plants.

Multifaceted plant G protein: interaction network, agronomic potential, and beyond

Heterotrimeric G protein and interacting effectors are relevant for agronomic significance. We can manipulate G protein and effectors, individually or in combination, to develop plant ideotypes by intelligent design breeding. Heterotrimeric guanine nucleotide-binding protein (G protein) is involved in a wide range of biological events, many of which with agronomic significance. In this review, we summarize recent advances of plant G protein research. We first retrieve maize G protein core subunits Gα, Gβ, and Gγ based on information of Arabidopsis and rice G proteins using integrated BLAST and domain confirmation. Then, we briefly introduce the distribution and function of G protein. We also describe the interaction between G protein and CLAVATA receptor, brassinosteroid signaling kinase complex, and MADS-domain transcription factor. Finally, we discuss the application of G protein knowledge in intelligent plant breeding with focus on the improvement of agronomically important traits.

Heterotrimeric G-Protein Signaling in Plants: Conserved and Novel Mechanisms

Heterotrimeric GTP-binding proteins are key regulators of a multitude of signaling pathways in all eukaryotes. Although the core G-protein components and their basic biochemistries are broadly conserved throughout evolution, the regulatory mechanisms of G proteins seem to have been rewired in plants to meet specific needs. These proteins are currently the focus of intense research in plants due to their involvement in many agronomically important traits, such as seed yield, organ size regulation, biotic and abiotic stress responses, symbiosis, and nitrogen use efficiency. The availability of massive sequence information from a variety of plant species, extensive biochemical data generated over decades, and impressive genetic resources for plant G proteins have made it possible to examine their role, unique properties, and novel regulation. This review focuses on some recent advances in our understanding of the mechanistic details of this critical signaling pathway to enable the precise manipulation and generation of plants to meet future needs.

Dissecting the Genetic Basis of Grain Size and Weight in Barley (Hordeum vulgare L.) by QTL and Comparative Genetic Analyses

Grain size and weight are crucial components of barley yield and quality and are the target characteristics of domestication and modern breeding. Despite this, little is known about the genetic and molecular mechanisms of grain size and weight in barley. Here, we evaluated nine traits determining grain size and weight, including thousand grain weight (Tgw), grain length (Gl), grain width (Gw), grain length-width ratio (Lwr), grain area (Ga), grain perimeter (Gp), grain diameter (Gd), grain roundness (Gr), and factor form density (Ffd), in a double haploid (DH) population for three consecutive years. Using five mapping methods, we successfully identified 60 reliable QTLs and 27 hotspot regions that distributed on all chromosomes except 6H which controls the nine traits of grain size and weight. Moreover, we also identified 164 barley orthologs of 112 grain size/weight genes from rice, maize, wheat and 38 barley genes that affect grain yield. A total of 45 barley genes or orthologs were identified as potential candidate genes for barley grain size and weight, including 12, 20, 9, and 4 genes or orthologs for barley, rice, maize, and wheat, respectively. Importantly, 20 of them were located in the 14 QTL hotspot regions on chromosome 1H, 2H, 3H, 5H, and 7H, which controls barley grain size and weight. These results indicated that grain size/weight genes of other cereal species might have the same or similar functions in barley. Our findings provide new insights into the understanding of the genetic basis of grain size and weight in barley, and new information to facilitate high-yield breeding in barley. The function of these potential candidate genes identified in this study are worth exploring and studying in detail.

Comprehensive Analysis of the Cadmium Tolerance of Abscisic Acid-, Stress- and Ripening-Induced Proteins (ASRs) in Maize

In plants, abscisic acid-, stress-, and ripening-induced (ASR) proteins have been shown to impart tolerance to multiple abiotic stresses such as drought and salinity. However, their roles in metal stress tolerance are poorly understood. To screen plant Cd-tolerance genes, the yeast-based gene hunting method which aimed to screen Cd-tolerance colonies from maize leaf cDNA library hosted in yeast was carried out. Here, maize ZmASR1 was identified to be putative Cd-tolerant through this survival screening strategy. In silico analysis of the functional domain organization, phylogenetic classification and tissue-specific expression patterns revealed that maize ASR1 to ASR5 are typical ASRs with considerable expression in leaves. Further, four of them were cloned for testifying Cd tolerance using yeast complementation assay. The results indicated that they all confer Cd tolerance in Cd-sensitive yeast. Then they were transiently expressed in tobacco leaves for subcellular localization analysis and for Cd-challenged lesion assay, continuously. The results demonstrated that all 4 maize ASRs tested are localized to the cell nucleus and cytoplasm in tobacco leaves. Moreover, they were confirmed to be Cd-tolerance genes in planta through lesion analysis in Cd-infiltrated leaves transiently expressing them. Taken together, our results demonstrate that maize ASRs play important roles in Cd tolerance, and they could be used as promising candidate genes for further functional studies toward improving the Cd tolerance in plants.

Characterization of Heterotrimeric G Protein γ4 Subunit in Rice

Heterotrimeric G proteins are the molecule switch that transmits information from external signals to intracellular target proteins in mammals and yeast cells. In higher plants, heterotrimeric G proteins regulate plant architecture. Rice harbors one canonical α subunit gene (RGA1), four extra-large GTP-binding protein genes (XLGs), one canonical β-subunit gene (RGB1), and five γ-subunit genes (tentatively designated RGG1, RGG2, RGG3/GS3/Mi/OsGGC1, RGG4/DEP1/DN1/qPE9-1/OsGGC3, and RGG5/OsGGC2) as components of the heterotrimeric G protein complex. Among the five γ-subunit genes, RGG1 encodes the canonical γ-subunit, RGG2 encodes a plant-specific type of γ-subunit with additional amino acid residues at the N-terminus, and the remaining three γ-subunit genes encode atypical γ-subunits with cysteine-rich C-termini. We characterized the RGG4/DEP1/DN1/qPE9-1/OsGGC3 gene product Gγ4 in the wild type (WT) and truncated protein Gγ4∆Cys in the RGG4/DEP1/DN1/qPE9-1/OsGGC3 mutant, Dn1-1, as littele information regarding the native Gγ4 and Gγ4∆Cys proteins is currently available. Based on liquid chromatography-tandem mass spectrometry analysis, immunoprecipitated Gγ4 candidates were confirmed as actual Gγ4. Similar to α-(Gα) and β-subunits (Gβ), Gγ4 was enriched in the plasma membrane fraction and accumulated in the developing leaf sheath. As RGG4/DEP1/DN1/qPE9-1/OsGGC3 mutants exhibited dwarfism, tissues that accumulated Gγ4 corresponded to the abnormal tissues observed in RGG4/DEP1/DN1/qPE9-1/OsGGC3 mutants.

Comparative analysis of Cd-responsive maize and rice transcriptomes highlights Cd co-modulated orthologs

Background

Metal tolerance is often an integrative result of metal uptake and distribution, which are fine-tuned by a network of signaling cascades and metal transporters. Thus, with the goal of advancing the molecular understanding of such metal homeostatic mechanisms, comparative RNAseq-based transcriptome analysis was conducted to dissect differentially expressed genes (DEGs) in maize roots exposed to cadmium (Cd) stress.

Results

To unveil conserved Cd-responsive genes in cereal plants, the obtained 5166 maize DEGs were compared with 2567 Cd-regulated orthologs in rice roots, and this comparison generated 880 universal Cd-responsive orthologs groups composed of 1074 maize DEGs and 981 rice counterparts. More importantly, most of the orthologous DEGs showed coordinated expression pattern between Cd-treated maize and rice, and these include one large orthologs group of pleiotropic drug resistance (PDR)-type ABC transporters, two clusters of amino acid transporters, and 3 blocks of multidrug and toxic compound extrusion (MATE) efflux family transporters, and 3 clusters of heavy metal-associated domain (HMAD) isoprenylated plant proteins (HIPPs), as well as all 4 groups of zinc/iron regulated transporter protein (ZIPs). Additionally, several blocks of tandem maize paralogs, such as germin-like proteins (GLPs), phenylalanine ammonia-lyases (PALs) and several enzymes involved in JA biosynthesis, displayed consistent co-expression pattern under Cd stress.

Out of the 1074 maize DEGs, approximately 30 maize Cd-responsive genes such as ZmHIPP27, stress-responsive NAC transcription factor (ZmSNAC1) and 9-cis-epoxycarotenoid dioxygenase (NCED, vp14) were also common stress-responsive genes reported to be uniformly regulated by multiple abiotic stresses. Moreover, the aforementioned three promising Cd-upregulated genes with rice counterparts were identified to be novel Cd-responsive genes in maize.

Meanwhile, one maize glutamate decarboxylase (ZmGAD1) with Cd co-modulated rice ortholog was selected for further analysis of Cd tolerance via heterologous expression, and the results suggest that ZmGAD1 can confer Cd tolerance in yeast and tobacco leaves.

Conclusions

These novel findings revealed the conserved function of Cd-responsive orthologs and paralogs, which would be valuable for elucidating the genetic basis of the plant response to Cd stress and unraveling Cd tolerance genes.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5109-8) contains supplementary material, which is available to authorized users.

Iris lactea var. chinensis (Fisch.) cysteine-rich gene llCDT1 enhances cadmium tolerance in yeast cells and Arabidopsis thaliana

IlCDT1, a cysteine-rich protein, was isolated from Iris lactea var. chinensis (Fisch.) (I. lactea var. chinensis). Its transcription was up-regulated by the exogenous application of Cd. The truncated IlCDT1 (25-54) containing 14 Cys residues confers Cd tolerance to yeast as the intact IlCDT1, indicating that Cys residues are required for Cd tolerance presumably by chelating Cd. When the gene was constitutively expressed in A. thaliana, root length of transgenic lines was longer than that of wild-type under 100 μM or 200 μM Cd stress. However, Cd absorption in wild-type was more than in two trangenic lines under 100 μM Cd exposure. IlCDT1 may directly bind Cd, through chelating Cd and avoiding the Cd uptake into the cells. Together, IlCDT1 may be a promising gene for the Cd tolerance improvement.

SUMMARY

Cysteine-rich gene llCDT1 enhances cadmium tolerance in yeast cells and Arabidopsis thaliana.

Emerging themes in heterotrimeric G-protein signaling in plants

Heterotrimeric G-proteins are key signaling components involved during the regulation of a multitude of growth and developmental pathways in all eukaryotes. Although the core proteins (Gα, Gβ, Gγ subunits) and their basic biochemistries are conserved between plants and non-plant systems, seemingly different inherent properties of specific components, altered wirings of G-protein network architectures, and the presence of novel receptors and effector proteins make plant G-protein signaling mechanisms somewhat distinct from the well-established animal paradigm. G-protein research in plants is getting a lot of attention recently due to the emerging roles of these proteins in controlling many agronomically important traits. New findings on both canonical and novel G-protein components and their conserved and unique signaling mechanisms are expected to improve our understanding of this important module in affecting critical plant growth and development pathways and eventually their utilization to produce plants for the future needs. In this review, we briefly summarize what is currently known in plant G-protein research, describe new findings and how they are changing our perceptions of the field, and discuss important issues that still need to be addressed.

The potential of genetic engineering of plants for the remediation of soils contaminated with heavy metals

The genetic engineering of plants to facilitate the reclamation of soils and waters contaminated with inorganic pollutants is a relatively new and evolving field, benefiting from the heterologous expression of genes that increase the capacity of plants to mobilize, stabilize and/or accumulate metals. The efficiency of phytoremediation relies on the mechanisms underlying metal accumulation and tolerance, such as metal uptake, translocation and detoxification. The transfer of genes involved in any of these processes into fast-growing, high-biomass crops may improve their reclamation potential. The successful phytoextraction of metals/metalloids and their accumulation in aerial organs have been achieved by expressing metal ligands or transporters, enzymes involved in sulfur metabolism, enzymes that alter the chemical form or redox state of metals/metalloids and even the components of primary metabolism. This review article considers the potential of genetic engineering as a strategy to improve the phytoremediation capacity of plants in the context of heavy metals and metalloids, using recent case studies to demonstrate the practical application of this approach in the field.

Duplicated RGS (Regulator of G-protein signaling) proteins exhibit conserved biochemical but differential transcriptional regulation of heterotrimeric G-protein signaling in Brassica species

G-alpha (Gα) and ‘Regulator of G-protein Signaling (RGS)’ proteins are the two key components primarily involved in regulation of heterotrimeric G-proteins signaling across phyla. Unlike Arabidopsis thaliana, our knowledge about G-protein regulation in polyploid Brassica species is sparse. In this study, we identified one Gα and two RGS genes each from three species of Brassica ‘U’ triangle and assessed the effects of whole genome triplication on the divergence of gene sequence and structure, protein-protein interaction, biochemical activities, and gene expression. Sequence and phylogenetic analysis revealed that the deduced Gα and RGS proteins are evolutionarily conserved across Brassica species. The duplicated RGS proteins of each Brassica species interacted with their cognate Gα but displayed varying levels of interaction strength. The Gα and the duplicated RGS proteins of Brassica species exhibited highly conserved G-protein activities when tested under in-vitro conditions. Expression analysis of the B. rapa RGS genes revealed a high degree of transcriptional differentiation across the tested tissue types and in response to various elicitors, particularly under D-glucose, salt and phytohormone treatments. Taken together, our results suggest that the RGS-mediated regulation of G-protein signaling in Brassica species is predominantly governed by stage and condition-specific expression differentiation of the duplicated RGS genes.

Arabidopsis Type III Gγ Protein AGG3 Is a Positive Regulator of Yield and Stress Responses in the Model Monocot Setaria viridis

Heterotrimeric G-proteins are key regulators of a multitude of growth and development pathways in eukaryotes. Along with the conserved G-protein components found in all organisms, plants have certain novel variants with unique architecture, which may be involved in the regulation of plant-specific traits. The higher plant-specific type III (or Class C) Gγ protein, which possesses a large C terminal extension, represented by AGG3 in Arabidopsis, is one such variant of canonical Gγ proteins. The type III Gγ proteins are involved in regulation of many agronomically important traits in plants, including seed yield, organ size regulation, abscisic acid (ABA)-dependent signaling and stress responses, and nitrogen use efficiency. However, the extant data, especially in the monocots, present a relatively complex and sometimes contradictory picture of the regulatory role of these proteins. It remains unclear if the positive traits observed in certain naturally occurring populations are due to the presence of specific allelic variants of the proteins or due to the altered expression of the gene itself. To address these possibilities, we have overexpressed the Arabidopsis AGG3 gene in the model monocot Setaria viridis and systematically evaluated its role in conferring agriculturally relevant phenotypes. Our data show that AtAGG3 is indeed functional in Setaria and suggest that a subset of the traits affected by the type III Gγ proteins are indeed positively correlated with the gene expression level, while others might have more complex, allele specific regulation.

De novo characterization of the Iris lactea var. chinensis transcriptome and an analysis of genes under cadmium or lead exposure

Iris lactea var. chinensis (I. lactea var. chinensis) is tolerant to accumulations of cadmium (Cd) and lead (Pb). In this study, the transcriptome of I. lactea var. chinensis was investigated under Cd or Pb stresses. Using the gene ontology database, 31,974 unigenes were classified into biological process, cellular component and molecular function. In total, 13,132 unigenes were involved in enriched Encyclopedia of Genes and Genomes (KEGG) metabolic pathways, and the expression levels of 5904 unigenes were significantly changed after exposure to Cd or Pb stresses. Of these, 974 were co-up-regulated and 1281 were co-down-regulated under the two stresses. The transcriptome expression profiles of I. lactea var. chinensis under Cd or Pb stresses obtained in this study provided a resource for identifying common mechanisms in the detoxification of different heavy metals. Furthermore, the identified unigenes may be used for the genetic breeding of heavy-metal tolerant plants.

Extra Large G-Protein Interactome Reveals Multiple Stress Response Function and Partner-Dependent XLG Subcellular Localization

The three-member family of Arabidopsis extra-large G proteins (XLG1-3) defines the prototype of an atypical Gα subunit in the heterotrimeric G protein complex. Recent evidence indicate that XLG subunits operate along with its Gβγ dimer in root morphology, stress responsiveness, and cytokinin induced development, however downstream targets of activated XLG proteins in the stress pathways are rarely known. To assemble a set of candidate XLG-targeted proteins, a yeast two-hybrid complementation-based screen was performed using XLG protein baits to query interactions between XLG and partner protein found in glucose-treated seedlings, roots, and Arabidopsis cells in culture. Seventy two interactors were identified and >60% of a test set displayed in vivo interaction with XLG proteins. Gene co-expression analysis shows that >70% of the interactors are positively correlated with the corresponding XLG partners. Gene Ontology enrichment for all the candidates indicates stress responses and posits a molecular mechanism involving a specific set of transcription factor partners to XLG. Genes encoding two of these transcription factors, SZF1 and 2, require XLG proteins for full NaCl-induced expression. The subcellular localization of the XLG proteins in the nucleus, endosome, and plasma membrane is dependent on the specific interacting partner.

The DENSE AND ERECT PANICLE 1 (DEP1) gene offering the potential in the breeding of high-yielding rice

The erect panicle model super-rice can rationally transform the solar energy into accumulated organic matter (biomass) and increase grain yield. The phenotype of erect panicle architecture controlled by DENSE AND ERECT PANICLE 1 (DEP1) has been used in rice breeding for nearly a century owing to its high-yield, lodging tolerance with strong stem, reasonable population structure and high nitrogen use efficiency. DEP1 is a G protein γ subunit that is involved in the regulation of erect panicle, number of grains per panicle, nitrogen uptake, and stress-tolerance through the G protein signal pathway. Here we review the development of erect panicle rice varieties, DEP1 alleles and regulatory network, and its physiological and morphological functions. Additionally, the further increasing the yield potential of erect-panicle super-rice, and the development of molecular designing breeding for indica-japonica hybrid rice with the dep1 gene are also prospected.

Rice G-protein subunits qPE9-1 and RGB1 play distinct roles in abscisic acid responses and drought adaptation

Heterotrimeric GTP-binding protein (G-protein)-mediated abscisic acid (ABA) and drought-stress responses have been documented in numerous plant species. However, our understanding of the function of rice G-protein subunits in ABA signalling and drought tolerance is limited. In this study, the function of G-protein subunits in ABA response and drought resistance in rice plants was explored. It was found that the transcription level of qPE9-1 (rice Gγ subunit) gradually decreased with increasing ABA concentration and the lack of qPE9-1 showed an enhanced drought tolerance in rice plants. In contrast, mRNA levels of RGB1 (rice Gβ subunit) were significantly upregulated by ABA treatment and the lack of RGB1 led to reduced drought tolerance. Furthermore, the results suggested that qPE9-1 negatively regulates the ABA response by suppressing the expression of key transcription factors involved in ABA and stress responses, while RGB1 positively regulates ABA biosynthesis by upregulating NCED gene expression under both normal and drought stress conditions. Taken together, it is proposed that RGB1 is a positive regulator of the ABA response and drought adaption in rice plants, whereas qPE9-1 is modulated by RGB1 and functions as a negative regulator in the ABA-dependent drought-stress responses.

Transcriptomic screening for cyclotides and other cysteine-rich proteins in the metallophyte Viola baoshanensis

Cysteine (Cys)-rich proteins (CRPs) are frequently associated with plant defense and stress resistance. Viola baoshanensis is a cadmium (Cd) hyper-accumulating plant whose CRPs-based defense systems are so far poorly understood. Next generation sequencing (NGS) techniques and a specialist searching tool, CrpExcel, were employed for identifying CRPs in V. baoshanensis. The transcriptome sequences of V. baoshanensis were assembled primarily from 454FLX/Hiseq2000 reads of plant cDNA sequencing libraries. CrpExcel was then used to search the ORFs and 9687 CRPs were identified, and included zinc finger (ZF) proteins, lipid transfer proteins, thaumatins and cyclotide precursors. Real-time PCR results showed that all CRP genes tested are constitutively expressed, but the genes of defensive peptides showed greater up-regulated expression than those of ZF-proteins in Cd- and/or wounding (Wd) treatments of V. baoshanensis seedlings. The NGS-derived sequences of cyclotide precursor genes were verified by RT-PCR and ABI3730 sequencing studies, and 32 novel cyclotides were identified in V. baoshanensis. In general, the metal-binding sites of ZF-containing CRPs also represented the potential vulnerable targets of toxic metals. This study provides broad insights into CRPs-based defense systems and stress-vulnerable targets in V. baoshanensis. It now brings the number of cyclotide sequences in V. baoshanensis to 53 and based on projections from this work, the number of cyclotides in the Violaceae is now conservatively estimated to be >30000.

Whole-genome analysis revealed the positively selected genes during the differentiation of indica and temperate japonica rice

To investigate the selective pressures acting on the protein-coding genes during the differentiation of indica and japonica, all of the possible orthologous genes between the Nipponbare and 93–11 genomes were identified and compared with each other. Among these genes, 8,530 pairs had identical sequences, and 27,384 pairs shared more than 90% sequence identity. Only 2,678 pairs of genes displaying a Ka/Ks ratio significantly greater than one were revealed, and most of these genes contained only nonsynonymous sites. The genes without synonymous site were further analyzed with the SNP data of 1529 O. sativa and O. rufipogon accessions, and 1068 genes were identified to be under positive selection during the differentiation of indica and temperate japonica. The positively selected genes (PSGs) are unevenly distributed on 12 chromosomes, and the proteins encoded by the PSGs are dominant with binding, transferase and hydrolase activities, and especially enriched in the plant responses to stimuli, biological regulations, and transport processes. Meanwhile, the most PSGs of the known function and/or expression were involved in the regulation of biotic/abiotic stresses. The evidence of pervasive positive selection suggested that many factors drove the differentiation of indica and japonica, which has already started in wild rice but is much lower than in cultivated rice. Lower differentiation and less PSGs revealed between the Or-It and Or-IIIt wild rice groups implied that artificial selection provides greater contribution on the differentiation than natural selection. In addition, the phylogenetic tree constructed with positively selected sites showed that the japonica varieties exhibited more diversity than indica on differentiation, and Or-III of O. rufipogon exhibited more than Or-I.

Evolution, expression differentiation and interaction specificity of heterotrimeric G-protein subunit gene family in the mesohexaploid Brassica rapa

Heterotrimeric G-proteins, comprising of Gα, Gβ, and Gγ subunits, are important signal transducers which regulate many aspects of fundamental growth and developmental processes in all eukaryotes. Initial studies in model plants Arabidopsis and rice suggest that the repertoire of plant G-protein is much simpler than that observed in metazoans. In order to assess the consequence of whole genome triplication events within Brassicaceae family, we investigated the multiplicity of G-protein subunit genes in mesohexaploid Brassica rapa, a globally important vegetable and oilseed crop. We identified one Gα (BraA.Gα1), three Gβ (BraA.Gβ1, BraA.Gβ2, and BraA.Gβ3), and five Gγ (BraA.Gγ1, BraA.Gγ2, BraA.Gγ3, BraA.Gγ4, and BraA.Gγ5) genes from B. rapa, with a possibility of 15 Gαβγ heterotrimer combinations. Our analysis suggested that the process of genome triplication coupled with gene-loss (gene-fractionation) phenomenon have shaped the quantitative and sequence diversity of G-protein subunit genes in the extant B. rapa genome. Detailed expression analysis using qRT-PCR assays revealed that the G-protein genes have retained ubiquitous but distinct expression profiles across plant development. The expression of multiple G-protein genes was differentially regulated during seed-maturation and germination stages, and in response to various phytohormone treatments and stress conditions. Yeast-based interaction analysis showed that G-protein subunits interacted in most of the possible combinations, with some degree of subunit-specific interaction specificity, to control the functional selectivity of G-protein heterotrimer in different cell and tissue-types or in response to different environmental conditions. Taken together, this research identifies a highly diverse G-protein signaling network known to date from B. rapa, and provides a clue about the possible complexity of G-protein signaling networks present across globally important Brassica species.

Overexpression of rice OsREX1-S, encoding a putative component of the core general transcription and DNA repair factor IIH, renders plant cells tolerant to cadmium- and UV-induced damage by enhancing DNA excision repair

Screening of 40,000 Arabidopsis FOX (Full-length cDNA Over-eXpressor gene hunting system) lines expressing rice full-length cDNAs brings us to identify four cadmium (Cd)-tolerant lines, one of which carried OsREX1-S as a transgene. OsREX1-S shows the highest levels of identity to Chlamydomonas reinhardtii REX1-S (referred to as CrREX1-S, in which REX denotes Required for Excision) and to yeast and human TFB5s (RNA polymerase II transcription factor B5), both of which are components of the general transcription and DNA repair factor, TFIIH. Transient expression of OsREX1-S consistently localized the protein to the nucleus of onion cells. The newly generated transgenic Arabidopsis plants expressing OsREX1-S reproducibly displayed enhanced Cd tolerance, confirming that the Cd-tolerance of the initial identified line was conferred solely by OsREX1-S expression. Furthermore, transgenic Arabidopsis plants expressing OsREX1-S exhibited ultraviolet-B (UVB) tolerance by reducing the amounts of cyclobutane pyrimidine dimers produced by UVB radiation. Moreover, those transgenic OsREX1-S Arabidopsis plants became resistant to bleomycin (an inducer of DNA strand break) and mitomycin C (DNA intercalating activity), compared to wild type. Our results indicate that OsREX1-S renders host plants tolerant to Cd, UVB radiation, bleomycin and mitomycin C through the enhanced DNA excision repair.

Structural and functional properties of the rat P2X4 purinoreceptor extracellular vestibule during gating

P2X receptors are ATP-gated cation channels consisting of three subunits that are mutually intertwined and form an upper, central, and extracellular vestibule with three lateral portals and the channel pore. Here we used cysteine and alanine scanning mutagenesis of the rat P2X4R receptor V47–V61 and K326–N338 sequences to study structural and functional properties of extracellular vestibule during gating. Cysteine mutants were used to test the accessibility of these residue side chains to cadmium during closed-open-desensitized transitions, whereas alanine mutants served as controls. This study revealed the accessibility of residues E51, T57, S59, V61, K326, and M336 to cadmium in channels undergoing a transition from a closed-to-open state and the accessibility of residues V47, G53, D331, I332, I333, T335, I337, and N338 in channels undergoing a transition from an open-to-desensitized state; residues E56 and K329 were accessible during both transitions. The effect of cadmium on channel gating was stimulatory in all reactive V47–V61 mutants and inhibitory in the majority of reactive K326–N338 mutants. The rat P2X4 receptor homology model suggests that residues affected by cadmium in the closed-to-open transition were located within the lumen of the extracellular vestibule and toward the central vestibule; however, the residues affected by cadmium in the open-to-desensitized state were located at the bottom of the vestibule near the pore. Analysis of the model assumed that there is ion access to extracellular and central vestibules through lateral ports when the channel is closed, with residues above the first transmembrane domain being predominantly responsible for ion uptake. Upon receptor activation, there is passage of ions toward the residues located on the upper region of the second transmembrane domain, followed by permeation through the gate region.