Overproduction of high purity HapG(Xooc) from Xanthomonas oryzae functions as a growth and anti-virus factor in tobacco

HapG(Xooc), a member of the harpin group of proteins from pathogenic bacterium Xanthomonas oryzae pv. oryzicola, can induce a hypersensitive response (HR) and pathogen defense as well as enhance growth like a nutrition in plants. However, the biochemical mechanisms of Harpins in non-host plants still remains unclear. To obtain the crystals of HapG(Xooc) for further spatial structural studies, here, we first established a high purity and stable purified protocol for overproduction. The results of SDS-PAGE demonstrated a recombinant plasmid, pET-30a-hpa1, was successfully constructed and revealed the optimum conditions of HapG(Xooc) expression and purification. Additionally, the polyclonal antibody of HapG(Xooc) at a titer 1:50,000 was prepared by the high purity antigen for further protein-protein interaction studies between HapG(Xooc) and receptors of plants. The biological analysis indicated that HapG(Xooc), as a tobacco nutrition, significantly promoted the growth of tobacco root and induced defense response against tobacco mosaic virus (TMV) infection.