Journal of Genetics and Genomics

Wide hybridization: engineering the next leap in wheat yield

Daowen Wang

2009, 36(9): 509-510. doi: 10.1016/S1673-8527(08)60141-1

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Genome evolution in allopolyploid wheat—a revolutionary reprogramming followed by gradual changes

Moshe Feldman, Avraham A. Levy

2009, 36(9): 511-518. doi: 10.1016/S1673-8527(08)60142-3

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Allopolyploidy accelerates genome evolution in wheat in two ways: 1) allopolyploidization triggers rapid genome alterations (revolutionary changes) through the instantaneous generation of a variety of cardinal genetic and epigenetic changes, and 2) the allopolyploid condition facilitates sporadic genomic changes during the life of the species (evolutionary changes) that are not attainable at the diploid level. The revolutionary alterations, occurring during the formation of the allopolyploid and leading to rapid cytological and genetic diploidization, facilitate the successful establishment of the newly formed allopolyploid in nature. On the other hand, the evolutionary changes, occurring during the life of the allopolyploids, increase the intra-specific genetic diversity, and consequently, increased fitness, adaptability and competitiveness. These phenomena, emphasizing the dynamic plasticity of the allopolyploid wheat genome with regards to both structure and function, are described and discussed in this review.

Rapid genomic changes in polyploid wheat and related species: implications for genome evolution and genetic improvement

Bao Liu, Chunming Xu, Na Zhao, Bao Qi, Josphert N. Kimatu, Jinsong Pang, Fangpu Han

2009, 36(9): 519-528. doi: 10.1016/S1673-8527(08)60143-5

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A polyploid organism by possessing more than two sets of chromosomes from one species (autopolyploidy) or two or more species (allopolyploidy) is known to have evolutionary advantages. However, by what means a polyploid accommodates increased genetic dosage or divergent genomes (allopolyploidy) in one cell nucleus and cytoplasm constitutes an enormous challenge. Recent years have witnessed efforts and progress in exploring the possible mechanisms by which these seemingly intangible hurdles of polyploidy may be ameliorated or eventually overcome. In particular, the documentation of rapid and extensive non-Mendelian genetic and epigenetic changes that often accompany nascent polyploidy is revealing: the resulting non-additive and novel gene expression at global, regional and local levels, and timely restoration of meiotic chromosomal behavior towards bivalent pairing and disomic inheritance may ensure rapid establishment and stabilization as well as its long-term evolutionary success. Further elucidation on these novel mechanisms underpinning polyploidy will promote our understanding on fundamental issues in evolutionary biology and in our manipulation capacities in future genetic improvement of important crops that are currently polyploids in genomic constitution. This review is intended to provide an updated discussion on these interesting and important issues within the scope of a specific yet one of the most important plant groups—polyploid wheat and its related species.

An overview of plant centromeres

Guixiang Wang, Xueyong Zhang, Weiwei Jin

2009, 36(9): 529-537. doi: 10.1016/S1673-8527(08)60144-7

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The centromere is a defining region that mediates chromosome attachment to kinetochore microtubules and proper segregation of the sister chromatids. Intriguingly, satellite DNA and centromeric retrotransposon as major DNA constituents of centromere showed baffling diversification and species-specific. However, the key kinetochore proteins are conserved in both plants and animals, particularly the centromere-specific histone H3-like protein (CENH3) in all functional centromeres. Recent studies have highlighted the importance of epigenetic mechanisms in the establishment and maintenance of centromere identity. Here, we review the progress and compendium of research on plant centromere in the light of recent data.

Synthetic hexaploid wheat and its utilization for wheat genetic improvement in China

Wuyun Yang, Dengcai Liu, Jun Li, Lianquan Zhang, Huiting Wei, Xiaorong Hu, Youliang Zheng, Zhouhu He, Yuchun Zou

2009, 36(9): 539-546. doi: 10.1016/S1673-8527(08)60145-9

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Synthetic hexaploid wheat (Triticum turgidum × Aegilops tauschii) was created to explore for novel genes from T. turgidum and Ae. tauschii that can be used for common wheat improvement. In the present paper, research advances on the utilization of synthetic hexaploid wheat for wheat genetic improvement in China are reviewed. Over 200 synthetic hexaploid wheat (SHW) accessions from the International Maize and Wheat Improvement Centre (CIMMYT) were introduced into China since 1995. Four cultivars derived from these, Chuanmai 38, Chuanmai 42, Chuanmai 43 and Chuanmai 47, have been released in China. Of these, Chuanmai 42, with large kernels and resistance to stripe rust, had the highest average yield (> 6 t/ha) among all cultivars over two years in Sichuan provincial yield trials, outyielding the commercial check cultivar Chuanmai 107 by 22.7%. Meanwhile, by either artificial chromosome doubling via colchicine treatment or spontaneous chromosome doubling via a union of unreduced gametes (2n) fromT. turgidum-Ae. tauschii hybrids, new SHW lines were produced in China. Mitotic-like meiosis might be the cytological mechanism of spontaneous chromosome doubling. SHW lines with genes for spontaneous chromosome doubling may be useful for producing new SHW-alien amphidiploids and double haploid in wheat genetic improvement.

Progress of chromosome engineering mediated by asymmetric somatic hybridization

Guangmin Xia

2009, 36(9): 547-556. doi: 10.1016/S1673-8527(08)60146-0

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Plant somatic hybridization has progressed steadily over the past 35 years. Many hybrid plants have been generated from fusion combinations of different phylogenetic species, some of which have been utilized in crop breeding programs. Among them, asymmetric hybrid, which usually contains a fraction of alien genome, has received more attention because of its importance in crop improvement. However, few studies have dealt with the heredity of the genome of somatic hybrid for a long time, which has limited the progress of this approach. Over recent ten years, along with the development of an effective cytogenetical tool “in situ hybridization (ISH)”, asymmetric fusion of common wheat (Triticum aestivum L.) with different grasses or cereals has been greatly developed. Genetics, genomes, functional genes and agricultural traits of wheat asymmetric hybrids have been subject to systematic investigations using gene cloning, genomic in situ hybridization (GISH) and molecular makers. The future goal is to fully elucidate the functional relationships among improved agronomic traits, the genes and underlying molecular mechanisms, and the genome dynamics of somatic introgression lines. This will accelerate the development of elite germplasms via somatic hybridization and the application of these materials in the molecular improvement of crop plants.

Thinopyrum ponticum and Th. intermedium: the promising source of resistance to fungal and viral diseases of wheat

Hongjie Li, Xiaoming Wang

2009, 36(9): 557-565. doi: 10.1016/S1673-8527(08)60147-2

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Thinopyrum ponticum and Th. intermedium provide superior resistance against various diseases in wheat (Ttricum aestivum). Because of their readily crossing with wheat, many genes for disease resistance have been introduced from the wheatgrasses into wheat. Genes for resistance to leaf rust, stem rust, powdery mildew, Barley yellow dwarf virus, Wheat streak mosaic virus, and its vector, the wheat curl mite, have been transferred into wheat by producing chromosome translocations. These genes offer an opportunity to improve resistance of wheat to the diseases; some of them have been extensively used in protecting wheat from damage of the diseases. Moreover, new resistance to diseases is continuously detected in the progenies of wheat-Thinopyrum derivatives. The present article summaries characterization and application of the genes for fungal and viral disease-resistance derived from Th. ponticum and Th. intermedium.

Research progress in BYDV resistance genes derived from wheat and its wild relatives

Zengyan Zhang, Zhishan Lin, Zhiyong Xin

2009, 36(9): 567-573. doi: 10.1016/S1673-8527(08)60148-4

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Barley yellow dwarf virus (BYDV) may cause a serious disease affecting wheat worldwide. True resistance to BYDV is not naturally found in wheat. BYDV resistance genes are found in more than 10 wild relative species belonging to the genera of Thinopyrum, Agropyron, Elymus, Leymus, Roegneria, and Psathyrostachy. Through wide crosses combining with cell culture, use of ph mutants, or irradiation, 3 BYDV resistance genes in Th. intermedium, including Bdv2, Bdv3 and Bdv4, were introgressed into common wheat background. Various wheat-Th. intermedium addition and substitution, translocation lines with BYDV-resistance were developed and characterized, such as 7D-7Ai#1 (bearing Bdv2), 7B-7Ai#1, 7D-7E (bearing Bdv3), and 2D-2Ai-2 (bearing Bdv4) translocations. Three wheat varieties with BYDV resistance from Th. intermedium were developed and released in Australia and China, respectively. In addition, wheat-Agropyron cristatum translocation lines, wheat-Ag. pulcherrimum addition and substitution lines, and a wheat-Leymus multicaulis addition line (line24) with different resistance genes were developed. Cytological analysis, morphological markers, biochemical markers, and molecular markers associated with the alien chromatin carrying BYDV resistance genes were identified and applied to determine the presence of alien, chromosomes or segments, size of alien chromosome segments, and compositions of the alien chromosomes. Furthermore, some resistance-related genes, such asRGA, P450, HSP70, protein kinases, centrin, and transducin, were identified, which expressed specifically in the resistance translocation lines with Bdv2. These studies lay the foundations for developing resistant wheat cultivars and unraveling the resistance mechanism against BYDV.

Utilization of blue-grained character in wheat breeding derived from Thinopyrum poticum

Qi Zheng, Bin Li, Hongwei Li, Zhensheng Li

2009, 36(9): 575-580. doi: 10.1016/S1673-8527(08)60149-6

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The blue grain trait in common wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD), which is caused by blue pigments in the aleurone layer, was originally derived from the tall wheatgrass (Thinopyrum ponticum Liu & Wang = Agropyron elongatum, 2n = 10x = 70, StStStStE^eE^eE^bE^bE^xE^x) during chromosome engineering research. Over the last few decades, there have been continued interests in the genetic mechanism of this blue coloration and the practical utilization of the blue aleurone character as a phenotypic marker. This article reviews the research history and the recent progress of the studies on blue-grained wheat, with emphases on genetic and biochemical analysis and practical applications of blue-grained wheat.

2009 Vol. 36, No. 9