The Putative Key Transcription Factors Involved In Developing Maize Seed

Based on the analysis of the genome-wide expression dataset of60tissues representing11major developmental organs of inbred line B73,218transcription factor genes (TFs) were predicted to be involved in maize seed development with significantly higher expression levels in the25seed tissues than that of other organs. Subsequently, on the base of expression profile analysis and phylogenetic tree analysis, we predicted that the candidate genes may have important roles in maize seed development, which could provides a solid foundation for future functional dissection of these candidate genes.The major results of this study are following:1.4116genes show significantly higher expression levels in seed developmental tissues than that of other tissues, including2708structural genes,218TFs, and also1190unknown genes. Expression analysis showed that712of4116genes were significantly expressed in the endosperm tissues,67genes was significantly expressed in embryos tissues, while the remaining genes (about3337genes) were highly expressed in both of the endosperm or embryo tissues with no significant difference between those two seed organs.2.230metabolic pathways were successfully annotated through the KEGG pathway annotation of the2708structural genes. The candidate genes were mainly annotated in three main regions, including the sugar metabolic pathways, the fatty acid metabolic pathways and the ribosome pathways. In addition, the gene involved in starch synthesis pathway, anthocyanin biosynthetic pathway, and amino acid metabolic pathways were also significantly expressed in maize seed tissues, which indicated that the products of these pathways are the main components of maize seeds.3. Based on the expression analysis, it was shown that the maize starch is mainly synthesized in the endosperm tissue, and its synthetic period is from12DAP to24DAP; the fatty acid is mainly synthesized in the embryo tissue, and its synthetic period is from16DAP to24DAP; the storage proteins were synthesized in both of the embryo and endosperm tissues, their synthetic period are mainly from12DAP to24DAP; whereas the amino acids are mainly synthesized in the embryo and endosperm tissues, and their synthetic period in the endosperm are mainly from12DAP to22DAP, in the embryo from 16DAP to24DAP.4. A total of218TFs that were significantly expressed in maize seed tissues were identified, which can be classified into43TF families. The number of TFs in each TF family is different, with the MYB, AP2and B3TF families are the largest ones. Moreover, the expression levels of candidate genes in each seed tissue are generally different, where the majority of candidate genes significantly exhibited in the endosperm tissues. For example, there are19MYB TFs were highly expressed in endosperm tissues. Phylogenetic tree analysis showed that these MYB genes could be divided into4subfamilies. Among which, ZmMYBO12and ZmMYB151belong to G25subfamily whose homologous genes in Arabidopsis thaliand had been confirmed to involve in the regulation of seed embryo development. Moreover, we also identified4AP2genes that were highly expressed in the embryo and endosperm tissues,7B3genes were highly expressed in all of the three maize seeds tissues (the endosperm, embryo and seed coat). Phylogenetic tree analysis showed that their orthologous genes in other plants were all involved in controlling of the seed size, starch biosynthesis, and seed development and maturation processes, etc. Therefore, it was suggested that the maize genes clustered in the same subfamilies may share similar functional features in see development. Similarly, the other TFs, such as MADS, WRKY, homobox, NAC and Trihelix genes were also indicated to have similar functions with their corresponding orthologous genes in different physiological and biochemical process of maize seed development, by the same method.