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3 Management of plant diseases using biotechnology tools


Hello! Welcome to the third talk of this week that is management of plant diseases through utilization of biotechnological tools. What are the advantages of development of biotechnological approaches? It can help us to understand or boost our knowledge regarding plant recognition of infection, then it can help us to mine R-genes in plants, it can also help us to upregulate defence pathways in a plant system, it can help us again disarming host susceptibility genes, then producing Antimicrobial compounds, silencing essential pathogen genes, Modifying Host Targets of pathogenicity or virulence factors, it can also help us to detoxify pathogenic toxins, engineering plants using CRISPR/Cas Immune system and reducing infection courts. So these are some of the advantages that we have when we apply bio technological tools.

Let us talk about the recent tool that is CRISPR Cas9 system. So this is the system basically we designed a single-stranded RNA with desired sequences and these sequences should have some complimentary sites on the target organism, whether it is a plant, or it is a any microbial agent. What we do here is that the guide RNA which is engineered basically for the desired sequences, they it is integrated with a nucleus which is known as Cas9 they are cloned together in a vector and this is introduced into the target organism whether it is a plant or a microbial agent. So what the vector mediated transfer does is that the guide RNA will take the RNA to the target site where it has some complementation and this nucleus enzymes then degrade this host target and it is then synthesized accordingly to the sequence of the guide RNA. So when we resequenced the gene from the newly transgenic cell then we will see the modifications of the gene that was targeted. So with this we can help managing plant diseases by affecting certain genes in the plant which may be helpful to the pathogen for disease progression. So let us take an example of their successful case. Application in plant disease management included there was Editing of three homeoalleles in wheat that confers heritable resistance to the powdery mildew pathogen. So this is the target site and the genes that was introduced modified the sequences at the target region and there was this is the wild-type (WT) and the rest when the pathogen was introduced on the transgenic plants different responses was seen and a particular change in a particular gene has led to complete a very significant resistance against the pathogen. This is the wild-type and this is the transgenic plant where you can see there is no development of powdery mildew on the leaf in comparison to a significant amount of disease development in the leaf. Microscopic studies has also revealed the same this is the wild-type or native plant where you can see development of the pathogen was quite distinct but at the same time period development of the pathogen on the transgenic plant showed very high resistance against the pathogen. Then another technology is RNAi in plant disease management that is RNA interference. Either in this particular technology one can use a double-stranded RNA or a hairpin RNA this double-stranded or hairpin RNA is degraded into smaller double-stranded fragments of approximately 21 nucleotide bases by an enzyme known as Dicer that is present in the plant and animals. So this Dicer breakdowns this double-stranded RNA into smaller fragments and one of this fragment is degraded within the cytoplasm. Then this guide RNA the single-stranded RNA that is left out it then incorporated into a complex known as our RISC complex, RNA inducing silencing complex and this guide RNA then take this RISE complex to the target site where it has a complementation site in the host of whether it is a plant animal or a microbial agent. When the guide RNA pairs with the complementary RNA then the Organoids proteins that are present within the RISC complex degrade this host RNA into smaller fragments and which is known as the RNA silencing and that is how because of its degradation the target gene is not expressed and if it is a vital gene for the pathogen then the pathogen will not be able to cause disease because of non expression of this particular gene. So it is successfully employed against fungal infection in plants, then in checking parasitic plant infection in higher plants then it to check some symbionts non-desirable in plants, then it was also used to check insect damage to plants as well as nematode damage to plants. So this is a tool again which has been successfully being used against a variety of plant pests or parasites. Another example of successful implementation of RNAi is that when tobacco plants that were silenced within the GST genes GST 1 and GST 2 then this tobacco plants were able to fight with the pathogen Phytophthora parasitics var. nicotianae.

So you can see that control plants were completely impacted and they were almost in the verge of killing at the same time there was no lesion or there was very small lesion was observed in the silenced plants and they were showing resistance against the pathogen. So in comparison to control the symptom was induced in RNAi plants were very very significantly low. so this has again showed the implication of this particular technology in plant disease management.

Similarly, there can be Interfamily Transfer of PRRs that is Pattern Recognition Receptors. As we mentioned earlier plant respond to the pathogen PAMP or pathogen DAMPS through some receptors and these receptors are known as PRRs. So pair plants have different types of PRRs that are able to recognize different PAMPs or DAMPs. So Interfamily transfer of plants say for example Arabidopsis is a cruciferous plant if PRRs from Arabidopsis can be transferred to say Nicotiana that is solanaceous plants then Nicotiana will also be able to resist pathogens that are being resisted in Arabidopsis. So with this concept this particular technology was developed where it was seen that transfer of Arabidopsis thaliana PRRs that is the specific PRR is EFR to Nicotiana which has then conferred resistance to a variety of bacterial pathogens. These are Pseudomonas syringae and Pseudomonas syringae pv. tabaci.

So here you can see that this is the wild type plant and this is the PRR transferred Nicotiana plant and when it is challenged by Pseudomonas Pseudomonas syringae pv. tabaci then the wild-type plant was totally diseased where the EFR transferred transgenic plants where nearly disease-free. The same time when it is the wild type plant and this is the EFR transferred plant against the when it was challenged with the pathogen pseudomonas syringae pv. tabaci then it was seen that the wild-type plant is diseased whereas the EFR transferred plants were almost disease free. So it has again shown us that this is another technology along with CRISPR and RNAi the transfer inter-family transfer of PRRs can provide good resistance against a wide variety of pathogens if we are able to do it successfully. So these tools and techniques are being recently been developed and they are showing quite promise in managing plant disease management and with this we conclude our talk with the emphasis on that more resources are required to make it commercially viable under field conditions.

Thank you.



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