• Hansong Dong

      Articles written in Journal of Biosciences

    • Combinative effects of a bacterial type-III effector and a biocontrol bacterium on rice growth and disease resistance

      Haiying Ren Ganyu Gu Juying Longa Qian Yin Tingquan Wu Tao Song Shujian Zhang Zhiyi Chen Hansong Dong

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      Expression of HpaGXoo, a bacterial type-III effector, in transgenic plants induces disease resistance. Resistance also can be elicited by biocontrol bacteria. In both cases, plant growth is often promoted. Here we address whether biocontrol bacteria and HpaGXoo can act together to provide better results in crop improvement. We studied effects ofPseudomonas cepacia on the rice variety R109 and the hpaGXoo-expressing rice line HER1. Compared to R109, HER1 showed increased growth, grain yield, and defense responses toward diseases and salinity stress. Colonization of roots byP. cepacia caused 20% and 13% increase, in contrast to controls, in root growth of R109 and HER1. Growth of leaves and stems also increased in R109 but that of HER 1 was inhibited. WhenP. cepacia colonization was subsequent to plant inoculation withRhizoctonia solani, a pathogen that causes sheath blight, the disease was less severe than controls in both R109 and HER1; HER1, nevertheless, was more resistant, suggesting thatP.cepacia and HpaGXoo cooperate in inducing disease resistance. Several genes that critically regulate growth and defense behaved differentially in HER1 and R109 while responding toP. cepacia. In R109 leaves, theOsARF1 gene, which regulates plant growth, was expressed in consistence with growth promotion byP. cepacia. Inversely,OsARF1 expression was coincident with inhibition in growth of HER1 leaves. In both plants, the expression ofOsEXP1, which encodes an expansin protein involved in plant growth, was concomitant with growth promotion in leaves instead of roots, in response toP. cepacia. We also studiedOsMAPK, a gene that encodes a mitogen-activated protein kinase and controls defense responses toward salinity and infection by pathogens in rice. In response toP. cepacia, an early expression ofOsMAPK was coincident with R109 resistance to the disease, while HER1 expressed the gene similarly whetherP. cepacia was present or not. Evidently,P. cepacia and GXoo-gene mediated resistance may act differently in rice growth and resistance. Whereas combinative effectsof P. cepacia and HpaGXoo in disease resistance have a great potential in agricultural use, it is interesting to study mechanisms that underlie interactions involving biocontrol bacteria, type-III effectors and pathogens.

    • 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.

    • HrpNEa -induced deterrent effect on phloem feeding of the green peach aphid Myzus persicae requires AtGSL5 and AtMYB44 genes in Arabidopsis thaliana

      Beibei Lü Weiwei Sun Shuping Zhang Chunling Zhang Jun Qian Xiaomeng Wang Rong Gao Hansong Dong

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      In Arabidopsis thaliana (Arabidopsis) treated with the harpin protein HrpNEa, resistance to the green peach aphid Myzus persicae, a generalist phloem-feeding insect, develops with induced expression of the AtMYB44 gene. Special GLUCAN SYNTHESIS-LIKE (GSL) genes and 𝛽-1,3-glucan callose play an important role in plant defence responses to attacks by phloem-feeding insects. Here we report that AtGLS5 and AtMYB44 are both required for HrpNEa-induced repression of M. persicae feeding from the phloem of Arabidopsis leaves. In 24 h successive surveys on large-scale aphid populations, the proportion of feeding aphids was much smaller in HrpNEa-treated plants than in control plants, and aphids preferred to feed from the 37 tested atgsl mutants rather than the wild-type plant. The atgsl mutants were generated previously by mutagenesis in 12 identified AtGSL genes (AtGSL1 through AtGSL12); in the 24 h survey, both atgsl5 and atgsl6 tolerated aphid feeding, and atgsl5 was the most tolerant. Consistently, atgsl5 was also most inhibitive to the deterrent effect of HrpNEa on the phloem-feeding activity of aphids as monitored by the electrical penetration graph technique. These results suggested an important role of the AtGSL5 gene in the effect of HrpNEa. In response to HrpNEa, AtGSL5 expression and callose deposition were induced in the wild-type plant but not in atgsl5. In response to HrpNEa, moreover, the AtMYB44 gene known to be required for repression of aphid reproduction on the plant was also required for repression of the phloem-feeding activity. Small amounts of the AtGSL5 transcript and callose deposition were detected in the atmyb44 mutant, as in atgsl5. Both mutants performed similarly in tolerating the phloem-feeding activity and impairing the deterrent effect of HrpNEa, suggesting that AtGSL5 and AtMYB44 both contributed to the effect.

    • Hpa1 harpin needs nitroxyl terminus to promote vegetative growth and leaf photosynthesis in Arabidopsis

      Xiaojie Li Liping Han Yanying Zhao Zhenzhen You Chunling Zhang Zhenzhen You Hansong Dong Chunling Zhang

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      Hpa1 is a harpin protein produced by Xanthomonas oryzae, an important bacterial pathogen of rice, and has the growth-promoting activity in plants. To understand the molecular basis for the function of Hpa1, we generated an inactive variant protein, Hpa1𝛥NT, by deleting the nitroxyl-terminal region of the Hpa1 sequence and compared Hpa1𝛥NT with the full-length protein in terms of the effects on vegetative growth and related physiological responses in Arabidopsis. When Hpa1 was applied to plants, it acted to enhance the vegetative growth but did not affect the floral development. Enhanced plant growth was accompanied by induced expression of growth-promoting genes in plant leaves. The growth-promoting activity of Hpa1 was further correlated with a physiological consequence shown as promoted leaf photosynthesis as a result of facilitated CO2 conduction through leaf stomata and mesophyll cells. On the contrary, plant growth, growth-promoting gene expression, and the physiological consequence changed little in response to the Hpa1𝛥NT treatment. These analyses suggest that Hpa1 requires the nitroxyl-terminus to facilitate CO2 transport inside leaf cells and promote leaf photosynthesis and vegetative growth of the plant.

    • 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.

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