Function of Protein Kinases in Leaf Senescence of Plants

Leaf senescence is an evolutionarily acquired process and it is critical for plant fitness. During senescence, macromolecules and nutrients are disassembled and relocated to actively growing organs. Plant leaf senescence process can be triggered by developmental cues and environmental factors, proper regulation of this process is essential to improve crop yield. Protein kinases are enzymes that modify their substrates activities by changing the conformation, stability, and localization of those proteins, to play a crucial role in the leaf senescence process. Impressive progress has been made in understanding the role of different protein kinases in leaf senescence recently. This review focuses on the recent progresses in plant leaf senescence-related kinases. We summarize the current understanding of the function of kinases on senescence signal perception and transduction, to help us better understand how the orderly senescence degeneration process is regulated by kinases, and how the kinase functions in the intricate integration of environmental signals and leaf age information.

Endogenous U6 promoters improve CRISPR/Cas9 editing efficiencies in Sorghum bicolor and show potential for applications in other cereals

Endogenous U6 promoters increase CRISPR/Cas9 editing efficiency in sorghum and may be useful for gene editing applications in other cereals.

Non-GM Genome Editing Approaches in Crops

CRISPR/Cas-based genome editing technologies have the potential to fast-track large-scale crop breeding programs. However, the rigid cell wall limits the delivery of CRISPR/Cas components into plant cells, decreasing genome editing efficiency. Established methods, such as Agrobacterium tumefaciens-mediated or biolistic transformation have been used to integrate genetic cassettes containing CRISPR components into the plant genome. Although efficient, these methods pose several problems, including 1) The transformation process requires laborious and time-consuming tissue culture and regeneration steps; 2) many crop species and elite varieties are recalcitrant to transformation; 3) The segregation of transgenes in vegetatively propagated or highly heterozygous crops, such as pineapple, is either difficult or impossible; and 4) The production of a genetically modified first generation can lead to public controversy and onerous government regulations. The development of transgene-free genome editing technologies can address many problems associated with transgenic-based approaches. Transgene-free genome editing have been achieved through the delivery of preassembled CRISPR/Cas ribonucleoproteins, although its application is limited. The use of viral vectors for delivery of CRISPR/Cas components has recently emerged as a powerful alternative but it requires further exploration. In this review, we discuss the different strategies, principles, applications, and future directions of transgene-free genome editing methods.

Heterotrimeric G Proteins in Plants: Canonical and Atypical Gα Subunits

Heterotrimeric GTP-binding proteins (G proteins), consisting of Gα, Gβ and Gγ subunits, transduce signals from a diverse range of extracellular stimuli, resulting in the regulation of numerous cellular and physiological functions in Eukaryotes. According to the classic G protein paradigm established in animal models, the bound guanine nucleotide on a Gα subunit, either guanosine diphosphate (GDP) or guanosine triphosphate (GTP) determines the inactive or active mode, respectively. In plants, there are two types of Gα subunits: canonical Gα subunits structurally similar to their animal counterparts and unconventional extra-large Gα subunits (XLGs) containing a C-terminal domain homologous to the canonical Gα along with an extended N-terminal domain. Both Gα and XLG subunits interact with Gβγ dimers and regulator of G protein signalling (RGS) protein. Plant G proteins are implicated directly or indirectly in developmental processes, stress responses, and innate immunity. It is established that despite the substantial overall similarity between plant and animal Gα subunits, they convey signalling differently including the mechanism by which they are activated. This review emphasizes the unique characteristics of plant Gα subunits and speculates on their unique signalling mechanisms.

Manipulating assimilate availability provides insight into the genes controlling grain size in sorghum

Variation in grain size, a major determinant of grain yield and quality in cereal crops, is determined by both the plant's genetic potential and the available assimilate to fill the grain in the absence of stress. This study investigated grain size variation in response to variation in assimilate supply in sorghum using a diversity panel (n = 837) and a backcross-nested association mapping population (n = 1421) across four experiments. To explore the effects of genetic potential and assimilate availability on grain size, the top half of selected panicles was removed at anthesis. Results showed substantial variation in five grain size parameters with high heritability. Artificial reduction in grain number resulted in a general increase in grain weight, with the extent of the increase varying across genotypes. Genome-wide association studies identified 44 grain size quantitative trait locus (QTL) that were likely to act on assimilate availability and 50 QTL that were likely to act on genetic potential. This finding was further supported by functional enrichment analysis and co-location analysis with known grain number QTL and candidate genes. RNA interference and overexpression experiments were conducted to validate the function of one of the identified gene, SbDEP1, showing that SbDEP1 positively regulates grain number and negatively regulates grain size by controlling primary branching in sorghum. Haplotype analysis of SbDEP1 suggested a possible role in racial differentiation. The enhanced understanding of grain size variation in relation to assimilate availability presented in this study will benefit sorghum improvement and have implications for other cereal crops.

GTP binding by Arabidopsis extra-large G protein 2 is not essential for its functions

The extra-large guanosine-5'-triphosphate (GTP)-binding protein 2, XLG2, is an unconventional Gα subunit of the Arabidopsis (Arabidopsis thaliana) heterotrimeric GTP-binding protein complex with a major role in plant defense. In vitro biochemical analyses and molecular dynamic simulations show that affinity of XLG2 for GTP is two orders of magnitude lower than that of the conventional Gα, AtGPA1. Here we tested the physiological relevance of GTP binding by XLG2. We generated an XLG2(T476N) variant with abolished GTP binding, as confirmed by in vitro GTPγS binding assay. Yeast three-hybrid, bimolecular fluorescence complementation, and split firefly-luciferase complementation assays revealed that the nucleotide-depleted XLG2(T476N) retained wild-type XLG2-like interactions with the Gβγ dimer and defense-related receptor-like kinases. Both wild-type and nucleotide-depleted XLG2(T476N) restored the defense responses against Fusarium oxysporum and Pseudomonas syringae compromised in the xlg2 xlg3 double mutant. Additionally, XLG2(T476N) was fully functional restoring stomatal density, root growth, and sensitivity to NaCl, but failed to complement impaired germination and vernalization-induced flowering. We conclude that XLG2 is able to function in a GTP-independent manner and discuss its possible mechanisms of action.

An easy-to-perform, culture-free Campylobacter point-of-management assay for processing plant applications

Aims

Current culture‐based methods for detection and determination of Campylobacter levels on processed chickens takes at least 2 days. Here we sought to develop a new complete, low‐cost and rapid (approximately 2·5 h) detection system requiring minimal operator input.

Methods and Results

We observed a strong correlation between culture‐based cell counts and our ability to detect either Campylobacter jejuni or Campylobacter coli by loop‐mediated isothermal amplification from the same samples. This knowledge was used to develop a rapid and simple five‐step assay to quantify Campylobacter, which was subsequently assessed for its specificity, reproducibility and accuracy in quantifying Campylobacter levels from processed chickens. The assay was found to be highly specific for C. jejuni and C. coli and was capable of distinguishing between samples that are either within or exceeding the industry set target of 6000 Campylobacter colony forming units (CFU) per carcass (equivalent to 12 CFU per ml of chicken rinse) with >90% accuracy relative to culture‐based methods.

Conclusions

Our method can reliably quantify Campylobacter counts of processed chickens with an accuracy comparable to culture‐based assays but provides results within hours as opposed to days.

Significance and Impact of the Study

The research presented here will help improve food safety by providing fast Campylobacter detection that will enable the implementation of real‐time risk management strategies in poultry processing plants to rapidly test processed chickens and identify effective intervention strategies. This technology is a powerful tool that can be easily adapted for other organisms and thus could be highly beneficial for a broad range of industries.

Nucleotide exchange-dependent and nucleotide exchange-independent functions of plant heterotrimeric GTP-binding proteins

Heterotrimeric guanine nucleotide-binding proteins (G proteins), which are composed of α, β, and γ subunits, are versatile, guanine nucleotide-dependent, molecular on-off switches. In animals and fungi, the exchange of GDP for GTP on Gα controls G protein activation and is crucial for normal cellular responses to diverse extracellular signals. The model plant Arabidopsis thaliana has a single canonical Gα subunit, AtGPA1. We found that, in planta, the constitutively active, GTP-bound AtGPA1(Q222L) mutant and the nucleotide-free AtGPA1(S52C) mutant interacted with Gβγ1 and Gβγ2 dimers with similar affinities, suggesting that G protein heterotrimer formation occurred independently of nucleotide exchange. In contrast, AtGPA1(Q222L) had a greater affinity than that of AtGPA1(S52C) for Gβγ3, suggesting that the GTP-bound conformation of AtGPA1(Q222L) is distinct and tightly associated with Gβγ3. Functional analysis of transgenic lines expressing either AtGPA1(S52C) or AtGPA1(Q222L) in the gpa1-null mutant background revealed various mutant phenotypes that were complemented by either AtGPA1(S52C) or AtGPA1(Q222L). We conclude that, in addition to the canonical GDP-GTP exchange-dependent mechanism, plant G proteins can function independently of nucleotide exchange.

Now for the hard ones: is there a limit on CRISPR genome editing in crops?

This article comments on the following paper: Martín-Pizarro C, Triviño JC, Posé D. 2019. Functional analysis of the TM6 MADS-box gene in the octoploid strawberry by CRISPR/Cas9-directed mutagenesis. Journal of Experimental Botany 70, 885–895.

A simple and cost-effective method for screening of CRISPR/Cas9-induced homozygous/biallelic mutants

BACKGROUND

The CRISPR/Cas9 system is being used for genome editing purposes by many research groups in multiple plant species. Traditional sequencing methods to identify homozygous mutants are time-consuming, laborious and expensive.

RESULTS

We have developed a method to screen CRISPR/Cas9-induced mutants through Mutation Sites Based Specific Primers Polymerase Chain Reaction (MSBSP-PCR). The MSBSP-PCR method was successfully used to identify homozygous/biallelic mutants in Nicotiana tabacum and Arabidopsis thaliana, and we speculate that it can be used for the identification of CRISPR/Cas9-induced mutants in other plant species. Compared to traditional sequencing methods, MSBSP-PCR is simpler, faster and cheaper.

CONCLUSIONS

The MSBSP-PCR method is simple to implement and can save time and cost in the screening of CRISPR/Cas9-induced homozygous/biallelic mutants.

A transient transformation system for gene characterization in upland cotton (Gossypium hirsutum)

BACKGROUND

Genetically modified cotton accounts for 64% of the world's cotton growing area (22.3 million hectares). The genome sequencing of the diploid cotton progenitors Gossypium raimondii and Gossypium arboreum as well as the cultivated Gossypium hirsutum has provided a wealth of genetic information that could be exploited for crop improvement. Unfortunately, gene functional characterization in cotton is lagging behind other economically important crops due to the low efficiency, lengthiness and technical complexity of the available stable transformation methods. We present here a simple, fast and efficient method for the transient transformation of G. hirsutum that can be used for gene characterization studies.

RESULTS

We developed a transient transformation system for gene characterization in upland cotton. Using β-glucuronidase as a reporter for Agrobacterium-mediated transformation assays, we evaluated multiple transformation parameters such as Agrobacterium strain, bacterial density, length of co-cultivation, chemicals and surfactants, which can affect transformation efficiency. After the initial characterization, the Agrobacterium EHA105 strain was selected and a number of binary constructs used to perform gene characterization studies. 7-days-old cotton seedlings were co-cultivated with Agrobacterium and transient gene expression was observed 5 days after infection of the plants. Transcript levels of two different transgenes under the control of the cauliflower mosaic virus (CaMV) 35S promoter were quantified by real-time reverse transcription PCR (qRT-PCR) showing a 3-10 times increase over the levels observed in non-infected controls. The expression patterns driven by the promoters of two G. hirsutum genes as well as the subcellular localization of their corresponding proteins were studied using the new transient expression system and our observations were consistent with previously published results using Arabidopsis as a heterologous system.

CONCLUSIONS

The Agrobacterium-mediated transient transformation method is a fast and easy transient expression system enabling high transient expression and transformation efficiency in upland cotton seedlings. Our method can be used for gene functional studies such as promoter characterization and protein subcellular localization in cotton, obviating the need to perform such studies in a heterologous system such as Arabidopsis.

Advanced DNA-Based Point-of-Care Diagnostic Methods for Plant Diseases Detection

Diagnostic technologies for the detection of plant pathogens with point-of-care capability and high multiplexing ability are an essential tool in the fight to reduce the large agricultural production losses caused by plant diseases. The main desirable characteristics for such diagnostic assays are high specificity, sensitivity, reproducibility, quickness, cost efficiency and high-throughput multiplex detection capability. This article describes and discusses various DNA-based point-of care diagnostic methods for applications in plant disease detection. Polymerase chain reaction (PCR) is the most common DNA amplification technology used for detecting various plant and animal pathogens. However, subsequent to PCR based assays, several types of nucleic acid amplification technologies have been developed to achieve higher sensitivity, rapid detection as well as suitable for field applications such as loop-mediated isothermal amplification, helicase-dependent amplification, rolling circle amplification, recombinase polymerase amplification, and molecular inversion probe. The principle behind these technologies has been thoroughly discussed in several review papers; herein we emphasize the application of these technologies to detect plant pathogens by outlining the advantages and disadvantages of each technology in detail.

Host Delivered RNAi, an efficient approach to increase rice resistance to sheath blight pathogen (Rhizoctonia solani)

Rhizoctonia solani, the causal agent of rice sheath blight disease, causes significant losses worldwide as there are no cultivars providing absolute resistance to this fungal pathogen. We have used Host Delivered RNA Interference (HD-RNAi) technology to target two PATHOGENICITY MAP KINASE 1 (PMK1) homologues, RPMK1-1 and RPMK1-2, from R. solani using a hybrid RNAi construct. PMK1 homologues in other fungal pathogens are essential for the formation of appressorium, the fungal infection structures required for penetration of the plant cuticle, as well as invasive growth once inside the plant tissues and overall viability of the pathogen within the plant. Evaluation of transgenic rice lines revealed a significant decrease in fungal infection levels compared to non-transformed controls and the observed delay in disease symptoms was further confirmed through microscopic studies. Relative expression levels of the targeted genes, RPMK1-1 and RPMK1-2, were determined in R. solani infecting either transgenic or control lines with significantly lower levels observed in R. solani infecting transgenic lines carrying the HD-RNAi constructs. This is the first report demonstrating the effectiveness of HD-RNAi against sheath blight and offers new opportunities for durable control of the disease as it does not rely on resistance conferred by major resistance genes.

Novel Chitinase Gene LOC_Os11g47510 from Indica Rice Tetep Provides Enhanced Resistance against Sheath Blight Pathogen Rhizoctonia solani in Rice

Sheath blight disease (ShB), caused by the fungus Rhizoctonia solani Kühn, is one of the most destructive diseases of rice (Oryza sativa L.), causing substantial yield loss in rice. In the present study, a novel rice chitinase gene, LOC_Os11g47510 was cloned from QTL region of R. solani tolerant rice line Tetep and used for functional validation by genetic transformation of ShB susceptible japonica rice line Taipei 309 (TP309). The transformants were characterized using molecular and functional approaches. Molecular analysis by PCR using a set of primers specific to CaMv 35S promoter, chitinase and HptII genes confirmed the presence of transgene in transgenic plants which was further validated by Southern hybridization. Further, qRT-PCR analysis of transgenic plants showed good correlation between transgene expression and the level of sheath blight resistance among transformants. Functional complementation assays confirmed the effectiveness of the chitinase mediated resistance in all the transgenic TP309 plants with varying levels of enhanced resistance against R. solani. Therefore, the novel chitinase gene cloned and characterized in the present study from the QTL region of rice will be of significant use in molecular plant breeding program for developing sheath blight resistance in rice.

Specific and Sensitive Isothermal Electrochemical Biosensor for Plant Pathogen DNA Detection with Colloidal Gold Nanoparticles as Probes

Developing quick and sensitive molecular diagnostics for plant pathogen detection is challenging. Herein, a nanoparticle based electrochemical biosensor was developed for rapid and sensitive detection of plant pathogen DNA on disposable screen-printed carbon electrodes. This 60 min assay relied on the rapid isothermal amplification of target pathogen DNA sequences by recombinase polymerase amplification (RPA) followed by gold nanoparticle-based electrochemical assessment with differential pulse voltammetry (DPV). Our method was 10,000 times more sensitive than conventional polymerase chain reaction (PCR)/gel electrophoresis and could readily identify P. syringae infected plant samples even before the disease symptoms were visible. On the basis of the speed, sensitivity, simplicity and portability of the approach, we believe the method has potential as a rapid disease management solution for applications in agriculture diagnostics.

Genome Editing in Cotton with the CRISPR/Cas9 System

Genome editing is an important tool for gene functional studies as well as crop improvement. The recent development of the CRISPR/Cas9 system using single guide RNA molecules (sgRNAs) to direct precise double strand breaks in the genome has the potential to revolutionize agriculture. Unfortunately, not all sgRNAs are equally efficient and it is difficult to predict their efficiency by bioinformatics. In crops such as cotton (Gossypium hirsutum L.), with labor-intensive and lengthy transformation procedures, it is essential to minimize the risk of using an ineffective sgRNA that could result in the production of transgenic plants without the desired CRISPR-induced mutations. In this study, we have developed a fast and efficient method to validate the functionality of sgRNAs in cotton using a transient expression system. We have used this method to validate target sites for three different genes GhPDS, GhCLA1, and GhEF1 and analyzed the nature of the CRISPR/Cas9-induced mutations. In our experiments, the most frequent type of mutations observed in cotton cotyledons were deletions (∼64%). We prove that the CRISPR/Cas9 system can effectively produce mutations in homeologous cotton genes, an important requisite in this allotetraploid crop. We also show that multiple gene targeting can be achieved in cotton with the simultaneous expression of several sgRNAs and have generated mutations in GhPDS and GhEF1 at two target sites. Additionally, we have used the CRISPR/Cas9 system to produce targeted gene fragment deletions in the GhPDS locus. Finally, we obtained transgenic cotton plants containing CRISPR/Cas9-induced gene editing mutations in the GhCLA1 gene. The mutation efficiency was very high, with 80.6% of the transgenic lines containing mutations in the GhCLA1 target site resulting in an intense albino phenotype due to interference with chloroplast biogenesis.

Whole-Genome Analysis of Candidate genes Associated with Seed Size and Weight in Sorghum bicolor Reveals Signatures of Artificial Selection and Insights into Parallel Domestication in Cereal Crops

Seed size and seed weight are major quality attributes and important determinants of yield that have been strongly selected for during crop domestication. Limited information is available about the genetic control and genes associated with seed size and weight in sorghum. This study identified sorghum orthologs of genes with proven effects on seed size and weight in other plant species and searched for evidence of selection during domestication by utilizing resequencing data from a diversity panel. In total, 114 seed size candidate genes were identified in sorghum, 63 of which exhibited signals of purifying selection during domestication. A significant number of these genes also had domestication signatures in maize and rice, consistent with the parallel domestication of seed size in cereals. Seed size candidate genes that exhibited differentially high expression levels in seed were also found more likely to be under selection during domestication, supporting the hypothesis that modification to seed size during domestication preferentially targeted genes for intrinsic seed size rather than genes associated with physiological factors involved in the carbohydrate supply and transport. Our results provide improved understanding of the complex genetic control of seed size and weight and the impact of domestication on these genes.

Genome Editing in Cotton with the CRISPR/Cas9 System

Genome editing is an important tool for gene functional studies as well as crop improvement. The recent development of the CRISPR/Cas9 system using single guide RNA molecules (sgRNAs) to direct precise double strand breaks in the genome has the potential to revolutionize agriculture. Unfortunately, not all sgRNAs are equally efficient and it is difficult to predict their efficiency by bioinformatics. In crops such as cotton (Gossypium hirsutum L.), with labor-intensive and lengthy transformation procedures, it is essential to minimize the risk of using an ineffective sgRNA that could result in the production of transgenic plants without the desired CRISPR-induced mutations. In this study, we have developed a fast and efficient method to validate the functionality of sgRNAs in cotton using a transient expression system. We have used this method to validate target sites for three different genes GhPDS, GhCLA1, and GhEF1 and analyzed the nature of the CRISPR/Cas9-induced mutations. In our experiments, the most frequent type of mutations observed in cotton cotyledons were deletions (∼64%). We prove that the CRISPR/Cas9 system can effectively produce mutations in homeologous cotton genes, an important requisite in this allotetraploid crop. We also show that multiple gene targeting can be achieved in cotton with the simultaneous expression of several sgRNAs and have generated mutations in GhPDS and GhEF1 at two target sites. Additionally, we have used the CRISPR/Cas9 system to produce targeted gene fragment deletions in the GhPDS locus. Finally, we obtained transgenic cotton plants containing CRISPR/Cas9-induced gene editing mutations in the GhCLA1 gene. The mutation efficiency was very high, with 80.6% of the transgenic lines containing mutations in the GhCLA1 target site resulting in an intense albino phenotype due to interference with chloroplast biogenesis.

Whole-Genome Analysis of Candidate genes Associated with Seed Size and Weight in Sorghum bicolor Reveals Signatures of Artificial Selection and Insights into Parallel Domestication in Cereal Crops

Seed size and seed weight are major quality attributes and important determinants of yield that have been strongly selected for during crop domestication. Limited information is available about the genetic control and genes associated with seed size and weight in sorghum. This study identified sorghum orthologs of genes with proven effects on seed size and weight in other plant species and searched for evidence of selection during domestication by utilizing resequencing data from a diversity panel. In total, 114 seed size candidate genes were identified in sorghum, 63 of which exhibited signals of purifying selection during domestication. A significant number of these genes also had domestication signatures in maize and rice, consistent with the parallel domestication of seed size in cereals. Seed size candidate genes that exhibited differentially high expression levels in seed were also found more likely to be under selection during domestication, supporting the hypothesis that modification to seed size during domestication preferentially targeted genes for intrinsic seed size rather than genes associated with physiological factors involved in the carbohydrate supply and transport. Our results provide improved understanding of the complex genetic control of seed size and weight and the impact of domestication on these genes.

Whole Genome Sequencing Reveals Potential New Targets for Improving Nitrogen Uptake and Utilization in Sorghum bicolor

Nitrogen (N) fertilizers are a major agricultural input where more than 100 million tons are supplied annually. Cereals are particularly inefficient at soil N uptake, where the unrecovered nitrogen causes serious environmental damage. Sorghum bicolor (sorghum) is an important cereal crop, particularly in resource-poor semi-arid regions, and is known to have a high NUE in comparison to other major cereals under limited N conditions. This study provides the first assessment of genetic diversity and signatures of selection across 230 fully sequenced genes putatively involved in the uptake and utilization of N from a diverse panel of sorghum lines. This comprehensive analysis reveals an overall reduction in diversity as a result of domestication and a total of 128 genes displaying signatures of purifying selection, thereby revealing possible gene targets to improve NUE in sorghum and cereals alike. A number of key genes appear to have been involved in selective sweeps, reducing their sequence diversity. The ammonium transporter (AMT) genes generally had low allelic diversity, whereas a substantial number of nitrate/peptide transporter 1 (NRT1/PTR) genes had higher nucleotide diversity in domesticated germplasm. Interestingly, members of the distinct race Guinea margaritiferum contained a number of unique alleles, and along with the wild sorghum species, represent a rich resource of new variation for plant improvement of NUE in sorghum.

Field Demonstration of a Multiplexed Point-of-Care Diagnostic Platform for Plant Pathogens

Effective disease management strategies to prevent catastrophic crop losses require rapid, sensitive, and multiplexed detection methods for timely decision making. To address this need, a rapid, highly specific and sensitive point-of-care method for multiplex detection of plant pathogens was developed by taking advantage of surface-enhanced Raman scattering (SERS) labeled nanotags and recombinase polymerase amplification (RPA), which is a rapid isothermal amplification method with high specificity. In this study, three agriculturally important plant pathogens (Botrytis cinerea, Pseudomonas syringae, and Fusarium oxysporum) were used to demonstrate potential translation into the field. The RPA-SERS method was faster, more sensitive than polymerase chain reaction, and could detect as little as 2 copies of B. cinerea DNA. Furthermore, multiplex detection of the three pathogens was demonstrated for complex systems such as the Arabidopsis thaliana plant and commercial tomato crops. To demonstrate the potential for on-site field applications, a rapid single-tube RPA/SERS assay was further developed and successfully performed for a specific target outside of a laboratory setting.

Functional Characterization of Novel Chitinase Genes Present in the Sheath Blight Resistance QTL: qSBR11-1 in Rice Line Tetep

Rice sheath blight disease caused by Rhizoctonia solani is one of the most devastating diseases in rice leading to heavy yield losses. Due to the polygenic nature of resistance, no major resistance gene with complete host resistance against R. solani has been reported. In this study, we have performed molecular and functional analysis of the genes associated with the major R. solani-resistance QTL qSBR11-1 in the indica rice line Tetep. Sequence analysis revealed the presence of a set of 11 tandem repeats containing genes with a high degree of homology to class III chitinase defense response genes. Real-time quantitative PCR analysis showed that all the genes are strongly induced 36 h after R. solani infection. Comparison between the resistant Tetep and the susceptible HP2216 lines shows that the induction of the chitinase genes is much higher in the Tetep line. Recombinant protein produced in vitro for six of the eleven genes showed chitinolytic activity in gel assays but we did not detect any xylanase inhibitory activity. All the six in vitro expressed proteins show antifungal activity with a clear inhibitory effect on the growth of the R. solani mycelium. The characterized chitinase genes can provide an important resource for the genetic improvement of R. solani susceptible rice lines for sheath blight resistance breeding.

Simplified Assays for Evaluation of Resistance to Alternaria brassicicola and Turnip Mosaic Virus

Studying the natural defense mechanisms developed by model plants such as Arabidopsis is an important approach towards the improvement of crop species. The availability of mutants as well as the relative easiness to silence any gene in Arabidopsis provides an invaluable source of genotypes that can be used to discover new elements involved in the defense response. Here we describe simple and reliable methods to evaluate susceptibility/resistance to the pathogenic fungus Alternaria brassicicola and the viral pathogen Turnip mosaic virus.

Yeast Three-Hybrid System for the Detection of Protein-Protein Interactions

Protein-protein interaction studies provide useful insights into biological processes taking place within the living cell. A number of techniques are available to unravel large structural protein complexes, functional protein modules, and temporary protein associations occurring during signal transduction. The choice of method depends on the nature of the proteins and the interaction being studied. Here we present an optimized and simplified yeast three-hybrid method for analysis of protein interactions involving three components.

Evidence for an unusual transmembrane configuration of AGG3, a class C Gγ subunit of Arabidopsis

Heterotrimeric G proteins are crucial for the perception of external signals and subsequent signal transduction in animal and plant cells. In both model systems, the complex comprises one Gα, one Gβ, and one Gγ subunit. However, in addition to the canonical Gγ subunits (class A), plants also possess two unusual, plant-specific classes of Gγ subunits (classes B and C) that have not yet been found in animals. These include Gγ subunits lacking the C-terminal CaaX motif (class B), which is important for membrane anchoring of the protein; the presence of such subunits gives rise to a flexible sub-population of Gβ/γ heterodimers that are not necessarily restricted to the plasma membrane. Plants also contain class C Gγ subunits, which are twice the size of canonical Gγ subunits, with a predicted transmembrane domain and a large cysteine-rich extracellular C-terminus. However, neither the presence of the transmembrane domain nor the membrane topology have been unequivocally demonstrated. Here, we provide compelling evidence that AGG3, a class C Gγ subunit of Arabidopsis, contains a functional transmembrane domain, which is sufficient but not essential for plasma membrane localization, and that the cysteine-rich C-terminus is extracellular.

Re-purposing bridging flocculation for on-site, rapid, qualitative DNA detection in resource-poor settings

Developing molecular diagnostics in resource-poor settings is challenging. As such, we purpose-built a novel bridging flocculation assay for qualitative evaluation of isothermally amplified DNA by naked eye. The flocculation assay was dependent on pH, DNA polymer amounts and lengths. The method was first applied to the rapid and sensitive detection of important plant pathogens and subsequently extended to other pathogens across the animal kingdom to demonstrate the wide applications of our approach.

Down-regulation of Fusarium oxysporum endogenous genes by Host-Delivered RNA interference enhances disease resistance

Fusarium oxysporum is a devastating pathogen causing extensive yield losses in a variety of crops and development of sustainable, environmentally friendly methods to improve crop resistance is crucial. We have used Host-Delivered RNA interference (HD-RNAi) technology to partially silence three different genes (FOW2, FRP1, and OPR) in the hemi-biotrophic fungus F. oxysporum f. sp. conglutinans. Expression of double stranded RNA (dsRNA) molecules targeting fungal pathogen genes was achieved in a number of transgenic Arabidopsis lines. F. oxysporum infecting the transgenic lines displayed substantially reduced mRNA levels on all three targeted genes, with an average of 75, 83, and 72% reduction for FOW2, FRP1, and OPR, respectively. The silencing of pathogen genes had a clear positive effect on the ability of the transgenic lines to fight infection. All transgenic lines displayed enhanced resistance to F. oxysporum with delayed disease symptom development, especially FRP1 and OPR lines. Survival rates after fungal infection were higher in the transgenic lines compared to control wild type plants which consistently showed survival rates of 10%, with FOW2 lines showing 25% survival; FRP1 lines 30-50% survival and OPR between 45 and 70% survival. The down-regulation effect was specific for the targeted genes without unintended effects in related genes. In addition to producing resistant crops, HD-RNAi can provide a useful tool to rapidly screen candidate fungal pathogenicity genes without the need to produce fungal knockout mutants.

The pineapple AcMADS1 promoter confers high level expression in tomato and Arabidopsis flowering and fruiting tissues, but AcMADS1 does not complement the tomato LeMADS-RIN (rin) mutant

A previous EST study identified a MADS box transcription factor coding sequence, AcMADS1, that is strongly induced during non-climacteric pineapple fruit ripening. Phylogenetic analyses place the AcMADS1 protein in the same superclade as LeMADS-RIN, a master regulator of fruit ripening upstream of ethylene in climacteric tomato. LeMADS-RIN has been proposed to be a global ripening regulator shared among climacteric and non-climacteric species, although few functional homologs of LeMADS-RIN have been identified in non-climacteric species. AcMADS1 shares 67 % protein sequence similarity and a similar expression pattern in ripening fruits as LeMADS-RIN. However, in this study AcMADS1 was not able to complement the tomato rin mutant phenotype, indicating AcMADS1 may not be a functionally conserved homolog of LeMADS-RIN or has sufficiently diverged to be unable to act in the context of the tomato network of interacting proteins. The AcMADS1 promoter directed strong expression of the GUS reporter gene to fruits and developing floral organs in tomato and Arabidopsis thaliana, suggesting AcMADS1 may play a role in flower development as well as fruitlet ripening. The AcMADS1 promoter provides a useful molecular tool for directing transgene expression, particularly where up-regulation in developing flowers and fruits is desirable.

Molecular inversion probe: a new tool for highly specific detection of plant pathogens

Highly specific detection methods, capable of reliably identifying plant pathogens are crucial in plant disease management strategies to reduce losses in agriculture by preventing the spread of diseases. We describe a novel molecular inversion probe (MIP) assay that can be potentially developed into a robust multiplex platform to detect and identify plant pathogens. A MIP has been designed for the plant pathogenic fungus Fusarium oxysporum f.sp. conglutinans and the proof of concept for the efficiency of this technology is provided. We demonstrate that this methodology can detect as little as 2.5 ng of pathogen DNA and is highly specific, being able to accurately differentiate Fusarium oxysporum f.sp. conglutinans from other fungal pathogens such as Botrytis cinerea and even pathogens of the same species such as Fusarium oxysporum f.sp. lycopersici. The MIP assay was able to detect the presence of the pathogen in infected Arabidopsis thaliana plants as soon as the tissues contained minimal amounts of pathogen. MIP methods are intrinsically highly multiplexable and future development of specific MIPs could lead to the establishment of a diagnostic method that could potentially screen infected plants for hundreds of pathogens in a single assay.

Microarray analysis of gene expression profiles in ripening pineapple fruits

BACKGROUND

Pineapple (Ananas comosus) is a tropical fruit crop of significant commercial importance. Although the physiological changes that occur during pineapple fruit development have been well characterized, little is known about the molecular events that occur during the fruit ripening process. Understanding the molecular basis of pineapple fruit ripening will aid the development of new varieties via molecular breeding or genetic modification. In this study we developed a 9277 element pineapple microarray and used it to profile gene expression changes that occur during pineapple fruit ripening.

RESULTS

Microarray analyses identified 271 unique cDNAs differentially expressed at least 1.5-fold between the mature green and mature yellow stages of pineapple fruit ripening. Among these 271 sequences, 184 share significant homology with genes encoding proteins of known function, 53 share homology with genes encoding proteins of unknown function and 34 share no significant homology with any database accession. Of the 237 pineapple sequences with homologs, 160 were up-regulated and 77 were down-regulated during pineapple fruit ripening. DAVID Functional Annotation Cluster (FAC) analysis of all 237 sequences with homologs revealed confident enrichment scores for redox activity, organic acid metabolism, metalloenzyme activity, glycolysis, vitamin C biosynthesis, antioxidant activity and cysteine peptidase activity, indicating the functional significance and importance of these processes and pathways during pineapple fruit development. Quantitative real-time PCR analysis validated the microarray expression results for nine out of ten genes tested.

CONCLUSIONS

This is the first report of a microarray based gene expression study undertaken in pineapple. Our bioinformatic analyses of the transcript profiles have identified a number of genes, processes and pathways with putative involvement in the pineapple fruit ripening process. This study extends our knowledge of the molecular basis of pineapple fruit ripening and non-climacteric fruit ripening in general.

Developing pineapple fruit has a small transcriptome dominated by metallothionein

In a first step toward understanding the molecular basis of pineapple fruit development, a sequencing project was initiated to survey a range of expressed sequences from green unripe and yellow ripe fruit tissue. A highly abundant metallothionein transcript was identified during library construction, and was estimated to account for up to 50% of all EST library clones. Library clones with metallothionein subtracted were sequenced, and 408 unripe green and 1140 ripe yellow edited EST clone sequences were retrieved. Clone redundancy was high, with the combined 1548 clone sequences clustering into just 634 contigs comprising 191 consensus sequences and 443 singletons. Half of the EST clone sequences clustered within 13.5% and 9.3% of contigs from green unripe and yellow ripe libraries, respectively, indicating that a small subset of genes dominate the majority of the transcriptome. Furthermore, sequence cluster analysis, northern analysis, and functional classification revealed major differences between genes expressed in the unripe green and ripe yellow fruit tissues. Abundant genes identified from the green fruit include a fruit bromelain and a bromelain inhibitor. Abundant genes identified in the yellow fruit library include a MADS box gene, and several genes normally associated with protein synthesis, including homologues of ribosomal L10 and the translation factors SUI1 and eIF5A. Both the green unripe and yellow ripe libraries contained high proportions of clones associated with oxidative stress responses and the detoxification of free radicals.

Isolation of a novel G-protein gamma-subunit from Arabidopsis thaliana and its interaction with Gbeta

There is increasing evidence that heterotrimeric G-proteins (G-proteins) are involved in many plant processes including phytohormone response, pathogen defence and stomatal control. In animal systems, each of the three G-protein subunits belong to large multigene families; however, few subunits have been isolated from plants. Here we report the cloning of a second plant G-protein gamma-subunit (AGG2) from Arabidopsis thaliana. The predicted AGG2 protein sequence shows 48% identity to the first identified Arabidopsis Ggamma-subunit, AGG1. Furthermore, AGG2 contains all of the conserved characteristics of gamma-subunits including a small size (100 amino acids, 11.1 kDa), C-terminal CAAX box and a N-terminal alpha-helix region capable of forming a coiled-coil interaction with the beta-subunit. A strong interaction between AGG2 and both the tobacco (TGB1) and Arabidopsis (AGB1) beta-subunits was observed in vivo using the yeast two-hybrid system. The strong association between AGG2 and AGB1 was confirmed in vitro. Southern and Northern analyses showed that AGG2 is a single copy gene in Arabidopsis producing two transcripts that are present in all tissues tested. The isolation of a second gamma-subunit from A. thaliana indicates that plant G-proteins, like their mammalian counterparts, may form different heterotrimer combinations that presumably regulate multiple signal transduction pathways.

Completing the heterotrimer: isolation and characterization of an Arabidopsis thaliana G protein gamma-subunit cDNA

Heterotrimeric G proteins consist of three subunits (alpha, beta, and gamma). alpha- and beta- subunits have been previously cloned in plants, but the gamma-subunit has remained elusive. To isolate the gamma-subunit of a plant heterotrimeric G protein an Arabidopsis thaliana yeast two-hybrid library was screened by using a tobacco G-beta-subunit as the bait protein. One positive clone (AGG1) was isolated several times; it displays significant homology to the conserved domains of mammalian gamma-subunits. The predicted AGG1 protein sequence contains all of the typical characteristics of mammalian gamma-subunits such as small size (98 amino acids, 10.8 kDa), presence of a C-terminal CAAX box to direct isoprenyl modification, and an N-terminal alpha-helix region capable of forming a coiled-coil interaction with the beta-subunit. Northern and Southern analyses showed that AGG1 is a single-copy gene in Arabidopsis with a similar expression pattern to the Arabidopsis beta-subunit, AGB1 [Weiss, C. A., Garnaat, C. W., Mukai, K., Hu, Y. & Ma, H. (1994) Proc. Natl. Acad. Sci. USA 91, 9554-9558]. By using the yeast two-hybrid system, we show that AGG1 strongly interacts with tobacco and Arabidopsis beta-subunits. The in vivo results have been confirmed by using in vitro methods to prove the interaction between AGG1 and the Arabidopsis beta-subunit. As previously observed in mammalian systems, both the coiled-coil domain and the WD repeat regions of the beta-subunit are essential for AGG1 interaction. Also in agreement with previous observations, the removal of the N-terminal alpha-helix of the AGG1 greatly reduces but does not completely block the interaction.

Characterization of ATDRG1, a member of a new class of GTP-binding proteins in plants

We report the initial characterization of an Arabidopsis thaliana cDNA (atdrg1), a member of a new class of GTP-binding proteins (G-proteins) in plants. The predicted ATDRG1 protein contains all five structural motifs characteristic of the G-protein superfamily. Apart from these motifs, the amino acid sequence differs substantially from all known G-proteins except for a recently discovered new family named developmentally regulated G-proteins (DRGs). Sequences closely related to atdrg1 are found in species as distant as human (80% amino acid conservation), Drosophila (74%), yeast (77%) and Caenorhabditis elegans (77%). The remarkable evolutionary conservation of these proteins suggests an important, but as yet unclear role. Phylogenetic analysis of the available homologous sequences strongly suggests a diphyletic origin of the eukaryotic DRG proteins. Northern analysis shows high levels of atdrg1 mRNA in all Arabidopsis tissues studied, and homologues of atdrg1 are present throughout the plant kingdom. In situ hybridization reveals that atdrg1 is highly expressed in actively growing tissues and reproductive organs. Southern analysis indicates the presence of either one or two copies of atdrg1 in the Arabidopsis genome. Immunolocalization studies show that the protein is present in cytoplasmic vesicles found mainly in actively growing tissues suggesting a putative role for ATDRG1 in either the regulation of vesicle transport or the regulation of enzymes involved in storage protein processing.

Cloning and characterisation of a glutamate dehydrogenase cDNA from tomato (Lycopersicon esculentum L.)

A full-length cDNA (legdh1) has been cloned encoding glutamate dehydrogenase (GDH) from tomato (Lycopersicon esculentum L.). legdh1 is 1568 bp long and contains an open reading frame encoding a 44.8 kDa polypeptide with a putative mitochondrial-matrix-targeting pre-sequence at its N-terminus. Southern analysis indicates the existence of one copy of legdh1 per haploid genome, and no closely related genes were detected by Southern analysis at low stringency. We hypothesise that in tomato, the two GDH subunits may arise from post-transcriptional modifications of a single gene. Northern analysis reveals high expression of legdh1 in roots, lower levels of expression in stems, flowers and leaves, and no detectable expression in fruits. In general, there was no correlation between steady-state mRNA level and protein activity in the tissues analysed, again suggesting the importance of post-transcriptional events in the regulation of GDH. Comparison of cloned plant GDH proteins reveals a high degree of homology throughout the sequence except for a very specific, highly divergent region.

Calcium-dependent protein kinase gene expression in response to physical and chemical stimuli in mungbean (Vigna radiata)

Protein kinases are important in eukaryotic signal transduction pathways. In this study we designed degenerate oligonucleotides corresponding to two conserved regions of protein kinases and using the polymerase chain reaction (PCR) have amplified a 141 bp fragment of DNA from mungbeans (Vigna radiata Rwilcz cv. Berken). Sequence analysis of the PCR products indicates that they encode several putative protein kinases with respect to their identity with other known plant protein kinases. Using one of the six fragments (CPK3-8), we isolated a 2022 bp cDNA (VrCDPK-1) from a Vigna radiata lambda gt11 library. VrCDPK-1 has a 96 bp 5'-untranslated region and a 465 bp 3'-untranslated region and an open reading frame of 1461 bp. VrCDPK-1 contains all of the conserved regions commonly found in calcium dependent protein kinases (CDPK). VrCDPK-1 shares 24 to 89% sequence identity with previously reported sequences for plant CDPKs at the protein level. Southern analysis revealed the presence of several copies of the CDPK gene. VrCDPK-1 expression was stimulated when mungbean cuttings were treated with CaCl2, while treatment with MgCl2 had no effect. We are reporting for the first time a CDPK gene in mungbean which is inducible by mechanical strain. Cuttings treated with indole-3-acetic acid (IAA) or subjected to salt stress showed an increase in VrCDPK-1 expression. There was a dramatic stimulation in VrCDPK-1 expression 6 h after cuttings were treated with cycloheximide.

A mechanical strain-induced 1-aminocyclopropane-1-carboxylic acid synthase gene

Ethylene production is observed in all higher plants, where it is involved in numerous aspects of growth, development, and senescence. 1-Aminocyclopropane-1-carboxylic acid synthase (ACC synthase; S-adenosyl-L-methionine methylthioadenosine-lyase, EC 4.4.1.14) is the key regulatory enzyme in the ethylene biosynthetic pathway. We are reporting an ACC synthase gene in Vigna radiata (mung bean) that is inducible by mechanical strain. The ACC synthase cDNA AIM-1 was induced by mechanical strain within 10 min, reaching a maximum at 30 min, showing a dramatic reduction after 60 min, and showing no detectable message by 3 hr. The kinetics of induction for AIM-1 was similar to a mechanical strain-induced calmodulin (MBCaM-1) in V. radiata, whereas the kinetics of its decline from maximum was different. When plants were subjected to calcium-deficient conditions, supplemental calcium, calcium chelators, calcium storage releasers, calcium ionophore, or calmodulin antagonists, there was no effect on AIM-1, indicating that the mechanical strain-induced AIM-1 expression is a calcium-independent process. Induction of MBCaM-1 in all cases behaved in the same way as AIM-1, suggesting that they share similar mechanically activated cis- and/or trans-acting elements in their promoter.

Differential expression of two calmodulin genes in response to physical and chemical stimuli

Two different calmodulin (CaM) cDNAs (MBCaM-1 and MBCaM-2) were isolated from a vigna radiata lambda gt11 library by screening with a heterologous Arabidopsis cDNA probe (TCH-1). Both cDNAs are 85% homologous inside the coding region but are highly divergent outside this region. The polypeptides encoded by MBCaM-1 and MBCaM-2 are identical except for two conservative substitutions at positions 7 and 10. Southern analysis revealed that both cDNAs are encoded by different genes. Expression studies revealed different patterns of expression of both genes. MBCaM-1 mRNA exhibited a dramatic transient increase in response to touch, while MBCaM-2 expression showed a steady but small increase as compared to MBCaM-1. When plants were grown in complete darkness MBCaM-1 was undetectable and MBCaM-2 exhibited very low levels of expression. One hour after exposure of etiolated seedlings to light MBCaM-1 showed no change, while MBCaM-2 expression was increased. After a 6 h exposure to light there was an induction of both MBCaM-1 and MBCaM-2; however, the magnitude of this increase was much greater for MBCaM-2. When plants were grown under a 16 h light/8 h dark cycle the mRNA levels for MBCaM-1 were lower during the light period and increased during the beginning of the night cycle, while MBCaM-2 showed no change. Plants treated with indole-3-acetic acid had a peak in MBCaM-1 expression 6 h after treatment initiation with a slight decline 3 h after the peak, while MBCaM-2 showed a steady but small increase over time as compared to MBCaM-1. When plants were subjected to salt stress they showed an increase in MBCaM-1 expression 2 h after treatment initiation reaching a maximum after 4 h with no further increase after 6 h, while MBCaM-2 remained unchanged over the time course.

Identification of two new members of the 1-aminocyclopropane-1-carboxylate synthase-encoding multigene family in mung bean

The key enzyme regulating ethylene biosynthesis in higher plants is 1-aminocyclopropane-1-carboxylate (ACC) synthase. In mung bean (MB), the existence of three genes encoding this enzyme has previously been reported [Botella et al., Plant Mol. Biol. 18 (1992) 793-797], one of which corresponds to a full-length indole-3-acetic acid-inducible cDNA [Botella et al., Plant Mol. Biol. (1992) 425-436]. In this paper we report the cloning of two new genomic sequences coding for ACC synthase in MB (MAC-4 and MAC-5). MAC-4 is 1340 bp long and encodes 388 amino acids (aa) while MAC-5 is 1393 bp long and encodes for 391 aa. Genomic Southern analysis suggests the existence of only one copy of each gene in the genome.

Identification and characterization of a full-length cDNA encoding for an auxin-induced 1-aminocyclopropane-1-carboxylate synthase from etiolated mung bean hypocotyl segments and expression of its mRNA in response to indole-3-acetic acid

1-Aminocyclopropane-1-carboxylate (ACC) synthase (EC 4.4.1.14) is the key regulatory enzyme in the ethylene biosynthetic pathway. The identification and characterization of a full-length cDNA (pAIM-1) 1941 bp in length for indole-3-acetic acid (IAA)-induced ACC synthase is described in this paper. The pAIM-1 clone has an 87 bp leader and a 402 bp trailing sequence. The open reading frame is 1452 bp long encoding for a 54.6 kDa polypeptide (484 amino acids) which has a calculated isoelectric point of 6.0. In vitro transcription and translation experiments support the calculated molecular weight and show that the enzyme does not undergo processing. Eleven of the twelve amino acid residues which are conserved in aminotransferases are found in pAIM-1. The sequence for pMAC-1 which is one of the 5 genes we have identified in mung bean is contained in pAIM-1. pAIM-1 shares between 52 to 65% homology with previously reported sequences for ACC synthase at the protein level. There is little detectable pAIM-1 message found in untreated mung bean tissues; however, expression is apparent within 30 min following the addition of 10 microM IAA reaching a peak after approximately 5 h with a slight decrease in message after 12 h. These changes in message correlate with changes in ACC levels found in these tissues following treatment with 10 microM IAA.

Immunocytolocalization of Glutamine Synthetase in Green Leaves and Cotyledons of Lycopersicon esculentum

Glutamine synthetase was localized in leaves and cotyledons of young tomato (Lycopersicon esculentum Mill.) plants using immunogold techniques coupled to transmission electron microscopy. The enzyme occurs only in chloroplasts and is most probably a stroma constituent.

Immunocytolocalization of Ferredoxin-GOGAT in the Cells of Green Leaves and Cotyledons of Lycopersicon esculentum

Ferredoxin-glutamate synthase was localized in leaves and cotyledons of tomato (Lycopersicon esculentum, cv Hellfrucht früshstamm) seedlings by immunocytochemical methods. The present work established that the enzyme was not only a constituent of chloroplast stroma of the mesophyll cells, but also of the cells of xylem parenchyma and epidermis.

Different Characteristics of the Two Glutamate Synthases in the Green Leaves of Lycopersicon esculentum

The two glutamate synthases, NAD(P)H- and ferredoxin-dependent, from the green leaves of tomato plants (Lycopersicon esculentum L. cv Hellfrucht frühstamm) differed in their chemical properties and catalytic behavior. Gel filtration of NAD(P)H enzyme gave an apparent molecular size of 158 kilodalton, whereas the ferredoxin enzyme molecular size was 141 kilodalton. Arrhenius plots of the activities of the two enzymes showed that the NAD(P)H enzyme had two activation energies; 109.6 and 70.5 kilojoule per mole; the transition temperature was 22 degrees C. The ferredoxin enzyme however, had only one activation energy; 56.1 kilojoule per mole. The respective catalytic activity pH optima for the NAD(P)H- dependent and the ferredoxin dependent enzymes were around 7.3 and 7.8. In experiments to evaluate the effects of modulators aspartate enhanced the NAD(P)H-linked activity, with a K(a) value of 0.25 millimolar, but strongly inhibited that of the ferredoxin-dependent glutamate synthase with a K(i) of 0.1 millimolar. 3-Phosphoserine was another inhibitor of the ferredoxin dependent enzyme with a K(i) value of 4.9 millimolar. 3-Phosphoglyceric acid was a potent inhibitor of the ferredoxin-dependent form, but hardly affected the NAD(P)H-dependent enzyme. The results are discussed and interpreted to propose different specific functions that these activities may have within the leaf tissue cell.

Immunochemical comparison of glutamine synthetases from some solanaceae plants

The presence of different glutamine synthetase isoenzymes in different Solanaceae plants and their relative antigenicities against antiglutamine synthetase from tomato leaf serum were studied. All the plants tested showed one glutamine synthetase isoenzyme except for Mandragora autumnalis, which showed two, after discontinuous polyacrylamide gel electrophoresis and specific in situ assay. Antigenicities were compared by the double immunodiffusion technique. The Nicotiana glauca enzyme showed equal reactivity to that of Lycopersicon esculentum, but its antigenicity was higher than Withania frutescens, Datura stramonium, and Hyoscyamus niger. The study of relative antigenicities permitted differentiation of the glutamine synthetase enzymes from uncultivated species of Solanaceae.