Plant defensins: biological function, mechanisms of action and methods of analysis (review)

One of the actual problems of modern agriculture is crop loss due to various biotic and abiotic factors. In plants there is a multicomponent protection system, including the formation of protective barriers, activation the reaction of hypersensitivity and synthesis of antimicrobial peptides, which are low molecular weight compounds showing broad spectrum activity against fungi, bacteria and viruses. This group consists of several groups of peptides, including defensins, which are one of the most common classes of antimicrobial peptides and are detectable in all living organisms. Defensins are small (45-54 amino acids), cysteine-rich peptides involved in a different protective responses (B.P. Thomma et al., 2002). Genes which are coding plant defensins are expressed in different organs of plants, where their products are necessary for biotic and abiotic stresses. Thus, these peptides are extremely important in terms of getting crop lines that are resistant to pathogens and abiotic stresses. Defensins are characterized by a strong sequence variability that seems to correlate with a variety of mechanisms of action of these peptides that can induce pathogen's cell death by penetrating into a cell or by being on its surface (T.M. Shafee et al., 2016). Most of the plant defensins are characterized by the antifungal activity. Some defensins have antibacterial activity, which may be combined with activity against fungi. For a small number of plant defensins their participation in the processes of resistance to heavy metals, cold stress, drought, salinity, and in the development process is indicated. Modern approaches of molecular and computational biology allow an effective search for new forms of defensins activity by studying the wild, non-model plant objects. The development of next-generation sequencing methods («Next Generation Sequencing») make possible the intensive study of the transcriptomes of such objects. However, the correct annotation of the sequences of peptides, characterized by small size and high variability, can be done by usage the special programs, such as SPADA (Small Peptide Alignment Discovery Application) (P. Zhou et al., 2013). SPADA makes multiple sequence alignment of all known paralogous genes within a gene family and builds a predictive model for the search of new members of the same family. Prediction of newly identified active defensins and identification of conserved amino acids can also be performed by computational biology methods. An approach based on a multiple sequence alignment and subsequent cluster analysis allows dividing defensins into groups with similar functional activity (N.L. van der Weerden et al., 2013). Thus, the combination of modern methods of molecular and computational biology allows carrying out the study of this group of protective peptides with high efficiency.