• Ruoxue Liu

      Articles written in Journal of Biosciences

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

      Xiaojing Wu Tingquan Wu Juying Long Qian Yin Yong Zhang Lei Chen Ruoxue Liu Tongchun Gao Hansong Dong

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      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 HpaGXooc, a harpin protein from Xanthomonas oryzae pv. oryzicola, the pathogen that causes bacterial leaf streak in rice. Fragments HpaG1–94, HpaG10–42, and HpaG62–138, which contain the HpaGXooc 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 HpaGXooc 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, HpaG1–94 was more active than HpaGXooc 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 HpaHXooc and HpaG1–94 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 HpaG1–94 or HpaGXooc. Higher levels of gene expression were induced by the application of HpaG1–94 than HpaGXooc. Our results suggest that the harpin protein, especially the functional fragment HpaG1–94, can be used to effectively increase the yield and improve the biochemical properties of green tea, a drink with medicinal properties.

    • Thirty-seven transcription factor genes differentially respond to a harpin protein and affect resistance to the green peach aphid in Arabidopsis

      Ruoxue Liu Beibei Lü Xiaomeng Wang Chunling Zhang Shuping Zhang Jun Qian Lei Chen Haojie Shi Hansong Dong

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      The harpin protein HrpNEa induces Arabidopsis resistance to the green peach aphid by activating the ethylene signalling pathway and by recruiting EIN2, an essential regulator of ethylene signalling, for a defence response in the plant. We investigated 37 ethylene-inducible Arabidopsis transcription factor genes for their effects on the activation of ethylene signalling and insect defence. Twenty-eight of the 37 genes responded to both ethylene and HrpNEa, and showed either increased or inhibited transcription, while 18 genes showed increased transcription not only by ethylene but also by HrpNEa. In response to HrpNEa, transcription levels of 22 genes increased, with AtMYB44 being the most inducible, six genes had decreased transcript levels, and nine remained unchanged. When Arabidopsis mutants previously generated by mutagenicity at the 37 genes were surveyed, 24 mutants were similar to the wild type plant while four mutants were more resistant and nine mutants were more susceptible than wild type to aphid infestation. Aphid-susceptible mutants showed a greater susceptibility for atmyb15, atmyb38 and atmyb44, which were generated previously by T-DNA insertion into the exon region of AtMYB15 and the promoter regions of AtMYB38 and AtMYB44. The atmyb44 mutant was the most susceptible to aphid infestation and most compromised in induced resistance. Resistance accompanied the expression of PDF1.2, an ethylene signalling marker gene that requires EIN2 for transcription in wild type but not in atmyb15, atmyb38, and atmyb44, suggesting a disruption of ethylene signalling in the mutants. However, only atmyb44 incurred an abrogation in induced EIN2 expression, suggesting a close relationship between AtMYB44 and EIN2.

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