Jiming Jiang

Recent advances in alien gene transfer in wheat

SummaryThe recent advances in alien gene transfer from distantly-related species into wheat are reviewed in the present paper. The main achievements during the last ten years include the great expansion of the range of wide hybridization and development of new techniques for production and characterization of wheat-alien chromosome translocations. Updated results of wide hybridization since 1983 and comprehensive characterization of wheat-alien translocation lines in our laboratory are compiled. The future outlook for alien gene transfer in wheat is also discussed.

New 18S.26S ribosomal RNA gene loci: Chromosomal landmarks for the evolution of polyploid wheats

Three new 18S·26S rRNA gene loci were identified in common wheat by sequential N-banding and in situ hybridization (ISH) analysis. Locus Nor-A7 is located at the terminal area of the long arm of 5A in both diploid and polyploid wheats. Locus Nor-B6 is located in N-band 1BL2.5 of the long arm of chromosome 1B in Triticum turgidum and Triticum aestivum. ISH sites, similar to Nor-B6, were also detected on the long arms of chromosomes 1G in Triticum timopheevii and 1S in Aegilops speltoides, but their locations on the chromosomes were different from that of Nor-B6, indicating possible chromosome rearrangements in 1GL and 1BL during evolution. The third new locus, Nor-D8, was only found on the short arm of chromosome 3D in the common wheat Wichita. The loss of rRNA gene locus Nor-A3 and gain of repetitive DNA sequence pSc119 on the terminal part of 5AS suggest a structural modification of 5AS. Comparative studies of the location of the 18S·26S rRNA gene loci in polyploid wheats and putative A and B (G) genome progenitor species support the idea that: (1) Triticum monococcum subsp. urartu is the donor of both the A and At genome of polyploid wheats. (2) Ae. speltoides is closer to the B and G genome of polyploid wheats than Aegilops longissima and is the most probable progenitor of these two genomes.

Different species-specific chromosome translocations inTriticum timopheevii andT. turgidum support the diphyletic origin of polyploid wheats

Triticum timopheevii ssp.timopheevii andT. timopheevii ssp.araraticum were analysed by sequential N-banding and genomicin situ hybridization. Three chromosomes, 6At, 1G and 4G, were involved in At-G intergenomic translocations in all six lines analysed. These chromosomes may be derived from a cyclic translocation that is species-specific toT. timopheevii. In contrast,Triticum turgidum has a species-specific cyclic translocation involving chromosomes 4A, 5A and 7B. The discovery of different species-specific chromosome translocations supports the diphyletic hypothesis of the evolution of tetraploid wheats. The results from genomic blocking analysis also revealed that the chromosomes ofAegilops speltoides are closer to the G genome than the B genome chromosomes. The possible role of speciesspecific translocations in the evolution of wheat is discussed.

Radiation-induced nonhomoeologous wheat-Agropyron intermedium chromosomal translocations conferring resistance to leaf rust

SummaryThe Agropyron intermedium chromosome 7Ai #2 is the source of the leaf rust resistance gene Lr38 which was transferred to wheat by irradiation. The chromosomal constitutions of eight radiation-induced rust-resistant wheat-Agropyron intermedium derivatives were analyzed by C-banding and genomic in-situ hybridization (GISH). Five lines were identified as wheat Ag. intermedium chromosome translocation lines with the translocation chromosomes T2AS·2AL-7Ai#2L, T5AL · 5AS-7Ai # 2L, T1DS · 1DL-7Ai # 2L, T3DL · 3DS-7Ai#2L, and T6DS · 6DL-7Ai#2L. The sizes of the 7Ai#2L segments in mitotic metaphases of these translocations are 2.42 μm, 4.20 μm, 2.55 μm, 2.78 μm, and 4.19 μm, respectively. One line was identified as a wheat-Ag. intermedium chromosome addition line. The added Ag. intermedium chromosome in this line is different from 7Ai # 2. This line has resistance to leaf rust and stem rust. Based on the rust reactions, and the C-banding and GISH results, the remaining two lines do not contain any Ag. intermedium-derived chromatin.

Chromosome painting of Amigo wheat

Chromosome painting using multicolor fluorescence in situ hybridization showed that, in addition to the T1AL·1RS translocation derived from rye, a segment from chromosome 3Ae#1 of Agropyron elongatum (2n=10x =70), is present in Amigo wheat. The Agropyron chromosome segment is located on the satellite of chromosome 1B and the translocation chromosome is designated as T1BL·1BS-3Ae#1L. T1BL·1BS-3Ae#1L was inherited from Teewon wheat and carries resistance genes to stem rust (Sr24) and leaf rust (Lr24). The Agropyron chromosome segments in different Sr24/Lr24 carrier wheat lines, including Agent, TAP 48, TAP 67, Teewon, and Amigo, showed a diagnostic C-band, and were derived from the same chromosome, 3Ae#1.

Standard karyotype of Triticum umbellulatum and the characterization of derived chromosome addition and translocation lines in common wheat

A standard karyotype and a generalized idiogram of Triticum umbellulatum (syn. Aegilops umbellulata, 2n = 2x = 14) was established based on C-banding analysis of ten accessions of different geographic origin and individual T. umbellulatum chromosomes in T. aestivum — T. umbellulatum chromosome addition lines. Monosomic (MA) and disomic (DA) T. aestivum — T. umbellulatum chromosome addition lines (DA1U = B, DA2U = D, MA4U = F, DA5U = C, DA6U = A, DA7U = E = G) and telosomic addition lines (DA1US, DA1UL, DA2US, DA2UL, DA4UL, MA5US, (+ iso 5US), DA5UL, DA7US, DA7UL) were analyzed. Line H was established as a disomic addition line for the translocated wheat — T. umbellulatum chromosome T2DS·4US. Radiation-induced wheat — T. umbellulatum translocation lines resistant to leaf rust (Lr9) were identified as T40 = T6BL·6BS-6UL, T41 = T4BL·4BS-6UL, T44 = T2DS·2DL-6UL, T47 = ‘Transfer’ = T6BS·6BL-6UL and T52 = T7BL·7BS-6UL. Breakpoints and sizes of the transferred T. umbellulatum segments in these translocations were determined by in situ hybridization analysis using total genomic T. umbellulatum DNA as a probe

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

SummaryThree 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.

Cytogenetical studies in wheat XVI. Chromosome location of a new gene for resistance to leaf rust in a Japanese wheat-rye translocation line

SummaryA leaf rust resistant wheat-rye translocation stock, ST-1, introduced from Japan, comprised distinct morphological types. One type possessed a T1BL·1RS chromosome with genes Lr26, Yr9 and Sr31. A second type carried a new gene, Lr45, located in a large segment of rye chromosome translocated to wheat chromosome 2A. Its structure was identified as T2AS-2RS·2RL. Despite the homoeology of the 2A and 2R chromosomes and the high level of compensation provided by the translocation, Lr45 was not normally inherited and is probably associated with agronomic deficiencies that will prevent its exploitation in agriculture.

Introgression ofElymus trachycaulus chromatin into common wheat

A number of wheat—Elymus trachycaulus (2n= 4x= 28, genomically StStHtHt) chromosome addition, substitution, and translocation lines were isolated from the derivatives of anE. trachycaulus × wheat hybrid. Eighteen out of a total of 28 chromosome arms ofE. trachycaulus were recovered in the addition lines. The genomic affinity of individualE. trachycaulus chromosomes was analysed by comparative chromosome banding andin situ hybridization using genome-specific repetitive DNA sequences as probes. The homoeology of theE. trachycaulus chromosomes added to wheat was determined by storage protein, isozyme, and restriction fragment length polymorphism analysis. Alloplasmic wheat—E. trachycaulus chromosome additions were isolated which only involved chromosome 1Ht and 1St that carry fertility restoration geneRf-Ht1 andRf-St1, respectively. Based on the results of production and characterization of a wheat—E. trachycaulus 5Ht(5B) substitution line, it is likely that some wheat chromosomes can be well compensated genetically byE. trachycaulus chromosomes. Several spontaneous wheat—E. trachycaulus chromosome translocation lines were detected. All the translocation lines involved either 1Ht or 1St. To estimate the potential of recombination between wheat andE. trachycaulus chromosomes, a backcross population derived from a plant which was double monosomic for chromosomes 7A and 7AL·7AS—1StS and aph1b gene was developed. The plants from this population were analysed for 1St-specific genetic markers and no recombinant was recovered.

A 'zebra' chromosome arising from multiple translocations involving non-homologous chromosomes

An alloplasmic wheat line carrying a ‘zebra’ chromosome z5A was isolated from the derivatives of an Elymus trachycaulus x Triticum aestivum cv Chinese Spring hybrid. Chromosome z5A was named zebra because of its striped genomic in situ hybridization pattern. z5A consists of four chromosome segments derived from E. trachycaulus and four chromosome segments, including the centromere, from wheat. The short arm of z5A paired with the telocentric chromosome 1HtS of E. trachycaulus and the long arm with the long arm of normal 5A. z5A also carried several genetic markers derived from 1HtS. Chromosome 1Ht was the only E. trachycaulus chromosome found in the sib plants of a previous generation from which z5A was derived. Monosomic 5A and telocentric chromosome 5AL were also found in most of the sib plants. The zebra chromosome most probably originated from spontaneous multiple translocations between chromosomes 5A and 1HtS or 5A and 1Ht.