BIOTIC STRESSES AND TRANSGENIC CROPS WITH DIFFERENT BIOTIC STRESS RESISTANCE

 BIOTIC STRESSES AND TRANSGENIC CROPS WITH DIFFERENT BIOTIC STRESS RESISTANCE

INTODUCTION TO TRANSGENIC CROPS

By using genetic engineering approaches DNA of plants is modified, called as transgenic plants. Mostly used in agriculture. The aim to produce these plants is to introduce such traits which do not exist earlier. A genetically modified plant may have one or more genes artificially introduced to them either from related or unrelated plant species.

WHY DO WE USE GM TRANSGENIC CROPS

Certain causes are behind to modify plants such as to get best possible products.Before the advent of recombinant technology it was very difficult to produce such kind of products. A modified crop may have a changed color or its size to make it more appealing. Furthermore, tolerance to physical and biological harmful agents is one of the goal.

Insect resistance and to combat diseases are the major approaches of GM products. As with improvement of resistance, the use of pesticides and herbicides is also reduced.For that reason our food is more safer and its very beneficial for the farmers to save money, also it makes GM foods a cheaper source and more appealing and make it potentially profitable. Global food security is also a manifesto of transgenic products ( J. Singla et al. 2016).

BIOTIC STRESS

Biotic stress is caused in plants due to damage initiated by other living organism, including fungi, bacteria, viruses, weeds, insects and other nematodes or other native cultivated plants. Like abiotic stresses such as heat and drought, biotic stresses also cause the lack of nutrients, ability to survive and eventually can cause the death of plants. These stresses are the major cause of pre and post-harvest losses in agriculture field ( Madani et al. 2019).

Plants lack the adaptive immune system for that reason they can not memorize past infections. Yet they have an advanced plethora of erudite strategies to deal with these stresses and this information is encoded in their genetic code. Many of hundred biotic resistance genes are present in their genetic code ( Atinson  and Urwin 2012). These genetic codes are best understood  in some crops such as maize and rice etc. which proves that resistance genes are present.  In present era work on cereal crops is going to check for their resistance.

 

CHEMISTRY RELATED TO BIOTIC STRESSES

 

Infectious diseases are caused by biotic stresses that occur in harvested fruits. Plant defense system works against them in innate or systematic response. Soon after the infection reactive oxygen specie is produced and pathogen spread is burst by the oxidatives.Cell lignification occurs in response to infection and plant is more susceptible to parasites ( Cramer et al. 2011).

Defenses of plant contain certain enzymes and proteins and also some morphological and structural barriers which provide rigidity. Some chemicals like  beta-aminobutyric acid (BABA) or benzothiadiazole (BTH) also increase resistance

Hormones such as , salicylic acid (SA), jasmonic acid (JA) and the ethylene are very crucial in signaling, which mediate certain transcription factors. Abscisic acidenhance biotic stress resistance, it works with ethylene with protect plant against disease attack and make plant more liable. In this method , stomata is closed and entry of parasites is prohibited. Not only ABA and ROS works to protect plants but also some kinase protein helps to enhance plant defenses.

Pathogenesis-related (PR) is an important protein for plant resistance and their upregulations.. For this it is advised that with a rise in ABA countenance of specific TFs such as C-repeats binding factors (CBF) and cup-shaped cotyledon mediated by ABA can be increased, which causes upregulation of RP genes ( Rajeb et al. 2014).

CERTAIN BIOTIC STRESSES ARE;

(i)          VIRUSES

(ii)            BACTERIA

(iii)           FUNGI

(iv)           NEMATODS

(v)            ARACHNIDS

(vi)           WEEDS

(vii)          INSECTS

(viii)         HERBICIDES

VIRUSES

World-wide losses in crops are due to the plat-viruses. These viruses are the major economic loss for many countries, for example, there is a loss of 2$ billion sole in USA. Plant viruses arehard to regulate. Traditional methodscontain insecticidal sprays for killing vectors.In order to handle the viruses breeding resistant cultivars are promoted instead of conventional breeding, though it is being used for years, using this method many genes have been transferred from non-cultivated crops to cultivated crop ( Wahab et al. 2009). There are certain limitations are associated with the classical breeding as its more time consuming, lined genes may not be separated or resistance could be very difficult to be transferred. With the progress in science such as recombinant technology, it is possible to shift genes, also from certain bacteria or from the plants. The method of breeding has helped to overcome many dramatic conditions and enhanced crop plants with more resistance to invaders ( Ralf et al. 1988).

BACTERIA

Bacteria have both positive and negative impact on crops either it can enhance the production or can damage crops due to some pests. Bacteria, like rhizobia, azospirilla, and the agrobacteria used as seeds and improve crop production where-as  the others, like pseudomonads cause damage to crops. These are modified to work with the crops and to enhance their effectiveness and  helps to improve beneficial traits. By doing this we can see modification of bacteria and its introduction to field and its effect on the microflora. Environmental factors plays an impact role in existence of bacteria and to understand whether this bacteria is beneficial or not. Spreading of transgenic bacteria was limited ( Chakraborty et al. 2011). The shifting of bacteria can favor some plant bacteria already present at the same time it can disfavor certain fungal or bacterial populations in the rhizosphere of plants. It has more changes than the typical agriculture practices. In one case the genes were transferred from the resident plants to the bacteria ( Saha et al. 2006). No differences are found between the feast, perseverancewithin the ground and ecological effects on GM bacteria.Unmodified strain can be detected here.

FUNGI

With an advancement in biotechnology many antifungal proteins and peptides are found, which are important in , in vitro bioassay. Many genes and gene products are found which play their role in signaling pathways. In order to get more yield from transgenic crops many types of anti-fungal toxins are introduced that are taken from non plant sources. By utilizing these methods a decrease in fungal diseases is shown.Knowledge obtained from scientific techniques is useful to increase resistance . In transgenic plants use of multiple genes, working as a unit are more fruitful than the single gene. More improvement is still required to get fungal tolerance( Aimin et al. 2008).

INSECTS

Insecticidal proteins are programmed by numerous genes are very beneficial for agriculture. This new technology is also like many conventional insecticides can affect the insects like certain arthropods or other parasitoids, direly or indirectly way. These interactions are now can be used to eliminate incompatibilities.

HERBICIDES

There are alarmslike, the agronomy of genetically modified herbicide-tolerant(GMHT) plant crops preserved with extensive spectrum herbicide will rootweakening in the botanical variety and hence damage of biodiversity. Agronomy systems of these have diverse levels of inputs and organizationintrusions and some integrate the use of slight/no tillage. Research outcomes show a series of effects and the significance is to regulate whether research studies show changes in botanical diversity or weakening in plant population in GMHT compared with predictably managed crops.

WEEDS

Weeds and plants contend for the same possessions of nutrients, water, light and space for growth and development. Weeds are usuallyenduring species having profligate growth, deep root system and accomplished of opposing very proficiently with cultivated crops for  accessible resources and unfavorablydisturb the crop growth and production. Early slow growth mainly at early crop growth stages and broader plant arrangement of maize crop boosts fast and vital growth of weeds. It is supreme important that, race from weeds must be lessened to achieve optimalproduction. Among the different many weed control methods, the chemical techniquehave many recompenses in overturning weeds growth and to obtain healthy and vital stand. For last few yearsdifferentforms of selective and the non-selective herbicide type of molecules with a variation of mode of action wasrevealed. A fewexceptional non-selective herbicides can be used only when the respective crop was not present on a particular field. Todayup-to-date biotechnological tackles brought excellent discovery to agriculture.

 

NEMATODES

Plant parasitic-nematodes (PPNs), parasites the cause reduction in plant production. To protect some important crops it is necessary to manage these PPNs. Genetic engineering can play its role in this cause to biotic as well as abiotic stresses. Plant nematology is helping from the front in this respect to control nematodes, as nematode resistance is important for plant production. For this to happen certain resistance genes and also some anti-nematodal proteins are present.

 

GENETICALLY MODIFIED CROPS WITH AN IMPROVED RESISTANCE TO BIOTIC SRESSES

 

INTRODUCTION

Pests, weeds and diseases are important limiting aspects for cropproduction. The limitations linked with the different methods of breeding to improve resistance to many biotic stresses. Genetic modification is one of the key aspect in this respect. Many choices are provided to select resistance genes by genetic engineering.

 

INTRODUCTION TO BIOTIC STRESS RESISTANCE

In order to get better quality and quality food, reduction to biotic losses must be minimum. 10-16% food loss is due to pathogens. In the traditionallyagriculture techniques, cross breeding is only found in same individuals. Traditional breeders can not create resistance in the traits of many crops nor they can improve crops to new varieties.. To generate resistance we should find ways to introduce new genes from unrelated microorganisms, because traditional ways are more time consuming and they depend upon germplasm ( Grumet et al. 1990).

Chemical sprays may seem as good option but they can cause harm to environment and humans besides this resistance can be generated against them by pests. In last few years a lot of progress has been made due to genetic engineering.. This branch of science has made researchers to conduct more experiments and to find more and more resistance against parasites as well biotic factors ( Goldman et al. 1987).

In a large area of 175.2 million hectares transgenic crops are being cultivated, most of which developing countries are the growers. It is estimated that 19 out of 27 countries that grow transgenic crops are developing countries . Economic benefits to developing countries from GM crops were $47.9 billion in the years 1996-2012.

 

INSECTS RESISTANCE

 

Bt CROPS

A gram positive bacteria that produces CRY protein during sporolation, cytotoxins are also produced by this. Specialty of CRY protein is that , it is toxic to many insects but not to humans and other animals .

Insecticidal CRY proteins are encode by Bt genes that are transferred to crops to enhance resistance. This protein is solubilized in the mid gut and then is digested by proteases, some peptides bins to the epithelial cells receptor and cause death of pests. This mechanism is not working in all plant species.Over 175.5 million hectares are now being used for GM crop production (Amarger et al. 2002)

Bt potato plants have also been planted in North America which  are protected against Liptinotarsa decemlinata. It is also plated in Europe and cry3Aa is a component of it. Bt maize has been produced, Bt cotton has also been there, cultivation area of Bt cotton is 18 million hectares.

In India Bt eggplant is planted and commercialized, it targets Leucinodes oranalis For Plutella xylostella Bt crucifer is used. Bt rice is shortly be commercialized and it is a Bt toxin ( Aparna et al. 2007). Several trials have also been made to commercialize genetically modified rice, to increase its production, environmental factors upon it. For this purpose preproduction of many GMO rice is held, almost 4 varieties are present over there. In Iran cry3a gene was used to protect against Hypera postica. This gene is produced from the Bt alfalfa. Bt traits are not limited to this several other Cry genes are found there a few are cry1Ac, cry1Ab and cry1F. These genes are found in soybean ( Schuler et al. 1999).

FOR PROTEASE INHIBITORS (PI)

Digestive system is often effected by proteases that alter their protolytic activity. They ae found in many parts but storage tissues and seeds are their major storage place. Most common types of proteic are cystein and serine protease inhibitors (Roy et al. 2011).The major function of these, is to activate the defense system. PI gene transfer was the biggest challenge at that time,to do so cowpea was used from insect resistance specie was created. PI was transported to a plant species and  there was an increase  in the insect resistance in plants. Cowpea also encodes the trypsin and trypsin inhibitor CpTI, which we can say Cowpea Trypsin Inhibitor (James et al. 2013).

These CpTIs along with the Bt are transported to china for experiment in year 2000. Near about 15% results accounted more efficient than the previous ones in year 2005. Bt cotton cultivars were used with these CpTIs. Some of well-studiedcystein PIs is Oryzacystatin, from rice. This PI is effectively used for wheat, eggplants and oilseed rape. Beetle and aphid protection is provided by this. Potato proteinase inhibitor (pinII), Bar from Streptomyces higroscopicus and Bt are the three genes containing cry1Ac are found in Bt-Xtra (Gahan et al. 2010).

LECTINS

There major role is as, they are the carbohydrates-binding proteins. Like PI they are abundant in seeds and the storage tissues but difference is that most plants do not have the lectins. Their effectiveness is mostly shown in sap sucking Hemipetra. There effect is thereby insects-tolerant. Resistance is shown to brown plant hopper by the transgenic rice. Its two classes show resistance one is Galantus nivalis and other is Galantus agglutinin. Allium leaf of agglutinin(ASAL) have the same function to perform. This ASAL is transferred to rice pant to make it transgenic and to perform its insecticidal function properly ( BANR et al. 2000).

ALPHA-AMYLASE INHIBITORS

Seed weevils control is the first priority of these inhibitors, because starch is the main energy source of weevils.. Garden pea and other legume grains were delivered the gene of bean amylase inhibitor (Phaseolus vulgaris) by using a strong seed-specific promoter.Seeds produced by this methods are resistant against stockpiled product pests like larvae of burchid beetles and larvae of pea-weevil Bruchus pisorum. Chickenpea was introduced with Phaseolus vulgaris by the method of Agrobacterim-mediated transformation system, with the efficiency lower than 0.3%. Similarly Coffea arabica is genetically modified by these inhibitors. Its amylolytic activity is about 88% ( Combs et al. 2012).

ALTERNATIVE INSECTICIDAL GENES

Some species becomes the source of insecticidal events during their vegetative growth such as Bt that produces Vip3A protein. This protein is resistant against black cutworm (Agrotisipsilon). Mode of action of Vips is different than Cry proteins because of binding to the receptors of insect which Cry protein require insect’s gut. Certain gene strains such as Vip3Aa20 and vip3Aa1 show their function of insecticidal against many hosts like Western cutworm, corn earworm and black cutworm.

 

GENETIC ENGINEERING FOR RESISTANCE TO DISEASES IN PLANTS

 

RESISTANCE TO FUNGAL DISEASES

Composition of fungal cell wall is that it contains chitin and the beta-1,3-gulacanase, chitin is hydrolyzed by chitinase and later is hydrolyzed by the glucanase. Due to pathogen infection both of these enymes are produced, in their presence fungal growth is inhibited. In past few years, transformation of genes of chitinase and glucanase is made possible. Many of such methods are through the microbial mediated and direct method, and hence more fungal resistance occurs. These plants contain grapevine, cotton and peanut and tohidfar ( Reeck et al. 1997).Fungal disease resistance is shown in many plants such as carrot and tobacco due to these enzymes.

Polygalacturonase inhibiting protein (PGIP) can inhibit fungal-endopolygalacturonases, found in cell wall of many plant. Fusarim head-blight is a disease in wheat, where contamination of products may result, (thricothecene and deoxynivalenol-DON). DON contamination is dangerous for animal humans. In recent times a gene named as L3 is transferred to wheat to make it resistant to diseases. Also improved level of wheat is produced, kernel wheat ( Hilder et al. 1987). Phytophthora infestans is a disease of potato, also known as blight. To control this disease many biotechnology-driven techniques are used. In this regard R genes are separated from many sorces. Immunity of potato is enhanced by gene LipO, from its activity Rpi-blb1 was identified.Combined expression of these both results in discovery of more resistance gene for late-blight, Rpi-pta1.

 

Activating phytoalexins is another method to increase resistance in plants, defense mechanism is involved for this approach.Stilbene-synthase gene enhance resistance in grapes against Piriculiaorizae, barely was also improved against powdery mildew ( He et al. 2008).  To respond against phytoalexinsynthesis, mitrogen-activated protein kinase has been used in rice crop. It is effective against blast infestation and UV infestations.UV radiations are more important in this scenario because phytoalxin appearance in rice crop is enhanced by this. Some scientists have studies this MAPK in detail, they found that MAPKK and OsMMKK6 are two main heads of this cascade, they checked the latter in UV stress conditions and as a result, a transgenic rice crop is produced which is resistant to phytoalexins.

BACTERIAL DISEASES RESISTANCE

 

Certain natural causes are present which are causing bacterial-blight in rice crop such as Xanthomonas oryzae etc. It is believed that, in pathogensis-related genes , ethylene-responsive transcription factors are involved to maintain its expression. Cotton ERF was expressed in tobacco to get more resistant transgenic plants against Xanthomonas (Ribero et al. 2006).

Bacteria are in continuous search to produce hypersensitive response to their non-host plants and to get more resistant. Harpin genes are most effective for this because they encodes III secretory pathways.With  a series of reactions like reactive oxygen specie, local cell death occurs when these harpin genes are released to any crop and bacterial resistant plants are produced. Many scientists worked on Harpin they found that NEa is its useful strain, and its an inducer in systematic-acquired resistance (Oksman et al. 2002). This strain is present on the chromosomes of Erwinia. That is the major cause of fire-blight in apple plants. Improved strain of this Harpin gene increases resistance against bacterial diseases.Plant-ferredoxin like proteins expression is useful in bacterial disease-resistance, this PFLP contains N-terminal signal-peptides that helps in chloroplast localization. Most of the things have been done but PFLP relation with plant is still unclear. PFLP is photosynthetic in nature ( Li et al. 2005).

There are many ways have been introduced to get rid of bacterial resistance, such a method is to alter the genes encoding toxin-detoxifying enzyme, that will kill the pathogens, example is tabtoxin produced by certain organisms. .  This tabtoxin is effective in many ways ,many pathogens will try to guard from this. Also their guarding mechanism is known to us , as they do so by  interacting with the expression of this tabtoxin resistance gene. Some other are also protected by this such as P. syringae. The mechanism adopted by them is much different from others as they acetylate tabtoxin, as a consequence it become inactivated. Tobacco plants shows this ttr gene, which means low disease symptoms (Sharma et al. 2008).

RESISTANCE TO VIRAL DISEASES

 

Viruses are the major threat to plants, more than seven hundred plant viruses have been identified. These viruses cause many diseases and loss of crops. We have no as such protection against viruses , we are still using chemicals to stop viruses all this is happening because we don’t have much viricides to combat viruses . Genetic engineering is leading from the front in this regard, coat-mediated resistance is example of it, by using this technique viral resistance has been generated and commercialization of plants happens for instance potato event HLMT15-15 tolerance to Potato-leaf roll virus ( Saha et al. 2006).

Different strains of Papaya ring-spot virus have been found that affect papaya crop. But this virus strain is now under control by the help of viral coat-protein sequence , papaya hybrids are produced. Talk in the town is that scientists are trying to get more viral resistance by using plants with viral genes not coat protein genes (Powel et al. 1995). Transgenic tobacco was formed by a scientist which was co-expressed with cucumber mosaic virus, this is a double stranded RNA derivative which shows high resistance. Imperfect movement-protein viruses are also observed to provide resistance to many transgenic plants (Mortan et al. 2000).

 

In agriculture a new method to get resistance has also been introduced , called as antibody engineering. In this approach , protein content of pathogens is deactivated by expressing many different antibodies.

Not only these are the possible ways to treat viruses but also many other techniques has been introduced the working mechanism is quite similar to the above mentioned. One od the approach is Poke-weed antiviral protein and the other method is 2’,5’-oligoadenylate synthetase ( Lee et al. 2006).

HERBICIDES RESISTANCE

 

Till now 14 herbicide-tolerant plants have been commercialized, it is so extensive that 222 events are involved. These crops include cotton and maize etc. which have glyphosate tolerance. Many of different kind of genes are present in this type of improved crops such as gat and dmo which are tolerance genes (Neuhus et al. 1999).These crops are used as post-emergency herbicides. 5-enolpyruvylshikimae-3-phosphate synthase is also inhibited by the Glyphosate which plays an integral part in shikimate pathway. The mutated genes for EPSPS synthase are allocated with Glyphosate tolerance  that is used to differentiate enolpyruvate from Glyphosate which is the natural substrate of it, for instance these gene separated can enhance resistance upto 200 mM. EPSPS genes can be separated from many sources likePseudomonas stutzeri.LikeAmaranthus palmer many other plant species are under development for resistance(Melchers et al. 2000).

Acetylation of NH₂ group of phosphinothricin is the major preference in the production of herbicides. That specific gene is taken from the Streptomyces higroscopicus. Bar genes of sweet potato will become more and more resistant when a transgenic series of plants will have genes that encodes PAT ( Ballvora et al. 2002).

An isoenzyme with many catalytical activities, named as GmGSTU gene was introduced to tobacco in order to increase resistance from the soya-bean plant. This is mor catalytic for diphenylether herbicides. After a lot of research a gene, imidazolinone was introduced to maize plants to enhance tolerance (Vleeshower et al. 2008). By considering all the aspects in our mind and by keeping the results obtained from previous experiments, it is clear that crop loss has been lessened by different ways such as weed control. Glyphosate can also be converted to another non-toxic form like, N-acetylglyphosate, but to achieve this many kinds of improved genes are required and these can be obtained from certain bacteria as well. An example of such genes is glyphosate N-acetyltransferase. When we introduce GAT genes in any plant crop they become tolerant to Glyphosate (Zhu et al. 2012).

DISCUSSION

 

Resistance have been generated in pests, herbicides and many pathogens. Genetically modified plants which have acquired resistance are cotton, barely and 20 such other crops.Most of the transgenic plants have cleared certain biosafety requirement ( Champion et al. 2009).Successful results have been shown for pest and viral resistances but GM plants resistance against fungal and bacterial infections is much rare. More than tens of crops have been approved in USA, these crops include insect resistant potato and maize, virus resistant  papaya and other Bt expressing crops, and also viral coat protein . Other plants are also facing queuing for commercialization. Many Bt crops and viral crops are being commercialized in near future , also fungal and bacterial resistance crops are going to be introduced  (Otung et al. 2014).

 

Transfer viral pathogenic genes to plants genome by gene silencing, antisense RNA and RNAi techniques. There are different approaches are used to make plants resistance against fungus by boosting up their defense system, chitinase and glucanase are mostly used. As knowledge of defense system of plants is increasing the more we are getting closer to get better transgenic plants (Hallwass et al. 2014).

The bacterial infection is still under doubt, not more resistance is generated against them. But genes are being used that are encoding toxin detoxifying enzymes (Cardoso et al. 2014). No matter how much difficulties we are facing to get genetically modified organisms, this method is getting more and more importance and every year more land is used for this purpose. By witnessing the success of transgenic crops in biotic stresses it is of no doubt that this technique will be playing its role in abiotic stresses in near future.

 

CITATION TO PREVIOUS ARTICLE

 

“ Transgenic crops with an improved resistance to biotic stresses. A review “

(Tohidfar, 2015)