Abstract：With the development of high-throughput sequencing technique, the whole genome sequencing and transcriptome sequencing in maize (Zea mays) have been completed. The differentially expressed genes can be discovered by bioinformatic methods in different maize tissues, which will further reveal the molecular mechanism of the growth and development process. In this study, the transcriptome datasets of maize inbred lines Mo17 and B73, from the NCBI GEO database, were downloaded, and 5 genes (GRMZM2G311036, GRMZM2G336824, GRMZM2G059465, GRMZM2G124799, GRMZM2G147491), belonging to O-methyltransferase (OMT) gene family, which were expressed higher in roots than in shoots in both maize inbreds B73 and Mo17, were found, and additional 23 copies were identified from the maize B73 reference genome. The plant O-methyltransferases (OMTs) are dependent on S-Adenosyl-L-methionine (SAM), which can catalyze a variety of secondary metabolites such as flavonoids, alkaloids and phytoalexins that play an important role in various stages of plant growth and development, the resistance of the invasion of exotic pathogens. All 28 OMT genes were located on 8 chromosomes. Most of them contained 2 exons and one intron (except for GRMZM2G349791 and GRMZM2G104730, which contained one exon and 8 exons, respectively) with the length varied from 291 to 921 bp. The genes structures, conserved motifs and evolutionary analysis revealed that all the 27 OMTs belonged to a new type of OMT gene family that was different from the caffeic acid O-methyltransferase (COMT) and caffeoyl coenzyme A 3-O-methyltransferase (CCoAOMT). The new type of OMT genes contained more than 8 conservative motifs except GRMZM2G147503. They were the same protein family (O-methyltransferase COMT-type family) as COMT based on the prediction of protein family. Furthermore, the motifs 2, 4 and 9 were only presented in the new OMT gene family, while the motifs 5, 6 and 7 were shared by the new OMT and COMT, and the CCoAOMT (GRMZM2G127948) had no common conservative domain with them, which indicated that the new OMT and COMT were closely related to each other. This new OMT gene family could be divided into 5 clades, and 2 clades contained Bx7 and Bx10, respectively, which involved in the biosynthesis of benzoxazinoids, suggested that they play an important role in insect resistance in maize. This OMT gene family were expanded mainly by tandem duplication and segment duplication based on the locations and phylogeny. Expression analysis of the parents of maize NAM population showed that OMT genes had differential and complicated expression patterns. Furthermore, most of genes were expressed higher in vegetative growth stage than in reproductive period. In vegetative growth period, genes were expressed higher in roots than in other tissues, while genes were highly expressed in seeds of the reproductive growth stage. These results provide a certain theoretical basis and reference for further understanding the biological function and its application of OMT gene family, and provide an important guiding significance for studying the catalytic mechanism and expression regulation mode of the gene family.
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