Plants are subjected to a wide range of environmental stresses which reduces and limits the productivity of agricultural crops. Two types of environmental stresses are encountered to plants which can be categorized as 1 Abiotic stress and 2 Biotic stress. The abiotic stress causes the loss of major crop plants worldwide and includes radiation, salinity, floods, drought, extremes in temperature, heavy metals, etc. On the other hand, attacks by various pathogens such as fungi, bacteria, oomycetes, nematodes and herbivores are included in biotic stresses.
As plants are sessile in nature, they have no choice to escape from these environmental cues. Plants have developed various mechanisms in order to overcome these threats of biotic and abiotic stresses. They sense the external stress environment, get stimulated and then generate appropriate cellular responses. They do this by stimuli received from the sensors located on the cell surface or cytoplasm and transferred to the transcriptional machinery situated in the nucleus, with the help of various signal transduction pathways.
This leads to differential transcriptional changes making the plant tolerant against the stress. The signaling pathways act as a connecting link and play an important role between sensing the stress environment and generating an appropriate biochemical and physiological response.
Abiotic and Biotic Stress in Plants. Stress in plants refers to external conditions that adversely affect growth, development or productivity of plants [ 1 ]. Stresses trigger a wide range of plant responses like altered gene expression, cellular metabolism, changes in growth rates, crop yields, etc. A plant stress usually reflects some sudden changes in environmental condition. However in stress tolerant plant species, exposure to a particular stress leads to acclimation to that specific stress in a time time-dependent manner [ 1 ].
Plant stress can be divided into two primary categories namely abiotic stress and biotic stress. Abiotic stress imposed on plants by environment may be either physical or chemical, while as biotic stress exposed to the crop plants is a biological unit like diseases, insects, etc. Some stresses to the plants injured them as such that plants exhibit several metabolic dysfunctions [ 1 ]. The plants can be recovered from injuries if the stress is mild or of short term as the effect is temporary while as severe stresses leads to death of crop plants by preventing flowering, seed formation and induce senescence [ 1 ].
Such plants will be considered to be stress susceptible. However several plants like desert plants Ephemerals can escape the stress altogether [ 2 ]. Biotic stress in plants is caused by living organisms, specially viruses, bacteria, fungi, nematodes, insects, arachnids and weeds.
The agents causing biotic stress directly deprive their host of its nutrients can lead to death of plants. Biotic stress can become major because of pre- and postharvest losses.
Despite lacking the adaptive immune system plants can counteract biotic stresses by evolving themselves to certain sophisticated strategies. The resistant genes against these biotic stresses present in plant genome are encoded in hundreds.
The biotic stress is totally different from abiotic stress, which is imposed on plants by non-living factors such as salinity, sunlight, temperature, cold, floods and drought having negative impact on crop plants.To browse Academia. Skip to main content. Log In Sign Up. Piergiorgio Stevanato.
Mario Motto. Carlotta Balconi. Biancardi Enrico. Ashraf et al. Balconi et al. Plants must continuously defend them- selves against attacks from bacteria, viruses, fungi, invertebrates, and even other plants.
This chapter will therefore summarize the benefits and drawbacks of resis- tance versus chemical protection. Attempts will be made to provide a description on the effective genetic and molecular mechanisms that plants have developed to rec- ognize and respond to infection by a number of pathogens and pests, such as non- host resistance, constitutive barriers and race-specific resistance, including recent advances in elucidating the structure and molecular mechanisms used by plants to cope with pathogens and pest attacks.
This chapter also covers the most relevant problems in breeding for resistance to parasites and will include aspects related to specificity of defense mechanisms, specificity of parasitic ability, inheritance of resistance, gene-for-gene interaction, and durability of resistance.
Major consider- ations in breeding for resistance to parasites, conventional sources of resistance and possible alternatives, namely mutation breeding, genetic manipulations, tissue cultures, and molecular interventions to develop plants resistant to pests and pathogens will also be dealt.
The almost doubled population will require a more than proportional increase in food production. During the last decade, world grain yield increased around 0. The main task for breeders and agronomists will therefore be to increase yields while reducing the use of chemicals. In this context, the development of tolerant plants to biotic stresses is therefore an important objective of plant breeding strategies with relevant implications for both farmers and the seed and agrochemical industries.
In fact genetic resistance has several obvious advantages over the use of chemical pesticides or other methods for parasite control.
Biotic and Abiotic Stresses in Plants
These include nominal genetic permanency, negligible cost once cultivars are developed, and quite high efficiency.
The major downside of genetic resistance to biotic stresses is the fact that selection pressure is placed on parasites populations to develop means of overcoming the resistance, thus practically limiting the time of effectiveness Table 4. In this chapter the genetic, biochemical and molecular mechanisms by which plants defend themselves against attack from pathogens will be examined.
In addition breeding approaches towards their improvement will be described. Table 4.The accumulation of osmolytes like glycinebetaine GB in cell is known to protect organisms against abiotic stresses via osmoregulation or osmoprotection.
Transgenic plants engineered to produce GB accumulate very low concentration of GB, which might not be sufficient for osmoregulation. Therefore, other roles of GB like cellular macromolecule protection and ROS detoxification have been suggested as mechanisms responsible for abiotic stress tolerance in transgenic plants.
In addition, GB influences expression of several endogenous genes in transgenic plants. The new insights gained about the mechanism of stress tolerance in GB accumulating transgenic plants are discussed. The most common compatible solutes are betaines, sugars mannitol, sorbitol, and trehalosepolyols, polyamines, and amino acid proline.
Their accumulation is favored under water-deficit or salt stress as they provide stress tolerance to cell without interfering cellular machinery. Genes participating in the biosynthesis of different kinds of compatible solutes have been identified from varied sources. Genetic engineering with these endogenous or ectopic genes has therefore, been used successfully to synthesize compatible solutes in target organisms and improvement of stress tolerance.
Among the nitrogenous compounds, polyamines accumulate in a variety of plants in response to abiotic stresses like salt and drought. Genes involved in polyamines metabolism have been cloned and often used to alter polyamines levels in transgenic plants for conferring abiotic stress tolerance.
Like other compatible solutes, GB biosynthetic genes have also been widely used to improve abiotic stress tolerance in transgenic plants.
Although compatible solutes fall in different bio-chemical groups, similar roles have been assigned to them in plant protection against stresses. However, a precise role of compatible solutes, including GB, in abiotic stress tolerance is largely unknown and two basic functions attributed to these solutes are osmotic adjustment and cellular compatibility. Osmotic adjustment occurs through concentration dependent effects on osmotic pressure to absorb more water from surroundings. In cellular compatibility mechanism, these compounds replace water in biochemical reactions thereby, maintaining normal metabolism during stress.
At such low levels, compatible solutes might not contribute significantly to osmotic adjustment. Therefore, these compounds are also suggested to be involved in ROS scavenging, macromolecules nucleic acids, proteins, lipids protection, and act as reservoir of carbon and nitrogen source.
Present review highlights the new emerging roles of GB in protecting plants against environmental stresses. Glycinebetaine GB accumulates in a variety of organisms under abiotic stresses and has been studied in great details.
These enzymes are mainly found in chloroplast stroma and their activity is increased in response to salt stress. Major cereals like wheat, maize and barley do not accumulate significant amount of GB naturally. The BADH transcripts are processed in an unusual manner in rice resulting in removal of translational initiation codon, loss of functional domains and premature stop codons.
Exactly similar observations were made for CMO transcripts in rice by same group. Interestingly, BADH gene has been linked to fragrance in rice. This approach has been successfuly used in diverse plant species, e. Among the different GB biosynthetic genes, choline oxidase codA from A. This gene converts choline into GB in one step. Availability of endogenous choline, therfore, could limit the GB biosynthesis in transgenic plants. However, a recent report indicates on limiting roles of choline availability on GB accumulation in GB deficient nearly isogenic lines of sorgham and maize.
Constitutive accumulation of compatible solutes like ployamines, proline and trehalose resulted in abnormal plant phenotype.
Therefore, stress-inducible expression of genes encoding these solutes is often suggested.
Advances in Plant Tolerance to Biotic Stresses
Su et al. GB accumulation following the salt stress was higher in lines with constitutive expression, suggesting that constitutive accumulation of GB is beneficial for stress tolerance without any phenotypic abnormality to plants.
In some cases, localized accumulation of GB within the cell was found to affect the performence of transgenic plants under stress. GB synthesizing enzymes have been targeted to cytosol, mitochondria and chloroplast. In transgenic rice with chloroplast targeted GB accumulation, protection of photosynthetic machinery against salt and cold stress was better than in plants with cytosolic GB accumulation, even though GB accumulation was 5-fold higher in later plants.
These results suggested that GB accumulation in chloroplast is a better strategy for engineering abiotic stress tolerance in plants.Plants are constantly confronted to both abiotic and biotic stresses that seriously reduce their productivity. Plant responses to these stresses are complex and involve numerous physiological, molecular, and cellular adaptations. Recent evidence shows that a combination of abiotic and biotic stress can have a positive effect on plant performance by reducing the susceptibility to biotic stress.
Such an interaction between both types of stress points to a crosstalk between their respective signaling pathways. This review aims at giving an insight into cross-tolerance between abiotic and biotic stress, focusing on the molecular level and regulatory pathways. Plants have to deal with various and complex types of interactions involving numerous environmental factors. In the course of evolution, they have evolved specific mechanisms allowing them to adapt and survive stressful events.
Exposure of plants to biotic and abiotic stress induces a disruption in plant metabolism implying physiological costs [ 1234 ], and thus leading to a reduction in fitness and ultimately in productivity [ 5 ].
Abiotic stress is one of the most important features of and has a huge impact on growth and, consequently, it is responsible for severe losses in the field. Moreover, biotic stress is an additional challenge inducing a strong pressure on plants and adding to the damage through pathogen or herbivore attack [ 7891011 ].
A crucial step in plant defense is the timely perception of the stress in order to respond in a rapid and efficient manner. In recent years, research has mainly concentrated on understanding plant responses to individual abiotic or biotic stresses [ 19202122 ], although the response to simultaneous stresses is bound to lead to a much more complex scenario [ 18 ].
From the perception of the stimulus stress to the final response in cells, plants use various signaling pathways depending on the challenge s. Research on multiple stresses has been trying to simulate natural conditions, but in the field, conditions are not controlled, and one stress can strongly influence the primary stress defense response of the plants [ 18 ]. Moreover, plants can show different degrees of sensitivity depending on the field condition and the developmental stage of the plant [ 24 ].
Additional factors that can influence an interaction are the intensity of the stress and the plant species. Various interactions can take place between the defenses induced after perception of the stresses.
They depend on the specific combination of stresses and even on the degree of simultaneity [ 152526 ]. It is not clear whether simultaneous stresses are rather antagonistic, synergistic or additive, inducing more or less susceptibility to a specific kind of stress [ 2728 ]. Combination of two stressors can have a negative and additive effect on plants, the second stress being the one that leads to a greater damage [ 29 ].
On the other hand, the combination of stresses can also lead to antagonistic responses in the plants [ 3031 ]. Common beans exposed to drought stress display more symptoms when infected by Macrophomina phaseolina [ 29 ] and treatment of detached tomato leaves with exogenously applied ABA increases the susceptibility of wild type plants to Botrytis cinerea [ 32 ].
Interestingly, one possible outcome of multiple stress exposure is that plants that are able to defend themselves facing one stress can become more resistant to other stresses [ 33 ]. This phenomenon is called cross-tolerance, showing that plants possess a powerful regulatory system that allows them to adapt quickly to a changing environment [ 333435 ].Plants being sessile in nature encounter numerous biotic agents, including bacteria, fungi, viruses, insects, nematodes and protists.
A great number of publications indicate that biotic agents significantly reduce crop productivity, although there are some biotic agents that symbiotically or synergistically co-exist with plants. Nonetheless, scientists have made significant advances in understanding the plant defence mechanisms expressed against biotic stresses. These mechanisms range from anatomy, physiology, biochemistry, genetics, development and evolution to their associated molecular dynamics.
Using model plants, e. However, there are drawbacks and insufficiencies in precisely deciphering and deploying these mechanisms, including only modest adaptability of some identified genes or QTLs to changing stress factors. Thus, more systematic efforts are needed to explore and expand the development of biotic stress resistant germplasm. In this chapter, we provided a comprehensive overview and discussed plant defence mechanisms involving molecular and cellular adaptation to biotic stresses.
The latest achievements and perspective on plant molecular responses to biotic stresses, including gene expression, and targeted functional analyses of the genes expressed against biotic stresses have been presented and discussed.
Plant Responses to Simultaneous Biotic and Abiotic Stress: Molecular Mechanisms
Plant Genomics. Biotic stresses are the damage to plants caused by other living organisms such as bacteria, fungi, nematodes, protists, insects, viruses and viroids.
Numerous biotic stresses are of historical significance, for instance, the potato blight in Ireland, coffee rust in Brazil, maize leaf blight caused by Cochliobolus heterostrophus in the United States and the great Bengal famine in [ 1 ]. These are some of the major events that devastated food production and led to millions of human deaths and migration to other countries in the past. Presently, the occurrence of new pathogen races and insect biotypes poses further threat to crop production [ 2 ].
Thus, disease or insect pest outbreaks are expected to continue to cause food production losses or even worsen by expanding to the areas they were not prevalent before [ 4 ]. This has important implications for the management options available. Using a combination of options provides certainly more reliability. However, in areas where resources are limiting, e. Thus, exploring the mechanisms of resistance regulated by these resistance alleles is required to enable their exploitation for improving the cultivated elite germplasm that support most of the rural poor livelihoods.
Plant mechanisms of resistance to various pathogens and insect pests are known to involve an array of morphological, genetic, biochemical and molecular processes [ 5 ]. These mechanisms may be expressed continuously constitutively as preformed resistance, or they may be inducible and deployed only after attack. Plant success in deploying these resistance mechanisms is an evolved ability to persist in unfavourable and variable environments [ 6 ].
Effector induced resistance or vertical resistance, often interchangeably translated in modern terms as effector triggered immunity ETIis the most successful means of controlling pathogens able to evade PTI [ 6 ]. ETI engages a compensatory mechanism within the defense network to transcriptionally coordinate and boost the defense output against pathogens. Although R gene mediated resistance is generally not durable, ETI is now effectively deployed through pyramiding of several resistance R -genes in the same cultivar, which increases resistance durability and spectrum.
SAR provides long-term defense against a broad-spectrum of pathogens and insects. Plants also defend themselves through RNA interference to target and inactivate invading nucleic acids from viruses, and more recently fungal pathogens. These are the aspects that this chapter has addressed to provide background information for a more detailed discussion of the diverse aspects of plant defence patterns, including qualitative and quantitative mechanisms and their associated molecular patterns.
Although pathogenic mechanisms would be interesting to the reader, this chapter does not delve extensively into this aspect, except to mention it as a consideration in emphasizing certain aspects of plant resistance. For additional background, the reader is referred to excellent reviews and the references therein that address plant-pathogen interaction.
Plants respond to various pathogens through an intricate and dynamic defence system. The mechanism of defence has been classified as innate and systemic plant response.Similarly, large Similarly, large losses of grain yields in plants occur as a result of pathogen attack, in particular during vulnerable stages of grain development and germination. In addition, the predicted scarcity of fresh water implies that the intensity of abiotic stresses will increase.
Hence, there is an urgency to develop crop varieties that are resilient to abiotic stresses to ensure food security and safety for many years to come. Progress acquired via breeding to develop abiotic stress-tolerant crops is slow due to multigene origins of plant adaptive responses and involvement of complex genetic mechanisms.
For plants to survive under stress conditions, they have evolved complex mechanisms to perceive external signals that allow plants to respond to changing environmental conditions. These mechanisms include stress perception, signal transduction, transcriptional activation of stress-responsive target genes, and synthesis of stress-related proteins and other molecules, which assist plants to cope with adverse environmental conditions through biochemical and physiological manifestations.
Importantly, understanding the connection between a plant initial stress response and downstream events to adjust to altered conditions is one of the grand challenges in plant biology. Intensive research over the last decade has gradually unravelled the mechanisms that underlie how plants cope with abiotic stresses, but many aspects remain unresolved. The complete understanding of physiological, biochemical and molecular responses and tolerance mechanisms, and identification of potential unknown stress-responsive pathways and genes in abiotic plant stress tolerance will contribute to better understanding of underlying molecular mechanisms.
Discoveries of novel genes and pathways, analyses of expression patterns and the determination of function of genes during abiotic stress adaptation will provide the basis for effective engineering strategies with the aim to enhance abiotic stress tolerance of crop plants. The new knowledge acquired through this research will help in the application of stress responsive determinants and in engineering of plants with enhanced tolerance to abiotic stresses.
In this Research Topic, we intend to incorporate the contributions from leading plant scientists focusing on a variety of abiotic stress tolerance mechanisms using physiological, biochemical, molecular, structural and systems biology approaches.
Important Note : All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.
With their unique mixes of varied contributions from Original Research to Review Articles, Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area!
Plant Responses to Simultaneous Biotic and Abiotic Stress: Molecular Mechanisms
Find out more on how to host your own Frontiers Research Topic or contribute to one as an author. Research Topic Mechanisms of abiotic stress responses and tolerance in plants: physiological, biochemical and molecular interventions. Submission closed. Overview Articles Authors Impact Comments.The following points highlight the two methods employed by plants to cope with biotic stresses.
The methods are: 1. Hypersensitive Response and 2. Secondary Acquired Resistance. On being attacked by insects or a pathogenic microorganism, typically a plant responds with:.
All these responses are collectively known as hypersensitive response or reaction HR. These are products of defense-related genes that are activated by microbial infection and include hydrolytic enzymes such as:.
The hypersensitive response culminates in rapid death of cells around the infection site depriving pathogen of the nutrient supply and limiting its spread in host plant and leaving necrotic lesions small regions of dead tissues at the site of invasion. The rest of the plant however, remains unaffected. Recent researches have shown that the hypersensitive response is preceded by accumulation of nitric oxide NO and active oxygen species including the superoxide anion O 2 —hydrogen peroxide H 2 O 2 and hydroxyl radical OH.
The production of active oxygen species known as the oxidative burst and nitric oxide a secondary messenger in many signalling pathways in animals and plants appears to be prerequisite for activation of hypersensitive response. Induction of PCD is prevented in absence of any of these two signals. The latter in turn are converted into hydrogen peroxide and hydroxyl radicals. The active oxygen species especially the hydroxyl radicals may contribute to PCD as part of the hypersensitive response or these may act to kill the pathogen directly.
Not all plants are resistant to disease caused by pathogens. Researchers have shown that resistance of plants to microbial pathogens has an underlying genetic basis. The pathogens carry avr genes virulence genes while the host plants carry corresponding resistance genes called R genes. Disease occurs when the pathogen lacks avr genes or the host plant does not carry dominant R genes. The avr genes are believed to encode enzymes for the production of specific substances called elicitors while R genes encode protein receptors that recognise and bind with these elicitors to initiate the hypersensitive response.
The elicitors L. The receptor proteins encoded by R genes are located on plasma-membrane and have a leucine- rich domain which is repeated inexactly many times in the amino-acid sequence. R genes comprise one of the biggest gene families in plants.
The hypersensitive response described earlier is limited to near vicinity of the initial site of infection by pathogen. But, often the entire host plants develops increased resistance against pathogens over a period of time ranging from few hours to several days following initial infection at one site of the plant.
SAR appears to result from increased levels of some secondary metabolites and other defense compounds such as chitinases and other hydrolytic enzymes. However, the mechanism of SAR is not clearly understood. One component of the signalling pathway is likely to be salicylic acid SA that is a benzoic acid derivative and a secondary metabolite.