Molecular Systematical Studies On Chinese Waxy Corn

The glutinous endosperm of the waxy corn was controlled by a recessive mutation named wax, which locates in the 9th chromosome. The waxy corn, with many excellent characters, better quality, higher economy value, is the important raw material for food industry, textile, paper-making, micro brew and feedstuff.It was well accepted that the waxy corn was the single gene mutation of the flint corn. Zeng Mengqian (1981) thought that the Chinese waxy corn had many pristine characters as well as the 5th band of the distinct peroxide enzyme, so that the waxy corn was originated in China and perhaps had some relationships with the Coix L.. Li Maoxue (1990) revealed that the karyotype of the waxy corn was more related to pop corn, while the latter was well known as the primordial type. HuangYubi (1997) put forward that the genome of the waxy corn had too much differences from that of the normal maize. Therefore, it was impossible that the waxy corn was mutated from the normal one just by single gene mutation, and it worth to research its origin. It can be seen that the origin place, the origin path of the waxy corn are not obvious till today. To clarify the evolution of the maize family, the origin and evolution of the waxy corn and reconstruct the Zea L. phylogenesis are important to the academic research of maize.Recently molecular systematics makes great progresses and many new theories and methods are applied to confirm the position or trace the origin of plant. In present research normal maize landraces and waxy corn landraces from the Southwest of China, special types of maize cultivar, relatives of maize were collected as experimental materials in this study. At the same time some sequences, which were determined by results of BLASTn were downloaded from GENBANK and were added in our data matrix. Five kinds of molecular markers including the 2nd intron of the mitochondrion genome, the intron rpL\6 of the chloroplast genome, and the glb1 gene sequence, the waxy gene sequence and the rDNA ITS region of the nucleus genosome were used to the waxy corn systematic study. This study reconstructed the Zea genus phylogenesis and emphasized on the systematic position of the waxy corn and the phylogenesis relationship between the waxy corn andZmays.ssp.parviglumis, the America cultivated maize and the Chinese normal maize. Based on the coalescent model, the population evolution history of the waxy corn was simulated and selection, gene flow, ecology factors in the speciation of the waxy corn and the population evolution were discussed in details. The domestication bottleneck of the waxy corn and its sense to modern maize breeding were also discussed. Furthermore, the phylogeography method was adopted to study the geographical origin of the waxy corn. And the following results are received:1. The ITS sequences of 3 waxy corn landraces, 2 America waxy mutants, and 4 special types of maize cultivar were sequenced. 26 sequences downloaded from GENBANK were added into the data matrix. The sequence analysis showed that the nucleotide polymorphisms of ITS of the waxy corn were more than the other species or subspecies in Zea L. Two Zea pseudogenes were found in the study. The MP tree showed that the Chinese maize (including waxy corn) has formed much independent clade. But the possible ancestors werer not in the same clad. It was indicated that the waxy corn has special origin and evolution path.2. Twenty glb1 sequences including 11 waxy corn landraces, 6 special types of cultivated maize and 3 relatives were sequenced. With 23 sequences downloaded from GENBANK 20 sequences were analyzed .The results showed that the nucleotide polymorphism of waxy corn was the most one among all taxa. The fixed differences and shared polymorphisms between all taxa sampled displayed that the waxy corn, Z.mays.ssp.parviglumis have less divergent time than and are more relative to normal maize (especially the America cultivated maize and Chinese normal maize). The waxy corn has obvious divergence to Zperennis, Z.diploperennis and Z. luxurians but is less relative to them than Z.mays.ssp.parviglumis, Z.mays.ssp.mexicana and cultivated maize. It was likely that the relationships between the waxy corn, Zmays.ssp.parviglumis and the normal cultivated maize are much close. But the possibility that the waxy corn wass mutated by the normal maize through single gene mutation was much little. It can be concluded that Zmays.ssp.parviglumis is possibly the ancestor of the cultivated corn and the waxy corn or Z.mays.ssp.parviglumis has the same ancestor with the waxy corn.3. The partial sequences of waxy gene of 23 materials including the waxy corn and the normal corn were sequenced. 40 sequences were downloaded from Genbank. Sequencescomparison, Tajiama'D test, Fu and Li's D* and Fu and Li's F* all indicated that the locus evolution of the waxy corn and the others is different, the waxy locus was effected by selection directly and its nucleotide polymorphisms decreased obviously which was related to the traditional eating habit of dwellers in the southwestern China. This is the first proved locus of the maize controlling the starth parthway which is related to artificial selection directly.4. The analysis of rpL16 sequence, ITS region and waxy gene all indicated that the genetic differentiation between coxi and waxy corn are so big that the waxy corn has no possibility of being origined from coix.5. According to phylogeography, the partial sequences of waxy gene of 77 materials including 43 waxy corn landraces and 34 non-waxy corn landraces were compared. Ten haplotypes were found in the 77 sampled sequences from different regions. Using most parsimony method and taking coix as outgroup we constructed the rooted haplotype tree. The geographical origin of the waxy corn is determined according to the topology of the MP tree, variation patterns of haplotypes and the geographical distribution of the originality haplotype. The results indicated that the waxy corn was originated from the southwest of china, exactly in partial special ecological area of the common boundary of Yunnan, Guangxi and Guizhou, which locates between 23 ° N~25° N, nearby 105° E.6. The 2nd intron of nad1 of the mitochondrion genome and the rpL16 of the chloroplast genome were sequenced. The systematic value of the two cytoplasmic DNA sequences in maize genes evolution was clarified. It is considered that The 2nd intron of nadl change faster than rpL16 and contain more systematical information for the recostruction of Zea genus.