Triticeae Genomics and Genetics, 2025, Vol.16, No.2, 79-91 http://cropscipublisher.com/index.php/tgg 87 demonstration that transgenic approaches can deliver resistance where conventional breeding fails, and it adds to global efforts to reduce diseases like “scab” (another term for Fusarium head blight - sometimes also called scab in corn and other cereals) (Rahnamaeian et al., 2009). In summary, the Japan NARO case study is a success story: they achieved strong Fusarium resistance and toxin reduction in barley (and wheat) by introducing a barley chitinase gene, and those transgenic lines maintained normal crop performance, showing promise for future development and even commercialization pending further approval. 7.2 ICRISAT: using antimicrobial peptides in barley for fungal resistance The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), along with other collaborators, has been exploring the use of antimicrobial peptides (AMPs) to enhance barley’s resistance to diseases like powdery mildew and rust. AMPs are small defensive proteins found in many organisms that can kill a broad range of microbes (bacteria, fungi, etc.), and importantly, pathogens don’t easily develop resistance to them. ICRISAT’s approach was to introduce a fruit fly-derived AMP gene called Metchnikowin (Mtk) into barley. Metchnikowin is a well-known antifungal peptide from Drosophila. They put this Mtk gene under a constitutive promoter in barley, meaning the barley would continuously produce the Mtk peptide in all tissues, giving it a standing army of antifungal molecules ready to attack pathogens as soon as they try to infect. At the same time, some studies have used tissue-specific promoters to limit the expression of human antimicrobial peptide LL-37 (Figure 1). The idea there is to avoid any potential growth impact by limiting where the AMP is expressed (since some AMPs at very high levels might theoretically stress a plant’s cells). In ICRISAT’s main approach with Mtk, they went the full constitutive route for maximal readiness, but it’s good to note they are aware of balancing expression strategies depending on the AMP (Mirzaee et al., 2021). Figure 1 PCR amplification of a 1 355 bp fragment of MBP::rhLL-37 gene from barley genomic DNA. M, 1 kb plus DNA ladder; WT, Wild type (non-transformed barley plant); lane 1, T5 and lanes 2-9, T6 progenies of a homozygous MBP::rhLL-37 transgenic barley line (Adopted from Mirzaee et al., 2021) In greenhouse experiments, barley plants transgenic for Mtk showed strong resistance to powdery mildew (Blumeria graminis). They had far fewer lesions and the fungal growth on leaves was scant compared to controls. Essentially, the powdery mildew fungus struggled to establish itself on these Mtk-producing plants. They also observed that Mtk could inhibit other fungi like Fusarium graminearum (the Fusarium that causes head blight). In lab assays, Mtk hindered Fusarium spore germination and hyphal growth. This is expected since Mtk is a broad-spectrum antifungal peptide. A particularly interesting finding from ICRISAT’s work is that high expression of Mtk seemed to activate other defense pathways in the barley. Molecular analyses showed upregulation of certain barley defense genes (like other PR proteins related to immune responses). This suggests that the presence of the AMP might be acting like a trigger, priming the plant’s own immune system - a phenomenon known as systemic acquired resistance or
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