Characteristics and Expression Pattern of MYC Genes in Triticum aestivum, Oryza sativa, and Brachypodium distachyon

Abstract

Myelocytomatosis oncogenes (MYC) transcription factors (TFs) belong to basic helix-loop-helix (bHLH) TF family and have a special bHLH_MYC_N domain in the N-terminal region. Presently, there is no detailed and systematic analysis of MYC TFs in wheat, rice, and Brachypodium distachyon. In this study, 26 TaMYC, 7 OsMYC, and 7 BdMYC TFs were identified and their features were characterized. Firstly, they contain a JAZ interaction domain (JID) and a putative transcriptional activation domain (TAD) in the bHLH_MYC_N region and a BhlH region in the C-terminal region. In some cases, the bHLH region is followed by a leucine zipper region; secondly, they display tissue-specific expression patterns: wheat MYC genes are mainly expressed in leaves, rice MYC genes are highly expressed in stems, and B. distachyon MYC genes are mainly expressed in inflorescences. In addition, three types of cis-elements, including plant development/growth-related, hormone-related, and abiotic stresses-related were identified in different MYC gene promoters. In combination with the previous studies, these results indicate that MYC TFs mainly function in growth and development, as well as in response to stresses. This study laid a foundation for the further functional elucidation of MYC genes.

Keywords: Brachypodium distachyon; MYC; bHLH; rice; wheat.

Figure 1

Chromosome location, homologous gene pairs of TaMYC, OsMYC, and BdMYC genes. Gray lines in the background indicate the collinear blocks within wheat, rice, and B. distachyon genomes, while the red lines highlight the homologous gene pairs.

Figure 2

Alignment of the 61 different myelocytomatosis oncogenes (MYC) proteins from plants and animals. Including 40 MYCs in this study, 8 Arabidopsis MYCs, and 13 animal MYCs proteins from previous studies as described above.

Figure 3

Phylogenetic tree of 61 MYC transcription factors (TFs). There are 48 plant MYCs and 13 known animal MYCs. The Ta, Os, Bd, and At represent wheat, rice, B. distachyon, and Arabidopsis, respectively.

Figure 4

(A) Phylogenetic relationships, (B) gene structures, (C) motifs, and (D) conserved regions of wheat, rice, and B. distachyon MYCs. The tree was constructed with 1000 bootstrap replications using MEGA7 based on the full-length protein sequence. The exon–intron structure of these genes was graphically displayed by the Gene Structure Display Server using the coding sequences (CDS) and DNA sequences of MYC genes. The protein sequence of MYC proteins was used to predict the conserved motifs/region by using the MEME Suite web server.

Figure 5

Main cis-elements in TaMYC, OsMYC, and BdMYC gene promoters.

Figure 6

Expression patterns of TaMYC, OsMYC, and BdMYC genes in different tissues. R, S, L, F indicate roots, stems, leaves, and inflorescences. The horizontal and vertical coordinates stand for four different tissues and the relative expression, respectively.

Figure 7

Expression patterns of TaMYC, OsMYC, and BdMYC genes under abiotic stresses; CK (H2O), Heat, Cold, PEG, Salt, ABA, GA indicate different treatments. The horizontal and vertical axes stand for different abiotic stresses and the relative expression, respectively.