Sequence of the structural gene for granule-bound starch synthase of potato (Solanum tuberosum L.) and evidence for a single point deletion in the amf allele

Relationships among Calibrachoa, Fabiana and Petunia (Petunieae tribe, Solanaceae) and a new generic placement of Argentinean endemic Petuniapatagonica

Calibrachoa Cerv., Fabiana Ruiz & Pav., and Petunia Juss. form a clade within tribe Petunieae (Solanaceae). Phylogenetic studies of Petunieae, either as part of a family-wide analysis or focusing on the genera Calibrachoa and Petunia, have either left Fabiana unsampled or included only a single species. These studies have found conflicting relationships among the three genera with all three possible topologies obtained. Petuniapatagonica (Speg.) Millán, originally described in the genus Nierembergia Ruiz & Pav., is morphologically distinct within Petunia and geographically disjunct from other members of the genus. For the first time, in this study we include multiple species of Fabiana, Calibrachoa, and Petunia, including P.patagonica. Using three chloroplast DNA regions and the nuclear gene GBSSI, or "waxy," our results provide strong support for a sister group relationship between Calibrachoa and Fabiana and for the placement of P.patagonica within Fabiana. Since there is already a species Fabianapatagonica Speg., we provide the new name Fabianaaustralis Alaria nom. nov. to replace Petuniapatagonica.

A modified procedure for the evaluation of the amylose and amylopectin content in potato starch

The article is devoted to the development of a technique for determining the content of amylose and amylopectin, effective for potato starch. Since potato starch is an important renewable raw material for a number of industries, it is important to have a throughput approach that allows potato starch samples to be tested quickly for the content of its constituent polysaccharides for potato breeding for starch properties and for starch industrial application. The developed technique includes elements of previously disjointed procedures for dissolution and spectrophotometric determination of amylose in starch, and combines the following advantages: 1) starch samples dissolve in an organic solvent (0.5 % solution of lithium bromide in dimethyl sulfoxide (DMS)); 2) measurement of light absorption is performed at two wavelengths, 550 and 510 nm, and 3) the technique is adapted for use with a plate spectrophotometer. This procedure allows starch polysaccharides to avoid to avoid hydrolysis during dissolution, allows the precise spectrophotometric determination of the concentration of amylose complex with iodine in solution, and opens the possibility of using this technique for throughput phenotyping. Applying a certain dissolution procedure, it is also possible to avoid the formation of gelled starch clots in solutions for spectrophotometry, which is important for the preparation of solutions containing amylose and amylopectin in the same proportions as in the original starch. The technique was tested on starch isolated from potato tubers varieties Lina, Velikan, Golubizna, Favorit of domestic selection. The technique developed can be used for phenotyping starch of an extended set of potato varieties (determining the content and composition of amylose in potato starch samples) to identify "trait-genotype” associations.

A soluble starch synthase I gene, IbSSI, alters the content, composition, granule size and structure of starch in transgenic sweet potato

Soluble starch synthase I (SSI) is a key enzyme in the biosynthesis of plant amylopectin. In this study, the gene named IbSSI, was cloned from sweet potato, an important starch crop. A high expression level of IbSSI was detected in the leaves and storage roots of the sweet potato. Its overexpression significantly increased the content and granule size of starch and the proportion of amylopectin by up-regulating starch biosynthetic genes in the transgenic plants compared with wild-type plants (WT) and RNA interference plants. The frequency of chains with degree of polymerization (DP) 5-8 decreased in the amylopectin fraction of starch, whereas the proportion of chains with DP 9-25 increased in the IbSSI-overexpressing plants compared with WT plants. Further analysis demonstrated that IbSSI was responsible for the synthesis of chains with DP ranging from 9 to 17, which represents a different chain length spectrum in vivo from its counterparts in rice and wheat. These findings suggest that the IbSSI gene plays important roles in determining the content, composition, granule size and structure of starch in sweet potato. This gene may be utilized to improve the content and quality of starch in sweet potato and other plants.

Genetic divergence and phylogeographic history of two closely related species (Leucomeris decora and Nouelia insignis) across the 'Tanaka Line' in Southwest China

BACKGROUND

Leucomeris decora and Nouelia insignis (Asteraceae) are narrowly and allopatrically distributed species, separated by the important biogeographic boundary Tanaka Line in Southwest China. Previous morphological, cytogenetic and molecular studies suggested that L. decora is sister to N. insignis. However, it is less clear how the two species diverged, whether in full isolation or occurring gene flow across the Tanaka Line. Here, we performed a molecular study at the population level to characterize genetic differentiation and decipher phylogeographic history in two closely related species based on variation examined in plastid and nuclear DNAs using a coalescent-based approach.

RESULTS

These morphologically distinct species share plastid DNA (cpDNA) haplotypes. In contrast, Bayesian analysis of nuclear DNA (nDNA) uncovered two distinct clusters corresponding to L. decora and N. insignis. Based on the IMa analysis, no strong indication of migration was detected based on both cpDNA and nDNA sequences. The molecular data pointed to a major west-east split in nuclear DNA between the two species corresponding with the Tanaka Line. The coalescent time estimate for all cpDNA haplotypes dated to the Mid-Late Pleistocene. The estimated demographic parameters showed that the population size of L. decora was similar to that of N. insignis and both experienced limited demographic fluctuations recently.

CONCLUSIONS

The study revealed comprehensive species divergence and phylogeographic histories of N. insignis and L. decora divided by the Tanaka Line. The phylogeographic pattern inferred from cpDNA reflected ancestrally shared polymorphisms without post-divergence gene flow between species. The marked genealogical lineage divergence in nDNA provided some indication of Tanaka Line for its role as a barrier to plant dispersal, and lent support to its importance in promoting strong population structure and allopatric divergence.

Characterization of the Granule-Bound Starch Synthase I Gene in Chenopodium

Chenopodium L. is a relatively under-studied genus that includes the cultivated seed crop quinoa (C. quinoa Willd.). Quinoa is an allotetraploid (2n = 4x = 36, AABB genomes) that is cultivated by subsistence farmers and commercial growers in the Andean regions of South America. Approximately 60% of a quinoa seed is starch, a glucose polymer that is an important carbohydrate energy source in the human diet. Seed starch is normally composed of amylose and amylopectin in a 1:3 ratio. The accumulation of the amylose fraction of starch is controlled by a single dominant gene in quinoa, GBSSI. We report the sequencing and characterization of the GBSSI gene in 18 accessions of Chenopodium, including Andean quinoa and the related Mesoamerican chenopod domesticate, C. berlandieri subsp. nuttalliae Saff. Two distinct homeologs (GBSSIa and GBSSIb) were identified in the tetraploid accessions, and 19 different alleles were identified, including three null mutants-one in an accession of quinoa and two in a waxy landrace of C. berlandieri subsp. nuttalliae. Expression analysis of the null mutants revealed that GBSSIa and GBSSIb were both strongly expressed late in seed development. GBSSI sequences were used to analyze the phylogenetic relationships between quinoa and other members of the Chenopodium genus. This study and the discovery of Chenopodium GBSSI null-mutants will assist in the development of new Chenopodium crops with novel starches.

Identification and characterization of granule bound starch synthase I (GBSSI) gene of tartary buckwheat (Fagopyrum tataricum Gaertn.)

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is increasingly considered as an important functional food material because of its rich nutraceutical compounds. Reserve starch is the major component of tartary buckwheat seed. However, the gene sequences and the molecular mechanism of tartary buckwheat starch synthesis are unknown so far. In this study, the complete genomic sequence and full-size cDNA coding tartary buckwheat granule-bound starch synthase I (FtGBSSI), which is responsible for amylose synthesis, were isolated and analyzed. The genomic sequence of the FtGBSSI contained 3947 nucleotides and was composed of 14 exons and 13 introns. The cDNA coding sequence of FtGBSSI shared 63.3%-75.1% identities with those of dicots and 56.6%-57.5% identities with monocots (Poaceae). In deduced amino acid sequence of FtGBSSI, eight motifs conserved among plant starch synthases were identified. A cleavage at the site IVC↓G of FtGBSSI protein produces the chloroplast transit sequence of 78 amino acids and the mature protein of 527 amino acids. The FtGBSSI mature protein showed an identity of 73.4%-77.8% with dicot plants, and 67.6%-70.4% with monocot plants (Poaceae). The mature protein was composed of 20 α-helixes and 16 β-strands, and folds into two main domains, N- and C-terminal domains. The critical residues which are involved in ADP and sugar binding were predicted. These results will be useful to modulate starch composition of buckwheat kernels with the aim to produce novel improved varieties in future breeding programs.

Species-specific identification from incomplete sampling: applying DNA barcodes to monitoring invasive solanum plants

Comprehensive sampling is crucial to DNA barcoding, but it is rarely performed because materials are usually unavailable. In practice, only a few rather than all species of a genus are required to be identified. Thus identification of a given species using a limited sample is of great importance in current application of DNA barcodes. Here, we selected 70 individuals representing 48 species from each major lineage of Solanum, one of the most species-rich genera of seed plants, to explore whether DNA barcodes can provide reliable specific-species discrimination in the context of incomplete sampling. Chloroplast genes ndhF and trnS-trnG and the nuclear gene waxy, the commonly used markers in Solanum phylogeny, were selected as the supplementary barcodes. The tree-building and modified barcode gap methods were employed to assess species resolution. The results showed that four Solanum species of quarantine concern could be successfully identified through the two-step barcoding sampling strategy. In addition, discrepancies between nuclear and cpDNA barcodes in some samples demonstrated the ability to discriminate hybrid species, and highlights the necessity of using barcode regions with different modes of inheritance. We conclude that efficient phylogenetic markers are good candidates as the supplementary barcodes in a given taxonomic group. Critically, we hypothesized that a specific-species could be identified from a phylogenetic framework using incomplete sampling-through this, DNA barcoding will greatly benefit the current fields of its application.

Monoclonal tobacco cell lines with enhanced recombinant protein yields can be generated from heterogeneous cell suspension cultures by flow sorting

Plant cell suspension cultures can be used for the production of recombinant pharmaceutical proteins, but their potential is limited by modest production levels that may be unstable over long culture periods, reflecting initial culture heterogeneity and subsequent genetic and epigenetic changes. We used flow sorting to generate highly productive monoclonal cell lines from a heterogeneous population of tobacco BY-2 cells expressing the human antibody M12 by selecting the co-expressed fluorescent marker protein DsRed located on the same T-DNA. Separation yielded ∼35% wells containing single protoplasts and ∼15% wells with monoclonal microcolonies that formed within 2 weeks. Thus, enriching the population of fluorescent cells from initially 24% to 90-96% in the six monoclonal lines resulted in an up to 13-fold increase in M12 production that remained stable for 10-12 months. This is the first straightforward procedure allowing the generation of monoclonal plant cell suspension cultures by flow sorting, greatly increasing the potential of plant cells as an economical platform for the manufacture of recombinant pharmaceutical proteins.

Isolation and characterization of the rye Waxy gene

Complete genomic and cDNA sequences of the Waxy gene encoding granule-bound starch synthase I (GBSSI) were isolated from the rye genome and characterized. The full-length rye Waxy genomic DNA and cDNA are 2767 bp and 1815 bp, respectively. The genomic sequence has 11 exons interrupted by 10 introns. The rye Waxy gene is GC-rich, with a higher GC frequency in the coding region, especially in the third position of the codons. Exon regions of the rye Waxy gene are more conserved than intron regions when compared with the homologous sequences of other cereals. The mature rye GBSSI proteins share more than 95% sequence identity with their homologs in wheat and barley. A phylogenetic tree based on sequence comparisons of available plant GBSSI proteins shows the evolutionary relationship among Waxy genes from rye and other plant genomes. The identification of the rye Waxy gene will enable the manipulation of starch metabolism in rye and triticale.

Precision breeding for novel starch variants in potato

Potato can be used as a source of modified starches for culinary and industrial processes, but its allelic diversity and tetraploid genome make the identification of novel alleles a challenge, and breeding such alleles into elite lines is a slow and difficult process. An efficient and reliable strategy has been developed for the rapid introduction and identification of new alleles in elite potato breeding lines, based on the ethylmethanesulphonate mutagenesis of dihaploid seeds. Using the granule-bound starch synthase I gene (waxy) as a model, a series of point mutations that potentially affect gene expression or enzyme function was identified. The most promising loss-of-function allele (waxy(E1100)) carried a mutation in the 5'-splice donor site of intron 1 that caused mis-splicing and protein truncation. This was used to establish elite breeding lineages lacking granule-bound starch synthase I protein activity and producing high-amylopectin starch. This is the first report of rapid and efficient mutation analysis in potato, a genetically complex and vegetatively propagated crop.

Potato glycosterol rhamnosyltransferase, the terminal step in triose side-chain biosynthesis

Steroidal glycoalkaloids (SGAs) are potentially harmful specialty metabolites found in Solanaceous plants. Two tri-glycosylated alkaloids, alpha-chaconine and alpha-solanine accumulate in potato tubers. Expressed sequence tags (ESTs) were identified in the available database by searching for protein homology to the Sgt1 (SOLtu:Sgt1) steriodalalkaloid galactosyltransferase. The EST sequence data was used to isolate Sgt3 cDNA sequences by polymerase chain reaction (PCR) from a wounded potato tuber cDNA library. The resulting 1515bp open reading frame of Sgt3, encodes a predicted SGT3 amino acid sequence that is 18 residues longer than, 45% identical to, and 58% homologous to the SGT1 protein. The amino-terminal region of the Sgt3 cDNA was used to create an antisense transgene under control of the granule bound starch synthase, GBSS6, promoter and the ubiquitin, Ubi3, polyadenylation signal. Analysis of SGA metabolites in selected transgenic tubers revealed a dramatic decrease in the accumulation of alpha-chaconine and alpha-solanine. This decrease was compensated by an increase in beta-solanine and beta-chaconine with minor accumulation of alpha-SGAs. These results allowed the identification of the function for SGT3 as the beta-solanine/beta-chaconine rhamnosyl transferase, the terminal step in formation of the potato glycoalkaloid triose side chains.

Assessing the potential for unintended effects in genetically modified potatoes perturbed in metabolic and developmental processes. Targeted analysis of key nutrients and anti-nutrients

Targeted compositional analysis was carried out on transgenic potato tubers of either cultivar (cv.) Record or cv. Desirée to assess the potential for unintended effects caused by the genetic modification process. The range of transgenic lines analysed included those modified in primary carbohydrate metabolism, polyamine biosynthesis and glycoprotein processing. Controls included wildtype tubers, tubers produced from plants regenerated through tissue culture (including a callus phase) and tubers derived from transformation with the 'empty vector' i.e. no specific target gene included (with the exception of the kanamycin resistance gene as a selectable marker). Metabolite analysis included soluble carbohydrates, glycoalkaloids, vitamin C, total nitrogen and fatty acids. Trypsin inhibitor activity was also assayed. These cover the major compounds recommended by the OECD in their Consensus Document on Compositional Considerations for New Varieties of Potatoes: Key Food and Feed Nutrients, Anti-Nutrients and Toxicants (2002). Data was statistically analysed using analysis of variance (ANOVA) for individual compounds and, where applicable, principal component analysis (PCA). In general, targeted compositional analysis revealed no consistent differences between GM lines and respective controls. No construct specifically induced unintended effects. Statistically significant differences between wildtype controls and specific GM lines did occur but appeared to be random and not associated with any specific construct. Indeed such significant differences were also found between wildtypes and both tissue culture derived tubers and tubers derived from transformation with the empty vector. This raises the possibility that somaclonal variation (known to occur significantly in potato, depending on genotype) may be responsible for an unknown proportion of any differences observed between specific GM lines and the wildtype. The most obvious differences seen in GC-MS profiles were between the two potato varieties used in the study.

Expression of an engineered granule-bound Escherichia coli maltose acetyltransferase in wild-type and amf potato plants

Starch is used in many industrial applications, but often requires chemical derivatization to enhance its properties before use. In particular, the stability of starch polymers in solution is improved by acetylation. A drawback of this treatment is the use of pollutant chemicals. A biological alternative to chemical derivatization was investigated by the expression of an amyloplast-targeted Escherichia coli maltose acetyltransferase (MAT) gene in tubers of wild-type (Kardal) and mutant amylose-free (amf) potato plants. MAT was expressed as such, or fused to the N- or C-terminus of a non-catalytic starch-binding domain (SBD) to target the starch granule. Starch granules derived from transgenic plants were found to contain acetyl groups, although their content was low, opening up an avenue to move away from the post-harvest chemical derivatization of starch. MAT inside starch granules was found to be active post-harvest when supplied with acetyl-coenzyme A and glucose or maltose, but it did not acetylate starch polymers in vitro. Starch granules from transformants in which MAT alone was expressed also showed MAT activity, indicating that MAT is accumulated in starch granules, and has affinity for starch by itself. Furthermore, starch granule morphology was altered, and fusion proteins containing MAT and SBD seemed to have a higher affinity for starch granules than two appended SBDs. These results are discussed against the background of the quaternary structure of MAT.

Ancestral reconstruction of flower morphology and pollination systems in Schizanthus (Solanaceae)

Concerted changes in flower morphology and pollinators provide strong evidence on adaptive evolution. Schizanthus (Solanaceae) has zygomorphic flowers and consists of 12 species of annual or biennial herbs that are distributed mainly in Chile and characterized by bee-, hummingbird-, and moth-pollination syndromes. To infer whether flowers diversified in relation to pollinator shifts, we traced the evolutionary trajectory of flower traits and visitors onto a phylogeny based on sequence data from ITS, waxy, and trnF/ndhJ DNA. Maximum-likelihood ancestral reconstruction of floral traits suggests that ancestral Schizanthus had a bee-pollination syndrome. The hummingbird syndrome evolved in S. grahamii, a high elevation species in the Andes. The moth syndrome evolved in the ancestor of three species that inhabit the Atacama Desert. Results of mapping flower visitors onto the phylogeny show that the shift from bee to hummingbird pollination concurred with a shift in pollinators as predicted by the syndromes. However, the same pattern was not found for the moth syndrome. Visits by moths were observed only in one of the three moth-syndrome species, and at a very low rate. This mismatch suggests either anachronic floral characters or maintenance of rare, imperceptible moth pollination backed up by capacity for autonomous selfing. Overall, results suggest that diversification of flower traits in Schizanthus has occurred in relation to pollinator shifts.

Post-transcriptional gene silencing of GBSSI in potato: effects of size and sequence of the inverted repeats

In the past, silencing of granule-bound starch synthase (GBSSI) in potato was achieved by antisense technology, where it was observed that inclusion of the 3' end of the GBSSI coding region increased silencing efficiency. Since higher silencing efficiencies were desired, GBSSI inverted repeat constructs were designed and tested in potato. First, large inverted repeats comprising the 5' and the 3' half of the GBSSI cDNA were tested. The 5' IR construct gave a significantly higher silencing efficiency than the 3' IR construct. Since it was not known whether the observed difference was due to the sequence or the orientation of the inverted repeat, the GBSSI cDNA was divided into three regions, after which each region was tested in small inverted repeats in two orientations. To this end large numbers of independent transformants were produced for each construct. The results suggested that there was no effect of inverted repeat orientation on silencing efficiency. The percentage of transformants showing strong inhibition varied from 48% for a 3'-derived construct to 87% for a 5' as well as a middle region-derived construct. Similar to the large inverted repeats, the 3' sequences induced the least efficient silencing implying that the observed differences in silencing efficiency are caused by sequence differences. The small inverted repeat constructs with a repeat size of 500-600 bp and a spacer of about 150 bp were more efficient silencing inducers than the large inverted repeat constructs where the size of the repeat was 1.1 or 1.3 kb whilst the size of spacer was 1.3 or 1.1 kb. The results presented here show that size and sequence of the inverted repeat influenced silencing efficiency.

Efficiency of transcriptional gene silencing of GBSSI in potato depends on the promoter region that is used in an inverted repeat

Transcriptional gene silencing (TGS) of the endogenous GBSSI promoter in potato was induced by inverted repeat constructs containing different regions of the GBSSI promoter. Clear differences in silencing efficiency were observed. The 35SGBP-IR construct, containing sequences from -766 to -168 bp relative to the transcription initiation site (TIS), induced weak silencing effects in 57-60% of the transformants. Weak silencing effects were also induced by the ASP-IR construct harbouring allele-specific sequences covering the region from -531 to -330 bp relative to the TIS, but only in a low percentage (4-5.5%) of the transformants. These percentages are too low to distinguish effects between the two potato cultivars. Therefore, this approach cannot be used to induce allele-specific TGS. Strong silencing effects were obtained in 49% of the transformants harbouring the full promoter inverted repeat construct. This construct contained sequences from -766 to +194 bp relative to the TIS. In the strongly silenced transformants no GBSSI mRNA could be detected by Northern blot analysis. This was accompanied by the accumulation of GBSSI promoter-specific small interfering RNAs. Methylation studies revealed that, in the weakly silenced 35SGBP-IR transformants, the HpaII site at -213 bp relative to the TIS was methylated. Apparently, methylation of this sequence does not result in strong silencing effects. In the full promoter transformants, both CG methylation and CNN methylation were detected. We show that, to obtain strong TGS, it is important to include sequences in the vicinity of the TIS.

Production of dextran in transgenic potato plants

The production of dextran in potato tubers and its effect on starch biosynthesis were investigated. The mature dextransucrase (DsrS) gene from Leuconostoc mesenteroides was fused to the chloroplastic ferredoxin signal peptide (FD) enabling amyloplast entry, which was driven by the highly tuber-expressed patatin promoter. After transformation of two potato genotypes (cv. Kardal and the amylose-free (amf) mutant), dextrans were detected by enzyme-linked immunosorbent assay (ELISA) in tuber juices of Kardal and amf transformants. The dextran concentration appeared two times higher in the Kardal (about 1.7 mg/g FW) than in the amf transformants. No dextran was detected by ELISA inside the starch granule. Interestingly, starch granule morphology was affected, which might be explained by the accumulation of dextran in tuber juices. In spite of that, no significant changes of the physicochemical properties of the starches were detected. Furthermore, we have observed no clear changes in chain length distributions, despite the known high acceptor efficiency of DSRS.

cDNA cloning, expression, and characterization of Taro SSII: a novel member of starch synthase II family

A novel soluble starch synthase II (SSII) gene was isolated from taro (Colocasia esculenta var. esculenta) tubers. This 2939 bp SSII transcript encodes 804 amino acids with a putative transit peptide of 52 residues. It displays 58-63% identity and 63-69% similarity with SSIIs from other sources. Alignment and phylogenetic analyses showed that taro SSII is more closely related with dicot SSIIs than with the monocot ones, though taro is a monocot. The identification of taro SSII clone as starch synthase was confirmed by the expression of its enzymatic activity in Escherichia coli. Genomic DNA blot analysis revealed a single copy or low number copies of SSII in taro. Expression profile showed that more transcript and protein were accumulated in tubers of 597 +/- 37 g fresh weight, that is, a stage of rapid starch synthesis, than tubers of other stages. By Western blot analysis, SSII was found in both soluble and granule bound portions of tuber extracts, and more SSII protein was found in aged leaves than in leaves of other stages. These results suggest that taro SSII is a novel starch synthase for the synthesis of both transit and storage starch.

Cloning, expression, and characterization of soluble starch synthase I cDNA from taro (Colocasia esculenta Var. esculenta)

Soluble starch synthase I (SSSI) cDNA was isolated from taro (Colocasia esculenta var. esculenta) by RT-PCR and rapid amplification of cDNA ends reaction. The transcript of this single-copy gene is 2340 bp and encodes 642 amino acids protein containing a putative transit peptide of 54 residues. Recombinant SSSI protein displayed both primer-dependent and primer-independent activities of starch synthase. More SSSI transcript was expressed in taro leaves than in tubers, with no evident expression in petioles; and more transcript and protein were found in tubers of 597 +/- 37 g of fresh weight than in smaller or larger ones. Two forms of SSSI, i.e., 72 and 66 kDa, exist in leaves, and only the 66 kDa form was found in tubers. The taro SSSI, proposed as a novel member, was located only in the soluble fraction of tuber extract, while SSSI from other sources exist in both soluble and granule-bound forms.

Comparison of tuber proteomes of potato varieties, landraces, and genetically modified lines

Crop improvement by genetic modification remains controversial, one of the major issues being the potential for unintended effects. Comparative safety assessment includes targeted analysis of key nutrients and antinutritional factors, but broader scale-profiling or "omics" methods could increase the chances of detecting unintended effects. Comparative assessment should consider the extent of natural variation and not simply compare genetically modified (GM) lines and parental controls. In this study, potato (Solanum tuberosum) proteome diversity has been assessed using a range of diverse non-GM germplasm. In addition, a selection of GM potato lines was compared to assess the potential for unintended differences in protein profiles. Clear qualitative and quantitative differences were found in the protein patterns of the varieties and landraces examined, with 1,077 of 1,111 protein spots analyzed showing statistically significant differences. The diploid species Solanum phureja could be clearly differentiated from tetraploid (Solanum tuberosum) genotypes. Many of the proteins apparently contributing to genotype differentiation are involved in disease and defense responses, the glycolytic pathway, and sugar metabolism or protein targeting/storage. Only nine proteins out of 730 showed significant differences between GM lines and their controls. There was much less variation between GM lines and their non-GM controls compared with that found between different varieties and landraces. A number of proteins were identified by mass spectrometry and added to a potato tuber two-dimensional protein map.

Mutan produced in potato amyloplasts adheres to starch granules

Production of water-insoluble mutan polymers in Kardal potato tubers was investigated after expression of a full-length (GtfI) and a truncated mutansucrase gene referred to as GtfICAT (GtfI without glucan-binding domain) from Streptococcus downei. Subsequent effects on starch biosynthesis at the molecular and biochemical levels were studied. Expression of the GtfICAT gene resulted in the adhesion of mutan material on starch granules, which stained red with erythrosine, and which was hydrolysed by exo-mutanase. In addition, GtfICAT-expressing plants exhibited a severely altered tuber phenotype and starch granule morphology in comparison to those expressing the full-length GtfI gene. In spite of that, no structural changes at the starch level were observed. Expression levels of the sucrose-regulated, AGPase and GBSSI genes were down-regulated in only the GTFICAT transformants, showing that GtfICAT expression interfered with the starch biosynthetic pathway. In accordance with the down-regulated AGPase gene, a lower starch content was observed in the GTFICAT transformants. Finally, the rheological properties of the GTFICAT starches were modified; they showed a higher retrogradation during cooling of the starch paste.

A four-gene study of evolutionary relationships in Solanum section Acanthophora

The "spiny solanums," Solanum subgenus Leptostemonum (Solanaceae), comprise a large lineage with over 350 species and include the cultivated eggplant, Solanum melongena. Despite the importance of this subgenus, phylogenetic relationships among these taxa are currently unclear. The present research contributes to this understanding while focusing on Solanum section Acanthophora, a group of ca. 19 species defined by the presence of simple hairs, rather than the stellate hairs common across the rest of subgenus Leptostemonum. In this study we inferred phylogenetic relationships among 29 Solanum taxa, including 14 species of section Acanthophora, using DNA sequence data from two nuclear regions (ITS and the granule-bound starch synthase gene [GBSSI or waxy]) and two chloroplast regions (trnT-trnF and trnS-trnG). This combination of gene regions resulted in a well resolved phylogenetic hypothesis, with results strongly suggesting that Solanum sect. Acanthophora is not monophyletic, although the majority of taxa comprise a monophyletic lineage that is sister to Solanum section Lasiocarpa. Of the four gene regions, waxy was especially useful for phylogenetic inference, with both a high percentage of parsimony-informative sites as well as a low level of homoplasy. Further studies in progress will help elucidate relationships of sect. Acanthophora with respect to other members of subgenus Leptostemonum.

Viburnum phylogeny: evidence from the duplicated nuclear gene GBSSI

DNA sequencing studies of the granule-bound starch synthase gene (GBSSI) indicate the presence of two loci in Viburnum. Gene trees from separate and combined phylogenetic analyses of the GBSSI paralogues are generally congruent with each other and with trees from previous analyses, especially those of Donoghue et al. [Syst. Bot. 29 (2004) 188] based on nuclear ribosomal ITS and chloroplast trnK intron DNA sequences. Specifically, our GBSSI trees confirm (i) the monophyly of some and non-monophyly of other traditionally recognized taxonomic sections, (ii) the presence of three major supra-sectional lineages within Viburnum, and (iii) the resolution of many species relationships within the section-level clades. Analyses of GBSSI also provide greater resolution of relationships within the largest supra-sectional lineage. Relationships at the base of the Viburnum phylogeny remain uncertain; in particular, the position of the root, relationships among the supra-sectional clades, and the exact placement of several smaller groups (e.g., Viburnum clemensiae, Viburnum urceolatum, and section Pseudotinus). In two lineages each GBSSI paralogue is represented by two distinct sequences. The presence of additional copies appears to be correlated with polyploidy in these clades. Placement of the homoeologues in our gene trees suggests the possibility of a hybrid origin for these polyploids.

Involvement of lysine-193 of the conserved "K-T-G-G" motif in the catalysis of maize starch synthase IIa

It has been suggested that the lysine residue in the conserved K-T-G-G motif could be the substrate ADP-glucose binding site of Escherichia coli glycogen synthase (GS). Since the K-X-G-G motif is highly conserved between E. coli GS and all the maize starch synthase (SS) isozymes, it has become widely accepted that the lysine in the conserved K-T-G-G motif may also function as the ADPGlc binding site of maize SS. We have used chemical modification and site-directed mutagenesis to study the function of lysine residues in SS. Pyridoxal-5'-phosphate inactivated maize SSIIa activity in a time and concentration dependent manner. ADPGlc completely protected SSIIa from inactivation by pyridoxal-5'-phosphate, indicating that lysine residue(s) could be important for ADPGlc binding and enzyme catalysis. In contrast to E. coli GS, mutation of conserved lysine193 (K-T-G-G) in maize SS did not alter the ADPGlc binding while significantly changing the enzyme activity toward different primers. Our results suggest that lysine-193 (K-T-G-G) is not directly involved in ADPGlc binding, instead mutation in the conserved lysine position affected the primer preference.

Effective production of marker-free transgenic strawberry plants using inducible site-specific recombination and a bifunctional selectable marker gene

Public concerns about the issue of the environmental safety of genetically modified plants have led to a demand for technologies allowing the production of transgenic plants without selectable (antibiotic resistance) markers. We describe the development of an effective transformation system for generating such marker-free transgenic plants, without the need for repeated transformation or sexual crossing. This system combines an inducible site-specific recombinase for the precise elimination of undesired, introduced DNA sequences with a bifunctional selectable marker gene used for the initial positive selection of transgenic tissue and subsequent negative selection for fully marker-free plants. The described system can be generally applied to existing transformation protocols, and was tested in strawberry using a model vector in which site-specific recombination leads to a functional combination of a cauliflower mosaic virus 35S promoter and a GUS encoding sequence, thereby enabling the histochemical monitoring of recombination events. Fully marker-free transgenic strawberry plants were obtained following two different selection/regeneration strategies.

Reduction of starch granule size by expression of an engineered tandem starch-binding domain in potato plants

Granule size is an important parameter when using starch in industrial applications. An artificial tandem repeat of a family 20 starch-binding domain (SBD2) was engineered by two copies of the SBD derived from Bacillus circulans cyclodextrin glycosyltransferase via the Pro-Thr-rich linker peptide from Xyn10A from Cellulomonas fimi. SBD2 and a single SBD were introduced into the amylose-free potato mutant, amf, using appropriate signal sequences. The accumulation of SBD2 into transgenic starch granules was much higher than that of SBD. In a number of transformants, particularly amfSS3, the starch granules were much smaller than in control plants. The amfSS3 mean granule size was 7.8 microm, compared with 15.2 microm in the control, whereas other starch properties were unaltered. This new starch combines the advantage of the high purity of potato starch with that of the small granule size of other crop species, such as cassava, taro and wheat. This starch may find application in the manufacture of biodegradable plastic films. Both genes were also expressed in Escherichia coli and the affinity for soluble starch of the purified recombinant proteins was determined. SBD2 had an approximately 10-fold higher affinity for starch than SBD, indicating that the two appended SBDs act in synergy when binding to their target polysaccharide ligand.

Starch properties of the sago palm (Metroxylon sagu Rottb.) in different soils

We investigated the relationships between starch concentrations and activities of starch synthetic enzymes in sago palms (Metroxylon sagu Rottb.) under acid sulfate and mineral soil conditions. Plants grown naturally that had reached their maturated stage were sampled. We found that the growth in acid sulfate soil is lower than that in mineral soil and that starch granules were larger and there was more amylase activity in acid sulfate soil than in mineral soil. Lower amylase activity in mineral soil could eliminate the degradation of starch, making the smaller granules suitable for storing large amounts of starch in a limited space inside cells.

The biosynthesis of starch granules

Although composed simply of glucose polymers, the starch granule is a complex, semicrystalline structure. Much of this complexity arises from the fact that the two primary enzymes of synthesis-starch synthase and starch-branching enzyme-exist as multiple isoforms. Each form has distinct properties and plays a unique role in the synthesis of the two starch polymers, amylose and amylopectin. The debranching enzyme isoamylase also has a profound influence on the synthesis of amylopectin. Despite much speculation, no acceptable model to explain the interactions of all of these enzymes to produce amylose and amylopectin has thus far emerged. The organization of newly synthesized amylopectin to form the semicrystalline matrix of the granule appears to be a physical process, implying the existence of complex interactions between biological and physical processes at the surface of the growing granule. The synthesis of the amylose component occurs within the amylopectin matrix.

Granule-bound starch synthase (GBSSI) gene phylogeny of wild tomatoes (Solanum L. section Lycopersicon [Mill.] Wettst. subsection Lycopersicon)

Eight wild tomato species are native to western South America and one to the Galapagos Islands. Different classifications of tomatoes have been based on morphological or biological criteria. Our primary goal was to examine the phylogenetic relationships of all nine wild tomato species and closely related outgroups, with a concentration on the most widespread and variable tomato species Solanum peruvianum, using DNA sequences of the structural gene granule-bound starch synthase (GBSSI, or waxy). Results show some concordance with previous morphology-based classifications and new relationships. The ingroup comprised a basal polytomy composed of the self-incompatible green-fruited species S. chilense and the central to southern Peruvian populations of S. peruvianum, S. habrochaites, and S. pennellii. A derived clade contains the northern Peruvian populations of S. peruvianum (also self-incompatible, green-fruited), S. chmielewskii, and S. neorickii (self-compatible, green-fruited), and the self-compatible and red- to orange- to yellow-fruited species S. cheesmaniae, S. lycopersicum, and S. pimpinellifolium. Outgroup relationships are largely concordant with prior chloroplast DNA restriction site phylogenies, support S. juglandifolium and S. ochranthum as the closest outgroup to tomatoes with S. lycopersicoides and S. sitiens as basal to these, and support allogamy, self-incompatibility, and green fruits as primitive in the tomato clade.

The granule-bound starch synthase (GBSSI) gene in the Rosaceae: multiple loci and phylogenetic utility

We sampled the 5' end of the granule-bound starch synthase gene (GBSSI or waxy) in Rosaceae, sequencing 108 clones from 18 species in 14 genera representing all four subfamilies (Amygdaloideae, Maloideae, Rosoideae, and Spiraeoideae), as well as four clones from Rhamnus catharticus (Rhamnaceae). This is the first phylogenetic study to use the 5' portion of this nuclear gene. Parsimony and maximum-likelihood analyses of 941 bases from seven complete and two partial exons demonstrate the presence of two loci (GBSSI-1 and GBSSI-2) in the Rosaceae. Southern hybridization analyses with locus-specific probes confirm that all four Rosaceae subfamilies have at least two GBSSI loci, even though only one locus has been reported in all previously studied diploid flowering plants. Phylogenetic analyses also identify four clades representing four loci in the Maloideae. Phylogenetic relationships inferred from GBSSI sequences are largely compatible with those from chloroplast (cpDNA: ndhF, rbcL) and nuclear ribosomal internal transcribed spacer (nrITS) DNA. Large clades are marked by significant intron variation: a long first intron plus no sixth intron in Maloideae GBSSI-1, a long fourth intron in Rosoideae GBSSI-1, and a GT to GC mutation in the 5' splice site of the fourth intron in all GBSSI-2 sequences. Our data do not support the long-held hypothesis that Maloideae originated from an ancient hybridization between amygdaloid and spiraeoid ancestors. Instead, Spiraeoideae genera (Kageneckia and Vauquelinia) are their closest relatives in all four GBSSI clades.

The structure and expression of the wheat starch synthase III gene. Motifs in the expressed gene define the lineage of the starch synthase III gene family

The endosperm of hexaploid wheat (Triticum aestivum [L.]) was shown to contain a high molecular weight starch synthase (SS) analogous to the product of the maize du1 gene, starch synthase III (SSIII; DU1). cDNA and genomic DNA sequences encoding wheat SSIII were isolated and characterized. The wheat SSIII cDNA is 5,346 bp long and contains an open reading frame that encodes a 1,628-amino acid polypeptide. A putative N-terminal transit peptide, a 436-amino acid C-terminal catalytic domain, and a central 470-amino acid SSIII-specific domain containing three regions of repeated amino acid similarity were identified in the wheat gene. A fourth region between the transit peptide and the SSIII-specific domain contains repeat motifs that are variable with respect to motif sequence and repeat number between wheat and maize. In dicots, this N-terminal region does not contain repeat motifs and is truncated. The gene encoding wheat SSIII, designated ss3, consists of 16 exons extending over 10 kb, and is located on wheat chromosome I. Expression of ss3 mRNA in wheat was detected in leaves, pre-anthesis florets, and from very early to middle stage of endosperm development. The entire N-terminal variable repeat region and the majority of the SSIII-specific domain are encoded on a single 2,703-bp exon. A gene encoding a class III SS from the Arabidopsis genome sequencing project shows a strongly conserved exon structure to the wheat ss3 gene, with the exception of the N-terminal region. The evolutionary relationships of the genes encoding monocot and dicot class III SSs are discussed.

The genes encoding granule-bound starch synthases at the waxy loci of the A, B, and D progenitors of common wheat

Three genes encoding granule-bound starch synthase (wx-TmA, wx-TsB, and wx-TtD) have been isolated from Triticum monococcum (AA), and Triticum speltoides (BB), by the polymerase chain reaction (PCR) approach, and from Triticum tauschii (DD), by screening a genomic DNA library. Multiple sequence alignment indicated that the wx-TmA, wx-TsB, and wx-TtD genes had the same extron and (or) intron structure as the previously reported waxy gene from barley. The lengths of the three wx-TmA, wx-TsB, and wx-TtD genes were 2834 bp, 2826 bp, and 2893 bp, respectively, each covering 31 bp in the untranslated leader and the entire coding region consisting of 11 exons and 10 introns. The three genes had identical lengths of exons, except exonl, and shared over 95% identity with each other within the exon regions. The majority of introns were significantly variable in length and sequence, differing mainly in length (1-57 bp) as a result of insertion and (or) deletion events. The deduced amino acid sequence from these three genes indicated that the mature WX-TMA, -TSB, and -TTD proteins contained the same number of amino acids, but differed in predicted molecular weight and isoelectric point (pI) due to amino acid substitutions (13-18). The predicted physical characteristics of the WX proteins matched the respective proteins in wheat very closely, but the match was not perfect. Furthermore the exon5 sequences of the wx-TmA, wx-TsB, and wx-TtD genes were different from a cDNA encoding a waxy gene of common wheat previously reported. The striking difference was that an insertion of 11 amino acids occurred in the cDNA sequence that could not be observed in the exons of the A, B, and D genes. It was noted, however, that the 3' end of intron4 of these genes could account for the additional 11 amino acids. The sequence information from the available waxy genes identified the intron4-exon5-intron5 region as being diagnostic for sequence variation in waxy. The sequence variation in the waxy genes provides the basis for primer design to distinguish the respective genes in common wheat, and its progenitors, using PCR.

The localization and expression of the class II starch synthases of wheat

The starch granules of hexaploid wheat (Triticum aestivum) contain a group of three proteins known as SGP-1 (starch granule protein-1) proteins, which have apparent molecular masses of 100, 108, and 115 kD. The nature and role of these proteins has not been defined previously. We demonstrate that these polypeptides are starch synthases that are present in both the starch granule and the soluble fraction at the early stages of wheat endosperm development, but that are exclusively granule bound at mid and late endosperm development. A partial cDNA clone encoding a fragment of the 100-kD protein was obtained by screening a wheat endosperm cDNA expression library using monoclonal antibodies. Three classes of cDNA were subsequently isolated from a wheat endosperm cDNA library by nucleic acid hybridization and were shown to encode the 100-, 108-, and 115-kD proteins. The cDNA sequences are highly homologous to class II starch synthases and have the highest homology with the maize SSIIa (starch synthase IIa) gene. mRNA for the SGP-1 proteins was detected in the leaf, pre-anthesis florets, and endosperm of wheat and is highly expressed in the leaf and in the grain during the early to mid stages of development. We discuss the roles of the SGP-1 proteins in starch biosynthesis in wheat.

Cytological evidence that the C-terminus of carnitine palmitoyltransferase I is on the cytosolic face of the mitochondrial outer membrane

Carnitine palmitoyltransferase I (CPT I) is a key enzyme in the regulation of beta-oxidation. The topology of this enzyme has been difficult to elucidate by biochemical methods. We studied the topology of a fusion protein of muscle-type CPT I (M-CPT I) and green fluorescent protein (GFP) by microscopical means. To validate the use of the fusion protein, designated CPT I-GFP, we checked whether the main characteristics of native CPT I were retained. CPT I-GFP was expressed in HeLa cells after stable transfection. Confocal laser scanning microscopy in living cells revealed an extranuclear punctate distribution of CPT I-GFP, which coincided with a mitochondrial fluorescent marker. Immunogold electron microscopy localized CPT I-GFP almost exclusively to the mitochondrial periphery and showed that the C-terminus of CPT I must be on the cytosolic face of the mitochondrial outer membrane. Western analysis showed a protein that was 6 kDa smaller than predicted, which is consistent with previous results for the native M-CPT I. Mitochondria from CPT I-GFP-expressing cells showed an increased CPT activity that was inhibited by malonyl-CoA and was lost on solubilization with Triton X-100. We conclude that CPT I-GFP adopts the same topology as native CPT I and that its C-terminus is located on the cytosolic face of the mitochondrial outer membrane. The evidence supports a recently proposed model for the domain structure of CPT I based on biochemical evidence.

Isolation and characterization of the three Waxy genes encoding the granule-bound starch synthase in hexaploid wheat

Complete genomic DNA sequences of three homoeologous Waxy structural genes, located on the chromosomes 7A, 4A, and 7D in hexaploid wheat (Triticum aestivum L. cv. Chinese Spring), were separately determined and analyzed. Those structural genes in lengths from start to stop codon were 2781bp in Wx-7A, 2794bp in Wx-4A, and 2862bp in Wx-7D, each of which consisted of 11 exons and ten introns. They were closely similar to one another in the nucleotide sequences, with 95.6-96.3% homology in mature protein regions, 88. 7-93.0% in transit-peptide regions, and 70.5-75.2% in the introns. These wheat Waxy genes were GC-rich when compared with standard values for plant genomes reported so far. This was reflected in the extremely high G/C occupation frequency at the third position of the codons in the coding regions. The sequence divergence in the exon regions was mostly due to the substitution of nucleotides, whereas that found in the introns was attributed to substitution, insertion and/or deletion of nucleotides. Only the Wx-4A gene contained a trinucleotide insertion (CAA) in the region encoding the transit peptide. Most of the substitutions observed in the exon regions were categorized as synonymous, and higher sequence similarities (96.5-97. 4%) were conserved at the protein level. The phylogenetic tree obtained in terms of the amino acid sequence variations showed a well-resolved phylogenetic relationship among wheat Waxy genes and those from other plants.

Identification of the soluble starch synthase activities of maize endosperm

This study identified the complement of soluble starch synthases (SSs) present in developing maize (Zea mays) endosperm. The product of the du1 gene, DU1, was shown to be one of the two major soluble SSs. The C-terminal 450 residues of DU1 comprise eight sequence blocks conserved in 28 known or predicted glucan synthases. This region of DU1 was expressed in Escherichia coli and shown to possess SS activity. DU1-specific antisera detected a soluble endosperm protein of more than 200 kD that was lacking in du1- mutants. These antisera eliminated 20% to 30% of the soluble SS activity from kernel extracts. Antiserum against the isozyme zSSI eliminated approximately 60% of the total soluble SS, and immunodepletion of du1- mutant extracts with this antiserum nearly eliminated SS activity. Two soluble SS activities were identified by electrophoretic fractionation, each of which correlated specifically with zSSI or DU1. Thus, DU1 and zSSI accounted for the great majority of soluble SS activity present in developing endosperm. The relative activity of the two isozymes did not change significantly during the starch biosynthetic period. DU1 and zSSI may be interdependent, because mutant extracts lacking DU1 exhibited a significant stimulation of the remaining SS activity.

Fission yeast alpha-glucan synthase Mok1 requires the actin cytoskeleton to localize the sites of growth and plays an essential role in cell morphogenesis downstream of protein kinase C function

In fission yeast protein kinase C homologues (Pck1 and Pck2) are essential for cell morphogenesis. We have isolated mok1(+) in a genetic screen to identify downstream effectors for Pck1/2. mok1(+) is essential for viability and encodes a protein that has several membrane-spanning domains and regions homologous to glucan metabolic enzymes. mok1 mutant shows abnormal cell shape, randomization of F-actin and weak cell wall. Biochemical analysis shows that Mok1 appears to have alpha-glucan synthase activity. Mok1 localization undergoes dramatic alteration during the cell cycle. It localizes to the growing tips in interphase, the medial ring upon mitosis, a double ring before and dense dot during cytokinesis. Double immunofluorescence staining shows that Mok1 exists in close proximity to actin. The subcellular localization of Mok1 is dependent upon the integrity of the F-actin cytoskeleton. Conversely, overexpression of mok1(+) blocks the translocation of cortical actin from one end of the cell to the other. pck2 mutant is synthetically lethal with mok1 mutant, delocalizes Mok1 and shows a lower level of alpha-glucan. These results indicate that Mok1 plays a crucial role in cell morphogenesis interdependently of the actin cytoskeleton and works as one of downstream effectors for Pck1/2.

Characterization of a granule-bound starch synthase isoform found in the pericarp of wheat

Waxy wheat (Triticum aestivum L.) lacks the waxy protein, which is also known as granule-bound starch synthase I (GBSSI). The starch granules of waxy wheat endosperm and pollen do not contain amylose and therefore stain red-brown with iodine. However, we observed that starch from pericarp tissue of waxy wheat stained blue-black and contained amylose. Significantly higher starch synthase activity was detected in pericarp starch granules than in endosperm starch granules. A granule-bound protein that differed from GBSSI in molecular mass and isoelectric point was detected in the pericarp starch granules but not in granules from endosperm. This protein was designated GBSSII. The N-terminal amino acid sequence of GBSSII, although not identical to wheat GBSSI, showed strong homology to waxy proteins or GBSSIs of cereals and potato, and contained the motif KTGGL, which is the putative substrate-binding site of GBSSI of plants and of glycogen synthase of Escherichia coli. GBSSII cross-reacted specifically with antisera raised against potato and maize GBSSI. This study indicates that GBSSI and GBSSII are expressed in a tissue-specific manner in different organs, with GBSSII having an important function in amylose synthesis in the pericarp.

Brittle-1, an adenylate translocator, facilitates transfer of extraplastidial synthesized ADP--glucose into amyloplasts of maize endosperms

Amyloplasts of starchy tissues such as those of maize (Zea mays L.) function in the synthesis and accumulation of starch during kernel development. ADP-glucose pyrophosphorylase (AGPase) is known to be located in chloroplasts, and for many years it was generally accepted that AGPase was also localized in amyloplasts of starchy tissues. Recent aqueous fractionation of young maize endosperm led to the conclusion that 95% of the cellular AGPase was extraplastidial, but immunolocalization studies at the electron- and light-microscopic levels supported the conclusion that maize endosperm AGPase was localized in the amyloplasts. We report the results of two nonaqueous procedures that provide evidence that in maize endosperms in the linear phase of starch accumulation, 90% or more of the cellular AGPase is extraplastidial. We also provide evidence that the brittle-1 protein (BT1), an adenylate translocator with a KTGGL motif common to the ADP-glucose-binding site of starch synthases and bacterial glycogen synthases, functions in the transfer of ADP-glucose into the amyloplast stroma. The importance of the BT1 translocator in starch accumulation in maize endosperms is demonstrated by the severely reduced starch content in bt1 mutant kernels.

GBSS T-DNA inserts giving partial complementation of the amylose-free potato mutant can also cause co-suppression of the endogenous GBSS gene in a wild-type background

The wild-type gene encoding granule-bound starch synthase (GBSS) is capable of both complementing the amylose-free (amf) potato mutant and inhibiting the endogenous GBSS gene expression in wild-type potato. Co-suppression of the endogenous GBSS gene, easily visualised by staining the starch with iodine, occurred when the full-size GBSS sequence (genomic), GBSS cDNA or even the mutant amf allele were introduced into the wild-type potato. Conversely, introduction of the GBSS promoter sequence alone, did not result in co-suppression in the 80 analysed transformants. Neither the orientation of the GBSS gene with respect to kanamycin resistance nor the presence of an enhancer influenced the frequency of plants showing a co-suppression phenotype. After crossing a partially complemented amf mutant with a homozygous wild-type plant, the F1 offspring segregated into plant phenotypes with normal and decreased expression of the GBSS gene. This decreased expression correlated with the presence of a linked block of five T-DNA inserts which was previously shown to be correlated with partial complementation of the amf mutant. This crossing experiment indicates that co-suppression can cause inhibition of gene expression of both inserted and endogenous wild-type GBSS genes. The frequency of partially complemented amf plants was equal to the frequency of co-suppressed wild types when a construct, with an enhancer in front of the GBSS promoter, was used (pWAM 101E). This might suggest that partial complementation of the amf genotype caused by unstable expression of the transgene can be overcome by inserting an enhancer in front of the GBSS promoter.

Strategies for the sustainable production of new biodegradable polyesters in plants: a review

In this study we review relevant pathways with regard to the production of poly(3-hydroxyalkanoates) (PHA) with medium chain length monomers in higher plants. On the basis of what is known of the genetics and the biochemistry of PHA formation in bacteria, and of fatty acid metabolism in various organisms, a number of possibilities for PHA production in model plants and in economically important crop plants are listed. Along with the molecular biology of PHA synthesis and fatty acid metabolism, we discuss theoretical and environmental considerations, metabolic engineering strategies, and plant transformation systems.Key words: polyhydroxyalkanoate, fatty acid, starch, potato, Arabidopsis.

Factors affecting the inhibition by antisense RNA of granule-bound starch synthase gene expression in potato

Inhibition of expression of specific genes by means of antisense RNA is widely used, although little information is available regarding conditions that affect the efficacy of inhibition. In this study, inhibition of granule-bound starch synthase (GBSS), a key enzyme in starch biosynthesis, is used as a model system. Eleven antisense constructs derived from the full-length GBSS cDNA, the genomic GBSS coding region (gDNA) or fragments of each of these sequences, were analysed with respect to their inhibitory effect. Introduction of full-length gDNA constructs yielded a lower percentage of transgenic clones showing complete inhibition than did introduction of the full-length cDNA constructs. This may be caused by a lower antisense binding capacity of the former due to the relatively low GC content in intron sequences present in the gDNA constructs. The presence of multiple T-DNA insertions was related to a higher degree of inhibition. Putative polyadenylation signals on the antisense strand of the GBSS gene resulted in a premature stop of transcription of some of the antisense genes, as demonstrated by the expression of smaller antisense RNA transcripts. Introduction of antisense constructs driven by the promoter of the (target) GBSS gene resulted in a higher percentage of clones with complete inhibition than introduction of antisense constructs driven by the 35S CaMV promoter. Complete antisense inhibition was achieved in 25% of the clones carrying the antisense construct pKGBA50, which is based on the GBSS promoter and the full-length GBSS cDNA. Thus, it is concluded that the use of pKGBA50 is very suitable for the modification of the composition of potato tuber starch via antisense RNA.

Isolation and characterization of a cDNA encoding granule-bound starch synthase in cassava (Manihot esculenta Crantz) and its antisense expression in potato

A tuber-specific cDNA library of cassava (Manihot esculenta Crantz) was constructed and a full-length cDNA for granule-bound starch synthase (GBSS, also known as waxy protein), the enzyme responsible for the synthesis of amylose in reserve starch, was cloned. Sequencing of the cloned cDNA showed that it has 74% identity with potato GBSS and 60-72% identity with GBSS from other plant species. The cDNA encodes a 608 amino acid protein of which 78 amino acids form a chloroplast/amyloplast transit peptide of 8.37 kDa. The mature protein has a predicted molecular mass of 58.61 kDa (530 amino acids). Comparison of the GBSS proteins of various plant species and glycogen synthase of bacteria showed extensive identity among the mature form of plant GBSS proteins, in which the monocots and dicots form two separate branches in the evolutionary tree. From analysis of the genomic DNA of allotetraploid cassava, it is shown that GBSS is a low-copy-number gene. GBSS transcript is synthesized in a number of different organs, but most abundantly in tubers. Potato plants were transformed with the cassava GBSS cDNA in antisense orientation fused between the potato GBSS promoter and the nopaline synthase terminator. The expression of the endogenous GBSS gene in these transgenic potato plants was partially or completely inhibited. Complete inhibition of GBSS activity by the cassava antisense gene resulted in absence of GBSS protein and amylose giving rise to almost complete amylose-free potato starch. This shows that also heterologous genes can be used to achieve antisense effects in other plant species.

Antisense regulation of the rice waxy gene expression using a PCR-amplified fragment of the rice genome reduces the amylose content in grain starch

The waxy gene encodes a granule-bound starch synthase. A 1.0-kb portion of the sequence of the rice waxy gene, which includes the region between exon 4 and exon 9, was inserted in an antisense orientation between the 35 S promoter and the GUS gene of pBI221. The resultant plasmid, pWXA23, was introduced into rice protoplasts by electroporation. GUS activity was clearly detected in derived callus lines, suggesting that the antisense component of the fusion gene was also expressed. Transgenic rice plants were regenerated from these callus lines and their GUS activity was confirmed. Some of the rice seeds from these transformants showed a significant reduction in the amylose content of grain starch, even though they had become polyploid. These results suggest that even when intron sequences are included, antisense constructs can bring about a reduced level of expression of a target gene. The utility of GUS, included as a reporter gene, for the simple detection of expression of an antisense gene, was apparent from these results.