Thionins - Nature's Weapons of Mass Protection

摘要

Fungal and bacterial diseases cause millions of dollars of crop damage, presenting an ongoing challenge for farmers, as well as undermining food safety. A broad-range protection system against microbial phytopathogens is needed to reduce or even eliminate crop yield dependence upon pesticides, which increase farmers' fixed costs globally or are not available/affordable to smallholder farmers in developing countries. While breeding crop resistance to multiple microbial diseases has been a desirable goal, numerous attempts to develop resistance by conventional breeding methods have had limited success. Thionins, a class of plant antimicrobial peptides, are excellent candidates for developing a broad-range plant defense system. They exhibit broad activity against bacteria and fungi, are effective at low concentrations, and rapidly damage microbial cells. Thionins act on membranes, greatly reducing the development of the pathogen resistance. Seed-specific thionins from wheat and barley are of particular interest because they meet requirements for genetic engineering of antimicrobial resistance in important crops. While reliable protection against microbial pathogens has been obtained in several plant species transgenically expressing leaf-specific thionins, inconsistent results have been reported for seed-specific thionins, even though high antimicrobial activity of thionins occurs in vitro. Despite extensive study, the natural mechanisms by which plants mobilize thionins to inhibit bacterial and fungal pathogens are ill-defined. Here, we summarize the considerable evidence that thionins are suitable for developing a reliable broad range antimicrobial defense system for agronomically important crops. New breakthroughs in understanding of thionin function in plant cells, and in particular the critical role of thionin signal peptide structure for regulation of thionin activity during its processing and transport in leaf tissues, should enable development of a thionin-based crop protection system.