DNA Methylation Analysis And QTL Mapping For Internode Elongation Of Maize(Zea Mays L.)

Plant height and ear height are important agronomic traits in maize breeding programs. These traits affect not only the corn yield, lodging resistance and ecological adaptation, but also significantly impact crop photosynthesis and other important physiological procedures. In recent years, geneticists and breeders pay more attention to uncover the genetic mechanism of plant height and ear height in order to guide the breeding of density-tolerant and lodging-resistant hybrid of maize.Elongation of maize internode is one of the most important agronomic traits, which determines the plant height and affects the ear height, the vertical distribution of leaf area and ear development. The plant height formation relies on the genetic regulation of internode elongation procedures.The maize inbred line Nongxi 531 was selected as major studied material. This study used methylated DNA immunoprecipitation combined with high-throughput sequencing and methylation-sensitive amplified polymorphism to analyse DNA methylation for internode elongation. Meanwhile, to elucidate the genetic basis of plant height in maize, we mapped QTL for plant height and ear height in a F2 population. The main results were as follows:1 The MeDIP-Seq analysis indicated that 82.02%, 9.94%, 8.04% sequences were mapped to repetitive retrotransposon region, gene region, intergenic region of the B73 reference genome. 383 and 513 genes with methylated coding were detected, 299 and 198 genes with methylated promoter were identified in the internode elongation procedures, repectively.2 Based on functional annotation and classification, the methylated genes were found to involved mainly in plant hormone signal transduction, transcription factors, cell division and elongation, kinases and phosphatases, photosynthesis, ion transport, transcriptional regulation and so on. simultaneously,many genes that related with the methyltransferase, acetyltransferase, ubiquitin - proteasome pathway were also detected.3 The MSAP analysis showed that the genomic methylation level of maize inbred line ranged from 34.9% to 39.5%. Significant difference in methylation level in the same period between different inbred lines was detected, and different methylation levels were observed in the same inbred line from different two periods. With the growth and development of the plants, the whole genome methylation levels increased.4 Sequencing of 29 differentially fragments and subsequent blast search revealed that, the fragment size were between 100-300bp, the methylated sequence distributed mainly in the promoter region with unknown function and EST sequences, also involved in the transcription factor family related with plant growth and development. The homologous sequence of M6 was endosperm-specific demethylation fragment which was released publicly.5 Total of 13 QTLs associated with the two measured traits, among which 8 QTLs for plant height were detected and the cumulation contributions to phenotypic variation were 47.4%, 5 QTLs for ear height were found, which explained phenotypic variation were 38.6% in all. These results will be interesting to test in other environmental conditions in the future, and the similar effect locus worthy for QTL fine mapping.