FISH Analysis Of 45S RDNA Gene In Agropyron Cristatum (L.) Gaertner (Poaceae:Triticeae)

Agropyron cristatum (L.) Gaertner is the typical species of the genus Agropyron Gaertner within the tribe Triticeae (Poaceae). It is perennial cross-pollination plant with P genome. Three ploidy levels were recognized in A. cristatum:diploid (2n=2x=14), tetraploid(2n=4x=28), and hexaploid(2n=6x=42). The natural habitats of A. cristatum are mainly in the extratropical regions of European Russia and southwestern Siberia. The distribution of A. cristatum are the most widely distribution range in the genus Agropyron Gaertner. As the wild relative of wheat, A. cristatum has a large collection of excellent genes, such as drought tolerance, cold tolerance, salinity tolerance, and resistance to diseases and pests, are valuable genetic resources for the genetic improvement of wheat. It is also an important component of grasslands and possess highly animal feed value, including many good traits that tender stem leaf, nutrient-rich, good palatability. Previous study mainly focused on the development and utilization of A. cristatum. However, there are still many unsolved questions to be answered from the perspective of population genetics, such as the genetic diversity between different ploidy chromosomes, the relationship of A. cristatum populations, and formation process of autopolyploid. In this study, the variation of 45S rDNA sites in the A. cristatum population were investigated using fluorescence in situ hybridization (FISH). These populations of A. cristatum were from East Asia, Central Asia, and Qinghai-Tibet Plateau. The main results showed as follows:1. The number of 45S rDNA sites range from 6 to 12 and 12 to 14 in A cristatum from Central Asia and East Asia, respectively. The number of 45S rDNA sites was the largest variational in Qinghai-Tibet Plateau population (8-18). The 45S rDNA sites showed a main distribution on the short arms, mostly in the terminal regions. In Central Asia population(except PI598628), the 45S rDNA sites mostly distributed on the terminal of short arms. The distribution of 45S rDNA sites were diverse on the chromosomes in Qinghai-Tibet Plateau and East Asia population, including on the terminal or interstitial-proximal of short arms and on the terminal, interstitial-terminal or interstitial-proximal of long arms. This suggested that 45S rDNA sites were polymorphism in A. cristatum from different geographical distribution.2. The number of 45S rDNA sites range from 6 to 8.8 to 17 and 18 in diploid. tetraploid and hexaploid. respectively. Along with ploidy increasing, the number of sites are not all equal ratio increasing. Besides PI598628 in diploid has one site on the terminal of long arm, the sites of diploid and hexaploid distribute on the terminal of short arm. The 45S rDNA sites located on the terminal and interstitial-proximal of short arm, on the terminal, interstitial-terminal. and interstitial-proximal of long arm in tetraploid A. cristatum. It is indicated that the number and distribution of 45S rDNA sites were polymorphism in different ploidy A. cristatum, especially in tetraploid. The polymorphism may be related to widely ecological adaptability in tetraploid.3. Karyotype analysis showed that the most of diploids A. cristatum were 1A types, the tetraploids and hexaploid were all 2A.45 S rDNA sites have nine kinds of distribution types and primarily on the terminal region of short arm (the "a" type). Distribution types of 45S rDNA sites mostly was the "a" type in Central Asia population. But types of 45S rDNA sites were diversity in East Asia and Qinghai-Tibet Plateau, especially in Qinghai-Tibet Plateau. It is speculated that Central Asia population may be the origin central.4. The same distribution types of 45S rDNA sites and karyotype types(1A) were in Central Asia diploid PI547279 from Orenburgskaya Oblast and PI598631 from Kazakhstan, indicated they were close relationship. Tetraploid (ZY12185, ZY12173) and hexaploid ZY12179 are all from Tongde county in Qinghai province. The same distribution types of 45S rDNA sites and karyotype types(2A) were in them, indicated they were close relationship.