Assay for Pathogen-Associated Molecular Pattern (PAMP)-Triggered Immunity (PTI) in Plants

To perceive potential pathogens in their environment, plants use pattern recognition receptors (PRRs) present on their plasma membranes. PRRs recognize conserved microbial features called pathogen-associated molecular patterns (PAMPs) and this detection leads to PAMP-triggered immunity (PTI), which effectively prevents colonization of plant tissues by non-pathogens1,2. The most well studied system in PTI is the FLS2-dependent pathway3. FLS2 recognizes the PAMP flg22 that is a component of bacterial flagellin

The tomato kinase Pti1 contributes to production of reactive oxygen species in response to two flagellin-derived peptides and promotes resistance to pseudomonas syringae Infection

The Pti1 kinase was identified from a reverse genetic screen as contributing to pattern-triggered immunity (PTI) against Pseudomonas syringae pv. tomato (Pst). The tomato genome has two Pti1 genes, referred to as Pti1a and Pti1b. A hairpin-Pti1 (hpPti1) construct was developed and was used to generate two independent stable transgenic tomato lines that had reduced transcript abundance of both genes. In response to P. syringae pv. tomato inoculation, these hpPti1 plants developed more severe disease symptoms, supported higher bacterial populations, and had reduced transcript accumulation of PTI-associated genes, as compared with wild-type plants. In response to two flagellin-derived peptides, the hpPti1 plants produced lesser amounts of reactive oxygen species (ROS) but showed no difference in mitogen-activated protein kinase (MAPK). Synthetic Pti1a and Pti1b genes designed to avoid silencing were transiently expressed in the hpPti1 plants and restored the ability of the plants to produce wild-type levels of ROS. Our results identify a new component of PTI in tomato that, because it affects ROS production but not MAPK signaling, appears to act early in the immune response.Instituto de Fisiología Vegeta

Virus-induced gene silencing database for phenomics and functional genomics in Nicotiana benthamiana

Virus-induced gene silencing (VIGS) is an important forward and reverse genetics method for the study of gene function in many plant species, especially Nicotiana benthamiana. However, despite the widespread use of VIGS, a searchable database compiling the phenotypes observed with this method is lacking. Such a database would allow researchers to know the phenotype associated with the silencing of a large number of individual genes without experimentation. We have developed a VIGS phenomics and functional genomics database (VPGD) that has DNA sequence information derived from over 4,000 N. benthamiana VIGS clones along with the associated silencing phenotype for approximately 1,300 genes. The VPGD has a built-in BLAST search feature that provides silencing phenotype information of specific genes. In addition, a keyword-based search function could be used to find a specific phenotype of interest with the corresponding gene, including its Gene Ontology descriptions. Query gene sequences from other plant species that have not been used for VIGS can also be searched for their homologs and silencing phenotype in N. benthamiana. VPGD is useful for identifying gene function not only in N. benthamiana but also in related Solanaceae plants such as tomato and potato. The database is accessible at http://vigs.noble.org.Noble Research Institute and NSF IOS-102564

Stacked Trait Products Are As Safe As Non-Genetically Modified (GM) Products Developed By Conventional Breeding Practices

International safety assessments and independent publications conclude that stacking genetically modified (GM) traits (events) through conventional breeding poses no greater risk to food or feed safety than stacking multiple non-GM traits by conventional breeding. Stacked trait products are not substantially different from their conventional comparator or their GM parent plants. Additional safety assessment of a stacked trait product produced by conventional breeding should not be required unless there is a plausible and testable hypothesis for interaction of the traits. However, the different approaches employed for the regulation of stacked trait products between countries results in asynchronous approvals, increasing the potential for trade flow disruptions, and adds to the regulatory burden for product developers. Considering their proven safety and benefit over the past 20+ years, regulatory authorities in some countries do not regulate stacked trait products, while others have simplified the approval process based on experience and sound science, reducing or eliminating the need for additional regulatory oversight. Countries that choose to regulate stacked trait products should consider integrating the more than 20 years of safety assessment experience, history of safe use, and global regulatory experience, in their approach to reduce redundancy, simplify regulations, and minimize the likelihood for trade disruption. doi: 10.21423/jrs-v09i1goodwi

Strategies for Development of Functionally Equivalent Promoters with Minimum Sequence Homology for Transgene Expression in Plants: cis-Elements in a Novel DNA Context versus Domain Swapping

The cauliflower mosaic virus 35S (35S) promoter has been extensively used for the constitutive expression of transgenes in dicotyledonous plants. The repetitive use of the same promoter is known to induce transgene inactivation due to promoter homology. As a way to circumvent this problem, we tested two different strategies for the development of synthetic promoters that are functionally equivalent but have a minimum sequence homology. Such promoters can be generated by (a) introducing known cis-elements in a novel or synthetic stretch of DNA or (b) “domain swapping,” wherein domains of one promoter can be replaced with functionally equivalent domains from other heterologous promoters. We evaluated the two strategies for promoter modifications using domain A (consisting of minimal promoter and subdomain A1) of the 35S promoter as a model. A set of modified 35S promoters were developed whose strength was compared with the 35S promoter per se using β-glucuronidase as the reporter gene. Analysis of the expression of the reporter gene in transient assay system showed that domain swapping led to a significant fall in promoter activity. In contrast, promoters developed by placing cis-elements in a novel DNA context showed levels of expression comparable with that of the 35S. Two promoter constructs Mod2A1T and Mod3A1T were then designed by placing the core sequences of minimal promoter and subdomain A1 in divergent DNA sequences. Transgenics developed in tobacco (Nicotiana tabacum) with the two constructs and with 35S as control were used to assess the promoter activity in different tissues of primary transformants. Mod2A1T and Mod3A1T were found to be active in all of the tissues tested, at levels comparable with that of 35S. Further, the expression of the Mod2A1T promoter in the seedlings of the T(1) generation was also similar to that of the 35S promoter. The present strategy opens up the possibility of creating a set of synthetic promoters with minimum sequence homology and with expression levels comparable with the wild-type prototype by modifying sequences present between cis-elements for transgene expression in plants

Disruption of the carA gene in Pseudomonas syringae results in reduced fitness and alters motility

Background: Pseudomonas syringae infects diverse plant species and is widely used in the study of effector function and the molecular basis of disease. Although the relationship between bacterial metabolism, nutrient acquisition and virulence has attracted increasing attention in bacterial pathology, there is limited knowledge regarding these studies in Pseudomonas syringae. The aim of this study was to investigate the function of the carA gene and the small RNA P32, and characterize the regulation of these transcripts. Results: Disruption of the carA gene (δcarA) which encodes the predicted small chain of carbamoylphosphate synthetase, resulted in arginine and pyrimidine auxotrophy in Pseudomonas syringae pv.Tomato DC3000. Complementation with the wild type carA gene was able to restore growth to wild-Type levels in minimal medium. Deletion of the small RNA P32, which resides immediately upstream of carA, did not result in arginine or pyrimidine auxotrophy. The expression of carA was influenced by the concentrations of both arginine and uracil in the medium. When tested for pathogenicity, δcarA showed reduced fitness in tomato as well as Arabidopsis when compared to the wild-Type strain. In contrast, mutation of the region encoding P32 had minimal effect in planta. δcarA also exhibited reduced motility and increased biofilm formation, whereas disruption of P32 had no impact on motility or biofilm formation. Conclusions: Our data show that carA plays an important role in providing arginine and uracil for growth of the bacteria and also influences other factors that are potentially important for growth and survival during infection. Although we find that the small RNA P32 and carA are co-Transcribed, P32 does not play a role in the phenotypes that carA is required for, such as motility, cell attachment, and virulence. Additionally, our data suggests that pyrimidines may be limited in the apoplastic space of the plant host tomato. Keywords: Pseudomonas syringae pv tomato, CarAB, P32, Virulence, Swarming, Biofilm formation Abbreviations: CFU, Colony forming units; CPSase, Carbamoylphosphate synthetase; FLOE, Fluorescently labeled oligonucleotide extension; G6PDH, Glucose-6-phosphate dehydrogenase; HR, Hypersensitive response; IVET, In vivo expression technology; KB, King\u27s B; MG, Mannitol-glutamate; qPCR, Quantitative real-Time PCR; RACE, Rapid amplification of cDNA ends; T3SS, The type III secretions system; VBMM, Vogel-bonner minimal medium