The Possible Origin Of The Triticum Petropavlovskyi Udacz. Et Migusch.:Evidences From Cytological Study And Phylogeny Among The Synthetic Hexaploid Wheat Between Triticum Polonicum And Aegilops Tauschii And Its Related Species

Xinjiang rice wheat (Triticum petropavlovskyi Udacz. et Migusch.) is one of the Chinese endemic wheat landraces, discovered in Tarim basin, Xinjiang Uygur Automous Region, China. The altitude distribution is 960-1200 m. The morphological traits of T. petropavlovskyi were obviously different with common wheat (T. aestivum L.), such as:higher plants (130-140 cm), glume and sheath with fuzz, naked seeds and so on. Moreover, the T. petropavlovskyi has some potential traits for crop breeding, such as:cold resistance, drought-resistant, barren resistantce. However, the origin of T. petropavlovskyi has still remained in debate, and three hypotheses have been proposed:(1) T. petropavlovskyi is an independent species is derived from a natural hybridization event between polish wheat (T. polonicum L.) and Aegilops tauschii Cosson; (2) T. petropavlovskyi is natural cross or backcross between T. polonicum and T. aestivum; (3) T. petropavlovskyi is a monogenic mutant of T. aestivum. In 2008, synthetic wheat was originated from the hybridization between T. polonicum and Aegilops tauschii by our research team. The artificial wheat was named SHW-DPW, which are important materials for studying the origin of T. petropavlovskyi.In present study, the synthetic wheat SHW-DPW was used to estimate the origin of T. petropavlovskyi from cytological and phylogeny analyses:(1) Crossing the T. petropavlovskyi, SHW-DPW to tetraploid and hexaploid wheat, respectively, and comparing the seed sets, self-fertility and chromosome pairing of F1 hybrids; (2) the relationsip between SHW-DPW and T. petropavlovskyi and the origin of T. petropavlovskyi were discussed based on the sequences of a single-copy gene Pgk-1; (3) the relationships between SHW-DPW and T. petropavlovskyi and primitive hexaploid wheats were discussed based on a single-copy nuclear gene Acc-1; (4) the relationships among the Chinese endemic landraces wheat were discussed based on two nuclear gene(Pgk-1 and Acc-1) and chloroplast DNA (trnH-psbA). The main results were described as follows:1. Intraspecific hybridizations between T. petropavlovskyi, SHW-DPW and tetraploid, hexaploid wheats were carried out to collect the data of seed set, fertility of F1 hybrid and meiotic pairing configuration to evaluate the possible origin of T. petropavlovskyi Udacz. et Migusch. The results showed that:(1) the seed set of crosses T. petropavlovskyi × T. polonicum and T. petropavlovskyi × T. aestivum cv. Chinese Spring was significantly high than other crosses between T. petropavlovskyi and tetraploid, hexaploid wheats; (2) the seed set of SHW-DPW × T. petropavlovskyi was inconspicuous comparing with other crosses between SHW-DPW and hexaploid wheats; (3) the fertilities of F1 hybrids of T. petropavlovskyi × T. polonicum were higher than other hybrids between T. petropavlovskyi and tetraploid wheats; the fertility of T. petropavlovskyi × T. aestivum ssp. yunnanense was obviously higher than other F1 hybrids between T. petropavlovskyi and hexaploid wheat; (4) the fertility of Fl hybrid SHW-DPW × T. dicoccoides and SHW-DPW × T. aestivum ssp. tibetanum was significantly high at the level of 5% and 1%(P< 0.01); (5) the c-value of T. petropavlovskyi × T. polonicum and T. petropavlovskyi x T. aestivum cv. Changning white wheat were significantly high among hybrids between T. petropavlovskyi and tetraploid, hexaploid wheats, at the level of 1%(P< 0.01); (6) the c-value of cross of SHW-DPW × T. polonicum was significantly high at the level of 5% and 1%(P< 0.01); average bivalents in the hybrid between SHW-DPW and T. petropavlovskyi was 18.19. These results indicated that some differents between T. petropavlovskyi and SHW-DPW were observed, and the relationships between T. petropavlovskyi and T. polonicum, Chinese landraces wheats were close.2. Single- and low-copy genes are less likely to be subject to concerted evolution, and they are appropriate tools to study the origin and evolution of polyploidy plant taxa. The plastid 3-phosphoglycerate kinase gene (Pgk-1) sequences from 44 accessions of Triticum and Aegilops, representing diploid, tetraploid, and hexaploid wheats, were used to study the origin of Triticum petropavlovskyi. The phylogenetic analysis was carried out on exon+intron, exon and intron sequences, using maximum likelihood, Bayesian inference and haplotype networking. The D genome sequences of Pgk-1 genes from T. petropavlovskyi are similar to the D genome orthologs in T. aestivum, while their relationships with Ae. tauschii is more distant. The A genome sequences of T. petropavlovskyi group with those of T. polonicum, but its Pgk-1 B genome sequences to some extent diverge from those of other species of Triticum. The results do not support for the origin of T. petropavlovskyi either as an independent allopolyploidization event between Ae. tauschii and T. polonicum, or as a monomendelian mutation in T. aestivum. Therefore, T. petropavlovskyi may originate via spontaneous introgression from T. polonicum into T. aestivum.3. A single-copy nuclear gene encoding plastid acetyl-CoA carboxylase (Acc-1) was used to study the relationships between T. petropavlovskyi and SHW-DPW, and 26 accessions of primitive hexaploid wheats. Sequence analyses indicated that there were two indels in Acc-1 gene, and the genetic diversity of T. petropavlovskyi was high. Phylogenetic analysis was performed using maximum likelihood, and Bayesian inference. The results showed that:(1) in the A genome, T. petropavlovskyi was clustered with Chinese endemic landraces wheat and T. macha (PI355511); (2) in the B genome,6 accessions of T. petropavlovskyi were located on different clades, one clade included T. petropavlovskyi (AS359), T. aestivum ssp. Tibetanum (AS910), T. sphaerococcum and T. compactum (PI132862); and another clade included 5 accessions of T. petropavlovskyi, T. macha (PI428178) and T. compactum (PI278541); (3) in D genome, three accessions of T. petropavlovskyi (AS356, AS358 and AS360) were clustered together, and T. petropavlovskyi (AS362) were clustered with T. macha (PI355511) and T. vavilovii (AS345) staying in different clade; (4) the SHW-DPW was not clustered with T. petropavlovskyi in A, B and D genome. These results indicated that the relationship between SHW-DPW and T. petropavlovskyi was distant, and the relationships between T. petropavlovskyi and the Chinese endemic landraces wheat, and primitive hexaploid wheat from west Asia were close. Therefore, we speculated that the T. petropavlovskyi was originated from the hybridization between external primitive hexaploid wheat and T. turgidum ssp. polonicum from Xinjiang, China, then crossed with the local hexaploid wheat.4. Two single-copy gene(Acc-1 and Pgk-1) and one cpDNA (trnH-psbA) were used to estimate the genetic diversity and phylogenetic relationship among 21 accessions of the Chinese endemic landraces wheat. Based on the DNA sequnces of Pgk-1 gene, we figured out that the genetic diversity of A, B and D genome was different. The diversity of B genome was higer than A genome, which was higher than D genome. The results indicated that diversity of Pgk-1 gene of T. petropavlovskyi was higher than other Chinese endemic landraces wheat; the T. aestivum ssp. yunnanense and T. aestivum ssp. tibetanum were lowest among the four species. The phylogenetic analyses from Pgk-1 indicated that the relationships between T. aesticum ssp. tibetanum and T. aestivum ssp. yunanense, and Sichuan white wheat complex were close. The DNA seuqnces of Acc-1 gene of D genome showed the highest genetic diversity, and the A genome was lowest. The genetic diversity of trnH-psbA sequences was low, three accessions, including T. petropavlovskyi (AS360), T. aestivum ssp. tibetanum (AS907) and T. aestivum ssp. yunnanense (AS339) have mutations in this cpDNA region. In the present study, the genetic diversity of B and D genome of the Chinese landraces wheat were higher than A genome, and the diversity of T. petropavlovskyi was higher than other Chinese endemic wheat landraces. The phylogenetic analyses indicated that the T. aestivum ssp. yunnanense and Sichuan white wheat complex might be diverged from T. aestivum ssp. tibetanum; the relationship between T. petropavlovskyi and T. aestivum ssp. tibetanum was closer than the relatioships between T. petropavlovskyi and T. aestivum ssp. yunnanense, Sichuan white complex. Futhermore, the origin of T. petropavlovskyi might have an unique way, and the A and B genome of T. petropavlovskyi have been changed.