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Journal Cover Plant Molecular Biology
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1573-5028 - ISSN (Online) 0167-4412
     Published by Springer-Verlag Homepage  [2210 journals]   [SJR: 1.769]   [H-I: 112]
  • Identification and characterization of CYP79D16 and CYP71AN24 catalyzing
           the first and second steps in        type-small-caps">l-phenylalanine-derived cyanogenic
           glycoside biosynthesis in the Japanese apricot,        class="a-plus-plus">Prunus mume Sieb. et Zucc.
    • Abstract: Japanese apricot, Prunus mume Sieb. et Zucc., belonging to the Rosaceae family, produces as defensive agents the cyanogenic glycosides prunasin and amygdalin, which are presumably derived from l-phenylalanine. In this study, we identified and characterized cytochrome P450s catalyzing the conversion of l-phenylalanine into mandelonitrile via phenylacetaldoxime. Full-length cDNAs encoding CYP79D16, CYP79A68, CYP71AN24, CYP71AP13, CYP71AU50, and CYP736A117 were cloned from P. mume ‘Nanko’ using publicly available P. mume RNA-sequencing data, followed by 5′- and 3′-RACE. CYP79D16 was expressed in seedlings, whereas CYP71AN24 was expressed in seedlings and leaves. Enzyme activity of these cytochrome P450s expressed in Saccharomyces cerevisiae was evaluated by liquid and gas chromatography–mass spectrometry. CYP79D16, but not CYP79A68, catalyzed the conversion of l-phenylalanine into phenylacetaldoxime. CYP79D16 showed no activity toward other amino acids. CYP71AN24, but not CYP71AP13, CYP71AU50, and CYP736A117, catalyzed the conversion of phenylacetaldoxime into mandelonitrile. CYP71AN24 also showed lower conversions of various aromatic aldoximes and nitriles. The K m value and turnover rate of CYP71AN24 for phenylacetaldoxime were 3.9 µM and 46.3 min−1, respectively. The K m value and turnover of CYP71AN24 may cause the efficient metabolism of phenylacetaldoxime, avoiding the release of the toxic intermediate to the cytosol. These results suggest that cyanogenic glycoside biosynthesis in P. mume is regulated in concert with catalysis by CYP79D16 in the parental and sequential reaction of CYP71AN24 in the seedling.
      PubDate: 2014-09-01
       
  • Generation mechanism of novel, huge protein bodies containing wild type or
           hypoallergenic derivatives of birch pollen allergen Bet v 1 in rice
           endosperm
    • Abstract: Tree pollen chimera 7 (TPC7), a hypoallergenic Bet v 1 tolerogen against birch pollen allergy, induces the formation of novel, huge protein bodies (referred to as TPC7 bodies) in rice endosperm, and is accumulated in high level. In the present study, we found that native Bet v 1 and TPC9, analog proteins of TPC7, were also deposited into novel protein bodies in rice endosperm. However, the novel protein bodies in Bet v 1 and TPC9 rice were much smaller and less abundant than those in TPC7 rice, reflected in lower amounts of accumulation of Bet v 1 and TPC9 than that of TPC7. A domain swapping experiment between TPC7 and Bet v 1 revealed that the latter half of TPC7 is important for the formation of the TPC7 body. We found that chaperons and folding enzymes such as BiP and protein disulfide isomerase were localized within the TPC7 body. TPC7 protein was extracted from TPC7 seeds as large aggregates with molecular masses greater than 669 kDa, or approximately 75 kDa under native or semi-native conditions. These TPC7 aggregates are thought to be responsible for the induction of TPC7 body formation. TPC7 accumulated to a maximum level of 550 μg/seed, which amounts to 23 % of total seed protein, while Bet v 1 and TPC9 accumulated much lower levels. The TPC7 body represents a promising reservoir, which may serve as a fusion partner for high-level production and sequestering storage of recombinant proteins.
      PubDate: 2014-09-01
       
  • A viable Arabidopsis
           pex13
    missense allele confers severe peroxisomal defects and
           decreases PEX5 association with peroxisomes
    • Abstract: Peroxisomes are organelles that catabolize fatty acids and compartmentalize other oxidative metabolic processes in eukaryotes. Using a forward-genetic screen designed to recover severe peroxisome-defective mutants, we isolated a viable allele of the peroxisome biogenesis gene PEX13 with striking peroxisomal defects. The pex13-4 mutant requires an exogenous source of fixed carbon for pre-photosynthetic development and is resistant to the protoauxin indole-3-butyric acid. Delivery of peroxisome-targeted matrix proteins depends on the PEX5 receptor docking with PEX13 at the peroxisomal membrane, and we found severely reduced import of matrix proteins and less organelle-associated PEX5 in pex13-4 seedlings. Moreover, pex13-4 physiological and molecular defects were partially ameliorated when PEX5 was overexpressed, suggesting that PEX5 docking is partially compromised in this mutant and can be improved by increasing PEX5 levels. Because previously described Arabidopsis pex13 alleles either are lethal or confer only subtle defects, the pex13-4 mutant provides valuable insight into plant peroxisome receptor docking and matrix protein import.
      PubDate: 2014-09-01
       
  • Chromate alters root system architecture and activates expression of genes
           involved in iron homeostasis and signaling in        class="a-plus-plus">Arabidopsis thaliana
    • Abstract: Soil contamination by hexavalent chromium [Cr(VI) or chromate] due to anthropogenic activities has become an increasingly important environmental problem. To date few studies have been performed to elucidate the signaling networks involved on adaptive responses to (CrVI) toxicity in plants. In this work, we report that depending upon its concentration, Cr(VI) alters in different ways the architecture of the root system in Arabidopsis thaliana seedlings. Low concentrations of Cr (20–40 µM) promoted primary root growth, while concentrations higher than 60 µM Cr repressed growth and increased formation of root hairs, lateral root primordia and adventitious roots. We analyzed global gene expression changes in seedlings grown in media supplied with 20 or 140 µM Cr. The level of 731 transcripts was significantly modified in response to Cr treatment with only five genes common to both Cr concentrations. Interestingly, 23 genes related to iron (Fe) acquisition were up-regulated including IRT1, YSL2, FRO5, BHLH100, BHLH101 and BHLH039 and the master controllers of Fe deficiency responses PYE and BTS were specifically activated in pericycle cells. It was also found that increasing concentration of Cr in the plant correlated with a decrease in Fe content, but increased both acidification of the rhizosphere and activity of the ferric chelate reductase. Supply of Fe to Cr-treated Arabidopsis allowed primary root to resume growth and alleviated toxicity symptoms, indicating that Fe nutrition is a major target of Cr stress in plants. Our results show that low Cr levels are beneficial to plants and that toxic Cr concentrations activate a low-Fe rescue system.
      PubDate: 2014-09-01
       
  • OsJAR1 is required for
           JA-regulated floret opening and anther dehiscence in rice
    • Abstract: Jasmonates are important phytohormones regulating reproductive development. We used two recessive rice Tos17 alleles of OsJAR1, osjar1-2 and osjar1-3, to study the biological function of jasmonates in rice anthesis. The florets of both osjar1 alleles stayed open during anthesis because the lodicules, which control flower opening in rice, were not withering on time. Furthermore, dehiscence of the anthers filled with viable pollen, was impaired, resulting in lower fertility. In situ hybridization and promoter GUS transgenic analysis confirmed OsJAR1 expression in these floral tissues. Flower opening induced by exogenous applied methyl jasmonate was impaired in osjar1 plants and was restored in a complementation experiment with transgenics expressing a wild type copy of OsJAR1 controlled by a rice actin promoter. Biochemical analysis showed that OsJAR1 encoded an enzyme conjugating jasmonic acid (JA) to at least Ile, Leu, Met, Phe, Trp and Val and both osjar1 alleles had substantial reduction in content of JA-Ile, JA-Leu and JA-Val in florets. We conclude that OsJAR1 is a JA-amino acid synthetase that is required for optimal flower opening and closing and anther dehiscence in rice.
      PubDate: 2014-09-01
       
  • Comparison of the physiological effects and transcriptome responses of
           Populus simonii under
           different abiotic stresses
    • Abstract: In the field, perennial plants such as poplar (Populus spp.) must adapt to simultaneous exposure to various abiotic stresses, which can affect their growth and survival. However, the mechanisms for stress-specific adaption in response to different abiotic stresses remain unclear. Thus, understanding the unique acclimation process for each abiotic treatment will require a comprehensive and systematic comparison of the responses of poplar to different abiotic stresses. To compare the responses to multiple stresses, we compared physiological effects and transcriptome changes in poplar under four abiotic stresses (salinity, osmotic, heat and cold). Photosynthesis and antioxidant enzymes changed significantly after 6 h abiotic stress treatment. Therefore, using 6 h abiotic stress treatment groups for transcriptome analysis, we identified a set of 863 differentially expressed genes (653 up-regulated and 210 down-regulated) common to osmotic, salinity, heat and cold treatment. We also identified genes specific to osmotic (1,739), salinity (1,222), cold (2,508) and heat (3,200), revealing that salinity stress has the fewest differently-expressed genes. After gene annotation, we found differences in expression of genes related to electron transport, stomatal control, antioxidant enzymes, cell wall alteration, and phytohormone biosynthesis and signaling in response to various abiotic stresses. This study provides new insights to improve our understanding of the mechanisms by which poplar adapts under different abiotic stress conditions and provides new clues for further studies.
      PubDate: 2014-09-01
       
  • Major alterations in transcript profiles between C       class="a-plus-plus">3–C       class="a-plus-plus">4 and C       class="a-plus-plus">4 photosynthesis of an
           amphibious species Eleocharis
           baldwinii
    • Abstract: Engineering C4 photosynthetic metabolism into C3 crops is regarded as a major strategy to increase crop productivity, and clarification of the evolutionary processes of C4 photosynthesis can help the better use of this strategy. Here, Eleocharis baldwinii, a species in which C4 photosynthesis can be induced from a C3 –C4 state under either environmental or ABA treatments, was used to identify the major transcriptional modifications during the process from C3 –C4 to C4. The transcriptomic comparison suggested that in addition to the major differences in C4 core pathway, the pathways of glycolysis, citrate acid metabolism and protein synthesis were dramatically modified during the inducement of C4 photosynthetic states. Transcripts of many transporters, including not only metabolite transporters but also ion transporters, were dramatically increased in C4 photosynthetic state. Many candidate regulatory genes with unidentified functions were differentially expressed in C3 –C4 and C4 photosynthetic states. Finally, it was indicated that ABA, auxin signaling and DNA methylation play critical roles in the regulation of C4 photosynthesis. In summary, by studying the different photosynthetic states of the same species, this work provides the major transcriptional differences between C3 –C4 and C4 photosynthesis, and many of the transcriptional differences are potentially related to C4 development and therefore are the potential targets for reverse genetics studies.
      PubDate: 2014-09-01
       
  • Interaction between the transcription factor AtTIFY4B and begomovirus AL2
           protein impacts pathogenicity
    • Abstract: The begomovirus AL2 protein is a transcriptional activator, a silencing suppressor, and inhibitor of basal defense. AL2 forms a complex at the CP promoter, through interaction with a plant-specific DNA-binding protein, Arabidopsis PEAPOD2 (also known as TIFY4B). AtTIFY4B has three domains (PPD, TIFY and CCT_2) conserved between homologs from different plant species. We confirmed that the AL2 protein from Tomato golden mosaic virus and Cabbage leaf curl virus interacts with TIFY4B from Arabidopsis, tomato and Nicotiana benthamiana in the nucleus of plant cells. Bimolecular Fluorescence Complementation demonstrated that the interaction involves both the TIFY and CCT_2 domains. Surprisingly, amino acids 84–150 can prevent AtTIFY4B from localizing to the nucleus, and interaction with AL2 results in some of the protein re-entering the nucleus. When AtTIFY4B is over-expressed, we observe an increase in mean latent period, where systemic symptoms are detected on average, 4 days later than in mock treated plants. This appears to be a consequence of reduced viral DNA titers, possibly related to the role of TIFY4B in cell cycle arrest. Our results point to a potential role for TIFY4B in host defense against geminiviruses. Expression of TIFY4B in N. benthamiana increases in response to geminivirus infection, which would result in suppression of proliferation, reducing viral replication. Geminiviruses may counter this defense response through an interaction between AL2 and TIFY4B, which would inhibit TIY4B function. The consequence of this inhibition would be failure to arrest the cell cycle, providing an environment conducive for geminivirus replication.
      PubDate: 2014-09-01
       
  • Characterization of five subgroups of the        class="a-plus-plus">sieve element occlusion gene
           family in Glycine max
           reveals genes encoding non-forisome P-proteins, forisomes and forisome
           tails
    • Abstract: P-proteins are structural phloem proteins discussed to be involved in the rapid sealing of injured sieve elements. P-proteins are found in all dicotyledonous and some monocotyledonous plants, but additional crystalloid P-proteins, known as forisomes, have evolved solely in the Fabaceae. Both types are encoded by members of the sieve element occlusion (SEO) gene family, which comprises seven phylogenetic subgroups. The Fabaceae-specific subgroup 1 contains genes encoding forisome subunits in e.g. Medicago truncatula, Vicia faba, Dipteryx panamensis and Canavalia gladiata whereas basal subgroup 5 encodes P-proteins in Nicotiana tabacum (tobacco) and Arabidopsis thaliana. The function of remaining subgroups is still unknown. We chose Glycine max (soybean) as a model to investigate SEO proteins representing different subgroups in one species. We isolated native P-proteins to determine the SEO protein composition and analyzed the expression pattern, localization and structure of the G. max SEO proteins representing five of the subgroups. We found that subgroup 1 GmSEO genes encode forisome subunits, a member of subgroup 5 encodes a non-forisome P-protein and subgroup 2 GmSEO genes encode the components of forisome tails, which are present in a restricted selection of Fabaceaen species. We therefore present the first molecular characterization of a Fabaceae non-forisome P-protein and the first evidence that forisome tails are encoded by a phylogenetically-distinct branch of the SEO gene family.
      PubDate: 2014-09-01
       
  • Expression of a gene encoding a rice RING zinc-finger protein, OsRZFP34,
           enhances stomata opening
    • Abstract: By oligo microarray expression profiling, we identified a rice RING zinc-finger protein (RZFP), OsRZFP34, whose gene expression increased with high temperature or abscisic acid (ABA) treatment. As compared with the wild type, rice and Arabidopsis with OsRZFP34 overexpression showed increased relative stomata opening even with ABA treatment. Furthermore, loss-of-function mutation of OsRZFP34 and AtRZFP34 (At5g22920), an OsRZFP34 homolog in Arabidopsis, decreased relative stomata aperture under nonstress control conditions. Expressing OsRZFP34 in atrzfp34 reverted the mutant phenotype to normal, which indicates a conserved molecular function between OsRZFP34 and AtRZFP34. Analysis of water loss and leaf temperature under stress conditions revealed a higher evaporation rate and cooling effect in OsRZFP34-overexpressing Arabidopsis and rice than the wild type, atrzfp34 and osrzfp34. Thus, stomata opening, enhanced leaf cooling, and ABA insensitivity was conserved with OsRZFP34 expression. Transcription profiling of transgenic rice overexpressing OsRZFP34 revealed many genes involved in OsRZFP34-mediated stomatal movement. Several genes upregulated or downregulated in OsRZFP34-overexpressing plants were previously implicated in Ca2+ sensing, K+ regulator, and ABA response. We suggest that OsRZFP34 may modulate these genes to control stomata opening.
      PubDate: 2014-09-01
       
  • The role of the MCM2-7 helicase complex during        class="a-plus-plus">Arabidopsis seed development
    • Abstract: The MINICHROMOSOME MAINTENANCE 2-7 (MCM2-7) complex, a ring-shaped heterohexamer, unwinds the DNA double helix ahead of the other replication machinery. Although there is evidence that individual components might have other roles, the essential nature of the MCM2-7 complex in DNA replication has made it difficult to uncover these. Here, we present a detailed analysis of Arabidopsis thaliana mcm2-7 mutants and reveal phenotypic differences. The MCM2-7 genes are coordinately expressed during development, although MCM7 is expressed at a higher level in the egg cell. Consistent with a role in the egg cell, heterozygous mcm7 mutants resulted in frequent ovule abortion, a phenotype that does not occur in other mcm mutants. All mutants showed a maternal effect, whereby seeds inheriting a maternal mutant allele occasionally aborted later in seed development with defects in embryo patterning, endosperm nuclear size, and cellularization, a phenotype that is variable between subunit mutants. We provide evidence that this maternal effect is due to the necessity of a maternal store of MCM protein in the central cell that is sufficient for maintaining seed viability and size in the absence of de novo MCM transcription. Reducing MCM levels using endosperm-specific RNAi constructs resulted in the up-regulation of DNA repair transcripts, consistent with the current hypothesis that excess MCM2-7 complexes are loaded during G1 phase, and are required during S phase to overcome replicative stress or DNA damage. Overall, this study demonstrates the importance of the MCM2-7 subunits during seed development and suggests that there are functional differences between the subunits.
      PubDate: 2014-09-01
       
  • Transcriptome comparison reveals the patterns of selection in domesticated
           and wild ramie (Boehmeria
           nivea
    L. Gaud)
    • Abstract: Ramie is an old fiber crop, cultivated for thousands of years in China. The cultivar ramie evolved from the wild species Qingyezhuma (QYZM, Boehmeria nivea var. tenacissima). However, the mechanism of domestication of this old fiber crop is poorly understood. In order to characterize the selective pattern in ramie domestication, orthologous genes between the transcriptomes of domesticated ramie variety Zhongzhu 1 (ZZ1) and wild QYZM were assessed using bidirectional best-hit method and ratio of non-synonymous (Ka) to synonymous (Ks) nucleotide substitutions was estimated. Sequence comparison of 56,932 and 59,246 unigenes from the wild QYZM and domesticated ZZ1, respectively, helped identify 10,745 orthologous unigene pairs with a total orthologous length of 10.18 Mb. Among these unigenes, 85 and 13 genes were found to undergo significant purifying and positive selection, respectively. Most of the selected genes were homologs of those involved in abiotic stress tolerance or disease resistance in other plants, suggesting that abiotic and biotic stresses were important selective pressures in ramie domestication. Two genes probably related to the fiber yield of ramie were subjected to positive selection, which may be caused by human manipulation. Thus, our results show the pervasive effects of artificial and natural selections on the accelerated domestication of ramie from its wild relative.
      PubDate: 2014-09-01
       
  • A novel method to identify the DNA motifs recognized by a defined
           transcription factor
    • Abstract: The interaction between a protein and DNA is involved in almost all cellular functions, and is vitally important in cellular processes. Two complementary approaches are used to detect the interactions between a transcription factor (TF) and DNA, i.e. the TF-centered or protein–DNA approach, and the gene-centered or DNA–protein approach. The yeast one-hybrid (Y1H) is a powerful and widely used system to identify DNA–protein interactions. However, a powerful method to study protein–DNA interactions like Y1H is lacking. Here, we developed a protein–DNA method based on the Y1H system to identify the motifs recognized by a defined TF, termed TF-centered Y1H. In this system, a random short DNA sequence insertion library was generated as the prey DNA sequences to interact with a defined TF as the bait. Using this system, novel interactions were detected between DNA motifs and the AtbZIP53 protein from Arabidopsis. We identified six motifs that were specifically bound by AtbZIP53, including five known motifs (DOF, G-box, I-box, BS1 and MY3) and a novel motif BRS1 [basic leucine zipper (bZIP) Recognized Site 1]. The different subfamily bZIP members also recognize these six motifs, further confirming the reliability of the TF-centered Y1H results. Taken together, these results demonstrated that TF-centered Y1H could identify quickly the motifs bound by a defined TF, representing a reliable and efficient approach with the advantages of Y1H. Therefore, this TF-centered Y1H may have a wide application in protein–DNA interaction studies.
      PubDate: 2014-08-10
       
  • Functions of        class="a-plus-plus">EDS1-       class="a-plus-plus">like and        class="a-plus-plus">PAD4 genes in grapevine
           defenses against powdery mildew
    • Abstract: The molecular interactions between grapevine and the obligate biotrophic fungus Erysiphe necator are not understood in depth. One reason for this is the recalcitrance of grapevine to genetic modifications. Using defense-related Arabidopsis mutants that are susceptible to pathogens, we were able to analyze key components in grapevine defense responses. We have examined the functions of defense genes associated with the salicylic acid (SA) pathway, including ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), EDS1-LIKE 2 (EDL2), EDL5 and PHYTOALEXIN DEFICIENT 4 (PAD4) of two grapevine species, Vitis vinifera cv. Cabernet Sauvignon, which is susceptible to E. necator, and V. aestivalis cv. Norton, which is resistant. Both VaEDS1 and VvEDS1 were previously found to functionally complement the Arabidopsis eds1-1 mutant. Here we show that the promoters of both VaEDS1 and VvEDS1 were induced by SA, indicating that the heightened defense of Norton is related to its high SA level. Other than Va/VvEDS1, only VaEDL2 complemented Arabidopsis eds1-1, whereas Va/VvPAD4 did not complement Arabidopsis pad4-1. Bimolecular fluorescence complementation results indicated that Vitis EDS1 and EDL2 proteins interact with Vitis PAD4 and AtPAD4, suggesting that Vitis EDS1/EDL2 forms a complex with PAD4 to confer resistance, as is known from Arabidopsis. However, Vitis EDL5 and PAD4 did not interact with Arabidopsis EDS1 or PAD4, correlating with their inability to function in Arabidopsis. Together, our study suggests a more complicated EDS1/PAD4 module in grapevine and provides insight into molecular mechanisms that determine disease resistance levels in Vitis species native to the North American continent.
      PubDate: 2014-08-09
       
  • Transcriptomic profiling revealed an important role of cell wall
           remodeling and ethylene signaling pathway during salt acclimation in
           Arabidopsis
    • Abstract: Plants can successfully improve their resistance to previously lethal salinity stress by a short exposure to low levels of salt stress, a process known as salt acclimation (SA). In spite of its fundamental significance in theoretical study and agricultural practice, the molecular mechanisms underlying plant SA remain elusive. In this study, we found that salt acclimated Arabidopsis young seedlings can survive subsequent 200 mM NaCl stress. RNA-seq was performed to analyze the genome-wide transcriptional response under SA conditions. Among 518 differentially expressed genes (DEGs) under SA, 366 up-regulated genes were enriched for cell wall biosynthesis, osmoregulation, oxidative stress, or transcription factors. Seven DEGs participate in the synthesis of lignin and 24 DEGs encode plant cell wall proteins, suggesting the importance of cell wall remodeling under SA. Furthermore, in comparison to non-acclimated salt stress, 228 of 245 DEGs were repressed by acclimated salt stress, including many genes related to ethylene biosynthesis and signaling pathway. In addition, MAPK6, a major component of the ethylene signaling pathway, was found to play a crucial role in SA. Our transcriptomic analysis has provided important insight on the roles of transcription factors, cell wall remodeling, and the ethylene biosynthesis and signaling pathways during SA in Arabidopsis.
      PubDate: 2014-08-05
       
  • Genomic profiling of rice roots with short- and long-term chromium stress
    • Abstract: Cr(VI) is the most toxic valency form of Cr, but its toxicity targets and the cellular systems contributing to acquisition of tolerance remain to be resolved at the molecular level in plants. We used microarray assay to analyze the transcriptomic profiles of rice roots in response to Cr(VI) stress. Gene ontology analysis revealed that the 2,688 Cr-responsive genes were involved in binding activity, metabolic process, biological regulation, cellular process and catalytic activity. More transcripts were responsive to Cr(VI) during long-term exposure (24 h, 2,097 genes), than short-term exposure (1- and 3-h results pooled, 1,181 genes). Long-term Cr(VI)-regulated genes are involved in cytokinin signaling, the ubiquitin–proteasome system pathway, DNA repair and Cu transportation. The expression of AS2 transcription factors was specifically modulated by long-term Cr(VI) stress. The protein kinases receptor-like cytoplasmic kinase and receptor-like kinase in flowers 3 were significantly upregulated with only short-term Cr(VI) exposure. In addition, 4 mitogen-activated protein kinase kinase kinases, 1 mitogen-activated protein kinase (MAPK) and 1 calcium-dependent protein kinase (CDPK) were upregulated with short-term Cr(VI) treatment. Expression of reactive oxygen species and calcium and activity of MAPKs and CDPK-like kinases were induced with increasing Cr(VI) concentration. These results may provide new insights into understanding the mechanisms of Cr toxicity and tolerance during different stages in rice roots.
      PubDate: 2014-07-24
       
  • WRKY45-dependent priming of diterpenoid phytoalexin biosynthesis in rice
           and the role of cytokinin in triggering the reaction
    • Abstract: Plant activators such as benzothiadiazole (BTH) protect plants against diseases by priming the salicylic acid (SA) signaling pathway. In rice, the transcription factor WRKY45 plays a central role in this process. To investigate the mechanism involved in defense-priming by BTH and the role of WRKY45 in this process, we analyzed the transcripts of biosynthetic genes for diterpenoid phytoalexins (DPs) during the rice–Magnaporthe oryzae interaction. The DP biosynthetic genes were barely upregulated in BTH-treated rice plants, but were induced rapidly after M. oryzae infection in a WRKY45-dependent manner. These results indicate that the DP biosynthetic genes were primed by BTH through WRKY45. Rapid induction of the DP biosynthetic genes was also observed after M. oryzae infection to WRKY45-overexpressing (WRKY45-ox) plants. The changes in gene transcription resulted in accumulation of DPs in WRKY45-ox and BTH-pretreated rice after M. oryzae infection. Previously, we reported that cytokinins (CKs), especially isopentenyladenines, accumulated in M. oryzae-infected rice. Here, we show that DP biosynthetic genes are regulated by the SA/CK synergism in a WRKY45-dependent manner. Together, we propose that CK plays a role in mediating the signal of M. oryzae infection to trigger the induction of DP biosynthetic genes in BTH-primed plants.
      PubDate: 2014-07-18
       
  • Artificial microRNA mediated gene silencing in plants: progress and
           perspectives
    • Abstract: Homology based gene silencing has emerged as a convenient approach for repressing expression of genes in order to study their functions. For this purpose, several antisense or small interfering RNA based gene silencing techniques have been frequently employed in plant research. Artificial microRNAs (amiRNAs) mediated gene silencing represents one of such techniques which can utilize as a potential tool in functional genomics. Similar to microRNAs, amiRNAs are single-stranded, approximately 21 nt long, and designed by replacing the mature miRNA sequences of duplex within pre-miRNAs. These amiRNAs are processed via small RNA biogenesis and silencing machinery and deregulate target expression. Holding to various refinements, amiRNA technology offers several advantages over other gene silencing methods. This is a powerful and robust tool, and could be applied to unravel new insight of metabolic pathways and gene functions across the various disciplines as well as in translating observations for improving favourable traits in plants. This review highlights general background of small RNAs, improvements made in RNAi based gene silencing, implications of amiRNA in gene silencing, and describes future themes for improving value of this technology in plant science.
      PubDate: 2014-07-15
       
  • The transcriptional response of apple alcohol acyltransferase (MdAAT2) to
           salicylic acid and ethylene is mediated through two apple MYB TFs in
           transgenic tobacco
    • Abstract: Volatile esters are major factors affecting the aroma of apple fruits, and alcohol acyltransferases (AATs) are key enzymes involved in the last steps of ester biosynthesis. The expression of apple AAT (MdAAT2) is known to be induced by salicylic acid (SA) or ethylene in apple fruits, although the mechanism of its transcriptional regulation remains elusive. In this study, we reveal that two apple transcription factors (TFs), MdMYB1 and MdMYB6, are involved in MdAAT2 promoter response to SA and ethylene in transgenic tobacco. According to electrophoretic mobility shift assays, MdMYB1 or MdMYB6 can directly bind in vitro to MYB binding sites in the MdAAT2 promoter. In vivo, overexpression of the two MYB TFs can greatly enhance MdAAT2 promoter activity, as demonstrated by dual luciferase reporter assays in transgenic tobacco. In contrast to the promoter of MdMYB1 or MdMYB6, the MdAAT2 promoter cannot be induced by SA or ethephon (ETH) in transgenic tobacco, even in stigmas in which the MdAAT2 promoter can be highly induced under normal conditions. However, the induced MYB TFs can dramatically enhance MdAAT2 promoter activity under SA or ETH treatment. We conclude that MdMYB1 and MdMYB6 function in MdAAT2 responses to SA and ethylene in transgenic tobacco, suggesting that a similar regulation mechanism may exist in apple.
      PubDate: 2014-06-04
       
  • Sequence comparison and phylogenetic analysis by the Maximum Likelihood
           method of ribosome-inactivating proteins from angiosperms
    • Abstract: Ribosome-inactivating proteins (RIPs) from angiosperms are rRNA N-glycosidases that have been proposed as defence proteins against virus and fungi. They have been classified as type 1 RIPs, consisting of single-chain proteins, and type 2 RIPs, consisting of an A chain with RIP properties covalently linked to a B chain with lectin properties. In this work we have carried out a broad search of RIP sequence data banks from angiosperms in order to study their main structural characteristics and phylogenetic evolution. The comparison of the sequences revealed the presence, outside of the active site, of a novel structure that might be involved in the internal protein dynamics linked to enzyme catalysis. Also the B-chains presented another conserved structure that might function either supporting the beta-trefoil structure or in the communication between both sugar-binding sites. A systematic phylogenetic analysis of RIP sequences revealed that the most primitive type 1 RIPs were similar to that of the actual monocots (Poaceae and Asparagaceae). The primitive RIPs evolved to the dicot type 1 related RIPs (like those from Caryophyllales, Lamiales and Euphorbiales). The gene of a type 1 RIP related with the actual Euphorbiaceae type 1 RIPs fused with a double beta trefoil lectin gene similar to the actual Cucurbitaceae lectins to generate the type 2 RIPs and finally this gene underwent deletions rendering either type 1 RIPs (like those from Cucurbitaceae, Rosaceae and Iridaceae) or lectins without A chain (like those from Adoxaceae).
      PubDate: 2014-06-01
       
 
 
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