The Report of the 7th International Triticeae Symposium

Shotaro Takenaka

Laboratory of Plant Genetics, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-Cho, Sakyo-Ku, Kyoto, Japan

Corresponding author: Shotaro Takenaka

E-mail: barontakenaka@hotmail.com

The seventh International Triticeae Symposium (7th ITS) was held at Sichuan Agricultural University in Chengdu, China from 9 to 13 June 2013. The symposium focused on the studies on tribe Triticeae. This tribe includes about 30 genera including the most important cereal crops (wheat, barley and rye). So far, the symposium had been held in Helsinborg (Sweden), Logan (USA), Aleppo (Syria), Cordoba (Spain), Prague (Czech Republic) and Kyoto (Japan).

About 120 researchers and students from 15 countries took part in this symposium. Participants including China transported from the Jinqiang Huaheng Hotel to venue by two motorcoaches and a microbus every day. Such transportation system was like a training camp however, I believed the system encouraged participants to communicate each other. There were 42 oral presentations and near 30 posters. They were grouped in 4 sections, namely Systematics and Phylogeny, Biodiversity and Conservation, Genetics and Genomics, Breeding and Utilization. Here I report some presentations focused on wheat, barley and rye from each sections.

Systematics and Phylogeny

Aegilops tauschii is the D genome donor of hexaploid wheat (Triticum aestivum: 2n = 6x = 42, DDAABB genome). “Genome wide survey of SNPs reveals the genetic structure of Aegilops tauschii, the D genome progenitor of wheat” by J. Wang, M. Luo, Z. Chen, F. M. You, Y. Wei, Y. Zheng and J. Dvorak reported population structure of 75 T. aestivum and 402 Ae. tauschii accessions. Genome wide SNP assay was used to genotype the accessions, in which 7,186 mapped SNPs represented 4.02 Gb D genome sequences. They pressed the points that Ae. tauschii was consisted of two lineages (Lineage 1 and Lineage 2) and that gene flow between the two lineages were very limited. They revealed that each lineage was consisted of two sub-lineages, that one sub-lineage within Lineage 2 from southwestern and southern Caspian was genetically more similar to D genome of wheat and that Ae. tauschii within Lineage 1 was contributed to only 4.4 % of genetic diversity of T. aestivum.

Ae. tauschii has two subspecies , ssp. tauschii and ssp. strangulata. “Intraspecies divergence of Aegilops tauschii Coss. As revealed by variation of chloroplast DNA non-coding sequences” by A. J. Dudnikov discussed evolutionary history of Ae. tauschii based on sequences of four chloroplast DNA non-cording regions, about 3,000 bp. He argued that Ae. tauschii originated in Caucasia and then differentiated into ssp. tauschii and ssp. strangulata at the beginning of its evolution. He considered that ssp. tauschii first start to expand its geographical distribution and rapidly occupied a vast area and that, in contrast to ssp. tauschii, ssp. strangulata lasted as a small isolated population for a long time span. Several form of ssp. strangulata, better adapted to relatively more moist and cool habitats, had originated within the isolated population and has gradually forced out ssp. tauschii from some part of its area in the west.

“Biodiversity in the Hordeeae: Shearing what is known and identifying what is not known” by M. E. Barkworth, E. Cabi, H. Al-Newani and C. Dyreson introduced web site platform, which uses SYMBIOTA software designed by Ed Gilbert of Arizona State University. The web site intends to share information accumulated in herbariums around the world (openherbarium.org).

Ae. speltoides is the B and G genome progenitor of tetraploid and hexaploid wheat. “Two genetic lineages in Aegilops speltoides – How many refugia in Aegilops species?” by T. Kawahara, N. Karashima and S. Takenaka examined genetic diversity of Waxy and Pgk1 genes in 142 Ae. speltoides accessions. They revealed that both genes divided in two groups and that combinations of each genetic group were consisted to expectation of random cross. So they concluded that the two different genetic groups do not represent genetic differentiation within species but show gene lineages in each locus. They believed that the two gene lineages would suggest the two refugia, possibly Black Sea coast and Mediterranean coast, during the Last Glacial.

“Novel traits of Leymus species that may contribute on wheat improvement” by H. Tsujimoto reported wheat lines with a pair of chromosomes of Leymus recemosus, L. mollis or Psathyrostachys huashanica. His presentation indicated that some alien chromosome addition wheat line showed high phosphorus efficiency and good growth under low phosphorus condition. To apply these traits of the addition lines to wheat breeding, transfer the chromosome arm or segment to the wheat genome is needed. The presentation further showed that a double monosomic addition line carrying semi-homologous chromosomes of L. recemosus and L. mollis could associate in the meiotic prophase but recombination does not occur between them. The line has good potential to survey the recombination-enhancing factor in wheat.

“Forming of Chinese wheat Species” by N. P. Goncharov discussed about three new polyploid wheat species discovered and/or described since the middle of the last century in China, T. petropavlovskyi Udacz. Et Migusch., T. yunnanense King and T. tibetianum Shao. He believed that T. petropavlovskyi is hybrid species carrying the T. polonicum gene P1 for long glumes. He further thought that T. yunnanense and T. tibetianum should be described as subspecies of T. spelta because spelt phenotypes in T. spelta, T. yunnanense and T. tibetianum was controlled by non-allelic genes.

Biodiversity and Conservation

R. von Bothmer, O. Westengen and S. Jeppsson introduced the Svalbard Global Seed Vault in “Is there a need for the Svalbard global seed vault and are our genetic resources safe for the future? Examples in the Triticeae”. The Global Seed Vault was built as a backup center for international plant genetic resources in 2008. The Vault is located in the arctic area at 78 ˚N, the Norwegian island of Spetsbergen. The Vault has an extra cooling device for keeping the temperature down to -18˚C, standard for gene bank material. In case there are serious breakdown of cooling device, the Vault in permafrost can keep the temperature down to -5˚C.

“English translation of the Russian “Flora of Cultivated Plants. Wheat” (Dorofeev et al. 1979): project progress report” by H. Knüpffer, A. A. Filatenko, K. Hammer, C. Jeffrey, T. Kawahara and L. A. Morrison reported progress of English translation project of the most recent taxonomic monograph of Triticum L. (Dorofeev VF, Filatenko AA, Migushova EF, Udaczin RA, Jakubziner MM. 1979. Flora of cultivated plants. Vol. 1. Wheat. Leningrad, 347 pp.). This important monograph is little known outside of Russia due to the language barrier. The translation project started in 1999 and was funded by CIMMYT. Publication of the translation by Springer (Vienna-New York) is projected for 2014.

“Aegilops conservation and breeding potentials” by V. Holubec, A. Hanzalová, V. Dumalasová and P. Bartoš evaluated agronomic important traits of Aegilops accessions (including 21 species, 1,082 accessions), which are conserved in the Gene Bank Prague, and 120 new introduced accessions. They investigated resistance for three different leaf rust races and three different stem rust races. They reported that some Aegilops species have resistant at least for one leaf rust race at high rates: Ae. speltoides (100%), Ae. lorentii (Ae. biuncialis, 91%) and Ae. triuncialis (88%). The same was at least for one stem rust race: Ae. speltoides (100%), Ae. cylindrica (97%), Ae. triuncialis (97%), Ae. neglecta (95%) and Ae. geniculata (95%).

“Evolution of emmer wheat based on the variations of 5’UTR region of Ppd-A1- evidences of gene flow between emmer and timopheevii wheat” by S. Takenaka and T. Kawahara discussed about genetic diversity and evolution of tetraploid wheat based on Ppd-A1 gene and its around DNA sequences. They showed that a part of domesticated emmer wheat was derived from introgression from wild emmer wheat around Israel. They further showed that there were multiple gene flows between emmer and timopheevii wheat under natural condition.

Genetics and Genomics

Common wheat is an allohexaploid species with the genome size of 17 Gb and 90% repetitive sequences. The largeness and complexity daunted to sequence the wheat genome-based scale. So in 2005, the International Wheat Genome Sequencing Consortium (IWGSC) was established and has proposed to map and sequence the wheat genome based on chromosome-by-chromosome approach. “A 1-Gb leap towards the hexaploid whet genome sequences” by F. Choulet, N. Glover, L. Pingault, J. Daron, S. Theil, N. Guilhot, A. Couloux, V. Barbe, A. Alberti, M. Alaux, P. Leroy, H. Šimková, J. Doležel, A. Bellec, H. Bergès, P. Sourdille, E. Paux, H. Quesneville, P. Wincher and C. Feuillet reported progress of the sequencing project of chromosome 3B (1 Gb). They sequenced 8,452 BAC clones of the MTP using NGS technology and obtained 4,999 scaffolds (N50 = 463 kb). They have produced a pseudomolecule covering 775 Mb anchored to genetic and phenotypic maps with more than 4,000 markers.

“Characterizing the structural and functional variations of the bread wheat chromosome 3B gene space” by P. Lise, C. Frederic, T. Sébastien, G. Natasha, S. Pierre, L. Philippe, G. Nicolas, B. Francois, A. Adriana, C. Arnaud, B. Valerie, IWGSC, Van del P. Klaas, W. Patrick, F. Catherine and P. Etienne reported fine transcription map based on a pseudomolecule described above and information of RNA-seq. They showed that 82% of the 6,812 predicted genes were expressed, with more than half displaying alternative splicing. 2,724 genes were expressed in the 15 conditions and 6% of the genes showed a condition-specific profile. They also reported that 2,393 new transcriptional active regions were identified in non-anotated regions.

“Using physical map and survey sequences to unravel the structure and composition of wheat chromosome arm 7DL” by L. Wang, X. Nie, H. Šimková, J. Safar, J. Doležel, E. David, M. Luo and W. Song reported progress of the sequencing project of chromosome 7DL carried out in the framework of IWGSC. A total of 50,304 clones were fingerprinted. An assembly resulted in 1,614 contigs (N50 = 296.4 kb) and 4,472 MTP clones were generated from the assembly. They showed that 846 contigs of wheat 7DL chromosome were anchored based on Ae. tauschii physical map. Furthermore, they reported that they survey sequenced 7DL-DNA using NGS technology and gained a total of 14.54 Gb (70x) to date. After de novo assembly, they obtained 160,021 contigs with the total base of 223 Mb (covering 65% of 7DL chromosome).

“Development of PCR based PLUG markers specific to individual rye chromosome arms” by J. Li, T. R. Endo and S. Nasuda reported PCR based markers for rye chromosome. The PLUG markers were selected from wheat PLUG markers whose chromosomal regions had been determined. Based on the homology between wheat and rye chromosomes, they showed complex structural rearrangements between them.

A plant cuticle, which is composed of cutin and wax, covers the surface of land plants and prevents uncontrolled water loss. “Cuticle mutants and gene isolation in barley (Hordeum vulgare)” by G. Chen, C. Li and T. Komatsuda investigated a cutin defective mutant of barley (eibi1). The mutant had thin cuticle and a low capacity to retain leaf water. They showed that Eibi1 encoded an HvABCG31 full transporter by genetic mapping and thought that the mutant was inhibited transportation of cutin. Furthermore they investigated eceriferum (cer) mutants, which had reduced or absent epicuticular wax crystal, and assigned the mutants to 79 loci. One of cer mutants, cer-zv, showed a significant reduction in cutin monomers but not wax therefore cer-zv mutant is the second cutin defective mutant. They showed cer-zv was located in the centromeric region of chromosome 4H.

“Major variation in spike form in the Triticeae specis” by T. Komatsuda discussed morphology of spike of barley (two- or six-row). The differences are controlled one gene Vrs1, which encodes homeodomain-leucine zipper I class transcription factor and is a paralog of HvHox2. He showed the differences of expression patterns and functions between VRS1 and HvHox2. The transcriptional activation activity of VRS1 and HvHox2 was conserved but expressed in different places. He thought that function of Vrs1 is to inhibit gynoecial development because the transcription level of Vrs1 was more than ten-fold greater than that of HvHox2 during the pistil development stage. Furthermore he reported that Vrs1 expression was up-regulated by Vrs4 (vrs4 is another six-row mutant).

Breeding and Utilization

Wheat is an allopolyploid which has two or more sets of related chromosomes. Despite their genome complexity, wheat behaves as diploid during meiosis because Ph1 locus, located on chromosome 5B, prevents pairing between homoeologous chromosomes. “Uses of the ph1 mutations as a genetic tool for breeding” by M. D. Rey, M.C Calderón and P. Prieto reported development of new wheat alien chromosome substitution line carrying chromosome segments from H. chilense. They first showed that inter specific recombination between wheat and H. chilense promoted efficiently in the background of the ph1 mutants.

“The responses of germinating barley seeds to salt stress” by W. Xue, J. Yan, X. Zhao, R. Wang, F. Tzion, A. Korol and J. Cheng proposed new index for evaluation of salt tolerance of crop. Salt tolerance is one of the most important traits of crop breeding. However, researches on the mechanisms of salt tolerance of seedlings are relatively poorer than those in growing plants. They invented index to evaluate seed germination responses to salt stress and applied the index to both Chinese barley cultivars and Israeli wild barley (H. spontaneum). The Chinese barley cultivars exhibited diverse salt tolerances with the values ranging from 29.1 to 310 mM (NaCl solution) and the Israeli wild barley exhibited high tolerances from 340 to 450 mM.

In recent years, the studies on barley and wheat have progressed rapidly. In 2010, whole genome sequencing of Brachypodium distachyon, a model plant for temperate grasses, finished and we can use the information for research on Triticeae (IBI, 2010). In Triticeae, most parts of barley (H. vulgare) genome have been sequenced (IBSC, 2012). In 2013, moreover, physical maps of Ae. tauschii and T. urartu have been reported (Luo et al. 2013, Ling et al. 2013). Because of the very large and complex genome structure, whole genome sequencing of wheat had been considered difficult. However, now the genome project of wheat has progressed under the initiative of IWGSC and the results were reported in this symposium. In this symposium, many researches on interspecific variation and phylogenetic evolution of perennial plant (Elymus, Leymus etc.) were presented. Further studies are needed because many questions are left unsolved regarding to the evolution and distribution of Triticeae.

The symposium was nicely organized under the joint auspices of Local Organizing Committee chaired by Prof. Yen Chi, International Organizing Committee and National Natural Sciences Foundation of China. The next International Triticeae Symposium will be held at IPK (Gatersleben, Germany).

Finally, My travel to China was supported by a grant from LOC of the 6th ITS. I would like to thank the supports.

References

International Barley Genome Sequencing Consortium (IBSC) (2012) A physical, genetic and functional sequence assembly of the barley genome. Nature 491: 711-716.

International Brachypodium Initiative (IBI) (2010) Genome sequencing and analysis of the model grass Brachypodium distachyon. Nature 463: 763–768.

Ling HQ, et al. (2013) Draft genome of the wheat A-genome progenitor Triticum urartu. Nature 496: 87–90.

Luo MC, et al. (2013) A 4-gigabase physical map unlocks the structure and evolution of the complex genome of Aegilops tauschii, the wheat D-genome progenitor. Proc Natl Acad Sci USA 110: 7940-7945.