Influence of homoeologous chromosomes on gene-dosage effects in allohexaploid wheat (Triticum aestivum L.)

In vitro octaploid induction of Populus hopeiensis with colchicine

BACKGROUND

Autopolyploids, especially artificial lines, provide model systems for understanding the mechanisms of gene dosage effects on trait variation owing to their relatively uniform genetic background. Here, a protocol for in vitro octaploid induction of Populus hopeiensis from leaf blades with colchicine treatment was established through investigation of the effects of different pre-culture durations, colchicine concentrations, and exposure times.

RESULTS

We found that pre-culture duration, colchicine concentration, and exposure time had significant effects on the survival rate, shoot regeneration rate, and octaploid induction rate of P. hopeiensis leaf blades. The highest octaploid induction rate (8.61%) was observed when leaf blades pre-cultured for 9 days were treated for 4 days with 100 μM colchicine. The ploidy level of all regenerated plantlets was analyzed by flow cytometry and further confirmed by chromosome counting. A total of 14 octaploids were obtained. The stomatal length, width, and density of leaf blades significantly differed between tetraploid and octaploid plants. Compared with diploid and tetraploid plants, octaploids had a slower growth rate, smaller leaf blade size, and shorter internodes.

CONCLUSIONS

We established an effective protocol for inducing octaploids in vitro from autotetraploid P. hopeiensis leaf blades by colchicine treatment.

Phenotypic, cytogenetic, and molecular marker analysis of Brassica napus introgressants derived from an intergeneric hybridization with Orychophragmus

Aneuploids of a single species that have lost or gained different chromosomes are useful for genomic analysis. The polyploid nature of many crops including oilseed rape (Brassica napus) allows these plants to tolerate the loss of individual chromosomes from homologous pairs, thus facilitating the development of aneuploid lines. Here, we selected 39 lines from advanced generations of an intergeneric hybridization between Brassica rapa and Orychophragmus violaceus with accidental pollination by B. napus. The lines showed a wide spectrum of phenotypic variations, with some traits specific to O. violaceus. Most lines had the same chromosome number (2n = 38) as B. napus. However, we also identified B. napus nulli-tetrasomics with 22 A-genome and 16 C-genome chromosomes and lines with the typical B. napus complement of 20 A-genome and 18 C-genome chromosomes, as revealed by FISH analysis using a C-genome specific probe. Other lines had 2n = 37 or 39 chromosomes, with variable numbers of A- or C-genome chromosomes. The formation of quadrivalents by four A-genome chromosomes with similar shapes suggests that they were derived from the same chromosome. The frequent homoeologous pairing between chromosomes of the A and C genomes points to their non-diploidized meiotic behavior. Sequence-related amplified polymorphism (SRAP) analysis revealed substantial genomic changes of the lines compared to B. rapa associated with O. violaceus specific DNA bands, but only a few genes were identified in these bands by DNA sequencing. These novel B. napus aneuploids and introgressants represent unique tools for studies of Brassica genetics and for Brassica breeding projects.

Using the Hexaploid Nature of Wheat To Create Variability in Starch Characteristics

In hexaploid crops, such as bread wheat, it should be possible to fine-tune phenotypic traits by identifying wild-type and null genes from each of the three genomes and combining them in a calculated manner. Here, we demonstrate this with gene combinations for two starch synthesis genes, SSIIa and GBSSI. Lines with inactive copies of both enzymes show a very dramatic change in phenotype, so to create intermediate phenotypes, we used marker-assisted selection to develop near-isogenic lines (NILs) carrying homozygous combinations of null alleles. For both genes, gene dosage effects follow the order B > D ≥ A; therefore, we completed detailed analysis of starch characteristics for NIL 3-3, which is null for the B-genome copy of the SSIIa and GBSSI genes, and NIL 5-5, which has null mutations in the B- and D-genome-encoded copies of both of these genes. The effects of the combinations on phenotypic traits followed the order expected on the basis of genotype, with NIL 5-5 showing the largest differences from the wild type, while NIL 3-3 characteristics were intermediate between NIL 5-5 and the wild type. Differences among genotypes were significant for many starch characteristics, including percent amylose, chain length distribution, gelatinization temperature, retrogradation, and pasting properties, and these differences appeared to translate into improvements in end-product quality, since bread made from type 5-5 flour showed a 3 day lag in staling.

Wheat tetrameric inhibitors of insect alpha-amylases: Alloploid heterosis at the molecular level

Tetrameric inhibitors of heterologous alpha-amylases have been characterized in allohexaploid wheat, Triticum aestivum (genomes AABBDD), as well as in Triticum turgidum (AABB) and Triticum tauschii (DD). Their subunits have been identified as the previously described CM proteins. Single oligomeric species were observed in T. Turgidum (subunits CM2, CM3A, and CM16) and in T. tauschii (CM1, CM3D, and CM17) by a two-dimensional electrophoretic method that does not dissociate the inhibitors in the first dimension. Multiple tetrameric species, resulting from different combinations of the subunits contributed by the two ancestral species, are observed by the same procedure in T. aestivum. The three types of subunits were required for significant activity when the inhibitor of T. turgidum was reconstituted from the purified subunits, whereas, in the case of T. tauschii, binary mixtures involving subunit CM1 also had some activity. Additional combinations of the subunits present in these two species, which occur in the allohexaploid T. aestivum, were also reconstituted, and their inhibitory activities ranged from 144% to 33% the activity of the reconstituted inhibitor from T. tauschii. The activity of these inhibitors toward the alpha-amylase (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) of the insect Tenebrio molitor is much greater than that against the salivary enzyme. These observations, together with the previously established chromosomal locations of genes encoding CM proteins, fit a model of alloploid heterosis at the molecular level.

Gene-dosage compensation of endosperm proteins in hexaploid wheat Triticum aestivum

Several aneuploid lines and one intervarietal substitution line of the hexaploid wheat Triticum aestivum (2n = 6x = 42; genomes AABBDD) cv. Chinese Spring were used to study the effects of different doses of chromosomes 1B, 1D, or 1A on the amount of the high molecular weight ("HMW") glutenins and gliadins of endosperm. These homeologous chromosomes carry HMW glutenin and gliadin gene clusters on their long and short arms, respectively. Increasing the dosage of chromosome 1B of Chinese Spring in plants having in their 3n endosperm zero or the normal three doses of the homeologue 1D, as well as in plants carrying in their endosperm one dose of 1B of the cultivar Timstein, had a dual effect: on one hand, a nonlinear increase in the amount of each subunit encoded by the chromosome whose dosage was elevated and, on the other hand, a compensating nonspecific decrease in the amount of other HMW glutenin and gliadin subunits encoded either by the homeoalleles on 1D or by the homoalleles on 1B of Timstein, respectively. Deletion of chromosome arm 1BL, which carries only a few HMW glutenin genes, had no significant effect on the amount of HMW glutenins encoded by 1DL and HMW gliadins encoded by 1DS and 1BS. However, deletion of 1BS or 1DS, each carrying many gliadin genes, caused a significant but nonspecific increase in the HMW glutenins and gliadins encoded by the remaining arms of 1B and 1D. The possible mechanism and evolutionary implications of gene-dosage compensation in polyploid wheat are discussed.

Dosage response of rye genes in a wheat background : 2. Secalin genes on 1RS

A series of hexaploid wheat lines containing zero, two or four doses of rye chromosome arm 1RS was used to investigate the response to changes in dosage by the rye genes when in a wheat background. The quantity of protein produced by the secalin protein genes contained on 1RS was directly related to the number of copies of 1RS present in the line. No response could be detected by representative wheat proteins suggesting that the increase in secalin protein observed was due to an increase in mRNA produced when four copies of the secalin gene was present. These results suggest that increasing the dosage of alien genes introgressed into wheat may be a useful tool for enhancing their expression.Mention of a trade name or proprietary product does not constitute a guarantee, warranty or recommendation of the product by the U.S. Department of Agriculture or the University of Missouri and does not imply its approval to the exclusion of other products that may be suitable.

Two-dimensional electrophoresis as a tool for structural and genetic studies of seed proteins from Poaceae and Fagaceae

The application of two-dimensional electrophoretic procedures to structural and genetic studies of seed proteins from Poaceae (including the cultivated cereals) and Fagaceae is described. The following related problems have been considered: covalent and non-covalent association of protein subunits in multiple oligomeric structures; chromosomal locations of genes encoding seed proteins; quantitation of gene products in relation to gene expression and regulation; purification of protein components to study their homology relationships and in vitro activities; evolutionary and phylogenetic relationships; identification of genetic stocks. Isoelectric focusing, pore-gradient electrophoresis, electrophoresis at different pH's, are among the separation procedures used in the first dimension, whereas sodium dodecyl sulfate-polyacrylamide gel electrophoresis and starch-gel electrophoresis at acid pH have been the preferred second-dimensional methods. Dissociating conditions (sodium dodecyl sulfate, Nonidet P-40, or urea) and reducing conditions (2-mercaptoethanol) have been used when required.

Chromosomal localization of structural genes and regulators in wheat by 2D electrophoresis of ditelosomic lines

Among the 782 spots observed in two-dimensional gel electrophoresis of denatured proteins from etiolated wheat shoots, 185 were found to be variable between the euploid and 26 ditelosomic lines of 'Chinese Spring'. Thirty-five structural genes were located on 17 chromosome arms. Numerous intensity changes showing alterations in protein levels were observed and led to the following statements: 1) regulators are frequently found and can be assigned for a same polypeptide to various chromosome arms; 2) for most polypeptides homoeologous arms do not manifest similar effects; 3) nevertheless, when affecting the same polypeptide, homoeologous arms display in most cases identical regulatory effects; 4) gene dosage compensation is observed in only one out of four homoeoallelic situations.

In Vitro Synthesis of Wheat (Triticum aestivum L.) Storage Proteins

Free and membrane-associated polysomes were isolated in approximately equal amounts from endosperm of wheat kernels harvested 20 days after anthesis. The presence of heparin in the homogenizing buffer minimized polysome degradation. Ribonucleic acid from the isolated polysomes, when translated in vitro in a wheat germ system, yielded products ranging in size from about 12,000 to about 80,000 daltons, including at least two polypeptides that co-migrated with seed extract proteins in sodium dodecyl sulfate polyacrylamide gel electrophoresis. The nature of the translation products of free and membrane-associated RNA are distinctly different, with membrane-associated RNA yielding a higher proportion of polypeptides in the size range of 30,000 to 37,000 daltons. Analysis of membrane-associated 3'-terminal polyadenylyl-containing RNA in vitro translation products, by solubility in 70% ethanol and by immunoprecipitation, indicates that the 33,000- to 37,000-dalton polypeptides contain gliadins, and the analysis provides evidence that these proteins are synthesized in association with membranous cell organelles. Gliadin polypeptides synthesized in vitro are larger than authentic gliadins and probably are precursors which, in vivo, undergo modification to yield the smaller final products.

Biochemical properties and level of expression of alcohol dehydrogenases in the allotetraploid plant Tragopogon miscellus and its diploid progenitors

This study demonstrates that homoeologous genes in two diploid plant species that specify different amounts of an enzyme maintain the same relative level of expression in an allotetraploid derivative. The three predominant alcohol dehydrogenase (ADH) isozymes (DD, DP, PP) in seeds of the recently evolved allotetraploid plant Tragopogon miscellus (Compositae) are dimers specified by Adh3-D and Adh3-P genes derived from its diploid progenitors T. dubius and T. pratensis. Seeds of T. pratensis contain twice as much ADH activity as those of T. dubius, while T. miscellus is intermediate. The three isozymes were similar in a number of catalytic properties; the densitometric ratio of the isozymes purified from T. miscellus was 1 DD : 4DP : 4PP for both ADH activity and protein; and dissociation-reassociation of the DP enzyme gave a 1:2:1 ratio of the three isozymes. Therefore, the enzymes were similar in specific activity, but twice as many P as D subunits were present in active enzymes in T. miscellus, precisely the difference in activity between the parents. In T. miscellus, the specific activity of ADH and its activity per mg tissue are intermediate to those of the diploids, because relative expression of the Adh gene in each genome is not influenced by the presence of the other genome.

Aneuploid analysis of low molecular weight gliadins from wheat

The chromosomal location of genes affecting five components from the low molecular weight gliadin (LMWG) fraction from wheat endosperm has been investigated by aneuploid analysis. Genes controlling these proteins were assigned to chromosomes 4B, 7A and 7D. Chromosomes from homoeologous groups 1, 2 and 6, where genes controlling classical gliadins are located, are not involved in the control of LMWG.

Down syndrome: gene dosage at the transcriptional level in skin fibroblasts

Chromosome imbalance (aneusomy) is the leading known cause of both spontaneous abortion and mental retardation in human beings. The primary abnormality is thought to result from quantitative changes of transcription products from the unbalanced genetic material. To document this point, I compared chromosome 21-specific transcription in skin fibroblasts from subjects with monosomy 21, disomy 21 (normal), and trisomy 21 (Down syndrome). Polyadenylylated RNA [poly(A)-RNA], which is enriched in messenger and messenger-precursor RNA sequences, was isolated from the above fibroblast lines. Radioactive DNA (cDNA) complementary to these RNAs was synthesized with reverse transcriptase (RNA-dependent DNA polymerase). These cDNAs were hybridized with (i) DNA from a cell line with a mouse genome plus human chromosome 21 and (ii) mouse DNA. Subtraction of the amount of hybridization in experiment ii from that in experiment i yielded a measure of human chromosome 21-specific RNA sequences. The results were consistent with gene dosage at the transcriptional level; for monosomy 21-derived cDNA, 0.6% (of the total cDNA) hybridized specifically to human chromosome 21; for disomy 21-derived cDNA, 2% hybridized; and for trisomy 21-derived cDNA, 3% hybridized. Thus, for DNA sequences on chromosome 21 in human skin fibroblasts, transcription depends on DNA dosage. Characterization of the chromosome 21-specific RNA sequences quantitated in these experiments could help to elucidate the mechanisms by which abnormal karyotypes result in abnormal phenotypes.

Some features of the inheritance of avenins, the alcohol soluble proteins of oat

The inheritance of avenin components, the prolamins (or alcohol soluble proteins) of Avena, is studied by means of gel electrophoresis. Avenin is composed of rather similar proteins which appear as a polymorphic group from a biochemical point of view. After a first preliminary investigation it showed a surprisingly high interspecific variability. The average number of its constituents increases with the ploidy level but it still is much lower than that of wheat gliadin.The avenin electrophoretic patterns of 47 samples (F4, F5 or F6 seeds) resulting from 3 hexaploid crosses are compared with the parental patterns. Four kinds of inheritance are observed. Roughly 50% of progeny profiles are identical to those of one of the parents. They are composed occasionally of partial sections of parental patterns. Complete additiveness occurs rather seldom. However, in one of the crosses a significant number of progeny samples show a band, one of the very slow moving constituents, which was not present in either of the parents.The study of avenin in F1 seeds, arising from reciprocal crosses between two homozygous parent plants, shows a significant effect of maternal gene dose in the triploid endosperm.Because of both the variability and the relatively small number of avenin constituents, these results show that typical endosperm proteins such as oat prolamin constitute a useful tool for phylogenetic studies of the genus Avena.