Abstract
Synthetic linear antimicrobial peptides with cationic α-helical structures, such as BP100, have potent and specific activities against economically important plant pathogenic bacteria. They are also recognized as valuable therapeutics and preservatives. However, highly active BP100 derivatives are often phytotoxic when expressed at high levels as recombinant peptides in plants. Here we demonstrate that production of recombinant phytotoxic peptides in transgenic plants is possible by strictly limiting transgene expression to certain tissues and conditions, and specifically that minimization of this expression during transformation and regeneration of transgenic plants is essential to obtain viable plant biofactories. On the basis of whole-genome transcriptomic data available online, we identified the Os.hsp82 promoter that fulfilled this requirement and was highly induced in response to heat shock. Using this strategy, we generated transgenic rice lines producing moderate yields of severely phytotoxic BP100 derivatives on exposure to high temperature. In addition, a threshold for gene expression in selected tissues and stages was experimentally established, below which the corresponding promoters should be suitable for driving the expression of recombinant phytotoxic proteins in genetically modified plants. In view of the growing transcriptomics data available, this approach is of interest to assist promoter selection for specific purposes.
Highlights
Antimicrobial peptides (AMPs) are key components of innate immunity in plants and animals, and are produced by microbes in antibiosis processes
We have recently showed that active BP100-derived peptides can be expressed as recombinant peptides in plants [7,8], demonstrated by the increased resistance of genetically modified (GM) plants to some rice pathogens [7] and by in vitro growth inhibition assays [8]
Biotechnological production of cationic a-helical antimicrobial peptides that have potent activities against pathogenic microorganisms is of great interest [35], but their constitutive expression is not compatible with the viability and fertility of host plants [7]
Summary
Antimicrobial peptides (AMPs) are key components of innate immunity in plants and animals, and are produced by microbes in antibiosis processes. A significant proportion are strongly cationic and have linear structures that adopt an amphipathic a-helical conformation that binds to the phospholipid membranes of target microbes before the hydrophobic face is inserted into the membrane bilayer This unique mode of action explains the lack of resistance in target pathogens, and makes AMPs valuable novel therapeutic agents against bacteria, fungi, viruses, parasites and tumor cells. We have recently showed that active BP100-derived peptides can be expressed as recombinant peptides in plants [7,8], demonstrated by the increased resistance of GM plants to some rice pathogens [7] and by in vitro growth inhibition assays [8] These recombinant BP100-derived peptides include endoplasmic reticulum (ER) retention motifs to minimize toxicity to the host plant. Not many cationic a-helical peptides can be expressed in transgenic plants following this strategy, they have potent activities against other types of pathogenic cells making them valuable as novel therapeutics and preservatives
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