3D Arm Research Articles

Characterization of wheat-alien translocations conferring resistance to diseases and pests: current status

Wild relatives of common wheat, Triticum aestivum, and related species are an important source of disease and pest resistance and several useful traits have been transferred from these species to wheat. C-banding and in situ hybridization analyses are powerful cytological techniques allowing the detection of alien chromatin in wheat. C-banding permits identification of the wheat and alien chromosomes involved in wheat-alien translocations, whereas genomic in situ hybridization analysis allows determination of their size and breakpoint positions. The present review summarizes the available data on wheat-alien transfers conferring resistance to diseases and pests. Ten of the 57 spontaneous and induced wheat-alien translocations were identified as whole arm translocations with the breakpoints within the centromeric regions. The majority of transfers (45) were identified as terminal translocations with distal alien segments translocated to wheat chromosome arms. Only two intercalary wheat-alien transloctions were identified, one induced by radiation treatment with a small segment of rye chromosome 6RL (H25) inserted into the long arm of wheat chromosome 4A, and the other probably induced by homoeologous recombination with a segment derived from the long arm of a group 7 Agropyron elongatum chromosome with Lr19 inserted into the long arm of 7D. The presented information should be useful for further directed chromosome engineering aimed at producing superior germplasm.

Neural network models of cortical functions based on the computational properties of the cerebral cortex

We describe a biologically plausible modelling framework based on the architectural and processing characteristics of the cerebral cortex. Its key feature is a multicellular processing unit ( cortical column) reflecting the modular nature of cortical organization and function. In this framework, we describe a neural network model of the neuronal circuits of the cerebral cortex that learn different functions associated with different parts of the cortex: 1) visual integration for invariant pattern recognition, performed by a cooperation between temporal and parietal areas; 2) visual-to-motor transformation for 3D arm reaching movements, performed by parietal and motor areas; and 3) temporal integration and storage of sensorimotor programs, performed by networks linking the prefrontal cortex to associative sensory and motor areas. The architecture of the network is inspired from the features of the architecture of cortical pathways involved in these functions. We propose two rules which describe neural processing and plasticity in the network. The first rule ( adaptive tuning if gating) is an analog of operant conditioning and permits to learn to anticipate an action. The second rule ( adaptive timing) is based on a bistable state of activity and permits to learn temporally separate events forming a behavioral sequence.

Molecular cytogenetic analysis of Agropyron elongatum chromatin in wheat germplasm specifying resistance to wheat streak mosaic virus

Three lines derived from wheat (6x) x Agropyron elongatum (10x) that are resistant to wheat streak mosaic virus (WSMV) were analyzed by chromosome pairing, banding, and in situ hybridization. Line CI15321 was identified as a disomic substitution line where wheat chromosome 1D is replaced by Ag. elongatum chromosome 1Ae-1. Line 87-94-1 is a wheat-Ag. elongatum ditelosomic addition 1Ae-1L. Line CI15322 contains an Ag. elongatum chromosome, 1Ae-2, that substitutes for chromosome 1D. The short arm of 1Ae-2 paired with the short arm of 1Ae-1 at metaphase I (MI) in 82% of the pollen mother cells (PMCs). However, the long arms of these two chromosomes did not pair with each other. In CI15322, the long arm of chromosome 4D has an Agropyron chromosome segment which was derived from the distal part of 1Ae-1L. This translocation chromosome is designated as T4DS·4DL-1L. T4DS·4DL-1Ae-1L has a 0.73 μm distal part of the long arm of 4D replaced by a 1.31 μm distal segment from 1Ae-1L. The major WSMV resistance gene(s) in these lines is located on the distal part of 1Ae-1L.

Molecular detection of Lophopyrum chromatin in wheat-Lophopyrum recombinants and their use in the physical mapping of chromosome 7D

In situ hybridisation and restriction fragment length polymorphism (RFLP) analysis were used to determine the relative location of the translocation breakpoint and the size of the integrated chromatin segment in hexaploid wheat-Lophopyrum translocation stocks. Three 7el2-7D recombinant stocks were Robertsonian translocations, 7DS.7el. The remaining recombinant stock (KS10-2) was 7elS.7el-7DL and contained only the distal one-half of the long arm of 7D. The recombinant stock with 7el1 (K11695) could be designated 7DS.7DL-7el where approximately the distal one-half of 7DL was replaced. RFLP analysis indicated that on the 7DL RFLP map the breakpoints for K11695 and KS10-2 are in different locations and that the two recombinants contain an overlapping region (a common region) of the Lophopyrum chromosome 7 in which Lr19, a leaf-rust resistant gene, is located. RFLP analysis also indicated that RFLP markers which mapped to within 1.5 cm of the centromere of chromosome 7D are located in the distal half of the long arm.

Chilling injury and chlorotic reactions of euploids and aneuploids of the group 6 homoeologues of common wheat

Aneuploid seedlings of the common wheat (Triticum aestivum L.) cv. Chinese Spring (CS) that are nullisomic or telosomic for the long arm of chromosome 6D are susceptible to chilling injury under prolonged exposure to 6 °C; normal euploids or telosomics for the short arm are not. Studies of seedling grown for various durations at 20 °C prior to growth at 6 °C showed that chilling injury was a juvenile phenomenon and that the extent of injury was inversely proportional to the duration of growth at 20 °C to a maximum of about 14 days. When reciprocal crosses were made between susceptible 6D nullisomics or long-arm ditelocentrics of CS and resistant 6D nullisomics of three spring and one winter wheat cultivars, progenies from aneuploid F1 hybrids all segregated for susceptibility as a recessive trait and at a frequency approximating a dihybrid ratio; no cytoplasmic effects were detected. Aneuploids of the group 6 homoeologues of the spring wheat cvs. Cadet and Rescue were resistant, as were group 6 whole-chromosome substitutions of eight different donor wheats in the recipient parent CS and 56 other euploids tested. Genes for resistance to chilling injury appear to involve the group 6 chromosomes and the short arm of 6D in Chinese Spring. In contrast with chilling injury, all aneuploid lines with only four doses of the "corroded" loci on group 6 chromosomes exhibited chlorotic symptoms.Key words: Triticum aestivum, chilling injury.

Chromosomal location in common wheat of a gene (Cmcl) from Aegilops squarrosa that conditions resistance to colonization by the wheat curl mite

Wheat streak mosaic is a destructive disease of wheat caused by wheat streak mosaic virus. Wheat streak mosaic virus is vectored by the wheat curl mite (Eriophyes tulipae Keifer). A single dominant gene conditioning resistance to colonization by the mite vector was transferred from Aegilops squarrosa L. to a synthetic amphiploid (AC PGR 16635) and then to common wheat (Triticum aestivum L. em. Thell.) through backcrossing. Because of its origin, the transferred gene was probably located in the D genome. Monosomics 1D through 7D were crossed with a homozygous resistant line with the pedigree Norstar*4/AC PGR 16635. Both 41- and 42-chromosome F1 plants were identified and selfed to obtain F2 seed. The observed proportion of resistant and susceptible plants in 6 of the 7 F2 families from monosomics, and in all 7 of the F2s from disomics, did not deviate significantly from a 3:1 ratio. However, the proportion of resistant plants from the F2 of monosomic 6D was significantly (p < 0.01) in excess of this ratio and susceptible plants from this family were nullisomic for all or part of 6D. In crosses with standard ditelosomic stocks, telocentrics from a ditelosomic derivative of susceptible individual of this F2 paired with 6D(L) but failed to pair with 6D(S). The F2 of heterozygous resistant plants that were monotelodisomic for the long arm of 6D(L) segregated approximately 19 resistant to 1 susceptible, while those from monotelodisomics for the short arm segregated normally (3 resistant to 1 susceptible, p = 0.27). These data show that the gene Cmcl for mite resistance is located on the short arm of chromosome 6D. Key words: Aegilops squarrosa, wheat streak mosaic virus.

Effect of different doses of group-2 chromosomes on homoeologous pairing in intergeneric wheat hybrids

While an extra dose of chromosome 2A of common wheat, previously reported to carry a pairing promoter on its short arm, did not increase pairing between homoeologous chromosomes in F1 hybrids between common wheat cv. Chinese Spring (CS) and Aegilops variabilis, two doses of chromosome 2D or 2B caused a significant increase in homoeologous pairing. Evidently, chromosomes 2D and 2B carry a pairing promoter(s). Studies of F1 hybrids between aneuploids of CS, either deficient for chromosome 2D or having it in an extra dose, and Ae. variabilis, Ae. longissima, and Secale cereale supported the finding that this chromosome carries a pairing promoter. Using ditelosomic lines, the promoter was found to be located on the short arm of 2D (2DS). It was deduced that the promoter of 2B is also located on the homoeologous short arm, i.e., on 2BS. Evidence was obtained that the long arm of 2D may carry a suppressor(s) of pairing. Thus, the short arm of 2A, 2D, and 2B carries a pairing promoter(s), while the long arm of 2D and possibly of 2A and 2B carry a minor suppressor(s). The promoters are more potent than the suppressors and the overall effect of group-2 chromosomes is pairing promotion.Key words: wheat, homoeologous pairing, pairing promoter, pairing suppressor, intergeneric hybrid, meiosis.

COMPENSATED MONOSOMIC 5B-TRISOMIC 5A PLANTS IN TETRAPLOID WHEAT

Tetraploid wheat plants monosomic 5B-trisomic 5A were obtained by crossing nullisomic 5B-tetrasomic 5A plants of Triticum aestivum with T. durum and backcrossing five times with T. durum. These plants were found to carry a translocated 5A-5D chromosome. By self-pollination they originated plants carrying both a 5A-5D and 5B-5D translocated chromosome. In the latter the break point was located distally to the pairing suppressor gene. The translocations must have occurred by homoeologous pairing and recombination in the long arm of chromosomes of the group 5. F1 hybrids of monosomic 5B-trisomic 5A plants with rye and Aegilops sharonensis showed high homologous pairing when 5B was absent. Pairing promotion associated with the terminal segment of the long arm of 5D attached to the 5B-5D chromosome end was detected. It was suggested that the long arm of chromosomes of the homoeologous group 5 of wheat might carry two separate loci with genes for antagonistic effects on the pairing of chromosomes.