Assessment Of Genetic Relationship Of Zea Species Based On RAPD Markers And ITS Sequences

Genetic relationships of teosinte and maize in Zea were estimated systematically based on randomly amplified polymorphic DNA (RAPD) markers and the internal transcribed spacer (ITS) sequences of nuclear ribosomal DNA in the present study. The main results are as follows:I. RAPD was used to identify the polymorphisms and relationships between 14 genotypes of teosinte and maize species. A total of 4500 polymorphisms out of 5303 repeatable products were obtained from 136 random decamer primers among teosinte and maize species, and the ratio of polymorphism was 84.86%, indicating complicated genetic background and extensive genetic diversity existing in Zea species. The genetic similarities among teosinte and maize species ranged from 0.585 to 0.809, and from 0.759 to 0.809 in the same genotypes from different geographical regions, and from 0.585 to 0.745 between different genotypes, demonstrating the accuracy of utilizing RAPD markers for genetic relationships analyses of Zea species.2. A consensus tree derived from RAPD cluster analysis indicated the genus Zea could be divided into section Luxuriantes consisting of Zea perennis, Zea diploperennis, Zea hoxurians and Zea nicaraguensis, and section Zea including Zea mays ssp. mexicana, Zea mays ssp. parviglumis, Zea mays ssp. huehuetenangensis and Zea mays ssp. mays. The results are consistent with the opinion that the genus Zea is classified into section Luxuriantes and section Zea according to Dobeley et al. and litis et al.. But the grouping of populations representing the Zea species in the subgenus interior clades is more congruent with growth habits than morphological data according to Wilkes.3. The entire ITS regions of the 14 taxa of Zea and 1 outgroup, Tripsacum dactyloides L., were sequenced in the present study. It showed that the lengths of the entire ITS regions of the 14 taxa of Zea analyzed varied from 597 to 605 bp, with an average of 601 bp. The GC content varied from 67.0 to 68.2%, with a mean value of 67.8%. In addition to the insertion/deletions, there were 78 variable sites (12.7%) among the aligned sequences, of which 10 positions (1.6%) were potentially phylogenetically informative sites. ITS sequence divergence ranged from 0.17 to 2.92% among taxa of Zea, with a mean value of 1.29%. The information of the ITS sequence data of Zea species obtained in our study is suited for phylogenetic inference.4. Phylogenetic analyses of the aligned ITS sequences were performed to construct the phylogenetic trees employing neighbor-joining (NJ) and maximum parsimony (MP) methods, selecting Tripsacum dactyloides L. as the outgroup. The results indicated the genus Zea was still classified into section Luxuriantes and section Zea, which are in agreement with the previous RAPD tree and support the classification of Zea according to Dobeley et al. and Iltis et al.. The phylogenetic tree based on neighbor-joining method was reconstructed combining our ITS sequences with published ITS sequences of Zea on the GenBank database, indicating our ITS sequences were grouped correctly with the corresponding taxa from GenBank. It shows that the ITS sequences are valuable to resolve the phylogenetic relationships in Zea.5. The present work provided the first molecular evidence for systematic assessment of genetic relationship of Zea nicaraguensis in Zea species. Both RAPD and ITS sequences analyses indicated that Zea nicaraguensis was clearly defined as being the taxon of section Luxuriantes, and Zea luxurians was the closest relative to Zea nicaraguensis in Zea. The taxonomic position of Zea mays ssp. huehuetenangensis was also established in our study. Zea mays ssp. huehuetenangensis was not treated as a variety of Zea mays ssp. parviglumis, the position of which was clearly established as basal to the other Zea mays.