Genome-wide Identification,Evolutionary And Expression Analyses Of The New O-methyltransferase Gene Family In Maize

With the development of high-throughput sequencing technology and transcriptomics, as well as the whole genome sequencing and transcriptome sequencing in maize, bioinformatic methods can be used to study the differentially expressed genes in different maize tissues, which will further reveal the molecular mechanism of growth and development process. In this study, we identified a new type of O-methyltransferase genes by GO annotation of the differentially expressed genes, which showed higher level in roots than in shoots. 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 the various stages of plant growth and development, the resistance of the invasion of exotic pathogens and so on. OMTs usually exist as the gene family in plants and animals. At present, the OMT genes have been widely studied in plants, while it concerned only a single or a few genes of a single species and limited in the grass family. In this study, a new type of OMT genes were obtained based on the analysis of transcriptional data, and additional copies were identified from the maize, rice, brachypodium, foxtail millet, and sorghum. And the homology, structure, expression and evolution relationships of them were analyzed. The main results are as follows:1. The transcriptome datasets of maize inbred lines (B73 and Mo 17) were downloaded from the GEO database, and the differentially expressed genes (DEGs) in different tissues were analyzed by bioinformatic methods. The GO annotation of these genes revealed that genes expressed higher in roots were mostly involved in the response to stress, with the activity of catalysis and binding. While genes expressed higher in shoots were significantly enriched in the photosynthesis pathway. Among them, a class of genes that were enriched in the roots had the activity of O-methyltransferase, including GRMZM2G311036, GRMZM2G336824, GRMZM2G059465, GRMZM2G124799, GRMZM2G147491 five genes.2. Additional twenty-three homologous copies were identified in the maize B73 reference genome, which are located on eight chromosomes, and contain two exons (except for GRMZM2G349791 and GRMZM2G104730, which contain one exon and eight exons, respectively) with the length varied from 291 to 921 bp. Because of the first two exons of GRMZM2G104730 have high identity to GRMZM2G104710, it was not included in the further analysis. The structures, conserved motifs and evolutionary analyses revealed that all 27 OMTs belonged to a new class of novel OMT gene family and different from the COMT and CCoAOMT. They contain more than 8 conservative motifs except GRMZM2G147503. They are the same protein family (O-methyltransferase COMT-type family) as COMT based on the prediction of protein family. Furthermore, the motifs 2,4,9 are only present in the new OMT gene family, while the motifs 5,6,7 are shared by the new OMT and COMT, while the CCoAOMT (GRMZM2G127948) has no common conservative domain with them, which indicated that the new OMT and COMT were closely related.3. The 13,28,29,41 OMT homologous genes were identified from the genomes of brachypodium, rice, foxtail millet and sorghum, respectively. Phylogenetic analysis showed that this new OMT gene family is a grass-specific gene family, which can be divided into seven clades. Genes from one clade are only present in Panicoideae subfamily, which included Bx10, the gene involved in the benzoxazinoids pathway, suggesting that this group might participate in insect resistance in Panicoideae. Most of genes were expanded by tandem duplication and segment duplication after the species split from their progenitor.4. Expression analysis of the parents of maize NAM population revealed that OMTgenes had differential and complicated expression patterns, andmost 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, whilegenes were highly expressed in seeds of the reproductive growth stage.