By proteases or due to binding of the peptides to certain cell envelope structures/compounds that decrease effective concentrations. Nevertheless, the difference in prokaryotic and eukaryotic membrane architecture already imparts selectivity of AMPs for microorganisms and reduces toxic side effects against cells of higher organisms. In plants several families of antimicrobial peptides have been identified, such as thionins, defensins, lipid transfer proteins, hevein-and knottin-like proteins and snakins, differing in structure, size and cysteine content. The role of antimicrobial peptides in defense is well established and their use in agriculture was already proposed when they were first discovered. Especially antimicrobial peptides from animals were analysed for their plant protecting potential. Magainin, cecropin and modified or chimeric forms of these two peptides were mainly used in in-vitro or ex-vivo studies against plant pathogens. However, since the cationic and hydrophobic characteristics of the antimicrobial peptides determine their mode of action, direct modification of these features allows the rational design of new AMPs. Here, we present the design of a novel set of antimicrobial peptides harbouring different structural and chemical properties, and depict their possible use in plant protection. Several of our designed peptides were highly toxic for a wide range of bacterial and fungal plant pathogens, e.g. Pseudomonas corrugata, Xanthomonas vesicatoria, and Cladosporium herbarum at CUDC-907 distributor concentrations below 1 mg/ ml, whereas no toxic effects against human cells or plant protoplasts were observed at these concentrations. Altogether, more than 60 peptides were designed and analyzed for their potential use as plant protecting agents in in-vitro inhibition assays. 
Furthermore, spraying the designed peptides on the surface of infected leaves demonstrated their antimicrobial activity directly on plants and displays a way of practical application. Leucine, isoleucine, valine, phenylalanine, alanine, methionine, glycine, serine, and threonine residues were used to generate hydrophobic regions. A helical structure of the peptides was ensured by inserting strong helix-forming amino acids, such as leucine and alanine. We selected a derivative of the scorpionderived antimicrobial peptide IsCT and the frog-derived peptide magainin II as templates. The mutation tool of the SWISS-Pdbviewer software was used to modify the template molecules and to design new peptides. The software enables to see directly a structural model of the designed peptides. To investigate, whether a distinct structural pattern is particular important for antimicrobial activity, four leading structures were designed, each containing four peptides differing in charge, hydrophobicity, location and size of the hydrophobic and charged clusters. A detailed description of the designing strategy can be found in the supplement. The amino acid sequences were analysed against an AMP database to ensure that they are differ from sequences of already known AMPs. Hydrophobicity was calculated based on the hydrophobicity scale for amino acids and pI values were calculated using the AZ 960 ExPASy ProtParam tool. The helical structure was predicted using NNPREDICT program for protein secondary structure prediction. Peptides of group I consist of a dominant charged cluster and a small hydrophobic region. Group II contains peptides with a dominant hydrophobic cluster and a small charged region. In all peptides of group III the hydrophobic and the charged regions have the same size and are separated lengthwise of the molecule. In peptides of group IV the charged regions are located at the N- and C-termini, which are separated by a central hydrophobic cluster. In peptides SP13 and SP16 the charged Nterminal and C-terminal parts are connected by a charged bar.