HpaXm from Xanthomonas citri subsp. malvacearum is a Novel Harpin with Two Heptads for Hypersensitive Response
2010
Miao, Wei-Guo, Nanjing Agricultural University, Nanjing, China | Song, Cong-Feng, Nanjing Agricultural University, Nanjing, China | Wang, Yu, Nanjing Agricultural University, Nanjing, China | Wang, Jin-Sheng, Nanjing Agricultural University, Nanjing, China
A novel harpin-like protein, HpaXm, was described from cotton leaf blight bacteria, Xanthomonas citri subsp. malvacearum. The hpaXm was found to be localized between hrp2 and hrcC. A phylogenetic analysis of the complete amino acid sequence or solely the 13 highly conserved residues H₂N-SEKQLDQLLTQLI-COOH in the N-terminal α-helix indicates that HpaXm is evolutionarily closer to HpaGXag and HpaXac than to Hpa1Xoo and Hpa1Xoc. A synthesized peptide containing two heptads, 39-LDQLLTQLIMALLQ-52, from the N-terminal α-helical region of HpaXm displayed comparable activity in inducing a hypersensitive response, but two other synthesized derivatives, HpaXmΔT44C and HpaXmΔM48Q, showed reduced HR-triggering activity. The data from a GST trap test revealed that HpaXm was released into the extracellular medium, hpaXm mutant deficient for the leader peptide (1-MNSLNTQIGANSSFL-15) was unable to be secreted outside cells but still induced HR in tobacco leaves.
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