Prediction And Characterization Of A Cationic Arginine-rich Plant Anitmicrobail Peptide Sm-985 From Teosinte(Zea Mays Ssp.mexicana)

Antimicrobial peptides(AMPs)are effective against different plant pathogens and newly considered as a part of plant defense systems.From bacteria to plants,AMPs can exist in all forms of life.The SM-985 is a cationic AMP isolated from the c DNA library of Mexican teosinte(Zea mays ssp.mexicana).A computational prediction server running with different algorisms were used to screen the teosinte c DNA library for AMPs,and the SM-985 peptide was predicted as AMP with high probability prediction values.The SM-985 is an arginine-rich peptide and composed of 21 amino acids(MW: 2671.06 Da).The physicochemical properties of SM-985 are very promising as an AMP,including net charge(+8),hydrophobicity ratio 23%,Boman index 5.19 kcal/mol,and isoelectric point 12.95.The SM-985 peptide has amphipathic ?-helix conformations.The antimicrobial activity of SM-985 was confirmed against 6 bacterial plant pathogens.The MIC of SM-985 against Gram-positive indicators Clavibacter fangii,C.michiganesis ssp.michiganesis,and B.subtilis 168 was 8 ?M while the MBC was 16 ?M,the MIC of SM-985 against Gram-negative indicators Gram-negative bacteria Pseudomonas syringae pv.tomato DC3000,Ralstonia solanacearum,Xanthomonas campestris pv.holcicola,X.oryzae pv.oryzae and E.coli BL21 were 4 ?M,< 4 ?M,< 4 ?M,4 ?M,and 8 ?M,respectively,while the MBC values of SM-985 were 16 ?M,4 ?M,4 ?M,8 ?M,and 16 ?M,respectively.The SM-985 peptide increased the permeability of bacterial membranes due to interactions between the amino acids with positive charges and negatively charged bacterial phospholipids.This interaction was determined by the treatment of the bacterial indicators with FITC-SM-985 peptide,which showed the high binding affinity of SM-985 to the bacterial membrane(whether Grampositive or Gram-negative).Two antimicrobial activity assays were conducted to confirm that the FITC tag has no impact on SM-985 antimicrobial activity.SEM and TEM images of the treated bacteria with SM-985 demonstrated cell membrane damage and cell lysis.In vivo antimicrobial activity was examined,and SM-985 prevented leaf spot disease infection caused by Pst DC3000 on Solanum lycopersicum and prevented the HR caused by Pst DC3000 on Nicotiana betnhamiana.Moreover,SM-985 showed sensitivity to calcium chloride salt,which is a common feature of cationic AMPs.