The well-known ciliate, Mesodinium Stein, 1863, is of great importance to marine microbial food webs and is related to the ＂red tides＂. However, it is possibly one of the most confusing ciliate taxa in terms of its ...The well-known ciliate, Mesodinium Stein, 1863, is of great importance to marine microbial food webs and is related to the ＂red tides＂. However, it is possibly one of the most confusing ciliate taxa in terms of its systematic position： either the morphological or the molecular data excluded it from all the other known assemblages or groups. In the current work, the sequences of small subunit ribosomal RNA （SSU rRNA） genes for all isolates available are analysed and an examination of the secondary structure patterns of related groups is carried out. The results indicate that （1） Mesodiniurn invariably represents a completely separated and isolated clade positioned between two subphyla of ciliates with very deep branching, which indicates that they should be a primitive or ancestral group for the subphylum Intramacronucleata; （2） the secondary structure of the SSU rRNA of Mesodinium species is unusual in that, while the secondary structure of V4 in Mesodinium sp. has the deletions common to all litostome ciliates, it has more extensive deletions in helix E23_8 and a longer helix E23_1; （3） combining the phylogenetic and morphological information, we suggest establishing Mesodiniea el. nov., including the order Mesodiniida Grain, 1994, belonging to the subphylum Intramacronucleata.展开更多
The biotrophic fungus Ustilago maydis causes corn smut disease, inducing tumor formation in its host Zea mays. Upon infection, the fungal hyphae invaginate the plasma membrane of infected maize ceils, establishing an ...The biotrophic fungus Ustilago maydis causes corn smut disease, inducing tumor formation in its host Zea mays. Upon infection, the fungal hyphae invaginate the plasma membrane of infected maize ceils, establishing an interface where pathogen and host are separated only by their plasma membranes. At this interface the fungal and maize sucrose transporters, UmSrtl and ZmSUT1, compete for extracellular sucrose in the corn smut/maize pathos- ystem. Here we biophysically characterized ZmSUT1 and UmSrtl in Xenopus oocytes with respect to their voltage-, pH- and substrate-dependence and determined affinities toward protons and sucrose. In contrast to ZmSUT% UmSrtl has a high affinity for sucrose and is relatively pH- and voltage-independent. Using these quantitative parameters, we developed a mathematical model to simulate the competition for extracellular sucrose at the contact zone between the fungus and the host plant. This approach revealed that UmSrtl exploits the apoplastic sucrose resource, which forces the plant transporter into a sucrose export mode providing the fungus with sugar from the phloem. Importantly, the high sucrose concen- tration in the phloem appeared disadvantageous for the ZmSUT1 preventing sucrose recovery from the apoplastic space in the fungus/plant interface.展开更多
Dear Editor, The plant hormone abscisic acid （ABA） governs drought stress management in plants. ABA signal transduction appears to be rather short. When under water stress con- ditions, the ABA level rises above a ...Dear Editor, The plant hormone abscisic acid （ABA） governs drought stress management in plants. ABA signal transduction appears to be rather short. When under water stress con- ditions, the ABA level rises above a certain threshold and the phytohormone binds to its cytosolic RCAR/PYR/PYL-type receptor （Levchenko et al,, 2005; Joshi-Saha et al., 2011）. Following receptor activation, protein phosphatases of the clade-A PP2C type are inactivated, allowing SnRK protein kinases to phosphorylate their targets, such as bZIP tran- scription factors （Fujii et al., 2009 and references therein）. In guard cells and oocytes, we could demonstrate that the same SnRK-PP2C pair OST1-ABI1 controls the opening of the slow anion channel SLACl （Geiger et al., 2009; Lee et al., 2009）. Besides this calcium-independent activation, SLAC1 is also activated by the calcium-dependent kinases CPK21 and 23, which can be inhibited by ABI1 （Geiger et al., 2010）.展开更多
Dear Editor, It has been known since the work of Francis Darwin that, in response to a reduction in atmospheric relative humidity （rh）, stomatal aperture decreases. Screening for Arabidopsis mutants compromised in ...Dear Editor, It has been known since the work of Francis Darwin that, in response to a reduction in atmospheric relative humidity （rh）, stomatal aperture decreases. Screening for Arabidopsis mutants compromised in stomatal responses to reduced rh resulted in the identification of two genes, OST1 and ABA2, that are involved in stomatal response to low rh conditions. Interestingly both encode proteins previously known to be involved in ABA signaling （Xie et al., 2006, and references therein）. These findings strongly suggested that, at least in part, the stomatal response to low rh is mediated by ABA and the intracellular ABA signaling pathway. Our most recent data show that low rh-induced stomatal closure can pro- ceed by guard cell autonomous ABA synthesis （Bauer et al., 2013）,展开更多
基金supported by the National Natural Science Foundation of China(31272285,41276139)King Saud University Deanship of Scientific Research(Research Group Project No.RGP-083)Special Foundation B of President of the Chinese Academy of Sciences(Y25102EN00)
文摘The well-known ciliate, Mesodinium Stein, 1863, is of great importance to marine microbial food webs and is related to the ＂red tides＂. However, it is possibly one of the most confusing ciliate taxa in terms of its systematic position： either the morphological or the molecular data excluded it from all the other known assemblages or groups. In the current work, the sequences of small subunit ribosomal RNA （SSU rRNA） genes for all isolates available are analysed and an examination of the secondary structure patterns of related groups is carried out. The results indicate that （1） Mesodiniurn invariably represents a completely separated and isolated clade positioned between two subphyla of ciliates with very deep branching, which indicates that they should be a primitive or ancestral group for the subphylum Intramacronucleata; （2） the secondary structure of the SSU rRNA of Mesodinium species is unusual in that, while the secondary structure of V4 in Mesodinium sp. has the deletions common to all litostome ciliates, it has more extensive deletions in helix E23_8 and a longer helix E23_1; （3） combining the phylogenetic and morphological information, we suggest establishing Mesodiniea el. nov., including the order Mesodiniida Grain, 1994, belonging to the subphylum Intramacronucleata.
基金supported by the Deutsche Forschungsgemeinschaft (DFG) within the Grant GE2195/1-1supported by grants from the King Saud Universitysupported by the FONDECYT grant N 1150054 from the Comisión Nacional Científicay Tecnológica of Chile
文摘The biotrophic fungus Ustilago maydis causes corn smut disease, inducing tumor formation in its host Zea mays. Upon infection, the fungal hyphae invaginate the plasma membrane of infected maize ceils, establishing an interface where pathogen and host are separated only by their plasma membranes. At this interface the fungal and maize sucrose transporters, UmSrtl and ZmSUT1, compete for extracellular sucrose in the corn smut/maize pathos- ystem. Here we biophysically characterized ZmSUT1 and UmSrtl in Xenopus oocytes with respect to their voltage-, pH- and substrate-dependence and determined affinities toward protons and sucrose. In contrast to ZmSUT% UmSrtl has a high affinity for sucrose and is relatively pH- and voltage-independent. Using these quantitative parameters, we developed a mathematical model to simulate the competition for extracellular sucrose at the contact zone between the fungus and the host plant. This approach revealed that UmSrtl exploits the apoplastic sucrose resource, which forces the plant transporter into a sucrose export mode providing the fungus with sugar from the phloem. Importantly, the high sucrose concen- tration in the phloem appeared disadvantageous for the ZmSUT1 preventing sucrose recovery from the apoplastic space in the fungus/plant interface.
文摘Dear Editor, The plant hormone abscisic acid （ABA） governs drought stress management in plants. ABA signal transduction appears to be rather short. When under water stress con- ditions, the ABA level rises above a certain threshold and the phytohormone binds to its cytosolic RCAR/PYR/PYL-type receptor （Levchenko et al,, 2005; Joshi-Saha et al., 2011）. Following receptor activation, protein phosphatases of the clade-A PP2C type are inactivated, allowing SnRK protein kinases to phosphorylate their targets, such as bZIP tran- scription factors （Fujii et al., 2009 and references therein）. In guard cells and oocytes, we could demonstrate that the same SnRK-PP2C pair OST1-ABI1 controls the opening of the slow anion channel SLACl （Geiger et al., 2009; Lee et al., 2009）. Besides this calcium-independent activation, SLAC1 is also activated by the calcium-dependent kinases CPK21 and 23, which can be inhibited by ABI1 （Geiger et al., 2010）.
文摘Dear Editor, It has been known since the work of Francis Darwin that, in response to a reduction in atmospheric relative humidity （rh）, stomatal aperture decreases. Screening for Arabidopsis mutants compromised in stomatal responses to reduced rh resulted in the identification of two genes, OST1 and ABA2, that are involved in stomatal response to low rh conditions. Interestingly both encode proteins previously known to be involved in ABA signaling （Xie et al., 2006, and references therein）. These findings strongly suggested that, at least in part, the stomatal response to low rh is mediated by ABA and the intracellular ABA signaling pathway. Our most recent data show that low rh-induced stomatal closure can pro- ceed by guard cell autonomous ABA synthesis （Bauer et al., 2013）,
