Molecular Evidence For Domestication Selection In The Waxy Site Of Chinese Waxy Maize

Waxy maize is a distinct kind of corn and mainly used for food, industrial amylopectin, textile industry and papermaking. Waxy maize has been found in China in 1909 and its exact history is unknown. Most researchers believed that the Chinese waxy maize arose from a gene mutation event after maize was introduced into China in 16^th century, while some argued that Coix lacryma-jobi was similar with the Chinese waxy maize. The most typical accessions of Chinese waxy maize are those landraces from Yunnan and Guangxi Provinces, the southwest of China (such as Four-row Wax, Yishannuo and Qiaojiabainuo). Waxy gene (wx) is the most important gene for glutinous cereals. The amount of apparent amylose will be decreased to less than 5% and amylopectin increase significantly when mutation or changes of expression occurred in this gene. The gene locus has been well documented based on widely maize accessions, but not the Chinese waxy maize. No selection has been detected in wx and Adh (alcohol dehydrogenase) loci in maize up to now. Beside of target gene, domestication selection will take hitchhiking effect or selection sweep around the target gene. In glutinous rice, for example, wx loci has been selected strongly and a sweep size of 250kb has been found.In this study, wx sequenced from the Chinese waxy maize, including 4 landraces (Four-row Wax etc.), 18 inbred lines and 4 hybrids, were partial (exon9-14) sequenced. As references, two flanking genes of wx and Adh gene (locating another chromosome) also were sequenced. Meanwhile, whole region from Four-row Wax and partial from Coix lacryma-jobi of waxy gene were determined. Our results indicated a strong selection in waxy locus and around genomic region (more than 53kb) during the processes of domestication of the Chinese waxy maize. Phylogenetic analysis didn't support the opinion of Chinese origin of the Chinese waxy maize regarding to no independent phylogenetic brand from other maize for the Chinese waxy maize. The landraces from Yunnan and Guangxi areas were grouped into different phylogenetic brands and with different types of maize. Four-row Wax and Qiaojiabainuo from Yunnan grouped with a yellow flint (EP1) while Yishannuo grouped with yellow dents (Tx601, MO17 etc.). The results suggested that a least two independent domestication processes may be for the Chinese waxy maize.