libro sulle piante nella risposta ai patogeni

Editors: Palmiro Poltronieri, Yiguo Hong 

Applied Plant Biotechnology for Improving Resistance to Biotic Stress. 1st Edition. Elsevier

Paperback ISBN: 9780128160305, eBook ISBN: 9780128160312

Table of Contents

1. Engineering Plant Leucine Rich Repeat- Receptors for Enhanced Pattern Triggered Immunity (PTI) and Effector Triggered Immunity (ETI)

2.Virus Induced Gene Silencing for Functional Genomics in Plants

3. Bringing PTI into the Field
4. NBS-LRR Genes -- Plant Health Sentinels: Structure, Roles Evolution and Biotechnological Applications
5. Informatic Tools and Platforms for Enhancing Plant R-Gene Discovery Processes
6. Spatial Transcriptional Response of Plants Induced by Compatible Pathogens and its Potential Use in Biosensor Plants
7. Grapevine; Resistance Genes, sRNAs and Immunity
8. Using Genomics Tools to Understand Plant Resistance Against Pathogens: A Case Study of Magnaporthe-Rice Interactions
9. Microbial Products and Secondary Metabolites in Plant Health
10. Molecular Tools to Investigate Sharka Disease in Prunus Species
11. Plant Viruses Against RNA Silencing-Based Defenses: Strategies and Solutions
12. Criniviruses Infecting Vegetable Crops
13. Role of Methylation During Geminivirus Infection
14. Foresight on Nanovesicles in Plant-Pathogen Interactions
15. The Role of Phytohormones in Plant-Viroid Interactions

Plants are continually challenged by varied pathogens, including bacteria, fungi, viruses, and nematodes. Physical barriers such as polysaccharides are the first line of avoidance for pathogens entrance and cell invasion. To protect themselves against the invaders, plants have evolved innate immunity through several mechanisms; receptor signalling, activation of transcription factors, reactive oxygen species, antimicrobial proteins, RNA silencing, and secondary metabolism components. Plant innate immunity is an efficient defence against plant pathogens. The first level of plant-microorganism interaction is the sensing of Microbial associated molecular patterns (MAMP) by recognising receptors, leading to Pattern triggered immunity (PTI). Non-race-specific inducers of defense are the elicitors, formed by a wide range of different types of molecules. PTI is sensing also Damage Associated Molecular Patterns (DAMPs). Pathogen strains evolved a series of effectors, penetrating the cells, to manipulate and modify a series of host protein targets, Effectors are sensed by Resistance proteins, often in association, a sensor and an executor, or an R guard or trap, sensed by an R executor. The perturbation of host proteins caused by effectors leads to effector-triggered immunity (ETI). Successful perception of a pathogen by PTI or ETI triggers intercellular signalling which results in expression of defence proteins and in the hypersensitive response (HR), or to Systemic Acquired Resistance (SAR).

Innate immunity is an efficient first line of defense against microbial and fungal pathogens, and in part is effective also against viruses. Viruses also can be sensed by LRR motives in Membrane Receptors. In Arabidopsis the constitutive activation of NIK1, a leucine-rich repeat receptor-like kinase (LRR-RLK) identified as a virulence target of the begomovirus nuclear shuttle protein (NSP). On the other side, similarly to Virus suppressors of RNA silencing (VSRs), VSRs are produced by fungi/oomycetes, to alter host RNA silencing machineries. For these reasons, the book does not focuses only on viruses or only on microorganisms, but includes a vast array of plant pathogens and the plant responses, proteins, RNAs and their mechanism leading to resistance.

Chapter 1, Plant Leucine rich repeat- receptors for enhanced PAMP- triggered immunity (PTI) and effector triggered immunity (ETI), presents an overview on plant Leucine Rich Repeat (LRR) receptors and resistance genes, their inter-species transfer, the engineering of Resistance proteins, and the biotechnologies applications to reinforce plant species immunity and response toward bacteria, fungi and viruses.

Chapter 2, VIGS: virus induced gene silencing and approaches in plant protection, describes post-transcriptional gene silencing (PTGS), during which viral gene expression is severely inhibited. A kind of PTGS, called virus-induced gene silencing (VIGS), is obtained using various virus vectors, and has been applied to research on plant functional genes. The chapter discusses the existing problems and the perspectives of the technology.

Chapter 3, Induction and transducing PTI to the field, enters in detail on the receptor activation and signaling pathways. The chapter discusses the opportunities and challenges provided by these approaches to enhance or alter the plant resistance and immunity, the constrains posed by regulatory authorities, the impact on beneficial microorganisms, and the outer membrane vesicles, with prospects to exploit nanovesicles as agrochemicals in crop protection.

Chapter 4, NBS-LRR genes—plant health sentinels: structure, roles, evolution and biotechnological applications, introduces information on mechanisms of action, regulation, patterns of expression, subcellular localization, origin, diversification, and evolution in plants. Aspects of plant-pathogen coevolution are discussed, as well as resistance-breaking mechanisms. The chapter presents the -omics technologies, i.e. genomics and transcriptomics, and emergence of the NLRomics, in the annotation and comparative analysis of NBS-LRR members at functional and structural level.

Chapter 5, Plant disease resistance gene discovery through use of informatic tools, describes plant genetic repositories, and the application of bioinformatics in the discovery of Resistance proteins, from proteome analysis to motif searches, to R-predictor application, to bibliographic searches, comparative genomics, gene expression analyses, to studies on R-gene-associated markers, to selection of genomic regions, and finally to the output of identification of R-candidates.

Chapter 6, Spatial transcriptional response of plants induced by compatible pathogens and its potential use in biosensor plants, reviews cropping and managements strategies, planting of resistant cultivars, bio control, and adjacent measures such as crop rotation. Pesticides applied in post pathogen infection rely on a timely symptom detection which is often not feasible. To increase visibility of symptoms of diseased crops and to engineer 'pseudo symptoms' a detailed understanding of the temporal and spatial reaction of the host plant is essential. This chapter summarizes research dedicated to the spatial gene expression as a response to pathogen attack in compatible plants. The prospect is to use early-induced genes for engineering biosensor plants as warnings to farmers for interventions with curative and site-specific pesticide treatments.

Chapter 7, Grapevine: resistance genes, small RNAs and immunity, introduces grapevine major disease, their pathogens, and the resistance mechanism. Resistant varieties, often introgressed from wild species through breeding, and by means of gene pyramiding, are at the basis of a sustainable agriculture. The chapter describes grapevine non-coding RNAs and RNA silencing mechanisms, and Silencing Suppressors in pathogens. The application of nanoparticles, extracellular vesicles, nanobodies, cross-kingdom RNA trafficking, and delivery of naked or enveloped nucleic acids is discussed.

Chapter 8, Using genomics tools to understand plant resistance against pathogens: a case study of Magnaporthe-rice interactions, introduces mechanisms of pathogen infection and plant resistance, and attempts to develop blast resistant cultivars. The chapter reviews the gene-for-gene interactions mediated by pathogen avirulence (AVR) genes and plant resistance (R) genes and shares experiences of whole genome sequencing (WGS)-based approaches to isolate blast AVR genes and rice R genes. The chapter also provides knowledge on interactions of the proteins coded by the isolated blast AVR genes and rice R genes.

Chapter 9, Microbial products and secondary metabolites in plant health, discusses beneficial microorganisms, as biocontrol agents promoting plant biotic stress response, and plant growth promoting agents. Biocontrol agents, antagonistic to the infection by plant pathogens, produce a secretome rich in effector proteins, and hormone precursors that modulate plant hormones and their activity. Jasmonic acid (JA) and Salicylic acid (SA) have a great role in biotic stress, in the activation of transcription factors, and the interplay between different hormones, leading to Induced Systemic Resistance (ISR). The chapter presents the knowledge on microbial effectors acting as MAMPs, and the effectoromics at the base of their beneficial activities. A brief overview on attenuation of immunity by symbiotic microorganisms is presented. A focus is given on Trichoderma spp. and their symbiotic relationship with plants, with description of the main products, secondary metabolites and effectors. Finally, a prospect on the application of chemical priming to improve plant resistance and ISR, and the development of new priming compounds is presented.

Chapter 10, Molecular tools for Plum Pox virus (PPX) diagnosis, introduces the causative agent of Sharka disease, and the methods available for its containment: removal of infected plants in the orchards, control of aphid populations in the orchards, cultivation of plant material featuring inborn resistance to the virus, feasible in apricot, but with no clear sources of resistance known for peach or plum. Transgenesis may provide genes of resistance through transformation and regeneration protocols, but its applicability is limited by transnational regulations. Lastly, the chapter discusses cutting-edge approaches of gene silencing.

Chapter 11, Plant viruses against RNA-silencing based defenses: Strategies and solutions, introduces plant antiviral immune system is the RNA silencing (RS) pathway. An overview is presented on the RS machinery targeting the double-stranded RNA, generating 21–24 nucleotides (nt) small interfering RNAs (siRNAs) that guide the cleavage of viral RNA in a sequence-specific manner. RS signals are amplified and transmitted cell-to-cell and systemically, in a process that is provided with self-regulatory feedback mechanisms. All the steps of the RS pathway are targeted by viral counterattack strategies that allow pathogens to escape host defenses and establish a successful infection. Viral suppressors of RNA silencing (VSRs) are virus-encoded proteins that interfere with RS by blocking or destabilizing the host antiviral functions. The chapter reviews the current knowledge on VSRs mechanisms of action, and describes the latest discoveries in this fascinating evolutionary arms race between plants and viruses.

Chapter 12, Criniviruses infecting vegetable crops, describes Criniviruses, in the family Closteroviridae, possessing bipartite genomes that are separately encapsidated in long filamentous virions. Members of the genus Crinivirus are semi-persistently transmitted by whiteflies. The chapter discusses the knowledge on the molecular biology, epidemiology, diagnostics and management of this virus group. A special emphasis is given to the description of the specific characteristics of virus species infecting major vegetable crops including tomato, cucurbits, tuber crops, lettuce and bean.

Chapter 13, Role of methylation during Geminivirus infection, presents DNA viruses and the epigenetic regulation mechanisms. This chapter reviews the relevance of DNA and histone methylation in controlling the infection of geminiviruses. Epigenetic marks are reversible molecular changes associated to DNA or histones, as regulators of gene expression and genome plasticity. The silencing marks are normally associated to the suppression of selfish genetic mobile elements, because their activation might lead to their uncontrolled proliferation and to genome instability. DNA viruses replicate their genome in the host nucleus hijacking host cellular factors, similarly to endogenous genetic elements, while host plants have adopted epigenetic mechanisms as defense strategies also against this kind of pathogens.

Chapter 14, Foresight on nanovesicles in plant-pathogen interactions, introduces the secretion of nanovesicles as a conserved mechanism to transfer biological material between organisms. Nanovesicles are classified in exosomes (with a diameter ranging between 50 nm and 120 nm), microvesicles (100–1000 nm) and apoptotic bodies (50–5000 nm). Although these vesicles impact on the host immunity, they have a very different protein composition and biogenesis. The chapter focuses on the exosome-host interaction and on how exosomes can modulate the host immunity. Since exosomes can shuttle biological macromolecules, the chapter delineates the role of small-RNAs packed into exosomes and their proposed role in regulating immunity, and possible biotechnological applications of exosomes/nanovesicles in plant protection.

Plasmopara viticola, Blumeria graminis, Botrytis cynerea, Verticillium dahliae, Zymoseptoria tritici, are taken as examples of cross-kingdom RNA transfer, that may be differentiated for the ability to uptake external naked long dsRNA, or in enveloped form, as vesicle provided with a plasma membrane. Finally, the chapter discusses the use of nanovesicles as agrochemicals for durable crop protection, in the delivery of elicitors, hairpin RNAs, or new chemical priming compounds.

Chapter 15, Changes in phytohormones and antioxidant enzyme activity in plants infected by Potato Spindle Tuber Viroid (PSTVd), introduces viroids, the smallest infecting agents based on RNA nucleic acids with genomes ranging from 246 to 401 nucleotides. Infected crops are potato, tomato, grapevine, hop, coconut palm, citruses, as well as ornamental plants. The chapter provides an overview of the effects of viroid infection, particularly potato spindle viroid disease, on the content of endogenous phytohormones and the expression of phytohormone–related genes in host plants, with a specific focus on salicylic acid, jasmonic acid, brassinosteroids and auxins. The effect of exogenous phytohormones on the development of viroid infections is described. Studies on mechanisms of phytohormone signaling involved in plant responses against pathogens and regulatory crosstalk between different signaling pathways are discussed. Finally, the chapter discuss host strategies to survive viroid attack and help the development of hormone–based breeding programs aiming to improve plant resistance/tolerance to viroids.

In recent years great progress has been made in understanding the interplay between plants and their hosts, especially the role of plant immunity, in regulating, attenuating or neutralizing invading pathogens, either viruses, bacteria or fungi. This book aims to integrate the knowledge from these fields and intersect them with the biotechnology methods to improve plant genomes for higher resistance and finely-tuned hormone signaling for the benefit of crop yield. In the future, plant biotechnology will provide new ways to improve plant immunity to pathogens and viruses. For this reason, several chapters, such as 9 and 14, also discuss methods such as CRISPR/Cas system for genome editing, able to modify and increase plant immunity and defences.