Plant Defensins: Tissue Specific Expression Leading to Distinctive Functions

Plant defensins are small, cysteine-rich cationic antimicrobial peptides that possess biological activity towards a broad range of pathogenic organisms. These defense peptides are ubiquitous within the plant kingdom and acts as the first line of plant defense. Plant defensins are expressed in several plant tissues, such as seedlings, leaves, tubers, ûowers, pods, roots and fruits. They are mainly secreted at peripheral layers of cells and play an integral role in protecting storage, developmental and reproductive parts of the plants, against pathogen attack or injury as part of a systemic defense response. The expression of plant defensins might be constitutive or can be induced in response to pathogenic attack, abiotic stress or downstream to hormone signaling pathways. Moreover, most defensins are localized and expressed in particular tissues, performing very specific functions, thereby bestowing various benefits in respective hosts. From past few years plant defensins have become interesting and important candidates in transgenic technology, owing to their multifunctional but specific biological roles, especially for their broadspectrum antifungal activity. This review summarizes about the biological roles displayed by plant defensins when constitutively over expressed in targeted tissues of transgenic plants, under the control of tissue specific promoters, and the predominant role exhibited by plant defensins in defense and developmental processes of plants.