The new CaSn gene belonging to the snakin family induces resistance against root-knot nematode infection in pepper

Abstract

The new CaSn gene belonging to the snakin family in pepper (Capsicum annuum) encodes a novel antimicrobial peptide and responds to root-knot nematode (Meloidogyne spp.) infection. CaSn was isolated and cloned using suppression subtractive hybridization (SSH), and the gene was characterized and expressed in Escherichia coli. The CaSnakin protein encoded by CaSn is an antimicrobial peptide consisting of a signal peptide of 23 amino acid residues, an acidic peptide of 14 amino acid residues (pI = 4.18), and a mature protein of 66 amino acid residues that corresponds to a molecular mass of 7.03 kDa. The peptide sequence has 12 conserved cysteines forming six disulfide bridges. CaSnakin is highly homologous to the peptide snakin-2 (StSN2) of potato (Solanum tuberosum); CaSnakin also shows 88.5% identity to StSN2. Phylogenetic tree analysis indicated that the CaSn gene belongs to subfamily II of the snakin family. Real-time quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) results showed that the CaSn gene was induced and expressed evidently by root-knot nematode infection; CaSn is also expressed in buds, stems, roots and leaves. The CaSnakin protein expressed in E. coli showed strong antimicrobial activity against free-living nematodes (Caenorhabditis elegans) and root-knot nematodes in vitro. In addition, the virus-induced gene silencing (VIGS) results revealed that the CaSn gene participates in the defense of plants against nematodes. In conclusion, the CaSn gene can be activated by nematode infections, and it plays an important role in host defense. As far as we know, this is the first investigation reporting the role of a snakin gene in the defense of plants against nematodes. In addition, the CaSn gene is the first gene of the snakin family isolated from pepper.