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PubMed2005

Modeling plant morphogenesis.

Applications of computational techniques to developmental plant biology include the processing of experimental data and the construction of simulation models. Substantial progress has been made in these areas over the past few years. Complex image-processing techniques are used to integrate sequences of two-dimensional images into three-dimensional descriptions of development over time and to extract useful quantitative traits. Large amounts of data are integrated into empirical models of developing plant organs and entire plants. Mechanistic models link molecular-level phenomena with the resulting phenotypes. Several models shed light on the possible properties of active auxin transport and its role in plant morphogenesis.

Computer Simulation↗
PubMed1999

GRAB proteins, novel members of the NAC domain family, isolated by their interaction with a geminivirus protein.

Geminiviruses encode a few proteins and depend on cellular factors to complete their replicative cycle. As a way to understand geminivirus-host interactions, we have searched for cellular proteins which interact with viral proteins. By using the yeast two-hybrid technology and the wheat dwarf geminivirus (WDV) RepA protein as a bait, we have isolated a family of proteins which we termed GRAB (for Geminivirus Rep A-binding). We report here the molecular characterization of two members, GRAB1 and GRAB2. We have found that the 37 C-terminal amino acids of RepA are required for interaction with GRAB proteins. This region contains residues conserved in an equivalent region of the RepA proteins encoded by other viruses of the WDV subgroup. The N-terminal domain of GRAB proteins is necessary and sufficient to interact with WDV RepA. GRAB proteins contain an unique acidic C-terminal domain while their N-terminal domain, of ca. 170 amino acids, are highly conserved in all of them. Interestingly, this conserved N-terminal domain of GRAB proteins exhibits a significant amino acid homology to the NAC domain present in proteins involved in plant development and senescence. GRAB1 and GRAB2 mRNAs are present in cultured cells and roots but are barely detectable in leaves. GRAB expression inhibits WDV DNA replication in cultured wheat cells. Our studies highlight the importance that the pathway(s) mediated by GRAB proteins, as well as by other NAC domain-containing proteins, might have on geminivirus DNA replication in connection to plant growth, development and senescence pathways.

Amino Acid Sequence↗
PubMed2005

Plant microRNAs and development.

MicroRNAs (miRNAs) act as negative regulators of gene expression in eukaryotes, a discovery that has opened an expanding field of biological research. Plant miRNAs are known to repress gene expression posttranscriptionally, mainly by guiding cleavage but also by attenuating the translation of target transcripts. In addition, it has been shown that plant miRNAs can also act at the transcriptional level by directing the methylation of target chromosomal loci. Genetic and biochemical approaches are quickly broadening our knowledge of the biogenesis and function of plant miRNAs. Computational approaches have uncovered an unexpectedly large number of miRNAs and their targets in plants. The targets of plant miRNAs often belong to families of transcription factors involved in the control of developmental processes. We review the status of research in this dynamic field, summarizing recent advances in our understanding of the biogenesis and mechanism of action of plant miRNAs, as well as in the developmental processes they regulate.

Base Sequence↗
PubMed2002

Selection and expression of peptides which can change the conformation of p20 protein of rice stripe virus.

Phages with high affinity to the P20 protein of rice stripe virus (RSV) were enriched from phage-displayed random 12-mer peptide library after three rounds of phage display screening. Nine different peptides from the enriched library were selected by enzyme-linked immunosorbent assay (ELISA). The P20 protein from raw extracts of rice leaves infected with RSV could be detected by those 9 peptides displayed on the phage, which suggested that a peptide could be an effective tool for diagnosis of RSV in rice and planthopper. Circular dichroism (CD) spectra of P20 fusion proteins with the binding phages and non-binding phages showed that the conformation of P20 protein was changed after binding to each of the 9 selected 12-mer peptides, which suggested that these peptides might disrupt the function of the P20 protein. Thereafter, those peptides might be used to develop plant resistance and disrupt virus transmission. Three of the 12-mer peptide genes were fused with the glutathione-S-transferase (GST) gene in the vector pGEX 3X. The fusion proteins were obtained from an Escherichia coli expression system and purified. The fusion proteins might have a potential to develop a plant peptide-based resistance to its pathogens and virus diagnosis. It also provided a tool (i) to confirm the inhibition of the function of P20 protein by the fusion peptides in vivo, and (ii) to detect the function of P20 protein and the interaction between the virus and its vector.

Electrophoresis, Polyacrylamide Gel↗
PubMed1999

Plants, animals and the logic of development.

Multicellular plants and animals have evolved independently from a unicellular, last common ancestor. Each lineage started with a common toolkit of functioning genes and evolved to complex, multicellular forms. Comparison of the genes used to serve similar functions shows how organisms can use different genes for similar ends and thereby reveals the principles of development.

Animals↗
PubMed2001

A gain-of-function mutation in IAA28 suppresses lateral root development.

The phytohormone auxin is important in many aspects of plant development. We have isolated an auxin-resistant Arabidopsis mutant, iaa28-1, that is severely defective in lateral root formation and that has diminished adult size and decreased apical dominance. The iaa28-1 mutant is resistant to inhibition of root elongation by auxin, cytokinin, and ethylene, but it responds normally to other phytohormones. We identified the gene defective in the iaa28-1 mutant by using a map-based positional approach and found it to encode a previously uncharacterized member of the Aux/IAA gene family. IAA28 is preferentially expressed in roots and inflorescence stems, and in contrast to other Aux/IAA genes, IAA28 transcription is not induced by exogenous auxin. Studies of the gain-of-function iaa28-1 mutant suggest that IAA28 normally represses transcription, perhaps of genes that promote lateral root initiation in response to auxin signals.

Amino Acid Sequence↗
PubMed2002

Brassinosteroid functions to protect the translational machinery and heat-shock protein synthesis following thermal stress.

In addition to their essential role in plant development, brassinosteroids have the ability to protect plants from various environmental stresses. Currently it is not understood how brassinosteroids control plant stress responses at the molecular level. We have begun an investigation into the molecular mechanisms underlying 24-epibrassinolide (EBR)-mediated stress resistance. Earlier we found that treatment of Brassica napus seedlings with EBR leads to a significant increase in their basic thermotolerance, and results in higher accumulation of four major classes of heat-shock proteins (hsps) as compared to untreated seedlings. Surprisingly, previous studies have shown that while hsp levels were significantly higher in treated seedlings during the recovery period, transcripts corresponding to these hsps were present at higher levels in untreated seedlings. To understand mechanisms controlling hsp synthesis in EBR-treated and untreated seedlings, we studied protein synthesis in vivo as well as in vitro, and assessed the levels of components of the translational machinery in these seedlings. We report here that increased accumulation of hsps in EBR-treated seedlings results from higher hsp synthesis, even when the mRNA levels are lower than in untreated seedlings, and that several translation initiation and elongation factors are present at significantly higher levels in EBR-treated seedlings as compared to untreated seedlings. These results suggest that EBR treatment limits the loss of some of the components of the translational apparatus during prolonged heat stress, and increases the level of expression of some of the components of the translational machinery during recovery, which correlates with a more rapid resumption of cellular protein synthesis following heat stress and a higher survival rate.

Adaptation, Physiological↗
PubMed1988

Mobilization and utilization of cyanogenic glycosides: the linustatin pathway.

In the seeds of Hevea brasiliensis, the cyanogenic monoglucoside linamarin (2-beta-d-glucopyranosyloxy-2-methylpropionitrile) is accumulated in the endosperm. After onset of germination, the cyanogenic diglucoside linustatin (2-[6-beta-d-glucosyl-beta-d-glucopyranosyloxy]-2- methylpropionitrile) is formed and exuded from the endosperm of Hevea seedlings. At the same time the content of cyanogenic monoglucosides decreases. The linustatin-splitting diglucosidase and the beta-cyanoalanine synthase that assimilates HCN, exhibit their highest activities in the young seedling at this time. Based on these observations the following pathway for the in vivo mobilization and metabolism of cyanogenic glucosides is proposed: storage of monoglucosides (in the endosperm)-glucosylation-transport of the diglucoside (out of the endosperm into the seedling)-cleavage by diglucosidase-reassimilation of HCN to noncyanogenic compounds. The presence of this pathway demonstrates that cyanogenic glucosides, typical secondary plant products serve in the metabolism of developing plants as N-storage compounds and do not exclusively exhibit protective functions due to their repellent effect.

Journal Article↗
PubMed2001

CYP83B1, a cytochrome P450 at the metabolic branch point in auxin and indole glucosinolate biosynthesis in Arabidopsis.

Auxins are growth regulators involved in virtually all aspects of plant development. However, little is known about how plants synthesize these essential compounds. We propose that the level of indole-3-acetic acid is regulated by the flux of indole-3-acetaldoxime through a cytochrome P450, CYP83B1, to the glucosinolate pathway. A T-DNA insertion in the CYP83B1 gene leads to plants with a phenotype that suggests severe auxin overproduction, whereas CYP83B1 overexpression leads to loss of apical dominance typical of auxin deficit. CYP83B1 N-hydroxylates indole-3-acetaldoxime to the corresponding aci-nitro compound, 1-aci-nitro-2-indolyl-ethane, with a K(m) of 3 microM and a turnover number of 53 min(-1). The aci-nitro compound formed reacts non-enzymatically with thiol compounds to produce an N-alkyl-thiohydroximate adduct, the committed precursor of glucosinolates. Thus, indole-3-acetaldoxime is the metabolic branch point between the primary auxin indole-3-acetic acid and indole glucosinolate biosynthesis in Arabidopsis.

Arabidopsis↗
PubMed2002

[Expression activity of maize Ubi-1 promoter in fertile transgenic maize plants].

The encoding sequence of gus gene from Escherichia coli was fused with maize Ubi-1 promoter and was introduced into maize genome via particle bombardment. Fertile transgenic maize plants were regenerated from bombarded type-I calluses which were derived from scutellar tissue of immature embryos based on PPT selection. Expression activity of gus gene under the control of Ubi-1 promoter was analysed using histochemical method, and the results showed that gus gene expressed in most tissues except anther. Ubi-GUS expression in pollen, egg cell and T1 immature embryos revealed that this promoter was active in early stages of plant development. Histochemically stained pollen grains of T0 plants showed a 1:1 segregation of the gus gene, which suggested that the foreign gene was inherited in Mendelian model in these plants. In addition, maize Ubi-1 promoter could reduce the copy number of foreign genes in transgenic maize plants, which might be useful in avoidance of gene silencing. T1 seeds have been harvested.

Blotting, Northern↗
PubMed1989

Survey of some cereal grains and legume seeds for aflatoxin contamination in the Sudan.

Aflatoxins were detected in some cereals and leguminous seeds collected from 2 cities in the Sudan (Wad Medani and Khartoum). The levels of the aflatoxins in these seeds were below the reported hazard threshold. Sound intact seeds contained low or no aflatoxins compared to significantly higher levels detectable in damaged and mouldy seeds of the tested crop plants. The optimum temperature for aflatoxin production was variable for different isolates of A. flavus. The optimum is 30 degrees C for the maize isolate and only 20 degrees C for the haricot bean isolate. Large amounts of aflatoxins B1, B2 and G1 were produced by the 2 isolates while aflatoxin G2 was only produced by the haricot bean isolate at optimum temperature. Aflatoxin B1 had significantly affected seed germination and plant development in both maize and haricot bean plants grown from seeds soaked in aflatoxin solutions. The influence was increasing with increasing concentration of the toxin.

Aflatoxins↗
PubMed2000

Spring phenology trends in Alberta, Canada: links to ocean temperature.

Warmer winter and spring temperatures have been noted over the last century in Western Canada. Earlier spring plant development in recent decades has been reported for Europe, but not for North America. The first-bloom dates for Edmonton, Alberta, were extracted from four historical data sets, and a spring flowering index showed progressively earlier development. For Populus tremuloides, a linear trend shows a 26-day shift to earlier blooming over the last century. The spring flowering index correlates with the incidence of El Niño events and with Pacific sea-surface temperatures.

Alberta↗
PubMed2004

The xipotl mutant of Arabidopsis reveals a critical role for phospholipid metabolism in root system development and epidermal cell integrity.

Phosphocholine (PCho) is an essential metabolite for plant development because it is the precursor for the biosynthesis of phosphatidylcholine, which is the major lipid component in plant cell membranes. The main step in PCho biosynthesis in Arabidopsis thaliana is the triple, sequential N-methylation of phosphoethanolamine, catalyzed by S-adenosyl-l-methionine:phosphoethanolamine N-methyltransferase (PEAMT). In screenings performed to isolate Arabidopsis mutants with altered root system architecture, a T-DNA mutagenized line showing remarkable alterations in root development was isolated. At the seedling stage, the mutant phenotype is characterized by a short primary root, a high number of lateral roots, and short epidermal cells with aberrant morphology. Genetic and biochemical characterization of this mutant showed that the T-DNA was inserted at the At3g18000 locus (XIPOTL1), which encodes PEAMT (XIPOTL1). Further analyses revealed that inhibition of PCho biosynthesis in xpl1 mutants not only alters several root developmental traits but also induces cell death in root epidermal cells. Epidermal cell death could be reversed by phosphatidic acid treatment. Taken together, our results suggest that molecules produced downstream of the PCho biosynthesis pathway play key roles in root development and act as signals for cell integrity.

Arabidopsis↗
PubMed2005

Identification of pathogen-responsive regions in the promoter of a pepper lipid transfer protein gene (CALTPI) and the enhanced resistance of the CALTPI transgenic Arabidopsis against pathogen and environmental stresses.

The 5' flanking region of the CALTPI gene, which encodes a basic lipid transfer protein, was isolated and characterized from the genomic DNA of Capsicum annuum. Four different regions of the promoter sequence of the CALTPI gene were fused to the beta-glucuronidase (GUS) coding region. In an Agrobacterium-mediated transient expression assay, the transcriptional activations of the promoter deletions were examined in tobacco leaves after infection with Pseudomonas syringae pv. tabaci, and treatment with ethylene and salicylic acid. The -808 bp region of the CALTPI gene promoter sequence exhibited full promoter activity. The W-box and ERE-box elements, which are essential for induction by all signals, were localized in the region between -555 bp and -391 bp upstream of the translation initiation site. A CALTPI transgene was then introduced under the control of the 35S promoter into the Arabidopsis ecotype Col-0. Transgenic Arabidopsis lines expressing the CALTPI gene developed rapidly compared to the wild-type plants, indicating that CALTPI may be involved in plant development. Overexpression of the CALTPI gene enhanced the resistance against infection by P. syringae pv. tomato and Botrytis cinerea. The transgenic plants expressing the CALTPI gene also showed high levels of tolerance to NaCl and drought stresses at various vegetative growth stages. No transcription of the PR-1, PR-2, PR-5, thionin, and RD29A genes was observed in untreated leaf tissues of the transgenic plants. The enhanced resistance to pathogen and environmental stresses in transgenic Arabidopsis correlated with the enhanced expression of the CALTPI gene.

Adaptation, Physiological↗