Expression of the hypersensitive response-assisting protein in Arabidopsis results in harpin-dependent hypersensitive cell death in response to Erwinia carotovora

Genetic modification to improve disease resistance in crops

Plant pathogens are a significant challenge in agriculture despite our best efforts to combat them. One of the most effective and sustainable ways to manage plant pathogens is to use genetic modification (GM) and genome editing, expanding the breeder's toolkit. For use in the field, these solutions must be efficacious, with no negative effect on plant agronomy, and deployed thoughtfully. They must also not introduce a potential allergen or toxin. Expensive regulation of biotech crops is prohibitive for local solutions. With 11-30% average global yield losses and greater local impacts, tackling plant pathogens is an ethical imperative. We need to increase world food production by at least 60% using the same amount of land, by 2050. The time to act is now and we cannot afford to ignore the new solutions that GM provides to manage plant pathogens.

Application of Genetic Engineering for Control of Bacterial Wilt Disease of Enset, Ethiopia's Sustainability Crop

Enset (Ensete ventricosum (Welw.) Cheesman) is one of the Ethiopia's indigenous sustainability crops supporting the livelihoods of about 20 million people, mainly in the densely populated South and Southwestern parts of the country. Enset serves as a food security crop for humans, animal feed, and source of fiber for the producers. The production of enset has been constrained by plant pests, diseases, and abiotic factors. Among these constraints, bacterial wilt disease has been the most important limiting factor for enset production since its outbreak five decades ago. There is no known bacterial wilt disease resistant genetic material in the enset genetic pool to transfer this trait to susceptible enset varieties through conventional breeding. Moreover, the absence of effective chemicals against the disease has left farmers without means to combat bacterial wilt for decades. Genetic engineering has been the alternative approach to develop disease resistant plant materials in other crops where traditional breeding tools are ineffective. This review discusses enset cultivation and recent developments addressing the control of bacterial wilt disease in enset and related crops like banana to help design effective strategies.

Genetically engineered bananas resistant to Xanthomonas wilt disease and nematodes

Banana is an important staple food crop feeding more than 100 million Africans, but is subject to severe productivity constraints due to a range of pests and diseases. Banana Xanthomonas wilt caused by Xanthomonas campestris pv. musacearum is capable of entirely destroying a plantation while nematodes can cause losses up to 50% and increase susceptibility to other pests and diseases. Development of improved varieties of banana is fundamental in order to tackle these challenges. However, the sterile nature of the crop and the lack of resistance in Musa germplasm make improvement by traditional breeding techniques either impossible or extremely slow. Recent developments using genetic engineering have begun to address these problems. Transgenic banana expressing sweet pepper Hrap and Pflp genes have demonstrated complete resistance against X. campestris pv. musacearum in the field. Transgenic plantains expressing a cysteine proteinase inhibitors and/or synthetic peptide showed enhanced resistance to a mixed species population of nematodes in the field. Here, we review the genetic engineering technologies which have potential to improve agriculture and food security in Africa.

Emerging Agricultural Biotechnologies for Sustainable Agriculture and Food Security

As global populations continue to increase, agricultural productivity will be challenged to keep pace without overtaxing important environmental resources. A dynamic and integrated approach will be required to solve global food insecurity and position agriculture on a trajectory toward sustainability. Genetically modified (GM) crops enhanced through modern biotechnology represent an important set of tools that can promote sustainable agriculture and improve food security. Several emerging biotechnology approaches were discussed in a recent symposium organized at the 13th IUPAC International Congress of Pesticide Chemistry meeting in San Francisco, CA, USA. This paper summarizes the innovative research and several of the new and emerging technologies within the field of agricultural biotechnology that were presented during the symposium. This discussion highlights how agricultural biotechnology fits within the context of sustainable agriculture and improved food security and can be used in support of further development and adoption of beneficial GM crops.

Transgenic banana plants expressing Xanthomonas wilt resistance genes revealed a stable non-target bacterial colonization structure

Africa is among the continents where the battle over genetically modified crops is currently being played out. The impact of GM in Africa could potentially be very positive. In Uganda, researchers have developed transgenic banana lines resistant to banana Xanthomonas wilt. The transgenic lines expressing hrap and pflp can provide a timely solution to the pandemic. However, the impact of the transgenes expression on non-target microorganisms has not yet been investigated. To study this effect, transgenic and control lines were grown under field conditions and their associated microbiome was investigated by 16S rRNA gene profiling combining amplicon sequencing and molecular fingerprinting. Three years after sucker planting, no statistically significant differences between transgenic lines and their non-modified predecessors were detected for their associated bacterial communities. The overall gammaproteobacterial rhizosphere microbiome was highly dominated by Xanthomonadales, while Pseudomonadales and Enterobacteriales were accumulated in the pseudostem. Shannon indices revealed much higher diversity in the rhizosphere than in the pseudostem endosphere. However, the expression of the transgenes did not result in changes in the diversity of Gammaproteobacteria, the closest relatives of the target pathogen. In this field experiment, the expression of the resistance genes appears to have no consequences for non-target rhizobacteria and endophytes.

Hypersensitive response - A biophysical phenomenon of producers

Hypersensitive response/reaction is a form of the cellular demise frequently linked alongside plant resistance against pathogen infection. Main transducers for this reaction are the intermediates of reactive oxygen and ion fluxes which are plausibly needed for hypersensitive response (Hpr Sen Rsp). An immediate and enormous energy production and its intra-cellular biochemical conduction are imperative for an Hpr Sen Rsp to be occurred. A number of studies proved that there are such diverse types of factors involved in triggering of Hpr Sen Rsp that morphologies of dead cells have become a vast topic of study. Hpr Sen Rsp could play a frolic role in plants as certain programmed cellular disintegrations in other organisms, to restrict pathogen growth. In fact, Hpr Sen Rsp can be involved in all types of tissues and most of the developmental stages.

Over-expression of rice leucine-rich repeat protein results in activation of defense response, thereby enhancing resistance to bacterial soft rot in Chinese cabbage

Pectobacterium carotovorum subsp. carotovorum causes soft rot disease in various plants, including Chinese cabbage. The simple extracellular leucine-rich repeat (eLRR) domain proteins have been implicated in disease resistance. Rice leucine-rich repeat protein (OsLRP), a rice simple eLRR domain protein, is induced by pathogens, phytohormones, and salt. To see whether OsLRP enhances disease resistance to bacterial soft rot, OsLRP was introduced into Chinese cabbage by Agrobacterium-mediated transformation. Two independent transgenic lines over-expressing OsLRP were generated and further analyzed. Transgenic lines over-expressing OsLRP showed enhanced disease resistance to bacterial soft rot compared to non-transgenic control. Bacterial growth was retarded in transgenic lines over-expressing OsLRP compared to non-transgenic controls. We propose that OsLRP confers enhanced resistance to bacterial soft rot. Monitoring expression of defense-associated genes in transgenic lines over-expressing OsLRP, two different glucanases and Brassica rapa polygalacturonase inhibiting protein 2, PDF1 were constitutively activated in transgenic lines compared to non-transgenic control. Taken together, heterologous expression of OsLRP results in the activation of defense response and enhanced resistance to bacterial soft rot.

Expression of sweet pepper Hrap gene in banana enhances resistance to Xanthomonas campestris pv. musacearum

Banana Xanthomonas wilt (BXW), caused by the bacterium Xanthomonas campestris pv. musacearum, is the most devastating disease of banana in the Great Lakes region of Africa. The pathogen's rapid spread has threatened the livelihood of millions of Africans who rely on banana fruit for food security and income. The disease is very destructive, infecting all banana varieties, including both East African Highland bananas and exotic types of banana. In the absence of natural host plant resistance among banana cultivars, the constitutive expression of the hypersensitivity response-assisting protein (Hrap) gene from sweet pepper (Capsicum annuum) was evaluated for its ability to confer resistance to BXW. Transgenic lines expressing the Hrap gene under the regulation of the constitutive CaMV35S promoter were generated using embryogenic cell suspensions of two banana cultivars: 'Sukali Ndiizi' and 'Mpologoma'. These lines were characterized by molecular analysis, and were challenged with Xanthomonas campestris pv. musacearum to analyse the efficacy of the Hrap gene against BXW. The majority of transgenic lines (six of eight) expressing Hrap did not show any symptoms of infection after artificial inoculation of potted plants in the screenhouse, whereas control nontransgenic plants showed severe symptoms resulting in complete wilting. This study demonstrates that the constitutive expression of the sweet pepper Hrap gene in banana results in enhanced resistance to BXW. We describe the development of transgenic banana varieties resistant to BXW, which will boost the arsenal available to fight this epidemic disease and save livelihoods in the Great Lakes region of East and Central Africa.

Playing the "Harp": evolution of our understanding of hrp/hrc genes

With the advent of recombinant DNA techniques, the field of molecular plant pathology witnessed dramatic shifts in the 1970s and 1980s. The new and conventional methodologies of bacterial molecular genetics put bacteria center stage. The discovery in the mid-1980s of the hrp/hrc gene cluster and the subsequent demonstration that it encodes a type III secretion system (T3SS) common to Gram negative bacterial phytopathogens, animal pathogens, and plant symbionts was a landmark in molecular plant pathology. Today, T3SS has earned a central role in our understanding of many fundamental aspects of bacterium-plant interactions and has contributed the important concept of interkingdom transfer of effector proteins determining race-cultivar specificity in plant-bacterium pathosystems. Recent developments in genomics, proteomics, and structural biology enable detailed and comprehensive insights into the functional architecture, evolutionary origin, and distribution of T3SS among bacterial pathogens and support current research efforts to discover novel antivirulence drugs.

Pythium infection activates conserved plant defense responses in mosses

The moss Physcomitrella patens (P. patens) is a useful model to study abiotic stress responses since it is highly tolerant to drought, salt and osmotic stress. However, very little is known about the defense mechanisms activated in this moss after pathogen assault. In this study, we show that P. patens activated multiple and similar responses against Pythium irregulare and Pythium debaryanum, including the reinforcement of the cell wall, induction of the defense genes CHS, LOX and PAL, and accumulation of the signaling molecules jasmonic acid (JA) and its precursor 12-oxo-phytodienoic acid (OPDA). However, theses responses were not sufficient and infection could not be prevented leading to hyphae colonization of moss tissues and plant decay. Pythium infection induced reactive oxygen species production and caused cell death of moss tissues. Taken together, these data indicate that Pythium infection activates in P. patens common responses to those previously characterized in flowering plants. Microscopic analysis also revealed intracellular relocation of chloroplasts in Pythium-infected tissues toward the infection site. In addition, OPDA, JA and its methyl ester methyl jasmonate induced the expression of PAL. Our results show for the first time JA and OPDA accumulation in a moss and suggest that this defense pathway is functional and has been maintained during the evolution of plants.

Resistance enhancement of transgenic tomato to bacterial pathogens by the heterologous expression of sweet pepper ferredoxin-I protein

ABSTRACT Expression of a foreign gene to enhance plant disease resistance to bacterial pathogens is a favorable strategy. It has been demonstrated that expressing sweet pepper ferredoxin-I protein (PFLP) in transgenic plants can enhance disease resistance to bacterial pathogens that infect leaf tissue. In this study, PFLP was applied to protect tomato (Lycopersicon esculentum cv. cherry Cln1558a) from the root-infecting pathogen, Ralstonia solanacearum. Independent R. solanacearum resistant T(1) lines were selected and bred to produce homozygous T(2) generations. Selected T(2) transgenic lines 24-18-7 and 26-2-1a, which showed high expression levels of PFLP in root tissue, were resistant to disease caused by R. solanacearum. In contrast, the transgenic line 23-17-1b and nontransgenic tomato, which showed low expression levels of PFLP in root tissue, were not resistant to R. solanacearum infection. The expansion of R. solanacearum populations in stem tissue of transgenic tomato line 24-18-7 was limited compared with the nontransgenic tomato Cln1558a. Using a detached leaf assay, transgenic line 24-18-7 was also resistant to maceration caused by E. carotovora subsp. carotovora; however, resistance to E. carotovora subsp. carotovora was less apparent in transgenic lines 26-2-1a and 23-17-1b. These results demonstrate that PFLP is able to enhance disease resistance at different levels to bacterial pathogens in individual tissue of transgenic tomato.