Altered Disease Development in the eui Mutants and Eui Overexpressors Indicates that Gibberellins Negatively Regulate Rice Basal Disease Resistance

National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
Molecular Plant (Impact Factor: 6.34). 05/2008; 1(3):528-37. DOI: 10.1093/mp/ssn021
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Gibberellins (GAs) form a group of important plant tetracyclic diterpenoid hormones that are involved in many aspects of plant growth and development. Emerging evidence implicates that GAs also play roles in stress responses. However, the role of GAs in biotic stress is largely unknown. Here, we report that knockout or overexpression of the Elongated uppermost internode (Eui) gene encoding a GA deactivating enzyme compromises or increases, respectively, disease resistance to bacterial blight (Xanthomonas oryzae pv. oyrzae) and rice blast (Magnaporthe oryzae). Exogenous application of GA(3) and the inhibitor of GA synthesis (uniconazol) could increase disease susceptibility and resistance, respectively, to bacterial blight. Similarly, uniconazol restored disease resistance of the eui mutant and GA(3) decreased disease resistance of the Eui overexpressors to bacterial blight. Therefore, the change of resistance attributes to GA levels. In consistency with this, the GA metabolism genes OsGA20ox2 and OsGA2ox1 were down-regulated during pathogen challenge. We also found that PR1a induction was enhanced but the SA level was decreased in the Eui overexpressor, while the JA level was reduced in the eui mutant. Together, our current study indicates that GAs play a negative role in rice basal disease resistance, with EUI as a positive modulator through regulating the level of bioactive GAs.

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Available from: Zuhua He, Nov 15, 2014
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    • "For example , in rice, the GAs have been shown to negatively regulate resistance to both the bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo) and fungal blast pathogen Magnaporthe oryzae (Yang et al., 2008; Qin et al., 2013). Moreover, recently, the production of GA by G. fujikuroi has also been reported to play a role in the virulence of this rice plant pathogen (Wiemann et al., 2013). "
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    ABSTRACT: Both plants and fungi produce ent-kaurene as a precursor to the gibberellin plant hormones. A number of rhizobia contain functionally conserved, sequentially acting ent-copalyl diphosphate and ent-kaurene synthases (CPS and KS, respectively), which are found within a well-conserved operon that may lead to the production of gibberellins.Intriguingly, the rice bacterial leaf streak pathogen Xanthomonas oryzae pv. oryzicola (Xoc) contains a homologous operon. Here, we report biochemical characterization of the encoded CPS and KS, and the impact of insertional mutagenesis on virulence and the plant defense response for these genes, as well as that for one of the cytochromes P450 (CYP112) found in the operon.Activity of the CPS and KS found in this phytopathogen was verified – that is, Xoc is capable of producing ent-kaurene. Moreover, knocking out CPS, KS or CYP112 led to mutant Xoc that exhibited reduced virulence. Investigation of the effect on marker gene transcript levels suggests that the Xoc diterpenoid affects the plant defense response, most directly that mediated by jasmonic acid (JA).Xoc produces an ent-kaurene-derived diterpenoid as a virulence factor, potentially a gibberellin phytohormone, which is antagonistic to JA, consistent with the recent recognition of opposing effects for these phytohormones on the microbial defense response.
    New Phytologist 11/2014; 206(1). DOI:10.1111/nph.13187 · 7.67 Impact Factor
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    • "Although the molecular mechanisms underlying the early steps of rice-Xoo interactions are poorly resolved, recent transcriptome analyses and combined metabolite and hormone profiling increasingly implicate a coordinated range of hormone pathways. For instance, in resistant rice responding to virulent Xoo, both JA and ET signaling were found to be strongly activated within one hour after pathogen attack [66], whereas suppression of auxin and GA signaling seems to occur significantly later, i.e. between 12 hpi and 3 dpi [56], [67]. Together with our results, these data therefore suggest that temporally separated transient hormone changes play an important role in configuring the plant’s response to Xoo attack, with both host and pathogen trying to sequentially engage distinct hormone pathways in defined temporal windows. "
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    ABSTRACT: The plant hormone abscisic acid (ABA) is involved in a wide variety of plant processes, including the initiation of stress-adaptive responses to various environmental cues. Recently, ABA also emerged as a central factor in the regulation and integration of plant immune responses, although little is known about the underlying mechanisms. Aiming to advance our understanding of ABA-modulated disease resistance, we have analyzed the impact, dynamics and interrelationship of ABA and the classic defense hormone salicylic acid (SA) during progression of rice infection by the leaf blight pathogen Xanthomonas oryzae pv. oryzae (Xoo). Consistent with ABA negatively regulating resistance to Xoo, we found that exogenously administered ABA renders rice hypersusceptible to infection, whereas chemical and genetic disruption of ABA biosynthesis and signaling, respectively, led to enhanced Xoo resistance. In addition, we found successful Xoo infection to be associated with extensive reprogramming of ABA biosynthesis and response genes, suggesting that ABA functions as a virulence factor for Xoo. Interestingly, several lines of evidence indicate that this immune-suppressive effect of ABA is due at least in part to suppression of SA-mediated defenses that normally serve to limit pathogen growth. Resistance induced by the ABA biosynthesis inhibitor fluridone, however, appears to operate in a SA-independent manner and is likely due to induction of non-specific physiological stress. Collectively, our findings favor a scenario whereby virulent Xoo hijacks the rice ABA machinery to cause disease and highlight the importance of ABA and its crosstalk with SA in shaping the outcome of rice-Xoo interactions.
    PLoS ONE 07/2013; 8(6):e67413. DOI:10.1371/journal.pone.0067413 · 3.23 Impact Factor
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    • "Interestingly, both SA and JA were elevated in the hpl3 mutant, which consequently showed enhanced disease resistance to Xoo (Tong et al., 2012). Consistently with previous reports (Mei et al., 2006; Yang et al., 2008), these studies indicate that both SA and JA are involved in rice immunity to fungal and bacterial pathogens. However, the synchronous activation of the SA and JA signaling pathways is likely rare in the Arabidopsis (Devadas and Raina, 2002). "
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    ABSTRACT: Plant hormones have been extensively studied for their importance in innate immunity particularly in the dicotyledonous model plant Arabidopsis thaliana. However, only in the last decade plant hormones were demonstrated to play conserved and divergent roles in fine-tuning immune in rice (Oryza sativa L.), a monocotyledonous model crop plant. Emerging evidences showed that salicylic acid (SA) play a role in rice basal defense but is differentially required by rice pattern recognition receptor (PRR) and resistance (R) protein-mediated immunity, and its function is likely dependent on the signaling pathway rather than the change of endogenous levels. Jasmonate (JA) plays an important role in rice basal defense against bacterial and fungal infection and may be involved in the SA-mediated resistance. Ethylene (ET) can act as a positive or negative modulator of disease resistance, depending on the pathogen type and environmental conditions. Brassinosteroid (BR) signaling and abscisic acid (ABA) either promote or defend against infection of pathogens with distinct infection/colonization strategies. Auxin and gibberellin (GA) are generally thought as negative regulators of innate immunity in rice. Moreover, GA interacts antagonistically with JA signaling in rice development and immunity through the DELLA protein as a master regulator of the two hormone pathways. In this review, we summarize the roles of plant hormones in rice immunity and discuss their interplays/cross-talk mechanisms and the complex regulatory network of plant hormone pathways in fine-tuning rice immunity and growth.
    Molecular Plant 04/2013; DOI:10.1093/mp/sst056 · 6.34 Impact Factor
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