不结球白菜BcLRK01基因对芜菁花叶病毒及胁迫诱导的响应

通过cDNA-AFLP技术,从芜菁花叶病毒(TuMV)侵染的不结球白菜幼叶中分离到一条差异表达的基因片段,克隆获得其cDNA全长为2 124bp,编码707个氨基酸的富亮氨酸重复类受体激酶,命名为BcLRK01。利用实时定量PCR研究了该基因在TuMV侵染及高盐、冷胁迫、水杨酸(SA)、茉莉酸(JA)、乙烯(ET)等处理下的表达情况,结果显示,TuMV侵染、高盐、冷胁迫、SA、JA和ET等均能诱导BcLRK01不同程度的表达,说明该基因可能是不结球白菜病毒病的病程相关基因,同时也参与高盐和冷胁迫以及SA、JA、ET等的信号途径。     

Ozone-induced expression of the Arabidopsis FAD7 gene requires salicylic acid, but not NPR1 and SID2

The Arabidopsis FAD7 gene encodes a plastid omega-3 fatty acid desaturase that catalyzes the desaturation of dienoic fatty acids to trienoic fatty acids in chloroplast membrane lipids. The expression of FAD7 was rapidly and locally induced by ozone exposure, which causes oxidative responses equivalent to pathogen-induced hypersensitive responses and subsequently activates various defense-related genes. This induction was reduced in salicylic acid (SA)-deficient NahG plants expressing SA hydroxylase, but was unaffected in etr1 and jar1 mutants, which are insensitive to ethylene and jasmonic acid (JA), respectively. The SA dependence of the FAD7 induction was confirmed by the exogenous application of SA. SA-induced expression of FAD7 in the npr1 mutant which is defective in an SA signaling pathway occurred to the same extent as in the wild type. Furthermore, in the sid2 mutant which lacks an enzyme required for SA biosynthesis, the expression of FAD7 was induced by ozone exposure. These results suggest that the ozone-induced expression of FAD7 gene requires SA, but not ethylene, JA, NPR1 and SID2.     

The plant growth-promoting fungus Penicillium simplicissimum GP17-2 induces resistance in Arabidopsis thaliana by activation of multiple defense signals

Arabidopsis thaliana grown in soil amended with barley grain inocula of Penicillium simplicissimum GP17-2 or receiving root treatment with its culture filtrate (CF) exhibited clear resistance to Pseudomonas syringae pv. tomato DC3000 (Pst). To assess the contribution of different defense pathways, Arabidopsis genotypes implicated in salicylic acid (SA) signaling expressing the NahG transgene or carrying disruption in NPR1 (npr1), jasmonic acid (JA) signaling (jar1) and ethylene (ET) signaling (ein2) were tested. All genotypes screened were protected by GP17-2 or its CF. However, the level of protection was significantly lower in NahG and npr1 plants than it was in similarly treated wild-type plants, indicating that the SA signaling pathway makes a minor contribution to the GP17-2-mediated resistance and is insufficient for a full response. Examination of local and systemic gene expression revealed that GP17-2 and its CF modulate the expression of genes involved in both the SA and JA/ET signaling pathways. Subsequent challenge of GP17-2-colonized plants with Pst was accompanied by direct activation of SA-inducible PR-2 and PR-5 genes as well as potentiated expression of the JA-inducible Vsp gene. In contrast, CF-treated plants infected with Pst exhibited elevated expression of most defense-related genes (PR-1, PR-2, PR-5, PDF1.2 and Hel) studied. Moreover, an initial elevation of SA responses was followed by late induction of JA responses during Pst infection of induced systemic resistance (ISR)-expressing plants. In conclusion, we hypothesize the involvement of multiple defense mechanisms leading to an ISR of Arabidopsis by GP17-2.     

Gene-Expression Patterns and Levels of Jasmonic Acid in Rice Treated with the Resistance Inducer 2,6-Dichloroisonicotinic Acid

Acquired disease resistance can be induced in rice (Oryza sativa) by a number of synthetic or natural compounds, but the molecular mechanisms behind the phenomenon are poorly understood. One of the synthetic inducers of resistance, 2,6-dichloroisonicotinic acid (INA), efficiently protected rice leaves from infection by the rice blast fungus Magnaporthe grisea (Hebert) Barr. A comparison of gene-expression patterns in plants treated with INA versus plants inoculated with the compatible pathogen M. grisea or the incompatible pathogen Pseudomonas syringae pv syringae revealed only a marginal overlap: 6 gene products, including pathogenesis-related proteins (PR1-PR9), accumulated in both INA-treated and pathogen-attacked leaves, whereas 26 other gene products accumulated only in INA-treated or only in pathogen-attacked leaves. Lipoxygenase enzyme activity and levels of nonconjugated jasmonic acid (JA) were enhanced in leaves of plants treated with a high dose of INA (100 ppm). Exogenously applied JA enhanced the gene induction and plant protection caused by lower doses of INA (0.1 to 10 ppm) that by themselves did not give rise to enhanced levels of endogenous (-)-JA. These data suggest that INA, aside from activating a pathogen-induced signaling pathway, also induces events that are not related to pathogenesis. JA acts as an enhancer of both types of INA-induced reactions in rice.     

Disease resistance against Magnaporthe grisea is enhanced in transgenic rice with suppression of omega-3 fatty acid desaturases

Linolenic acid (18:3) is the most abundant fatty acid in plant membrane lipids and is a source for various oxidized metabolites, called oxylipins. 18:3 and oxylipins play important roles in the induction of defense responses to pathogen infection and wound stress in Arabidopsis. However, in rice, endogenous roles for 18:3 and oxylipins in disease resistance have not been confirmed. We generated 18:3-deficient transgenic rice plants (F78Ri) with co-suppression of two omega-3 fatty acid desaturases, OsFAD7 and OsFAD8. that synthesize 18:3. The F78Ri plants showed enhanced resistance to the phytopathogenic fungus Magnaporthe grisea. A typical 18:3-derived oxylipin, jasmonic acid (JA), acts as a signaling molecule in defense responses to fungal infection in Arabidopsis. However, in F78Ri plants, the expression of JA-responsive pathogenesis-related genes, PBZ1 and PR1b, was induced after inoculation with M. grisea, although the JA-mediated wound response was suppressed. Furthermore, the application of JA methyl ester had no significant effect on the enhanced resistance in F78Ri plants. Taken together, our results indicate that, although suppression of fatty acid desaturases involves the concerted action of varied oxylipins via diverse metabolic pathways, 18:3 or 18:3-derived oxylipins, except for JA, may contribute to signaling on defense responses of rice to M. grisea infection.     

BWMK1 Responds to Multiple Environmental Stresses and Plant Hormones

Many plant mltogen-actlvated protein klnases （MAPKs） play an important role In regulating responses to both ablotlc and biotic stresses. The first reported rice MAPK gene BWMK1 Is Induced by both rice blast （Magnaporthe grisea） Infection and mechanical wounding. For further analysis of Its response to other environmental cues and plant hormones, such as jasmonlc acid （JA）, salicylic acid （SA）, and benzothladlazole （BTH）, the promoter of BWMKf was fused with the coding region of the β-glucuronldase （GUS） reporter gene. Two promoter-GUS constructs with a 1.0- and 2.5-kb promoter fragment, respectively, were generated and transformed into the Japonica rice cultIvars TP309 and Zhonghua 11. Expression of GUS was Induced in the transgenic lines by cold, drought, dark, and JA. However, light, SA, and BTH treatments suppressed GUS expression. These results demonstrate that BWMK1 Is responsive to multiple ablotlc stresses and plant hormones and may play a role In cross-talk between different signaling pathways.     

Molecular cloning and mRNA expression analysis of a novel rice (Oryzasativa L.) MAPK kinase kinase,OsEDR1, an ortholog of Arabidopsis AtEDR1, reveal its role in defense/stress signalling pathways and development

Mitogen-activated protein kinase (MAPK) cascade(s) is important for plant defense/stress responses. Though MAPKs have been identified and characterized in rice (Oryza sativa L.), a monocot cereal crop research model, the first upstream component of the kinase cascade, namely MAPK kinase kinase (MAPKKK) has not yet been identified. Here we report the cloning of a novel rice gene encoding a MAPKKK, OsEDR1, designated based on its homology with the Arabidopsis MAPKKK, AtEDR1. OsEDR1, a single copy gene in the genome of rice, encodes a predicted protein with molecular mass of 113046.13 and a pI of 9.03. Using our established two-week-old rice seedling in vitro model system, we show that OsEDR1 has a constitutive expression in seedling leaves and is further up-regulated within 15 min upon wounding by cut, treatment with the global signals jasmonic acid (JA), salicylic acid (SA), ethylene (ethephon, ET), abscisic acid, and hydrogen peroxide. In addition, protein phosphatase inhibitors, fungal elicitor chitosan, drought, high salt and sugar, and heavy metals also dramatically induce its expression. Moreover, OsEDR1 expression was altered by co-application of JA, SA, and ET, and required de novo synthesized protein factor(s) in its transient regulation. Furthermore, using an in vivo system we also show that OsEDR1 responds to changes in temperature and environmental pollutants-ozone and sulfur dioxide. Finally, OsEDR1 expression varied significantly in vegetative and reproductive tissues. These results suggest a role for OsEDR1 in defense/stress signalling pathways and development.