HpaXm from Xanthomonas citri subsp. malvacearum is a Novel Harpinwith Two Heptads for Hypersensitive Response

摘要

A novel harpin-like protein, HpaXm, was described fromcotton leaf blight bacteria, Xanthomonas citri subsp.malvacearum. The hpaXm was found to be localized betweenhrp2 and hrcC. A phylogenetic analysis of the completeamino acid sequence or solely the 13 highly conservedresidues H_2N-SEKQLDQLLTQLI-COOH in the N-terminala-helix indicates that HpaXm is evolutionarily closer toHpaGXag and HpaXac than to HpalXoo and HpalXoc. Asynthesized peptide containing two heptads, 39-LDQLLTQ-LIMALLQ-52, from the N-terminal a-helical region ofHpaXm displayed comparable activity in inducing ahypersensitive response, but two other synthesized derivatives,HpaXmΔT44C and HpaXmΔM48Q, showed reduced HR-triggering activity. The data from a GST trap testrevealed that HpaXm was released into the extracellularmedium, hpaXm mutant deficient for the leader peptide(1-MNSLNTQIGANSSFL-15) was unable to be secretedoutside cells but still induced HR in tobacco leaves.