An inspection of the domain between putative TATA box and translation start site in 79 plant genes

Multiple regions of a divergent promoter control the expression of the Agrobacterium rhizogenes aux1 and aux2 plant oncogenes

The two auxin biosynthesis genes, aux1 and aux2 of Agrobacterium rhizogenes strain A4, are located on opposite DNA strands with a short integenic region (394 bp) between their coding sequences. A functional analysis of this divergent promoter is presented. The transcription initiation sites of the two aux genes were determined and regions important for promoter activity were identified by deletion and transient expression analyses in tobacco protoplasts. The promoter activity of the aux intergenic region was demonstrated. A strong enhancer element contained within an 84 bp promoter fragment was identified. Far upstream regions were shown to have negative effects on the promoter activity of the short intergenic region. Interactions between positive elements in the intergenic region and negative effects of the upstream sequences may be the basis of strict control of the auxin biosynthesis necessary for the induction and maintenance of hairy root growth.

Molecular characterization of a xyloglucan-specific endo-(1-->4)-beta-D-glucanase (xyloglucan endo-transglycosylase) from nasturtium seeds

A novel xyloglucan-specific endo-(1-->4)-beta-D-glucanase, involved in the post-germinative mobilization of xyloglucan storage reserves, has previously been isolated from nasturtium (Tropaeolum majus L.) seed. Its mode of action has been shown, in vitro, to be one of transglycosylation except at low substrate (glycosylacceptor) concentrations when hydrolysis predominates. Here it is shown that this nasturtium seed xyloglucan endo-transglycosylase is encoded by a single gene which is transcribed and processed to a 1.5 kb mRNA. The isolation and DNA sequence analysis of a cDNA copy of the nasturtium xyloglucan endo-transglycosylase transcript is described. The cDNA encodes a 33.5 kDa precursor polypeptide which is subsequently processed to a 31 kDa mature protein. The precursor incorporates an N-terminal signal sequence which probably contains information relevant to the targeting of the enzyme to the cell wall. The computer-predicted isoelectric point (5.14) and low (approximately 0%) alpha-helix content of the deduced mature protein are in excellent agreement with the experimental data obtained using the purified enzyme. The deduced protein sequence lacks homology with known plant endo-(1-->4)-beta-D-glucanases, consistent with the unique properties of the enzyme. Database searches have revealed that a Brassica protein (meri-5) of previously unknown function, but abundantly expressed in expanding tissue, shares structural identity with the nasturtium xyloglucan endo-transglycosylase. The expression of a xyloglucan endo-transglycosylase in expanding tissue would be consistent with the contention that enzymes of this type are involved in cell wall loosening.

Characterization of a gene that is expressed early in somatic embryogenesis of Daucus carota

The EMB-1 mRNA of carrot (Daucus carota) was isolated as an embryo abundant cDNA clone (T.H. Ulrich, E.S. Wurtele, B.J. Nikolau [1990] Nucleic Acids Res 18: 2826). Northern analyses of RNA isolated from embryos, cultured cells, and a variety of vegetative organs indicate that the EMB-1 mRNA specifically accumulates in embryos, beginning at the early stages of embryo development. In situ hybridization with both zygotic and somatic embryos show that the EMB-1 mRNA begins to accumulate at low levels throughout globular embryos. Accumulation of EMB-1 mRNA increases and becomes more localized as embryos mature; in torpedo embryos, EMB-1 mRNA preferentially accumulates in the meristematic regions, particularly the procambium. The similarity in distribution of EMB-1 mRNA in both zygotic and somatic embryos indicates that much of the spatial pattern of expression of the emb-1 gene is dependent on the developmental program of the carrot embryo and does not require maternal or endosperm factors. The EMB-1 protein (relative molecular weight 9910) is a very hydrophilic protein that is a member of a class of highly conserved proteins (typified also by the Em protein of wheat and the Lea D19 protein of cotton) that may be ubiquitous among angiosperm embryos but whose functions are as yet unknown. The carrot genome appears to contain one or two copies of the emb-1 gene. A 1313-base pair DNA fragment of the carrot genome containing the emb-1 gene was isolated and sequenced. The gene is interrupted by a single intron of 99 base pairs. Primer extension experiments identify two EMB-1 mRNAs, differing by 6 bases at their 5' ends that are transcribed from this gene.

The plant hormone abscisic acid mediates the drought-induced expression but not the seed-specific expression of rd22, a gene responsive to dehydration stress in Arabidopsis thaliana

Nine cDNA clones, corresponding to genes that are responsive to dehydration (named RD), have been isolated from Arabidopsis thaliana. The sequence of a putative protein encoded by one of the RD cDNA clones, RD22, exhibits considerable homology to an unidentified seed protein (USP) of Vicia faba. Northern analysis showed that RD22 mRNA is induced by salt stress as well as by water deficit but not by cold or heat stress. RD22 mRNA appeared after the application of abscisic acid (ABA), an indication that transcription of RD22 mRNA is induced by endogenous ABA, the production of which is triggered by drought and salt stress. The induction of RD22 mRNA by ABA was inhibited by cycloheximide. Thus, it appears that protein synthesis is required for the induction of this mRNA by ABA. By contrast, protein synthesis was not required for the ABA-responsive induction RD29 mRNA, which corresponds to another dehydration-responsive gene of A. thaliana. These results suggest that there are at least two mechanisms for the induction of dehydration-responsive genes by ABA. RD22 mRNA was also expressed during the early and middle stages of seed development, showing a pattern of expression similar to that of USP. The seed-specific expression of RD22 seems not to be regulated by ABA. Structural analysis of the RD22 genomic clone revealed that the structural gene (designated rd22) contains three introns, and only a single copy of the gene is present in the A. thaliana genome, while the gene for USP from V. faba is actually a family of genes with 10 to 20 members.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of genes negatively regulated by phytochrome action in Lemna gibba and identification of a promoter region required for phytochrome responsiveness

As a step to understanding how the photoreceptor phytochrome acts to change the transcription of specific nuclear genes in Lemna gibba, we wish to compare promoter elements involved in negative regulation by phytochrome with those involved in positive regulation. We have isolated three genes negatively regulated by phytochrome, designated NR (negatively phytochrome regulated) genes (P.A. Okubara, E.M. Tobin [1991] Plant Physiol 96:1237-1245), and we have now sequenced two of these. The promoters of both contain some sequence motifs that are identical with motifs from other genes. We used a transient assay in L. gibba to demonstrate that approximately 1.7 kb pairs of the NPR1 promoter and 1.1 kb pairs of the NPR2 promoter could confer negative phytochrome regulation to a luciferase reporter gene. Deletion analysis of the NPR2 promoter showed that sequences between -208 and -82 from the transcription start were necessary for negative phytochrome regulation. However, this region was not sufficient to confer negative regulation by phytochrome to another promoter. Additionally, we noted that this region showed no similarity to a region identified as important for the negative regulation of the oat phyA promoter (W.B. Bruce, X.-W. Deng, P.H. Quail [1991] EMBO J 10:3015-3024), but it does contain a sequence element found in several other kinds of genes, including ones positively regulated by phytochrome. The deduced amino acid sequences of NPR1 and NPR2 were found to share similarities with many abscisic acid-induced or seed-abundant proteins. Thus, these genes, like other phytochrome-regulated genes, might respond to multiple regulatory signals.

Molecular characterization of one of the maize polygalacturonase gene family members which are expressed during late pollen development

A gene exhibiting homology to the polygalacturonases of several species, including tomato and Oenothera, has been shown by RNA dot-blot analysis and in situ hybridization experiments to be expressed post-first microspore mitosis in maize. A 2.87 kbp section of the promoter fused to E. coli beta-glucuronidase (uidA) coding sequence conferred the correct spatial and temporal expression in transgenic tobacco plants. However, low levels of expression were detected in other tissues, and in particular in the tissues surrounding the vascular branch points of leaf nodes. The maize polygalacturonase gene is one member of a highly conserved gene family. The lack of detectable expression in sporophytic tissues and the isolation of a number of related cDNAs from maize suggests that all expressed members of this family show the same spatial and temporal regulation.

Isolation of an asparagus intracellular PR gene (AoPR1) wound-responsive promoter by the inverse polymerase chain reaction and its characterization in transgenic tobacco

The Asparagus officinalis intracellular PR1 (AoPR1) gene is expressed in response to wounding and pathogen attack. We utilized the inverse polymerase chain reaction (IPCR) to isolate the cis-acting regulatory sequences of the AoPR1 gene following unsuccessful attempts to identify hybridizing clones in genomic libraries. Sequence analysis of two IPCR products revealed that a 347 bp intron was present in the AoPR1 gene and that it was probable that the AoPR1 regulatory sequence had been amplified. To test the AoPR1 cis-acting sequences for biological function a translational fusion was constructed with the beta-glucuronidase (GUS) reporter gene and tested in tobacco. These data demonstrated that sequences 982 bp from the probable start of transcription are sufficient to direct wound-inducible transcription and that there is no signal peptide encoded by the first 31 residues of the predicted AoPR1 protein. Histochemical localization of GUS activity in transgenic tobacco demonstrated strong activity localized to wound and pathogen invasion sites. GUS activity was also found in mature pollen grains.

Genomic DNA structure of a gene encoding cytosolic ascorbate peroxidase from Arabidopsis thaliana

A genomic DNA clone encoding cytosolic ascorbate peroxidase was isolated from a genomic library of Arabidopsis thaliana, using a cDNA for the enzyme as a probe. Nucleotide sequence and primer extension analyses of this gene (APX1) revealed nine exons split by eight introns, one of which is inserted in the 5'-untranslated region. The exon/intron organization of the APX1 gene differs from that of the guaiacol peroxidase genes.

The gene and the RNA for the precursor to the plastid-located glycerol-3-phosphate acyltransferase of Arabidopsis thaliana

The gene and the RNA from Arabidopsis thaliana for the plastid-located glycerol-3-phosphate acyltransferase (GPAT; EC 2.3.1.15) and their encoded product have been studied. The gene (designated ATS1) was isolated by screening a lambda DASH genomic library for cross-hybridization with a radiolabeled probe prepared from cDNA for GPAT from squash. cDNA clones representing the mRNA were isolated by screening a lambda ZAPII cDNA library for hybridization with a radiolabeled probe prepared from a DNA fragment of ATS1. The nucleotide sequences of the gene and the cDNA were determined, and the 5' end of the RNA was mapped by primer extension. Sequences similar to the TATA box, polyadenylation sequences and intron-splicing sequences were found at the expected locations. The pre-mRNA was 3288 nucleotides long and contained 5' and 3'-untranslated sequences of 57 and 442 nucleotides, respectively. The coding sequence of 1377 nucleotides was interrupted by 11 introns of 1412 nucleotides in total and the 3'-untranslated sequence contained another intron of 94 nucleotides. The open-reading frame encoded a polypeptide of 459 amino acid residues, the amino acid sequence of which was highly homologous to those of precursors to plastid-located GPATs from squash and pea. The enzymatic activity of a gene product that was over-produced in Escherichia coli confirmed the identity of the gene.

Gametophytic and sporophytic expression of an anther-specific Arabidopsis thaliana gene

Genomic and cDNA clones of the anther-specific APG gene from Arabidopsis thaliana and Brassica napus, which encodes a novel proline-rich protein, were isolated and characterized. Southern blotting and Northern analysis of male fertile and cytoplasmic male sterile varieties of B. napus showed that the APG gene is present as a single copy in the Arabidopsis genome, and that the B. napus APG gene is a member of a small anther-specific gene family. Analysis of developmentally staged B. napus flower buds indicated that APG transcript is confined to the anther during the period of microspore development. Reporter gene fusions established that the APG promoter directs expression in a number of cell types in anthers of transformed plants. This expression is consistent with the temporal pattern of mRNA accumulation in B. napus buds and follows a complex developmental pattern. Most significantly, the promoter is active in both sporophytic and gametophytic cell types, with activity of the transgene in each cell type being delineated by various cytological markers.

Characterization of a spinach gene responsive to low temperature and water stress

The characterization of a cDNA for an 85 kDa spinach protein, CAP85 (cold acclimation protein) that is responsive to cold acclimation and water stress is described. Both transcript and protein levels are increased during cold acclimation and water stress. A novel characteristic of CAP85 is the presence of an 11 amino acid, lysine-rich repeat, common to Group 2 LEAs (late embryogenesis abundant proteins), which is included within a larger repeating motif present in 11 copies. Two other motifs of 8 and 16 residues are also found in three and four copies, respectively. CAP85 like other dehydrins and cold-regulated polypeptides remains soluble upon boiling. Protein blot analyses indicate that CAP85 protein is expressed in all aerial tissues as well as in roots. RNA blots show the presence of mRNA for the 85 kDa protein in leaf, petiole, and root tissue. Cell fractionation studies suggest that CAP85 is predominantly found in the cytosol.

Gene structure and expression of rice seed allergenic proteins belonging to the alpha-amylase/trypsin inhibitor family

Genomic and two novel cDNA clones for rice seed allergenic protein (RA) belonging to the alpha-amylase/trypsin inhibitor family were isolated and their nucleotide sequences determined. Ten cysteine residues deduced from nucleotide sequences were completely conserved among three cDNA clones including a clone, RA17, reported previously. One genomic clone, lambda 4, contained two RA genes, RAG1 and RAG2. Although RAG1 was cloned at the 5' portion only, two RA genes were arranged divergently. Nucleotide sequencing and DNA blotting analyses showed that RA are encoded by a multigene family consisting of at least four members. The transcriptional initiation site of RAG1 was localized at A, 26 bp upstream of the putative translational initiation codon, ATG, by the primer extension assay. The putative TATA box and CAAT box existed about 45 bp and 147 bp upstream of the transcription initiation site, respectively. A conserved sequence (ATGCAAAA) which was similar to the sequence (TGCAAAA) identified in rice glutelin promoters was observed in the 5' region of the two genes. In addition, RNA blotting analyses provided that RA genes specifically expressed in ripening seed and their transcripts accumulated maximally between 15 and 20 days after flowering.

The nucleotide sequence of the 5' flanking region of the Arabidopsis ACS2 gene

The ACS2 gene of Arabidopsis thaliana encodes 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (EC 4.1.1.14) - the key regulatory enzyme in the biosynthetic pathway of the plant hormone ethylene. The gene is unique among ACC synthase genes isolated thus far in that it is highly expressed in both reproductive (e.g. flower) and vegetative tissues (e.g. leaves and roots). In addition, the accumulation of ACS2 transcripts is greatly induced by protein synthesis inhibition (Liang et al 1992). We report here the DNA sequence of the 5' flanking region of the ACS2 gene and an analysis of the sequence with respect to the potential cis-acting regulatory elements that can be recognized by DNA-binding proteins from plants and other organisms.

Structure of the cDNA coding for conglutin gamma, a sulphur-rich protein from Lupinus angustifolius

The sequence of cDNA coding for a sulphur-rich storage protein from Lupinus angustifolius L., conglutin gamma, was determined. The coding region contained an N-terminal leader peptide of 28 amino acids which directly preceded subunits of M(r) 28,239 and 16,517. Extensive sequence homology between the protein encoded by conglutin gamma cDNA and basic 7S globulin from soybean was observed. Sequence homology to proteins from other classes of storage proteins, 11S, 7S and 2S, was limited to short and highly fragmented sequences. The amino acid sequence, Asn-Gly-Leu-Glu-Glu-Thr, characteristic of the primary site for post-translational cleavage of the precursors of 11S proteins, was absent from the sequence predicted for prepro-conglutin gamma. It is concluded that conglutin gamma is a representative of a fourth type of storage protein in legumes, distinct from the 11S, 7S and 2S storage protein families.

Cloning, genetic mapping, and expression analysis of an Arabidopsis thaliana gene that encodes 1-aminocyclopropane-1-carboxylate synthase

A genomic clone of one member of the Arabidopsis thaliana (L.) Heynh. 1-aminocyclopropane-1-carboxylate (ACC) synthase (S-adenosyl-L-methionine methylthioadenosine-lyase, EC 4.4.1.14) gene family (AT-ACC1) was isolated and sequenced. A region of homology was found in the 5'-untranslated region with the promoter of a zucchini and a tomato ACC synthase gene. Comparison of its primary structure with other ACC synthases revealed conservation of seven peptide regions as well as similarity with 11 amino acids of the catalytic site of aminotransferases. Genomic DNA gel blotting suggested the existence of an ACC synthase multigene family in Arabidopsis, possibly with three other members, none of which is very closely related to AT-ACC1. The existence of at least one other gene was confirmed by the isolation of a cDNA (AT-ACC2) from a flower-specific cDNA library. The AT-ACC1 gene was mapped on the Arabidopsis restriction fragment length polymorphism map and is located on the top of chromosome 1. This position does not correspond to any known mutation on the genetic map. Expression of the AT-ACC1 gene was studied by reverse transcription-PCR on total RNA. Messenger accumulation was strong in young leaves and flowers. The gene was not induced by wounding of young leaves or in seedlings in the presence of auxin. Ethylene exposure of mature plants led to an induction of AT-ACC1 gene expression. It is suggested that AT-ACC1 protein has a role in developmental control of ethylene synthesis.

Isolation and characterization of a tobacco gene with homology to pectate lyase which is specifically expressed during microsporogenesis

A genomic clone has been isolated which contains an open reading frame of 1191 bp interrupted by two small introns. The ORF has been sequenced and the transcriptional start determined. The predicted amino acid sequence shows homology to the deduced amino acid sequences of two pollen-specific pectate lyase genes identified in tomato. The genomic clone was isolated using a partial cDNA clone, TP10, which had been isolated from a Nicotiana tabacum pollen cDNA library by means of differential screening. TP10 has been fully sequenced and contains an open reading frame of 792 bp which shows 96% homology to the ORF in the genomic clone. The transcript corresponding to TP10 is maximally expressed late in pollen development, and has not been detected in vegetative tissues.

Allelic diversity of the maize B regulatory gene: different leader and promoter sequences of two B alleles determine distinct tissue specificities of anthocyanin production

The B gene encodes a transcription factor of the basic helix-loop-helix class, which controls the synthesis of the anthocyanin pigments in maize. This gene, as well as the highly homologous R gene family, displays extensive allelic variation in that different alleles cause distinct distributions of anthocyanin pigments in different tissues and at different developmental times. The analysis of the expression of two B alleles, with distinct tissue-specific patterns of anthocyanin synthesis in plant and seed tissues, demonstrates that the amount of B transcripts correlates with the accumulation of anthocyanins in the various tissues. The comparison of the genomic clones for the two alleles reveals high sequence identity in the coding and 3'-flanking regions (98% and approximately 90%, respectively). In contrast, the most 5' region of their mRNAs and the 5'-flanking sequences share no significant sequence identity. This result suggests that the alleles diverged from each other by complex genome rearrangements rather than by simple base pair substitutions. We have used the high velocity microprojectile transformation assay to demonstrate that the differential expression of the two alleles in the seed is determined by their 5' variant sequences. Thus, the variation in tissue-specific anthocyanin synthesis in plants with these different B alleles is controlled at the level of B gene expression.

Subgenomic RNAs mediate expression of cistrons located internally on the genomic RNA of tobacco necrosis virus strain A

Upon infection of tobacco protoplasts, the genomic RNA of tobacco necrosis virus strain A (TNV-A) accumulates linearly in time. The accumulation patterns of the two subgenomic RNAs resemble those of endogenous mRNAs in that the peak levels are reached after several hours. The accumulation of the 1.3-kb subgenomic RNA is delayed by 1 h compared with that of the 1.6-kb subgenomic RNA, which illustrates the important role of the subgenomic RNAs in the regulation of TNV-A gene expression. The locations of the 5' nucleotides of the subgenomic RNAs reveal that the 5'-proximal cistrons of the 1.6- and 1.3-kb RNAs encode an 8-kDa protein from open reading frame (ORF) 3 and the coat protein from ORF 5, respectively. In a wheat germ translation system, a synthetic transcript resembling the 1.6-kb RNA expresses both ORFs 3 and 4. Moreover, the synthesis of the 6-kDa protein from ORF 4 depends on the translation efficiency of ORF 3, suggesting that in vivo, ORFs 3 and 4 are both expressed from the 1.6-kb RNA. The major in vitro translation product of TNV-A genomic RNA is the coat protein. We show that the region upstream of the coat protein promotes internal initiation of translation in vitro. However, this region is functionally inactive in vivo, suggesting that TNV-A genomic RNA is not important for coat protein synthesis in plants.

Structure and expression of a gene from Arabidopsis thaliana encoding a protein related to SNF1 protein kinase

The AKin10 gene from Arabidopsis thaliana encoding a putative Ser/Thr protein kinase (PK) has been isolated and characterized. The AKin10-encoding gene is located on a genomic 5.4-kb BamHI fragment and contains ten introns, one being located in the 5' untranslated region. The deduced amino acid sequence of AKin10 is 65% identical over the catalytic domain to the yeast PK (SNF1). SNF1 is essential for the derepression of many glucose-repressible genes, including Suc2 which encodes invertase. Southern blot hybridization experiments suggested the presence of one copy of the gene per haploid genome of A. thaliana. Northern hybridization experiments indicated that this gene is expressed in roots, shoots and leaves. AKin10 may play an important role in a signal transduction cascade regulating gene expression and carbohydrate metabolism in higher plants.

Purification, characterization and gene structure of (1-->3)-beta-glucanase isoenzyme GIII from barley (Hordeum vulgare)

A new member of the barley (1-->3)-beta-glucan glucanohydrolase family of enzymes has been purified from extracts of germinated grain and young seedlings by fractional precipitation with ammonium sulphate, ion-exchange chromatography, chromatofocussing and gel-filtration chromatography. The enzyme, which has been designated (1-->3)-beta-glucanase isoenzyme GIII, is a basic protein with an apparent molecular mass of 32 000 Da. Oligosaccharide products released by the enzyme during hydrolysis of the (1-->3)-beta-glucan, laminarin, indicate that the enzyme is an endohydrolase. A 2349-bp fragment of barley genomic DNA has been isolated and identified as the gene encoding the (1-->3)-beta-glucanase isoenzyme GIII. The open reading frame encoding the isoenzyme is interrupted by a single intron of 180 bp that splits a codon in the putative signal-peptide region. Northern-blot analyses with gene-specific probes indicate that the (1-->3)-beta-glucanase isoenzyme GIII mRNA accumulates in developing leaves; no mRNA transcripts were detected in the aleurone or scutellum of germinated grain, or in mature vegetative tissues. Although plant (1-->3)-beta-glucanases are generally classified as 'pathogenesis-related' proteins, the physiological function of the barley (1-->3)-beta-glucanase isoenzyme GIII is unclear.

Homologous genes for the C4 isoform of phosphoenolpyruvate carboxylase in a C3 and a C4 Flaveria species

The C4 isoform of phosphoenolpyruvate carboxylase (PEPCase) in Flaveria trinervia is encoded by the ppcA subgroup of the PEPCase gene family and is abundantly expressed in the mesophyll cells of leaves. The homologous ppcA genes in the C3 plant F pringlei are only weakly expressed and their transcripts do not show the strictly leaf-specific accumulation pattern observed for the F. trinervia genes. Two representative members of the ppcA subfamilies of F. trinervia (C4) and F. pringeli (C3)-named ppcA1-were characterized by Southern blotting, nucleotide sequencing and primer extension analysis. Comparison of the deduced amino acid sequences reveals a close similarity between C4 and C3 isoforms. Only few C4-specific positions can be detected when all known plant PEPCases are included in the comparison. A regulatory domain involved in light-dependent phosphorylation/dephosphorylation of the C4 and crassulacean acid metabolism (CAM) isoforms is present in the ppcA1 gene products of both the C3 and C4 Flaveria. The 5' flanking regions are essentially homologous. The putative promoter regions share several identical sequence motifs (CCAAT, AT-1 and GT-1 box III/III* elements). Additionally, alterations in elements that could contribute to differences in expression rates and light regulation are found. The significance of these findings is discussed with respect to the molecular evolution of C4 photosynthesis in Flaveria.

The isolation and characterisation of the tapetum-specific Arabidopsis thaliana A9 gene

The Brassica napus cDNA clone A9 and the corresponding Arabidopsis thaliana gene have been sequenced. The B. napus cDNA and the A. thaliana gene encode proteins that are 73% identical and are predicted to be 10.3 kDa and 11.6 kDa in size respectively. Fusions of an RNase gene and the reporter gene beta-glucuronidase to the A. thaliana A9 promoter demonstrated that in tobacco the A9 promoter is active solely in tapetal cells. Promoter activity is first detectable in anthers prior to sporogenous cell meiosis and ceases during microspore premitotic interphase. The deduced A9 protein sequence has a pattern of cysteine residues that is present in a superfamily of seed plant proteins which contains seed storage proteins and several protease and alpha-amylase inhibitors.

Structure and expression of kin2, one of two cold- and ABA-induced genes of Arabidopsis thaliana

We report the isolation of the second member, kin2, of a family of two cold-inducible genes of Arabidopsis thaliana. The proteins corresponding to the two genes have similarities to the small antifreeze proteins from Winter flounder. Kin1 and kin2 are organized in a close tandem array in the genome of A. thaliana. Both have three exons separated by introns with approximately the same length and location. The coding regions are highly conserved while the introns and especially the 3' flanking sequences of the mRNAs have diverged. The kin1 and kin2 genes are coordinately regulated in the cold. Unlike kin1, the kin2 mRNA has a detectable basal level, and accumulates to a higher level during acclimation. Both mRNAs are induced by 10 microM ABA but only kin2 responds strongly to drought and salinity stresses.

The structure and regulation of homeologous tobacco endochitinase genes of Nicotiana sylvestris and N. tomentosiformis origin

The fungicidal class I chitinases are believed to be important in the induced defense response of plants. We isolated and partially characterized genomic clones representing two members, CHN14 and CHN50, of the gene subfamily encoding these enzymes in Nicotiana tabacum L. cv. Havana 425. The coding sequences of genes CHN14, CHN50, and CHN48, which was cloned earlier, are identical at 79-95% of the positions. Tobacco is an amphidiploid species derived from ancestors most closely related to the present-day species N. sylvestris and N. tomentosiformis. Southern analysis of genomic DNA, comparison of deduced amino acid sequences, and partial sequencing of the purified enzymes suggest that the gene pairs CHN48/CHN50 and CHN14/CHN14' are homeologues. Gene CHN48, which encodes chitinase A (Mr ca. 34 kDa), and gene CHN14 are derived from N. tomentosiformis; whereas gene CHN50, which encodes chitinase B (Mr ca. 32 kDa), and gene CHN14' are derived from N. sylvestris. Class I chitinases are induced in leaves of plants treated with ethylene or infected with the fungal pathogen Cercospora nicotianae and in cultured cells transferred to medium without added auxin and cytokinin. RNase protection assays show that under these conditions transcripts encoded by the homeologues CHN48 and CHN50 account for greater than 90% of the total chitinase mRNA. The less abundant transcript, CHN48, consistently showed a greater degree of induction than CHN50. Expression of the homeologues CHN14 and CHN14' represented less than 10% of the total chitinase mRNA. They showed a pattern of hormonal regulation similar to CHN48 and CHN50, but transcripts of these genes were not detected in leaves infected with C. nicotianae. Therefore the two sets of homeologues are regulated in the same way by hormones and respond differently to infection by a pathogen.

The isolation and functional characterisation of a B. napus acyl carrier protein 5' flanking region involved in the regulation of seed storage lipid synthesis

Acyl carrier protein (ACP) is a key component of the fatty acid biosynthetic machinery in plants. A 1.4 kb 5' flanking region of a Brassica napus ACP gene (ACP05) was transcriptionally fused to the reporter gene beta-glucuronidase (GUS), and expression of the chimeric gene monitored in transgenic tobacco. GUS activity was found to increase through seed development reaching a maximum value, coincident with the most active phase of storage lipid synthesis that was, on average, 100-fold higher than that observed in leaf. In control plants transformed with CaMV 35S-GUS constructs, GUS activity was similar in leaf and all stages of seed development. Based on average values, the level of GUS expression obtained via the ACP promoter was comparable to that obtained from the CaMV 35S promoter. We therefore conclude that the isolated 5' ACP flanking sequence represents a strong promoter element involved in the developmental regulation of storage lipid synthesis in B. napus seed tissue. Putative regulatory elements in the 5' upstream region of ACP05 were identified by dot matrix analysis and by sequence comparison with the upstream regions from a second seed-expressed rape ACP gene and from an Arabidopsis ACP gene.

Control of gene expression in tobacco cells using a bacterial operator-repressor system

We have investigated the efficacy of using the Escherichia coli lac operator-repressor system to control plant gene expression. The lacI gene was modified to allow optimal expression in plant cells and then placed downstream of the cauliflower mosaic virus (CaMV) 35S RNA promoter. This construct was introduced into tobacco plants by leaf disc transformation. Transgenic tobacco plants synthesized significant quantities of LacI protein (up to 0.06% of total soluble protein). We have used the E.coli beta-glucuronidase gene (gus) as the reporter gene by placing it downstream of the maize chlorophyll a/b binding protein (CAB) gene promoter. Lac operators were introduced into several positions within the CAB promoter and operator-free plasmid was used as control. Repression was assessed by comparing the transient expression from CAB-operator-gus reporter constructs in protoplasts expressing lac protein, with that in control cells not expressing the repressor. Repression varied between 10 and 90% with different operator positions. Transient assays were also performed in the presence of the inducer, isopropyl-beta-D-thiogalactoside (IPTG). In lacI protoplasts the presence of IPTG manifested itself in a 4.2-fold relief of repression. The study was extended to show regulation of expression in stable transformants. Tobacco transformants harbouring a CAB-operator-gus reporter construct and the lacI gene were shown to have repressed GUS levels, but in the presence of IPTG, repression was relieved 15-fold. We conclude that the lac repressor can enter the plant cell nucleus, find its cognate operator sequence in the chromatin to form a repressor--operator complex and effectively block transcription of a downstream gene.

Characterization of rps17, rp19 and rpl15: three nucleus-encoded plastid ribosomal protein genes

Approximately two-thirds of the 55 to 60 plastid ribosomal proteins are encoded in the nucleus. Since the protein products of each of these genes are needed in equal amounts for ribosome assembly, their expression may be coordinately regulated by common mechanisms. To begin to understand how the expression of these genes is regulated, we have isolated cDNA and genomic clones for three plastid ribosomal protein genes from an Arabidopsis thaliana library. The genes rps17, rpl9 and rpl15, encoding plastid ribosomal proteins CS17, CL9 and CL15, respectively, are located in the nuclear genome and Southern blot data suggest that each is a single copy gene in A. thaliana. Northern blot data show that transcripts from rps17, rpl9 and rpl15 are much more abundant in leaves and stems than they are in roots. The nucleotide sequences of each of these three genes were determined and their transcriptional initiation sites identified. rps17 transcripts have multiple 5' ends suggesting that they are initiated at multiple sites or are post-transcriptionally processed at their 5' end. rpl9 and rpl15 apparently have unique transcriptional initiation sites but are post-transcriptionally processed to remove six and three introns, respectively, from their primary transcripts. We have examined the genomic sequences for motifs that may be important for the proper expression of these genes. A 7 bp sequence motif, whose consensus is 5'-AGGCCCA-3', flanked by AT-rich regions was identified between 38 and 73 nucleotides upstream of the rps17, rpl9 and rpl15 transcriptional initiation sites.

Complementary DNA cloning of poplar bark storage protein and control of its expression by photoperiod

Bark storage proteins accumulate in the bark of many woody plants during autumn and winter. In poplar (Populus deltoides Bartr. ex Marsh), the accumulation of the 32-kilodalton bark storage protein is controlled by photoperiod. We have isolated a full-length cDNA encoding for the poplar 32-kilodalton bark storage protein and determined its nucleotide sequence. The derived amino acid sequence shows that poplar bark storage protein is rich in serine, leucine, phenylalanine, and lysine. Poplar bark storage protein is similar to the poplar wound-induced cDNA clone 4 and clone 16 (TJ Parsons, HD Bradshaw, MP Gordon [1989] Proc Natl Acad Sci USA 86: 7895-7899). DNA gel blot analysis suggests that poplar bark storage protein is encoded by a multigene family of about five genes. Poplar plants grown in long days contained low levels of mRNA for the bark storage protein. Exposure to short days resulted in an increase in bark storage protein mRNA within 7 days. After 21 days of short day exposure, high levels of mRNA were detected. The accumulation of bark storage protein mRNA in response to short days was also observed in plants exposed to natural shortening daylengths. Our results indicate that the accumulation of poplar bark storage protein mRNA is controlled by photoperiod. This finding will provide a useful system for investigating photoperiodism in woody plants.

Primary structure of a barley-grain aspartic proteinase. A plant aspartic proteinase resembling mammalian cathepsin D

Two enzymatically active heterodimeric forms of an aspartic proteinase, a putative 32 kDa + 16 kDa precursor form and a putative 29 kDa + 11 kDa mature form, are present in resting barley grains (Sarkkinen, P., Kalkkinen, N., Tilgmann, C., Siuro, J., Kervinen, J. & Mikola, L., 1990, in the press). The cDNA corresponding to this enzyme has been cloned and sequenced. The full-length 1863-bp cDNA sequence codes for an open reading frame of 508 amino acids. The open reading frame consists of a 66-amino acid preprosequence and a 442-amino acid mature protein. Comparison of the N-terminal amino acid sequences of the enzyme subunits with the sequence of the cDNA clone indicates that the heterodimeric enzyme is translated as a proenzyme which is processed into two subunits. The localisation of the experimentally determined N-terminal amino acid sequences of all four subunits (32 kDa + 16 kDa and 29 kDa + 11 kDa) in the same transcript, as well as the detection of only one 2.0-kb mRNA on Northern blots from resting seeds, clearly indicates that the larger (32 kDa + 16 kDa) enzyme is an intermediate precursor form of the smaller (29 kDa + 11 kDa) enzyme. The processing pattern of the barley enzyme, which is the first sequenced plant aspartic proteinase, differs from that of all other known aspartic proteinases. The barley enzyme is highly similar to mammalian and yeast aspartic proteinases, especially to human and porcine cathepsin D. This similarity is clearly dispersed over two regions, separated by a dissimilar, barley-specific region of 104 amino acids.

Determination of steady-state mRNA levels of individual chlorophyll a/b binding protein genes of the tomato cab gene family

The steady-state levels of mRNA produced by 14 genes encoding members of the tomato chlorophyll a/b binding protein family were quantified. All genes were found to be expressed in leaf tissue, but the mRNAs accumulated to significantly different levels. The transcripts of cab 1A, cab 1B, cab 3A and cab 3B, encoding the Type I LHC proteins of photosystem II, are abundant, while low levels were measured for mRNAs encoding the Type II LHC II and the LHC I proteins. Sequences from the 5' upstream regions (-400 to translational start) of some cab genes were determined in this study, and a total of 16 tomato cab gene promoters for which sequences are now available were analyzed. Significant sequence conservation was found for those genes which are tandemly linked on the chromosome. However, the level of sequence conservation is different for the different cab subfamilies, e.g. 85% similarity between cab 1A and cab 1D vs. 45% sequence similarity between cab 3A and cab 3C upstream sequences. Characteristic GATA repeats with a conserved spacing were found in 5' upstream sequences of cab 1A-D, cab 3A-C, cab 11 and cab 12. The consensus sequence CCTTATCAT, which is believed to mediate light responsiveness, was found at different locations in the upstream sequences of cab 6B, cab 7, cab 8, cab 9, cab 10A, cab 10B and cab 11. In 11 out of 15 genes the transcription initiation site was found to center on the triplet TCA.

Construction of expression vectors based on the rice actin 1 (Act1) 5' region for use in monocot transformation

It has been previously reported that the 5' region of the rice actin 1 gene (Act1) promoted high-level expression of a beta-glucuronidase reporter gene (Gus) in transformed rice cells. In this paper we describe the construction of Act1-based expression vectors for use in monocot transformation. As part of the development of these vectors, we have evaluated the influence of the Act1 first intron, the Act1-Gus junction-encoded N-terminal amino acids, and the sequence context surrounding the Act1 and Gus translation initiation site on Act1-Gus gene expression in rice and maize cells. We have found that addition of Act1 intron 1 to the transcription unit of a Gus reporter gene under control of the cauliflower mosaic virus (CaMV) 35S promoter stimulated GUS activity more than 10-fold in transformed rice cells. Optimization of the sequence context around the Gus translation initiation site resulted in a 4-fold stimulation of Gus expression in transformed rice cells. By utilizing both the Act1 intron 1 and optimized Gus translation initiation site, a 40-fold stimulation in Gus expression from the CaMV 35S promoter has been achieved in transformed rice cells; very similar results were obtained in transformed maize cells. Taken together these results suggest that the Act1-based expression vectors described here should promote the expression of foreign genes in most, if not all, transformed monocot cells to levels that have not previously been attainable with alternative expression vectors.

Organ-Specific and Environmentally Regulated Expression of Two Abscisic Acid-Induced Genes of Tomato : Nucleotide Sequence and Analysis of the Corresponding cDNAs

The cDNAs, pLE4 and pLE25, represent mRNAs that accumulate in response to water deficit and elevated levels of endogenous abscisic acid in detached leaves of drought-stressed tomato (Lycopersicon esculentum Mill., cv Ailsa Craig) (A Cohen, EA Bray [1990] Planta 182: 27-33). DNA sequence analysis of pLE4 and pLE25 showed that the deduced polypeptides were 13.9 and 9.3 kilodaltons, respectively. Each polypeptide was hydrophilic, cysteine- and tryptophan-free, and found to be similar to previously identified proteins that accumulate during the late stages of embryogenesis. pLE4 and pLE25 mRNA accumulated in a similar organ-specific pattern in response to specific abiotic stresses. Yet, expression patterns of the corresponding genes in response to developmental cues were not similar. pLE25 mRNA accumulated to much higher levels in developing seeds than in drought-stressed vegetative organs. pLE4 mRNA accumulated predominantly in drought-stressed leaves. The similarities and differences in the accumulation characteristics of these two mRNAs indicates that more than one mechanism exists for the regulation of their corresponding genes.

Transcript mapping of Abutilon mosaic virus, a geminivirus

The transcripts of the DNA of Abutilon mosaic virus, a geminivirus with a bipartite genome (DNA A and DNA B), were characterized by Northern blot hybridization, S1 nuclease assay, primer extension analysis, and sequencing of the 3' termini of cDNA clones. It was shown that transcription is bidirectional and that the transcripts are polyadenylated. Two overlapping transcripts of 1.6 and 0.7 kb were mapped to the complementary strand of DNA A and two of 1.3 and 1.2 kb to the complementary strand of DNA B. One transcript of 0.9 kb was mapped to the viral sense in DNA A and one of 1.0 kb to the viral sense in DNA B. The ends of complementary and viral mRNA overlapped in both genome parts in regions rich in polyadenylation signals.

cDNA cloning, sequence analysis and seasonal expression of lignin-bispecific caffeic acid/5-hydroxyferulic acid O-methyltransferase of aspen

A cDNA clone (Ptomt 1) encoding a lignin-bispecific O-methyltransferase (OMT) was isolated by immunological screening of a lambda gt11 expression library prepared from mRNA of developing secondary xylem of aspen (Populus tremuloides). Nucleotide sequence analysis of Ptomt1 revealed an open reading frame of 1095 bp which encodes a polypeptide with a predicted molecular weight of 39,802, corresponding well with the size of the OMT polypeptide estimated by SDS-PAGE. Authenticity of Ptomt1 was demonstrated in part by detection of OMT activity and protein in extracts of Escherichia coli cultures transformed with a plasmid construct containing Ptomt1. In addition, peptides produced from a proteolytic digest of purified OMT and sequenced by automated Edman degradation matched to portions of the deduced amino acid sequence of Ptomt1. Comparison of this sequence to amino acid sequences of OMTs of diverse species identified regions of similarity which probably contribute to the binding site of S-adenosyl-L-methionine. Tissue-specific expression was demonstrated by northern analysis which showed that Ptomt1 hybridized to a 1.7 kb transcript from aspen developing secondary xylem and by tissue printing of aspen stems in which only the outer layer of xylem bound the antibody. A biphasic pattern of gene expression and enzyme activity for OMT was observed from xylem samples of aspen during the growing season which suggests linkage between gene expression for a monolignol biosynthetic enzyme and seasonal regulation of xylem differentiation in woody plants.

Multiple cDNAs of phosphoenolpyruvate carboxylase in the C4 dicot Flaveria trinervia

We have isolated and characterized cDNA clones for the leaf-specific C4-phosphoenolpyruvate carboxylase (PEPCase) from the dicotyledonous C4 plant Flaveria trinervia. The isolation of multiple cDNAs indicates that in this plant the C4 isoform is encoded by a small subgroup of the PEPCase gene family. The deduced amino acid sequence reveals a higher degree of similarity to the CAM and C3 isozymes of the dicotyledonous, facultative CAM plant Mesembryanthemum crystallinum than to the C4 PEPCases of monocotyledonous origin.

Structure of the glycoprotein gene of sonchus yellow net virus, a plant rhabdovirus

The nucleotide sequence of the glycoprotein (G) gene of sonchus yellow net virus (SYNV), a plant rhabdovirus, was determined from viral genomic and mRNA cDNA clones. The G cistron is 2045 nucleotides (nt) long and the G protein mRNA open reading frame (ORF), as determined from the cDNA sequence, contains 1896 nt and encodes a protein of 632 amino acids. Immunoblots with antibodies elecited against the purified glycoprotein from virus particles reacted with a fusion protein produced in Escherichia coli, indicating that the cloned ORF encodes the G protein. The 5' end of the G protein mRNA corresponds to nt 5111, relative to the 3' end of the viral (minus sense) genome, as determined by primer extension from mRNA isolated from infected plants, and extends to nt position 7155 on the genomic RNA. A 34-nt untranslated 5' leader sequence and a 115-nt untranslated 3' end flank the ORF on the mRNA. The gene junctions on either side of the G gene on the genomic RNA are identical to those previously described for other SYNV genes and are similar to sequences separating genes of animal rhabdoviruses. The predicted molecular weight of the G protein is 70,215 Da, a value less than the 77,000 Da estimated for the glycosylated G protein from virus particles. The deduced amino acid sequence of the SYNV G protein shares little direct relatedness with the G proteins of other rhabdoviruses, but appears to contain a similar signal sequence, a transmembrane anchor domain, and glycosylation signals. In addition, the SYNV G protein contains a putative nuclear targeting site near the carboxy terminus, which may be involved in transit to the nuclear membrane prior to morphogenesis.

The glutamine synthetase gene family of Arabidopsis thaliana: light-regulation and differential expression in leaves, roots and seeds

Glutamine synthetase (GS) plays an important role in the assimilation of nitrogen by higher plants. We present here a molecular analysis of the GS polypeptides, mRNAs, and genes of Arabidopsis thaliana. Western blot analysis of leaf and root protein extracts revealed at least two distinct GS polypeptides; 43 kDa and 39 kDa GS polypeptides were present in leaves, while only a 39 kDa GS was detected in roots. The 43 kDa GS polypeptide is light-inducible. In etiolated seedlings only the 39 kDa GS was detected. However, upon greening the 43 kDa GS increased to levels comparable to those observed in light-grown plants. Four distinct GS cDNA clones, lambda Atgsl1, lambda Atgsr1, lambda Atgsr2 and lambda Atkb6 were isolated and characterized. Their complete nucleotide and deduced amino acid sequences are presented. The coding sequences of the four clones are 70-88% similar while their 5' and 3' untranslated regions exhibit less than 50% similarity. Northern blots of leaf, root and germinated seed RNA revealed that the four cDNAs hybridize to mRNAs which are differentially expressed in the organs of Arabidopsis thaliana. lambda Atgsl1 is leaf-specific and hybridizes to a 1.6 kb mRNA. Both lambda Atgsr1 and lambda Atgskb6 hybridize to 1.4 kb mRNAs which are expressed in both roots and germinated seeds. lambda Atgsr2 hybridizes to a 1.4 kb mRNA, which is primarily expressed in roots with low levels of expression in seeds and leaves. lambda Atgsl1, which represents the leaf-specific mRNA, is induced by light. lambda Atgsl1 mRNA levels increase during the greening of etiolated seedlings while lambda Atgsr1 levels remain constant. Southern blot analysis indicated that the Arabidopsis genome contains at least four and possibly five distinct GS genes.

Structure of the Hordeum vulgare gene encoding dihydroflavonol-4-reductase and molecular analysis of ant18 mutants blocked in flavonoid synthesis

A full-length cDNA clone encoding barley dihydroflavonol-4-reductase was isolated from a kernel-specific cDNA library by screening with the cDNA of the structural gene (A1) for this enzyme from maize. Subsequently, the gene corresponding to the barley dihydroflavonol-4-reductase cDNA was cloned and sequenced. The gene contains three introns at the same positions as in the Zea mays gene, corresponding to the positions of the first three of the five introns present in the genes of Petunia hybrida and Antirrhinum majus. In vitro transcription and translation of the Hordeum vulgare cDNA clone yielded a protein which converts dihydroquercetin into 2,3-trans-3,4-cis-leucocyanidin with NADPH as cofactor. The protein has a deduced amino acid sequence of 354 residues and a molecular weight of 38,400 daltons. Dihydroflavonol reductases of barley, maize, petunia and snapdragon are highly polymorphic in the NH2- and C-terminal parts of the polypeptide chain while a central region of 324 residues contains 51% identical amino acids. This identity increases to 81% when only the barley and maize enzymes are compared. Recessive mutants in the Ant18 gene tested so far lack dihydroflavonol-4-reductase activity and accumulate small amounts of dihydroquercetin but have retained activity for at least two other enzymes in the flavonoid pathway. In testa-pericarp tissue of mutants ant18-159, ant18-162 and ant18-164, wild-type levels of steady state mRNA for dihydroflavonol reductase have been measured, while mRNA for this enzyme is not transcribed in mutant ant18-161. These data are consistent with the proposal that the Ant18 locus carries the structural gene for dihydroflavonol-4-reductase of barley.

The barley genes Acl1 and Acl3 encoding acyl carrier proteins I and III are located on different chromosomes

Acyl carrier protein (ACP) is an essential cofactor for plant fatty acid synthesis. Three isoforms occur in barley seedling leaves. The genes Acl1 and Acl3 coding for the predominant ACP I and the minor ACP III, respectively, have been cloned and characterized as has a full-length cDNA for ACP III. Both genes, extending over more than 2.5 kb, have a conserved mosaic structure of four exons and three introns which result in mRNAs of ca. 900 bases. Alignment of the DNA sequences demonstrates that homology is restricted to the two exons coding for the mature protein whereas the remaining segments of the genes including the transit peptide-coding domains lack homology. Southern blot analyses demonstrate that Acl1 and Acl3 represent single copy genes located on chromosomes 7 and 1, respectively. Primer extension analyses identified multiple transcription start sites in both genes. The promoter regions are remarkably different; that of Acl3 resembles those for mammalian housekeeping genes in having a high G + C content plus three copies of an RNA polymerase II recognition GC element and in lacking correctly positioned TATA boxes. These features are in accordance with the hypothesis that Acl1 is specifically expressed in leaf tissue whereas Acl3 is a constitutively expressed gene.

Cloning and Sequencing of the cDNA Encoding the Rubber Elongation Factor of Hevea brasiliensis

In Hevea brasiliensis, the rubber particle in the laticiferous vessel is the site of rubber (cis-1-4-polyisoprene) biosynthesis. A 14 kilodalton protein, rubber elongation factor (REF), is associated with the rubber particle in a ratio of one REF to one rubber molecule (Dennis M, Henzel W, Bell J, Kohr W, Light D [1989] J Biol Chem 264: 18618-18628; Dennis M, Light D [1989] J Biol Chem 264: 18608-18617). To obtain more information concerning the function of REF and its synthesis and assembly in the rubber particle, we isolated cDNA clones encoding REF. We used antibodies to REF to screen a Hevea leaf gammagt11 cDNA expression library and obtained several positive clones. Sequence analysis of the REF cDNA clones showed that the REF mRNA contains 121 nucleotides of 5'-nontranslated sequences and a 205 nucleotide 3'-nontranslated region. The open reading frame encodes the entire 14 kilodalton REF protein without any extra amino acids (Dennis M, Henzel W, Bell J, Kohr W, Light D [1989] J Biol Chem 264: 18618-18628). The REF cDNA was subcloned in pGEM-3Z/-4Z and expressed in vitro. The translation product is a 14 kilodalton protein that can be immunoprecipitated with antibodies to REF. Addition of microsomal membranes to the in vitro translation product did not alter the mobility of the REF protein. This, and the sequence data, indicate that REF is not made as a preprotein. Our results suggest that REF is synthesized on free polysomes in the laticifer cytoplasm and that assembly of the rubber particles is likely to occur in the cytosol.

Agrobacterium rhizogenes pRi8196 T-DNA: mapping and DNA sequence of functions involved in mannopine synthesis and hairy root differentiation

This paper presents the map and DNA sequence analysis of pRi8196 transferred DNA (T-DNA) genes encoding root-inducing and mannopine synthesis functions. A canonical 24-base-pair border repeat as well as two "pseudoborders" are present at the functional right T-DNA border. To the left of this border are homologs of the mas1' and mas2' genes of TR pRiA4. Next to these are five open reading frames (ORFs) homologous to ORFs 10-14 of TL of pRiA4. ORFs 10-12 (rolA, rolB, and rolC) are less related to their pRiA4 homologs than are the other large ORFs analyzed here. In contrast to T-DNA genes of pRiA4, pRi8196 T-DNA ORFs 11 and 12 (rolB and rolC) are sufficient to induce hairy roots on carrot disks.

Molecular characterization and genetic origin of the Brassica napus acetohydroxyacid synthase multigene family

The Brassica napus rapeseed cultivar Topas contains an acetohydroxyacid synthase (AHAS) multigene family consisting of five members (AHAS 1-5). DNA sequence analysis indicate that AHAS1 and AHAS3 share extensive homology. They probably encode the AHAS enzymes essential for plant growth and development. AHAS2 has diverged significantly from AHAS1 and AHAS3 and has unique features in the coding region of the mature polypeptide, transit peptide and upstream non-coding DNA, which raises the possibility that it has a distinct function. AHAS4 and AHAS5 have interrupted coding regions and may be defective. The complexity of the AHAS multigene family in the allotetraploid species B. napus is much greater than reported for Arabidopsis thaliana and Nicotiana tabacum. Analysis of the presumptive progenitor diploid species B. campestris and B. oleracea indicated that AHAS2, AHAS3 and AHAS4 originate from the A genome, whereas AHAS1 and AHAS5 originate from the C genome. Further variation within each of the AHAS genes in these species was found.