A reassessment of the course of evolution of wheat

Chromosome pairing in hybrids involving Triticum aestivum and new accessions of T. speltoides, and in an amphiploid of these species, indicates that T. speltoides can no longer be considered to be the donor of the B genome of the polyploid wheats. This necessitates a reconsideration of the genome relationships and evolutionary processes that gave rise to cultivated wheats.     

Domestication quantitative trait loci in Triticum dicoccoides,the progenitor of wheat

Wild emmer wheat, Triticum dicoccoides, is the progenitor of modern tetraploid and hexaploid cultivated wheats. Our objective was to map domestication-related quantitative trait loci (QTL) in T. dicoccoides. The studied traits include brittle rachis, heading date, plant height, grain size, yield, and yield components. Our mapping population was derived from a cross between T. dicoccoides and Triticum durum. Approximately 70 domestication QTL effects were detected, nonrandomly distributed among and along chromosomes. Seven domestication syndrome factors were proposed, each affecting 5-11 traits. We showed: (i) clustering and strong effects of some QTLs; (ii) remarkable genomic association of strong domestication-related QTLs with gene-rich regions; and (iii) unexpected predominance of QTL effects in the A genome. The A genome of wheat may have played a more important role than the B genome during domestication evolution. The cryptic beneficial alleles at specific QTLs derived from T. dicoccoides may contribute to wheat and cereal improvement.     

Genetic control of endosperm amylase activity and gibberellic Acid responses in standard-height and short-statured wheats

In contrast to standard-height wheat genotypes, short-statured wheats having major genes for dwarfness do not show increased seedling growth after treatment with gibberellic acid. Endogenous gibberellic acid induces synthesis of amylase in the endosperm of germinating seeds, but the amount of amylase synthesized is greatly increased by exogenous gibberellic acid treatment in standard-height and in short-statured wheats that have dwarfing genes from the variety “Norin 10.” “D6899,” which has the “Tom Thumb” gene for height reduction, had about one-fourth of the amylase activity of standard-height and Norin 10-derived, short-statured wheats. This genotype showed little or no increased amylase activity after gibberellic acid treatment. Genetic analyses showed that the amount of amylase synthesized was controlled by a single gene and was dependent on the number of copies of the structural gene present in the endosperm. Dwarfism in wheat may be related to a blockage in gibberellic acid utilization because other workers have found that the amount of endogenous amylase synthesized in Norin 10-derived, short-statured wheats is not growth-limiting, but it is not known if low amylase synthesis is related to dwarfism in the Tom Thumb derivative. No recombinants were recovered in a small population, suggesting that the Tom Thumb gene may pleiotropically affect plant height and the lack of response to gibberellic acid in amylase synthesis and seedling growth.     

Changes in genetic diversity in the red winter wheat regions of the United States

Pedigree and acreage data were utilized to determine trends in genetic diversity of soft red winter (SRW) and hard red winter (HRW) wheats. Four uniformity estimates were computed: (a) ₁, the mean relationship among all cultivars grown in a given year; (b) ₂, the mean relationship among primary cultivars; (c) ₃, the mean relationship of primary cultivars weighted by acreage; and (d) ₄, the mean relationship of primary cultivars grown in different years, weighted by acreage. In the SRW region, there has been a slow but steady increase in relationship among cultivars (₁ and ₂). There was a dramatic increase in field uniformity (₃) during the 1970s, but ₃ had sharply decreased by 1984 to its lowest point ever (0.22). All uniformity estimates decreased sharply for HRW wheats from 1919 to 1949 and have decreased gradually since. Uniformity is higher in HRW than in SRW wheats, primarily because of the persistence of a core of HRW germ plasm from cultivar `Turkey,' but the difference is diminishing. Both classes appear to be entering a new era of increasing diversity.     

Relationship of gliadin protein components to chromosomes in hexaploid wheats (Triticum aestivum L.)

The synthesis of the A-gliadin protein fraction derived from the endosperm of the grain of hexaploid bread wheats (Triticum aestivum L.), which is toxic in celiac disease, was associated with the α arm of the 6A chromosome through use of the substitution lines of “Cheyenne” chromosomes in “Chinese Spring”. The association was made through the use of ditelocentric stocks of Chinese Spring. The synthesis of many other gliadin components in the gel electrophoretic patterns of these two varieties could be associated with particular chromosomes as well. All genes detected were located in the chromosomes of homoeologous groups 1 and 6. It is possible to remove some of the proteins toxic to people with celiac disease from wheat (flour) by chromosome manipulation. If the toxic factor is not widely distributed among the storage protein components, it may be possible to produce a wheat that would be safe for celiac patients to eat.     

Variation in repeated nucleotide sequences sheds light on the phylogeny of the wheat B and G genomes

A general method based on variation in repeated nucleotide sequences was developed for the identification of diploid species most closely related to a specific genome of a polyploid species. The utility of this method was demonstrated by showing that Triticum speltoides is the most closely related extant species to both the B and G genomes of tetraploid wheats.     

Acc homoeoloci and the evolution of wheat genomes

The DNA sequences of wheat Acc-1 and Acc-2 loci, encoding the plastid and cytosolic forms of the enzyme acetyl-CoA carboxylase, were analyzed with a view to understanding the evolution of these genes and the origin of the three genomes in modern hexaploid wheat. Acc-1 and Acc-2 loci from each of the wheats Triticum urartu (A genome), Aegilops tauschii (D genome), Triticum turgidum (AB genome), and Triticum aestivum (ABD genome), as well as two Acc-2-related pseudogenes from T. urartu were sequenced. The 2.3-2.4 Mya divergence time calculated here for the three homoeologous chromosomes, on the basis of coding and intron sequences of the Acc-1 genes, is at the low end of other estimates. Our clock was calibrated by using 60 Mya for the divergence between wheat and maize. On the same time scale, wheat and barley diverged 11.6 Mya, based on sequences of Acc and other genes. The regions flanking the Acc genes are not conserved among the A, B, and D genomes. They are conserved when comparing homoeologous genomes of diploid, tetraploid, and hexaploid wheats. Substitution rates in intergenic regions consisting primarily of repetitive sequences vary substantially along the loci and on average are 3.5-fold higher than the Acc intron substitution rates. The composition of the Acc homoeoloci suggests haplotype divergence exceeding in some cases 0.5 Mya. Such variation might result in a significant overestimate of the time since tetraploid wheat formation, which occurred no more than 0.5 Mya.     

Expression of modified rye ribosomal RNA genes in wheat

Several wheats (Triticum aestivum L. em Thell.) containing the short arm of chromosome 1R from rye (Secale cereale L.) translocated to the long arm of wheat chromosome 1B were examined, by in situ hybridization with a biotinylated probe, for the expression of rye rRNA genes located in the nucleolus-organizing region (NOR) present on the short arm of 1R. The wheats analyzed contain a reduced rye NOR band, identified by a C-banding technique, that was assumed to have resulted from a deletion that reduced the number of rRNA genes and spacer units. Genes being actively transcribed could be recognized as dispersed label on DNA within the nucleolus, while those genes that were inactive were seen as condensed label. After in situ hybridization with a biotinylated rye NOR spacer probe, no evidence of rye rRNA gene activity was detected in the plants containing a reduced rye NOR band. Biotin-labeling of chromosomes containing a normal-sized rye NOR locus showed a degree of rye activity consistent with the results of a previous study that used a radioactive probe detected by autoradiography. It was determined previously that rye rRNA genes in a wheat background show significantly less activity than in diploid rye because the spacer units between the rRNA genes of rye are smaller than those of wheat, and in cereals the ribosomal locus with the larger spacer unit is preferentially transcribed. The present results indicate that the number of spacer units is also important in determining which NOR locus (i.e., rye or wheat) will be expressed when several ribosomal loci are present in a wheat background.     

INAUGURAL ARTICLE by a Recently Elected Academy Member:Plasmon analyses of Triticum (wheat) and Aegilops: PCR–single-strand conformational polymorphism (PCR-SSCP) analyses of organellar DNAs

To investigate phylogenetic relationships among plasmons in Triticum and Aegilops, PCR–single-strand conformational polymorphism (PCR-SSCP) analyses were made of 14.0-kb chloroplast (ct) and 13.7-kb mitochondrial (mt)DNA regions that were isolated from 46 alloplasmic wheat lines and one euplasmic line. These plasmons represent 31 species of the two genera. The ct and mtDNA regions included 10 and 9 structural genes, respectively. A total of 177 bands were detected, of which 40.6% were variable. The proportion of variable bands in ctDNA (51.1%) was higher than that of mtDNA (28.9%). The phylogenetic trees of plasmons, derived by two different models, indicate a common picture of plasmon divergence in the two genera and suggest three major groups of plasmons (Einkorn, Triticum, and Aegilops). Because of uniparental plasmon transmission, the maternal parents of all but one polyploid species were identified. Only one Aegilops species, Ae. speltoides, was included in the Triticum group, suggesting that this species is the plasmon and B and G genome donor of all polyploid wheats. ctDNA variations were more intimately correlated with vegetative characters, whereas mtDNA variations were more closely correlated with reproductive characters. Plasmon divergence among the diploids of the two genera largely paralleled genome divergence. The relative times of origin of the polyploid species were inferred from genetic distances from their putative maternal parents.     

Wheat deficient in gliadins: promising tool for treatment of coeliac disease.

The toxicity of two varieties of bread wheat, one poor in alpha and beta gliadins and the other poor in alpha, beta, gamma, and omega gliadins, has been tested. The peptic-tryptic digest of these wheats was assessed using coeliac mucosa in an in vitro organ culture system. A significantly lower toxicity was found in respect of bread wheat containing all gliadin fractions. These results suggest new opportunities for the treatment of coeliac disease.     

High level of interleukin-10 production by the activated t cell population within the rheumatoid synovial membrane

Objective. To characterize the cytokine profile of the activated T cell population derived from the synovial membrane of rheumatoid arthritis (RA) patients. Methods. Interleukin-2 (IL-2) was used to select for in vivo–activated T cells from the synovial membrane of 2 patients with RA, and the cells were cloned nonspecifically. The cytokine production profile of these clones was compared with that of clones derived from peripheral blood monocytes (PBM) by stimulating all clones for 24 hours with immobilized anti-CD3 (coated at 10 μg/ml) or phorbol-12-myristate-13-acetate (10 ng/ml) plus soluble anti-CD3 (1 μg/ml). Interferon-γ (IFNγ), IL-4, and IL-10, the cytokines that discriminate between Th1 and Th2 cells and are involved in immunoregulation, were assayed by enzyme-linked immunosorbent assay. Results. There was a difference in the cytokines produced by the clones derived from the rheumatoid membranes compared with clones derived from the periphery. Clones derived from both membranes and PBM were mostly IFNγ-producers, i.e., either a Th0 or a Th1 profile. There was a high proportion of IFNγ/high IL-10-producing cells derived from the joint, but not from the periphery. Of clones derived from the synovial membrane of each of 2 RA patients, 100% and 50% produced both 1–10 ng/ml IFNγ and >7 ng/ml IL-10, compared with <7% of clones derived from normal or RA peripheral blood. In addition, when autologous membrane and PBM were compared, the mean concentration of IL-10 produced by the clones derived from the synovial membrane sample was significantly different from those produced by clones derived from peripheral blood (P < 0.02). Conclusion. The cytokine profile of the T cell clones that were obtained from the RA joint after expansion with IL-2 is distinct from that of the T cells that are predominant in PBM. This supports the concept that the T cell subsets that accumulate in the joint are not a random sample. The high level of IL-10 production by clones derived from the synovium suggests that this cytokine may be a major contributor to the endogenous immunosuppression that occurs in RA.     

Chromosome constitution of polyploid wheats: Introduction of diploid wheat chromosome 4

Chromosome 4 of diploid wheat (chromosome d4) is not present in hexaploid wheat. This chromosome has been added to hexaploid wheat and observed not to pair meiotically with its 21 chromosomes. Also, chromosome d4 compensates for Cornerstone male sterility, which involves a recessive mutation in chromosome arm 4AS. Chromosome d4 has been separately substituted for chromosomes 4A and 4B. These two substituted hexaploid chromotypes have the entire genome of diploid wheat and may have agricultural significance. An alternative hypothesis of the evolution of polyploid wheats is proposed that involves the loss of chromosome d4 and the retention of two versions of chromosome 4B at the early tetraploid stage.     

Substances originating from the optic nerve of neonatal rabbit induce regeneration-associated response in the injured optic nerve of adult rabbit.

We have recently shown that cell bodies of an injured optic nerve of adult rabbit can be induced to express regeneration-associated response by external signals derived from nonneuronal cells of regenerating nerves of lower vertebrates. In this study it is shown that even substances derived from a nonregenerating mammalian system also can trigger such a regenerative response. Thus, substances derived from intact nerves of neonatal rabbits and of adult rabbits, to a lesser extent, were active in triggering a regeneration-associated response, whereas substances derived from injured nerves of adult rabbit were not. However, if subsequent to the injury the nerve was implanted with silicone tube containing medium conditioned by neonatal optic nerves, the substances derived from the implanted injured nerve were active. Thus, it appears that the ability of a periaxonal environment to provide triggering substances correlates with axonal growth. Therefore, we named these substances "growth-associated triggering factors" (GATFs). It is suggested that mammalian cells are unable to express a regenerative response after an injury due to the failure of their nonneuronal cells to produce regeneration-triggering substances. This disability may be circumvented by an appropriate implantation procedure.     

GSP-1 genes are linked to the grain hardness locus (Ha) on wheat chromosome 5D.

An important determinant of wheat grain quality is the hardness of the grain. The trait is controlled by a major locus, Ha, on the short arm of chromosome 5D. Purified starch granules from soft-grained wheats have associated with them 15-kDa polypeptides called grain softness proteins (GSPs) or "friabilins." Genes that encode one family of closely related GSP polypeptides - GSP-1 genes - were mapped using chromosome substitution lines to the group 5 chromosomes. An F2 population segregating for hard and soft alleles at the Ha locus on a near-isogenic background was used in a single-seed study of the inheritance of grain softness and of GSP-1 alleles. Grain softness versus grain hardness was inherited in a 3:1 ratio. The presence versus absence of GSPs in single seed starch preparations was coinherited with grain softness versus hardness. This showed that grain softness is primarily determined by seed, and not by maternal, genotype. In addition, no recombination was detected in 44 F2 plants between GSP-1 restriction fragment length polymorphisms and Ha alleles. Differences between hard and soft wheat grains in membrane structure and lipid extractability have been described and, of the three characterized proteins that are part of the mixture of 15-kDa polypeptides called GSPs, at least two, and probably all three, are proteins that bind polar lipids. The data are interpreted to suggest that the Ha locus may encode one or more members of a large family of lipid-binding proteins.     

Synoviocyte derived granulocyte macrophage colony stimulating factor mediates the survival of human lymphocytes.

Synoviocytes have been shown to be effector cells capable of synthesizing and secreting a variety of cytokines and growth factors. We demonstrate here that synoviocyte derived conditioned medium has immunoregulatory properties as it enhances human peripheral blood lymphocyte survival in a dose dependent manner in vitro. The effect elicited by synoviocyte derived conditioned medium from patients with rheumatoid arthritis (RA) was greater than that induced by synoviocyte derived conditioned medium from patients with osteoarthritis. Granulocyte-macrophage colony stimulating factor (GM-CSF) was found in synoviocyte derived conditioned medium with significantly higher levels present in synoviocyte derived conditioned medium from patients with RA. Recombinant human GM-CSF induced survival of human lymphocytes in vitro and a monoclonal antibody to human GM-CSF fully abrogated synoviocyte derived conditioned medium induced survival. Our results demonstrate that synoviocyte derived GM-CSF may be important in the retention of lymphocytes, which is a central pathological characteristic of the rheumatoid joint.     

Mannheimer Lecture. The quintessence of the making of the heart

In my Mannheimer lecture, designed to meet the needs of a mainly clinical audience, I present aspects of cardiac development that link basic science to clinically relevant problems. During development of the cardiac tube, and its subsequent changes as a dextrally looped structure, which is still connected to the dorsal body wall by a venous and an arterial pole, there are basic requirements. These consist of the development of myocardium, endocardium and the interposed cardiac jelly from the cardiogenic plates. In this primitive heart tube, septation and valvar formation then take place to convert it into a four-chambered heart. I demonstrate that the refining of the above events cannot take place without the addition of extracardiac populations of cells. These are presented as the "quintessence of heart development", and consist of cells derived from the neural crest, along with epicardially derived cells. Without these contributions, the embryos uniformly die of cardiac insufficiency. Important contributions are made by the cells derived from the neural crest to septation and the formation of the arterial valves, and possibly in differentiation of the central conduction system. The epicardially derived cells are essential for formation of the interstitial fibroblasts and the myocardium, as well as the coronary vascular system. I conclude by discussing specific malformations of the heart that might be linked to these extracardiac contributions.     

Experimental syphilis in the rabbit: passive transfer of immunity with immunoglobulin G from immune serum.

A preparation of immunoglobulin G isolated from a pool of immune sera derived from rabbits with long-term syphilis was shown to possess a high degree of purity as judged by immunodiffusion and protein electrophoresis. The antitreponemal power of the preparation of immunoglobulin G and that of the immune serum pool from which it was derived were found to be equivalent in both the skin protection and the systemic protection test. The observation that neither normal serum nor a pool of serum derived from animals "immunized" with Salmonella typhi, Escherichia coli, Streptococcus pyogenes, or zymosan was protective indicates that the protective power of the immune serum studied was due to specific antibodies residing principally, if not entirely, in the immunoglobulin G fraction of the serum.     

The Abundance of Ferritin in Yolk-Sac Derived Red Blood Cells of the Embryonic Mouse

Circulating red blood cells formed early in development have several distinctive properties which include retention of the nucleus (mammals), large size and characteristic haemoglobin type (mammals, birds, amphibia). The primitive or embryonic red cells of early development are replaced by the definitive red cells which contain fetal or adult haemoglobin; a second developmental change occurs in the haemoglobin of some mammals (man, cattle, sheep) but does not involve a cell replacement. Circulating yolk-sac derived red cells from embryonic mice are siderocytes; elevated ferritin levels are associated with the circulating red cells of bullfrog tadpoles, but not with those of the adult frog, again indicating that red cell iron metabolism can change during development. In order to extend the observations made on an amphibian to a mammal, the ferritin content of circulating red cells from embryonic mice was determined and found to be 0.65 mg/100 mg of soluble protein; no ferritin (less than or equal to 0.007 mg/100 mg of soluble protein) was detected in adult mouse red cells. Elevated ferritin levels appeared to be specifically associated with the yolk-sac derived population of red cells since a decline in red-cell ferritin content coincided with the replacement of yolk-sac derived red cells by definitive red cells derived from the liver. Fractionation of mixtures of yolk-sac derived and liver derived red cells showed that fractions rich in the definitive red cells contained less ferritin than the mixture. The results suggest that elevated ferritin levels may be a general characteristic of the circulating, haemoglobinized red cells formed early in development.