AP2/ERF Transcription Factor in Rice: Genome-Wide Canvas and Syntenic Relationships between Monocots and Eudicots.

The transcription factor family intimately regulates gene expression in response to hormones, biotic and abiotic factors, symbiotic interactions, cell differentiation, and stress signalling pathways in plants. In this study, 170 AP2/ERF family genes are identified by phylogenetic analysis of the rice genome (Oryza sativa l. japonica) and they are divided into a total of 11 groups, including four major groups (AP2, ERF, DREB, and RAV), 10 subgroups, and two soloists. Gene structure analysis revealed that, at position-6, the amino acid threonine (Thr-6) is conserved in the double domain AP2 proteins compared to the amino acid arginine (Arg-6), which is preserved in the single domain of ERF proteins. In addition, the histidine (His) amino acid is found in both domains of the double domain AP2 protein, which is missing in single domain ERF proteins. Motif analysis indicates that most of the conserved motifs, apart from the AP2/ERF domain, are exclusively distributed among the specific clades in the phylogenetic tree and regulate plausible functions. Expression analysis reveals a widespread distribution of the rice AP2/ERF family genes within plant tissues. In the vegetative organs, the transcripts of these genes are found most abundant in the roots followed by the leaf and stem; whereas, in reproductive tissues, the gene expression of this family is observed high in the embryo and lemma. From chromosomal localization, it appears that repetition and tandem-duplication may contribute to the evolution of new genes in the rice genome. In this study, interspecies comparisons between rice and wheat reveal 34 rice loci and unveil the extent of collinearity between the two genomes. It was subsequently ascertained that chromosome-9 has more orthologous loci for CRT/DRE genes whereas chromosome-2 exhibits orthologs for ERF subfamily members. Maximum conserved synteny is found in chromosome-3 for AP2 double domain subfamily genes. Macrosynteny between rice and Arabidopsis, a distant, related genome, uncovered 11 homologs/orthologs loci in both genomes. The distribution of AP2/ERF family gene paralogs in Arabidopsis was most frequent in chromosome-1 followed by chromosome-5. In Arabidopsis, ERF subfamily gene orthologs are found on chromosome-1, chromosome-3, and chromosome-5, whereas DRE subfamily genes are found on chromosome-2 and chromosome-5. Orthologs for RAV and AP2 with double domains in Arabidopsis are located on chromosome-1 and chromosome-3, respectively. In conclusion, the data generated in this survey will be useful for conducting genomic research to determine the precise role of the AP2/ERF gene during stress responses with the ultimate goal of improving crops.