Productivity and biochemical properties of green tea in response to full-length and functional fragments of HpaG_(Xooc), a harpin protein from the bacterial rice leaf streak pathogen Xanthomonas oryzae pv. oryzicola

摘要

Harpin proteins from plant pathogenic bacteria can stimulate hypersensitive cell death (HCD), drought tolerance, defence responses against pathogens and insects in plants, as well as enhance plant growth. Recently, we identified nine functional fragments of HpaG_(Xooc), a harpin protein from Xanthomonas oryzae pv. oryzicola, the pathogen that causes bacterial leaf streak in rice. Fragments HpaG_(1-94), HpaG_(10-42), and HpaG_(62-138), which contain the HpaG_(Xooc) regions of the amino acid sequence as indicated by the number spans, exceed the parent protein in promoting growth, pathogen defence and HCD in plants. Here we report improved productivity and biochemical properties of green tea (Camellia sinensis) in response to the fragments tested in comparison with HpaG_(Xooc) and an inactive protein control. Field tests suggested that the four proteins markedly increased the growth and yield of green tea, and increased the leaf content of tea catechols, a group of compounds that have relevance in the prevention and treatment of human diseases. In particular, HpaG_(1-94) was more active than HpaG_(Xooc) in expediting the growth of juvenile buds and leaves used as green tea material and increased the catechol content of processed teas. When tea shrubs were treated with HpaH_(Xooc) and HpaG_(1-94) compared with a control, green tea yields were over 55% and 39% greater, and leaf catechols were increased by more than 64% and 72%, respectively. The expression of three homologues of the expansin genes, which regulate plant cell growth, and the CsCHS gene encoding a tea chalcone synthase, which critically regulates the biosynthesis of catechols, were induced in germinal leaves of tea plants following treatment with HpaG_(1-94) or HpaG_(Xooc). Higher levels of gene expression were induced by the application of HpaG_(1-94) than HpaG_(Xooc). Our results suggest that the harpin protein, especially the functional fragment HpaG_(1-94), can be used to effectively increase the yield and improve the biochemical properties of green tea, a drink with medicinal properties.