PopW of Ralstonia solanacearum, a harpin that can induce tobacco resistance to tobacco mosaic virus. J. LI (1), H. Liu (1), J. Guo (1)
(1) Department of Plant Pathology, Nanjing Agricultural University, Nanjing, Jiangsu, China
Phytopathology 98:S89

Abstract: Harpins, such as HrpN of Erwinia amylovora, are extracellular glycine-rich proteins that elicit the hypersensitive reaction (HR). We identified popW of Ralstonia solanacearum, which encodes a protein similar to known harpins in characteristics of being acidic, rich in glycine and serine, and lacks cysteine. When infiltrated into plants, PopW induced rapid tissue collapse, which required active plant metabolism. The HR-eliciting activity was heat stable and protease sensitive. Thus, we concluded that PopW is a harpin. It had region homologous to pectate lyases of a unique class, but no pectate lyase activity was detected. This suggested that PopW may be targeted to the plant cell wall, and it was confirmed by subcellular location with the green florescent protein. However, popW mutants retained the wild-type ability to elicit the HR in nonhosts and to cause disease in hosts. Meanwhile, the PopW purified from E. coli by heterogeneous expression induced tobacco resistance against tobacco mosaic virus (TMV) by 100%. Expression level of the SAR marker gene PR-1 was obviously up-regulated after 12 hours PopW spraying tobacco leave. It was deduced that plant-signaling molecule salicylic acid (SA) plays an important role in PopW induced tobacco resistance against TMV, so it was the SA-dependent systemic acquired resistance (SAR). PopW was a harpin of Ralstonia solanacearum and it provided an attractive tool for the improvement of disease control.