[Show abstract][Hide abstract] ABSTRACT: Isoflavonoids are a class of phenylpropanoids made by legumes, and consumption of dietary isoflavonoids confers benefits to human health. Our aim is to understand the regulation of isoflavonoid biosynthesis. Many studies have shown the importance of transcription factors in regulating the transcription of one or more genes encoding enzymes in phenylpropanoid metabolism. In this study, we coupled bioinformatics and coexpression analysis to identify candidate genes encoding transcription factors involved in regulating isoflavonoid biosynthesis in Lotus (Lotus japonicus). Genes encoding proteins belonging to 39 of the main transcription factor families were examined by microarray analysis of RNA from leaf tissue that had been elicited with glutathione. Phylogenetic analyses of each transcription factor family were used to identify subgroups of proteins that were specific to L. japonicus or closely related to known regulators of the phenylpropanoid pathway in other species. R2R3MYB subgroup 2 genes showed increased expression after treatment with glutathione. One member of this subgroup, LjMYB14, was constitutively overexpressed in L. japonicus and induced the expression of at least 12 genes that encoded enzymes in the general phenylpropanoid and isoflavonoid pathways. A distinct set of six R2R3MYB subgroup 2-like genes was identified. We suggest that these subgroup 2 sister group proteins and those belonging to the main subgroup 2 have roles in inducing isoflavonoid biosynthesis. The induction of isoflavonoid production in L. japonicus also involves the coordinated down-regulation of competing biosynthetic pathways by changing the expression of other transcription factors.
[Show abstract][Hide abstract] ABSTRACT: Manihot esculenta (cassava) contains two cyanogenic glucosides, linamarin and lotaustralin, biosynthesized from l-valine and l-isoleucine, respectively. In this study, cDNAs encoding two uridine diphosphate glycosyltransferase (UGT) paralogs, assigned the names UGT85K4 and UGT85K5, have been isolated from cassava. The paralogs display 96% amino acid identity, and belong to a family containing cyanogenic glucoside-specific UGTs from Sorghum bicolor and Prunus dulcis. Recombinant UGT85K4 and UGT85K5 produced in Escherichia coli were able to glucosylate acetone cyanohydrin and 2-hydroxy-2-methylbutyronitrile, forming linamarin and lotaustralin. UGT85K4 and UGT85K5 show broad in vitro substrate specificity, as documented by their ability to glucosylate other hydroxynitriles, some flavonoids and simple alcohols. Immunolocalization studies indicated that UGT85K4 and UGT85K5 co-occur with CYP79D1/D2 and CYP71E7 paralogs, which catalyze earlier steps in cyanogenic glucoside synthesis in cassava. These enzymes are all found in mesophyll and xylem parenchyma cells in the first unfolded cassava leaf. In situ PCR showed that UGT85K4 and UGT85K5 are co-expressed with CYP79D1 and both CYP71E7 paralogs in the cortex, xylem and phloem parenchyma, and in specific cells in the endodermis of the petiole of the first unfolded leaf. Based on the data obtained, UGT85K4 and UGT85K5 are concluded to be the UGTs catalyzing in planta synthesis of cyanogenic glucosides. The localization of the biosynthetic enzymes suggests that cyanogenic glucosides may play a role in both defense reactions and in fine-tuning nitrogen assimilation in cassava.
[Show abstract][Hide abstract] ABSTRACT: There are 244 cytochrome P450 genes (and 28 pseudogenes) in the Arabidopsis genome. P450s thus form one of the largest gene families in plants. Contrary to what was initially thought, this family diversification results in very limited functional redundancy and seems to mirror the complexity of plant metabolism. P450s sometimes share less than 20% identity and catalyze extremely diverse reactions leading to the precursors of structural macromolecules such as lignin, cutin, suberin and sporopollenin, or are involved in biosynthesis or catabolism of all hormone and signaling molecules, of pigments, odorants, flavors, antioxidants, allelochemicals and defense compounds, and in the metabolism of xenobiotics. The mechanisms of gene duplication and diversification are getting better understood and together with co-expression data provide leads to functional characterization.
Full-text · Article · Jan 2011 · The Arabidopsis Book
[Show abstract][Hide abstract] ABSTRACT: Gene and genome duplication is a key driving force in evolution of plant diversity. This has resulted in a number of large multi-gene families. Two of the largest multi-gene families in plants are the cytochromes P450 (P450s) and family 1 glycosyltransferases (UGTs). These two families are key players in evolution, especially of plant secondary metabolism, and in adaption to abiotic and biotic stress. In the model plant Arabidopsis thaliana there are 246 and 112 cytochromes P450 and UGTs, respectively. The Arabidopsis P450, cytochromes b(5), NADPH-cytochrome P450 reductases, and family 1 glycosyltransferases website (http://www.P450.kvl.dk) is a sequence repository of manually curated sequences, multiple sequence alignments, phylogenetic trees, sequence motif logos, 3D structures, intron-exon maps, and customized BLAST datasets.
[Show abstract][Hide abstract] ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
[Show abstract][Hide abstract] ABSTRACT: Lotus japonicus accumulates the hydroxynitrile glucosides lotaustralin, linamarin, and rhodiocyanosides A and D. Upon tissue disruption, the hydroxynitrile glucosides are bioactivated by hydrolysis by specific beta-glucosidases. A mixture of two hydroxynitrile glucoside-cleaving beta-glucosidases was isolated from L. japonicus leaves and identified by protein sequencing as LjBGD2 and LjBGD4. The isolated hydroxynitrile glucoside-cleaving beta-glucosidases preferentially hydrolyzed rhodiocyanoside A and lotaustralin, whereas linamarin was only slowly hydrolyzed, in agreement with measurements of their rate of degradation upon tissue disruption in L. japonicus leaves. Comparative homology modeling predicted that LjBGD2 and LjBGD4 had nearly identical overall topologies and substrate-binding pockets. Heterologous expression of LjBGD2 and LjBGD4 in Arabidopsis (Arabidopsis thaliana) enabled analysis of their individual substrate specificity profiles and confirmed that both LjBGD2 and LjBGD4 preferentially hydrolyze the hydroxynitrile glucosides present in L. japonicus. Phylogenetic analyses revealed a third L. japonicus putative hydroxynitrile glucoside-cleaving beta-glucosidase, LjBGD7. Reverse transcription-polymerase chain reaction analysis showed that LjBGD2 and LjBGD4 are expressed in aerial parts of young L. japonicus plants, while LjBGD7 is expressed exclusively in roots. The differential expression pattern of LjBGD2, LjBGD4, and LjBGD7 corresponds to the previously observed expression profile for CYP79D3 and CYP79D4, encoding the two cytochromes P450 that catalyze the first committed step in the biosyntheis of hydroxynitrile glucosides in L. japonicus, with CYP79D3 expression in aerial tissues and CYP79D4 expression in roots.
[Show abstract][Hide abstract] ABSTRACT: Some plant secondary metabolites are classified as phytoanticipins. When plant tissue in which they are present is disrupted, the phytoanticipins are bio-activated by the action of beta-glucosidases. These binary systems--two sets of components that when separated are relatively inert--provide plants with an immediate chemical defense against protruding herbivores and pathogens. This review provides an update on our knowledge of the beta-glucosidases involved in activation of the four major classes of phytoanticipins: cyanogenic glucosides, benzoxazinoid glucosides, avenacosides and glucosinolates. New aspects of the role of specific proteins that either control oligomerization of the beta-glucosidases or modulate their product specificity are discussed in an evolutionary perspective.
[Show abstract][Hide abstract] ABSTRACT: Data mining methods have been used to identify 356 Cyt P450 genes and 99 related pseudogenes in the rice (Oryza sativa) genome using sequence information available from both the indica and japonica strains. Because neither of these genomes is completely available, some genes have been identified in only one strain, and 28 genes remain incomplete. Comparison of these rice genes with the 246 P450 genes and 26 pseudogenes in the Arabidopsis genome has indicated that most of the known plant P450 families existed before the monocot-dicot divergence that occurred approximately 200 million years ago. Comparative analysis of P450s in the Pinus expressed sequence tag collections has identified P450 families that predated the separation of gymnosperms and flowering plants. Complete mapping of all available plant P450s onto the Deep Green consensus plant phylogeny highlights certain lineage-specific families maintained (CYP80 in Ranunculales) and lineage-specific families lost (CYP92 in Arabidopsis) in the course of evolution.
[Show abstract][Hide abstract] ABSTRACT: The phylogeny of highly divergent multigene families is often difficult to validate but can be substantiated by inclusion of data outside of the phylogeny, such as signature motifs, intron splice site conservation, unique substitutions of conserved residues, similar gene functions, and out groups. The Family 1 Glycosyltransferases (UGTs) comprises such a highly divergent, polyphyletic multigene family. Phylogenetic comparisons of UGTs from plants, animals, fungi, bacteria, and viruses reveal that plant UGTs represent three distinct clades. The majority of the plant sequences appears to be monophyletic and have diverged after the bifurcation of the animal/fungi/plant kingdoms. The two minor clades contain the sterol and lipid glycosyltransferases and each show more homology to non-plant sequences. The lipid glycosyltransferase clade is homologous to bacterial lipid glycosyltransferases and reflects the bacterial origin of chloroplasts. The fully sequenced Arabidopsis thaliana genome contains 120 UGTs including 8 apparent pseudogenes. The phylogeny of plant glycosyltransferases is substantiated with complete phylogenetic analysis of the A. thaliana UGT multigene family, including intron-exon organization and chromosomal localization.
[Show abstract][Hide abstract] ABSTRACT: There are 272 cytochrome P450 genes (including 26 pseudogenes) in the Arabidopsis genome. P450s thus form one of the largest families of proteins in higher plants. This explosion of the P450 family is thought to have occurred via gene duplication and conversion, and to result from the need of sessile plants to adapt to a harsh environment and to protect themselves from pathogens and predators. P450s sometimes share less than 20% identity and catalyze extremely diverse reactions. Their biological functions range from the synthesis of structural macromolecules such as lignin, cutin or suberin, to the synthesis or catabolism of all types of hormone or signaling molecules, the synthesis of pigments and defense compounds, and to the metabolism of xenobiotics. In despite of a huge acceleration in our understanding of plant P450 functions in the recent years, the vast majority of these functions remain completely unknown.
Full-text · Article · Jan 2002 · The Arabidopsis Book
[Show abstract][Hide abstract] ABSTRACT: Cytochrome P450 (P450s) are heme-thiolate protein products of a very large gene superfamily, present in all kingdoms and involved in a variety of metabolic reactions. P450s are classified according to the degree of amino acid sequence identity, with P450s of the same family defined as having >40% identity, and P450s of the same subfamily having >55% identity. Currently, 273 P450 genes distributed over 45 families have been identified in Arabidopsis, and its genome is estimated to contain as many as 286. Genome-wide DNA microarrays make it possible to broadly correlate P450 gene activity with alterations in physiological or developmental states. A potential problem with microarray research is that sequence similarity between and within these families of closely related genes may lead to cross-hybridization. We designed experiments to systematically evaluate the specificity of P450 microarrays, and showed that conditions could be optimized to provide a very high degree of hybridization specificity. Under these conditions, and employing a 20% intensity value of maximum hybridization intensity as a cut-off, labeled P450 genes exhibited essentially no cross-hybridization between families and within subfamilies. We also compared the gene transcription levels of microarray probes derived from EST clones and from genomic DNA sequences for which ESTs were not available, using cDNA produced from RNA from various Arabidopsis tissue as the target. Many of the P450 genes displayed tissue-specific expression, leading to hypotheses as to the function of individual genes and their regulation. We also observed that several of the genomic sequences reported high levels of expression, highlighting the limitations of expression analysis based on ESTs alone.
[Show abstract][Hide abstract] ABSTRACT: The cytochrome P450 gene superfamily is represented by 80 genes in animal genomes and perhaps more than 300 genes in plant genomes. We analyzed about half of all Arabidopsis P450 genes, a very large dataset of truly paralogous genes. Sequence alignments were used to draw phylogenetic trees, and this information was compared with the intron-exon organization of each P450 gene. We found 60 unique intron positions, of which 37 were phase 0 introns. Our results confirm the polyphyletic origin of plant P450 genes. One group of these genes, the A-type P450s, are plant specific and characterized by a simple organization, with one highly conserved intron. Closely related A-type P450 genes are often clustered in the genome with as many as a dozen genes (e.g., of the CYP71 subfamily) on a short stretch of chromosome. The other P450 genes (non-A-type) form several distinct clades and are characterized by numerous introns. One such clade contains the two CYP51 genes, which are thought to encode obtusifoliol 14a demethylase. The two CYP51 genes have a single intron that is not shared with CYP51 genes from vertebrates or fungi, or with any other Arabidopsis P450 gene. Only a few of the Arabidopsis P450 genes are intronless (e.g., the CYP710A and CYP96A subfamilies). There was a relatively good correlation between intron conservation and phylogenetic relationships between members of the P450 subfamilies. Gene organization appears to be a useful tool in establishing the evolutionary relatedness of P450 genes, which may help in predictions of P450 function.
No preview · Article · Jun 2000 · DNA and Cell Biology