| By the time Columbus reached the new world maize fields were evident in both North and South America. It is believed that maize dates back even further than the inhabitance of native people. Maize is thought to have descended from a wild weedy species. However, most crops are obvioures related to a species that still preserved in nature, the crop and the wild plant are similar. This is not true for maize. In spite of extensive search of maize wild forms, none have been found. Its origin and the maize ear developed have been the mystery since maize has been found highly domestication, which is the most domesticated and evolutioned plant member from the plantac kingdom. Unraveling its twists and turns has challenged many botanists until now. Obviously, maize genome and genome duplications are important for understanding origin and evolution of maize.Regardless of its origin, maize has proved to be one of the most adaptable and variable members of the grass family, however, during its domestication from a wild weedy species, maize has gained many agronomically significant attributed but it has lost a lot of the useful genes. Like other crops, its close relatives of maize own a lot of useful genes, the introgression of deleterious genes into maize, breeder could take advantage of these special traits to improving maize breeding.In this study, we have been investigating origin and evolution of maize genomes by using molecular cytogenetics to analyze maize (the cultivated maize) and its wild relative species. For improving the biodiversity of germplasm in maize breeding, and to transfer desirable characters from maize relatives into maize, the performance of crossing ability characters and the genetic variations among the species of genus Zeaand its introgression hybridization offspring were studied. We found that:1. To investigate genome components among species of genus Zea, four species Z. mays (maize) (2n=20), Z. diploperennis (2n=20), Z. luxurians (2n=20) and Z. perennis (2n=40) in genus Zea were studied by GISH and Multi-color GISH (McGISH). Investigations have found that maize originated as polyploidy, containing several diverged groups of chromosome by several genome duplications.The general GISH observations were in general agreement with the hypothesis that maize is an allopolyploid and has the genomes constitution of A, B, C-genomic. Z.dipperennis and z.Iuxurians have the similar genome constitution with maize. Mc-GISH experiments provided more direct evidence that their genomes among Z. mays (maize), Z. diploperennis, and Z. luxurians were homologous with each other. However, the McGISH between maize and Z. perennis, revealed two color differention of chromosomes. Furthermore, Fi hybrids of maize x Z. perennis exhibited different color signals in three groups of chromosomes , which correspondingly appeared in 5 trivalents, 5 bivalents and 5 univalents. The three color differention of chromosomes in hybrid by GISH indicated that its contained genome-specific DNA sequencse to these chromosomes, respectively. And results suggested that these divergence of such genomes could be designated A, B, and C. Genome A was homologous with each other, while genomes B and C have diverged extensively. Z. perennis had genome C and A, and maize had genome B and A. Our results suggested that maize chromosomes 1, 7, 8, 9 and 10 belonged to genome A, which was homologous with Z. perennis, while chromosomes 2, 3, 4, 5,and 6 belonged to genome B.2. The average of meiotic configurations in Fi hybrid maize x Z.perennis was 4.66I+5.00II+5.12III. The original source of each meiotic configuration in Fi hybrid maizexZ.perennis was visualized by GISH, results showed that the formation of meiotic configurations in Fi were not random event. Based on principle of fluorescent color, the different fluorescent color represented different genomes, and suggesting that the hypothesis of A, B, C-genomic constitution were more reliable than the hypothesis of A, B-genomic constitution in genus Zea. McGISH results also revealed that the maize chromosome 2, 3, 4, 5 and 6 were likely to B-genomic, which were identified to form univalents in meiotic configurations of maizexZ.perennis (2n=30); and maize chromosome 1, 7, 8, 9 and 10 were A-genomic, these chromosomes got together with A-genomic chromosomes of Z.perennis to form trivalents; and bivalentsderived from a specific C-genomic chromosomes of Z.perennis. Our research provides strong evidence for the hypothesis of A, B, C-genomic constitution in genus Zea.3. The genetic relationships among the species of genus Zea involved in its introgession hybridization generations were evaluated by isoperoxidase electrohoretogram. Result indicated that the isoenzyme band number and activities of maize were lower than its relatives, and the annually species were lower the perennis species. The most of introgression hybrid were the intermediate isoenzyme patterns to the two parents. But the Fi of maizex Zea parviglumis and maizex Zea mexicana produced a new isoenzyme band by compared with its parents, it was proposed that the intro- or interspecific hybrid was easy to produce gene recombining for the moderately relationship parents.4. The crossing ability (seed set and pollen viability) between maize (inbred and hybrid) and it relatives (including annual and perennis) including its introgression hybridization progenies were investigated. The resuts were: 1) excepted for Zea parviglumis and Zea mexicana, much of wild maize directly crossed with maize, there were low seed set, cutting silk short and taking the "mediation" method can be achieved to improve it. 2)most of the wild maize and their interspecies hybrids have a strong photoperiod response and flowering in autumn or early of winter, it is necessary to take steps to control the duration of sunshine in order to reduce photoperid response. The cross ability of their interspecies hybrids were normal about PV>60% and SO50% excepted for the Fi between maize and Z. perennis. 3) the pollen viability possibly has the charactering of temperature-photoperiod response in the Fi of maizexZ.perennis, because the pollen viability were higher than 30% in May and September, whereas in Jun and July were lower than 5%.5. Using some specially treated and genomic affinities, few Faaneuploid of maize x Z. perennis could be obtained by chromosome elimination. Morphologic, cytological and SSR observation on F2 were conducted. Results showed that F2 have different plant types such as wild parent-like, internal type, maize-like. Frequency of F2 cells with 24, 25 and 26 chromosomes in aneuploids. Chromosome elimination, duo to maize x Z perennis (2n=30) plant with the most frequent configuration of 5 III +5II +5 I , which produced the chromosome elimination for aneuploids. The SSR assay further confirmed that maize chromosome 2, 3, 4, 5, 6were easy to be eliminated than maize chromosome 1, 7, 8, 9, 10 which could be deduced that maizechromosome 2, 3, 4, 5, 6 were easy to be univalents in meiotic configuration of Fi hybrid of maize * Z. perennis. Among these F2 aneuploid, it can be produced as addition or substitute line by cytogenesis project.6. To transfer desirable characters from Zea perennis into maize, we have generated interspecific hybrid and its backcross generations (BC1F3). The maize * Z. perennis BC1F3 resembled maize, with chromosome number 2n=20. The BC1F3 was studied by Multi-color GISH (McGISH) and simple-sequence repeats (SSRs) microsatellites markers. McGISH experiments provided direct evidence that BC1F3 was a maize-Z. perennis substitution line with introgression of three alien chromosomes from Z. perennis. The SSR assay further confirmed that a single chromosome 6 and the pair of chromosome 10 of maize were replaced by Z. perennis chromosomes in BC1F3.In conclusion, innovative results of this study are those that genome components among species of genus Zea have been identified by new developed molecular cytogenetic technique, the evolutional relationship among four species of genera Zea has been analyzed at the level of meiotic configurations, isoperoxidase electrohoretogram and molecular banding information. The introgression of desirable characters from teosinte into maize has been experimented. In maize-teosinte generations, there are a lot of considerable genetic and breeding materials, as well as unstable and stable mutations.
|
PDF Full Text Request