The rice pattern recognition receptor （PRR） XA21 confers race-specific resistance in leaf infection by bacterial blight Xathornonas oryzae pv. oryzae （Xoo）, and was shown to be primarily localized to the endoplasm...The rice pattern recognition receptor （PRR） XA21 confers race-specific resistance in leaf infection by bacterial blight Xathornonas oryzae pv. oryzae （Xoo）, and was shown to be primarily localized to the endoplasmic reticulum （ER） when expressed with its native promoter or overexpressed in the protoplast. However, whether the protein is still ER- localization in the intact cell when overexpressed remains to be identified. Here, we showed that XA21, its kinase-dead mutant XA21PK736EP and the triple autophosphorylation mutant XA21PS686AJT688AJS699A GFP fusions were primarily localized to the plasma membrane （PM） when overexpressed in the intact transgenic rice cell, and also localized to the ER in the transgenic protoplast. The transgenic plants constitutively expressing the wild-type XA21 or its GFP fusion displayed racespecific resistance to Xoo at the adult and seedling stages. XA21 and XA21PK736EP could be internalized probably via the SCAMP-positive early endosomal compartment in the protoplast, suggesting that XA21 might be endocytosed to initiate resistance responses during pathogen infection. We also established a root infection system and demonstrated that XA21 also mediated race-specific resistance responses to Xoo in the root. Our current study provides an insight into the nature of the XA21-mediated resistance and a practical approach using the root cell system to further dissect the cellular signaling of the PRR during the rice-Xoo interaction.展开更多
Camalexin （3-thiazol-2＇-yl-indole） is the major phytoalexin found in Arabidopsis thaliana. Several key intermediates and corresponding enzymes have been identified in camalexin biosynthesis through mutant screening...Camalexin （3-thiazol-2＇-yl-indole） is the major phytoalexin found in Arabidopsis thaliana. Several key intermediates and corresponding enzymes have been identified in camalexin biosynthesis through mutant screening and biochemical experiments. Camalexin is formed when indole-3-acetonitrile （IAN） is catalyzed by the cytochrome P450 monooxygenase CYP71A13. Here, we demonstrate that the Ara- bidopsis GH3.5 protein, a multifunctional acetyl-amido synthetase, is involved in camalexin biosynthesis via conjugating indole-3-carboxylic acid （ICA） and cysteine （Cys） and regulating camalexin biosynthesis genes. Camalexin levels were increased in the activation-tagged mutant gh3.5-1D in both Col-0 and cyp71A13-2 mutant backgrounds after pathogen infection. The recombinant GH3.5 protein catalyzed the conjugation of ICA and Cys to form a possible intermediate indole-3-acyl-cysteinate （ICA（Cys）） in vitro. In support of the in vitro reaction, feeding with ICA and Cys increased camalexin levels in Col-0 and gh3.5-1D. Dihydrocamalexic acid （DHCA）, the precursor of camalexin and the substrate for PAD3, was accumulated in gh3.5-1DIpad3-1, suggesting that ICA（Cys） could be an additional precursor of DHCA for camalexin biosynthesis. Furthermore, expression of the major camalexin biosynthesis genes CYP79B2, CYP71A12, CYP71A13 and PAD3 was strongly induced in gh3.5-1D. Our study suggests that GH3.5 is involved in camalexin biosynthesis through direct catalyzation of the formation of ICA（Cys）, and upregulation of the major biosynthetic pathway genes.展开更多
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 ...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 （Eu~ 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 GA3 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 GA3 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 OsGA2Oox2 and OsGA20xl were down-regulated during pathogen challenge. We also found that PRla 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.展开更多
文摘The rice pattern recognition receptor （PRR） XA21 confers race-specific resistance in leaf infection by bacterial blight Xathornonas oryzae pv. oryzae （Xoo）, and was shown to be primarily localized to the endoplasmic reticulum （ER） when expressed with its native promoter or overexpressed in the protoplast. However, whether the protein is still ER- localization in the intact cell when overexpressed remains to be identified. Here, we showed that XA21, its kinase-dead mutant XA21PK736EP and the triple autophosphorylation mutant XA21PS686AJT688AJS699A GFP fusions were primarily localized to the plasma membrane （PM） when overexpressed in the intact transgenic rice cell, and also localized to the ER in the transgenic protoplast. The transgenic plants constitutively expressing the wild-type XA21 or its GFP fusion displayed racespecific resistance to Xoo at the adult and seedling stages. XA21 and XA21PK736EP could be internalized probably via the SCAMP-positive early endosomal compartment in the protoplast, suggesting that XA21 might be endocytosed to initiate resistance responses during pathogen infection. We also established a root infection system and demonstrated that XA21 also mediated race-specific resistance responses to Xoo in the root. Our current study provides an insight into the nature of the XA21-mediated resistance and a practical approach using the root cell system to further dissect the cellular signaling of the PRR during the rice-Xoo interaction.
基金supported by grants from the Ministry of Science and Technology of China (2011CB100700 and 2007AA10Z107)from the CAS International Partnership Program for Creative Research Teams
文摘Camalexin （3-thiazol-2＇-yl-indole） is the major phytoalexin found in Arabidopsis thaliana. Several key intermediates and corresponding enzymes have been identified in camalexin biosynthesis through mutant screening and biochemical experiments. Camalexin is formed when indole-3-acetonitrile （IAN） is catalyzed by the cytochrome P450 monooxygenase CYP71A13. Here, we demonstrate that the Ara- bidopsis GH3.5 protein, a multifunctional acetyl-amido synthetase, is involved in camalexin biosynthesis via conjugating indole-3-carboxylic acid （ICA） and cysteine （Cys） and regulating camalexin biosynthesis genes. Camalexin levels were increased in the activation-tagged mutant gh3.5-1D in both Col-0 and cyp71A13-2 mutant backgrounds after pathogen infection. The recombinant GH3.5 protein catalyzed the conjugation of ICA and Cys to form a possible intermediate indole-3-acyl-cysteinate （ICA（Cys）） in vitro. In support of the in vitro reaction, feeding with ICA and Cys increased camalexin levels in Col-0 and gh3.5-1D. Dihydrocamalexic acid （DHCA）, the precursor of camalexin and the substrate for PAD3, was accumulated in gh3.5-1DIpad3-1, suggesting that ICA（Cys） could be an additional precursor of DHCA for camalexin biosynthesis. Furthermore, expression of the major camalexin biosynthesis genes CYP79B2, CYP71A12, CYP71A13 and PAD3 was strongly induced in gh3.5-1D. Our study suggests that GH3.5 is involved in camalexin biosynthesis through direct catalyzation of the formation of ICA（Cys）, and upregulation of the major biosynthetic pathway genes.
文摘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 （Eu~ 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 GA3 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 GA3 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 OsGA2Oox2 and OsGA20xl were down-regulated during pathogen challenge. We also found that PRla 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.
