• LEI CHEN

      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.

    • Autophagy requires Tip20 in Saccharomyces cerevisiae

      LEI CHEN CHUNLING ZHANG YUANCUN LIANG AIXIN LIU HANSONG DONG SHENSHEN ZOU

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      Autophagy is a highly conserved intracellular degradation pathway in eukaryotic cells that responds to environmentalchanges. Genetic analyses have shown that more than 40 autophagy-related genes (ATG) are directly involved in thisprocess in fungi. In addition to Atg proteins, most vesicle transport regulators are also essential for each step of autophagy.The present study showed that one Endoplasmic Reticulum protein in Saccharomyces cerevisiae, Tip20, which controlsGolgi-to-ER retrograde transport, was also required for starvation-induced autophagy under high temperature stress. Intip20 conditional mutant yeast, the transport of Atg8 was impaired during starvation, resulting in multiple Atg8 punctadispersed outside the vacuole that could not be transported to the pre-autophagosomal structure/phagophore assembly site(PAS). Several Atg8 puncta were trapped in ER exit sites (ERES). Moreover, the GFP-Atg8 protease protection assayindicated that Tip20 functions before autophagosome closure. Furthermore, genetic studies showed that Tip20 functionsdownstream of Atg5 and upstream of Atg1, Atg9 and Atg14 in the autophagy pathway. The present data show that Tip20,as a vesicle transport regulator, has novel roles in autophagy.

    • Real-time monitoring of translocation of selected type-III effectors from Xanthomonas oryzae pv. oryzae into rice cells

      BIAN HUIJIE LIYUAN ZHANG LEI CHEN WENZHAN WANG HONGTAO JI HANSONG DONG

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      Type-III (T3) effectors PthXo1 and AvrXa10 of Xanthomonas oryzae pv. oryzae are translocated into rice cells to inducevirulence and avirulence on susceptible- and resistant-rice varieties Nipponbare and IRBB10, respectively. The translocationneeds the bacterial T3 translocator Hpa1 and rice Oryza sativa plasma membrane protein OsPIP1;3. Here, weemployed the b-lactamase (BlaM) reporter system to observe PthXo1 and AvrXa10 translocation. The system wasestablished to monitor effectors of animal-pathogenic bacteria by quantifying the BlaM hydrolysis product [P] and fluorescenceresonance energy transfer (FRET) of the substrate. The feasibility of the BlaM reporter in rice protoplasts wasevaluated by three criteria. The first criterion indicated differences between both [P] and FRET levels among wild types andOsPIP1;3-overexpressing and OsPIP1;3-silenced lines of both Nipponbare and IRBB10. The second criterion indicateddifferences between [P] and FRET levels in the presence and absence of Hpa1. The last criterion elucidated the coincidenceof PthXo1 translocation with induced expression of the PthXo1 target gene in protoplasts of Nipponbare and the coincidenceof AvrXa10 translocation with induced expression of the AvrXa10 target gene in protoplasts of IRBB10. Theseresults provide an experimental avenue for real-time monitoring of bacterial T3 effector translocation into plant cells with apathological consequence.

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