Peanut(Arachis hypogea L.)bacterial wilt(BW)is a devastating disease caused by Ralstonia solanacearum that results in severe yield and quality losses.Plant defensins are short cysteine-rich peptides with antimicrobial activity.The role of defensin genes(Ah Def)in peanut is unclear.A genome-wide investigation of Ah Def genes was undertaken,and 12 identified Ah Def genes were classified into two groups containing the gamma-thionin domain formed by four disulfide pairs:Cys1-Cys8,Cys2-Cys5,Cys3-Cys6,and Cys4-Cys7.In silico analysis revealed that Ah Def genes showed highly conserved architectural features and contained cis-elements associated with phytohormone signaling and defense responses.A highly resistant cultivar,H108(R)and a susceptible accession,H107(S)were tested by R.solanacearum inoculation.H108(R)showed fewer symptoms than H107(S)owing to inhibition of bacterial reproduction and spread in the vascular bundles of roots and stems.In a transcriptomic expression profile,Ah Def genes,particularly Ah Def1.6 and Ah Def2.2,were up-regulated in H108(R)compared with H107(S)under R.solanacearum infection and phytohormone treatment.Subcellular localization showed that the Ah Def1.6 and Ah Def2.2 proteins were both expressed specifically on the plasma membrane.Overexpression of protein fusion Ah Def2.2-YFP in Nicotiana benthamiana and peanut leaves increased resistance to R.solanacearum,suggesting its role in response to BW infection.Ah Def2.2 may be valuable for peanut resistance breeding.
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