Zhang Lianquan

Polyploidy has been found to be very common in plants. Bread or common wheat (Triticum aestivum L., 2n=42) is a good example of allopolyploid made up of three diploid genomes A, B and D. Bread wheat has undergone two polyploidizations during its evolution. By the mimic of common wheat evolution, many synthetic hexaploid wheats have been produced. The synthetic wheat is very useful for genetic improvement of modern wheat. Moreover, common wheat has many distinctive scientific characteristics which make it an interesting model for the study of the organization and evolution of plant genomes. In our study, we studied the allohexaploidization by analyzing the process of artificially synthetic hexaploid wheat with emphasis on its application in genetics and breeding.
1. The crossability of Triticum turgidum with Aegilops tauschii
The crossability of Triticum turgidum with Aegilops tauschii are first investigated systematically. Without using embryo rescue technique, many hybrid seeds of tetraploid wheat with Ae. tauschii could germinate and produce plants in the present study. The higher crossabilities compared with the control in lines 7D(7A) and 4D(4B) suggested that 7A and 4B in tetraploid wheat cv. Langdon carried dominant crossability alleles inhibiting crossability with Ae. tauschii.
2. Meiotic restriction in emmer wheat is controlled by one or more nuclear genes that continue to function in derived lines.
Triticum turgidum ssp. turgidum has meiotic restitution gene(s). “Mitosis-like meiosis” is the functional mechanism of the meiotic restitution gene(s). Test crosses of the T. t. turgidum – Ae. tauschii amphidiploid with Ae. variabilis and rye suggested that the mitosis-like meiosis is controlled by nuclear gene(s) that are functional in the derived lines. This discovery implicates a potential application of such genes in production of double haploids.
3. The synthesis of new synthetic hexaploid wheats (Syn-SAU-N-X-Y) and new nullisomic-tetrasomic lines (Syn-SAU NXTY)
Lots of new synthetic hexaploid wheats have been obtained from crosses of five T. turgidum L. lines with Ae. tauschii, which were formed by chromosome autoduplication through unreduced gametes. Besides the values in wheat improvement, they are desirable materials for study of allohexaploidization due to without the using of chemical materials, such as embryo rescue and colchicine treatment during the synthetic process. By colchicine treatment of the hybrid plants between Triticum turgidum and Aegilops tauschii, a fertile wheat plant (SHW-L2) carrying 56 chromosomes was artificially synthesized.
New nullisomic-tetrasomic lines were obtained from crosses of Langdon D-genome substitution lines with Ae. tauschii, which were formed by chromosome autoduplication through unreduced gametes. They are different from previous Chinese Spring nullisomic-tetrasomic lines. The main differences were as follows: (1) for each of tetrasomics, there were four D chromosomes, two from Ae. tauschii and two from Chinese Spring; (2) they were obtained by manner of synthetic wheat, other genetic backgrounds were from T. turgidum L. and Ae. tauschii except that their two D chromosomes of the corresponding tetrasomics were from Chinese Spring.