INSIGHT INTO THE TRANSCRIPTIONAL REGULATION OF OSAAP6, A POSITIVE REGULATOR OF GRAIN PROTEIN, AND IDENTIFICATION OF GRAIN PROTEIN CONTENT-ASSOCIATED GENES

Protein malnutrition afflicts nearly one-third of the people worldwide. In order to develop genetically protein-enriched cereals, especially in rice as the most commonly used cereal, grain protein content (GPC)-associated genes and their transcriptional regulation have to be identified. OsAAP6 (Os01g0878700) was previously reported to function as a positive regulator of GPC in rice, whereas its transcriptional regulation remains poorly understood. Applying the bioinformatics tools, the transcriptional regulation of OsAAP6 expression as well as prioritize GPC genes were discerned in this study. The highest expression of the gene was found in callus and endosperm of seed. The presence of endosperm expression specific regulatory cis-elements such as two Sk1 and one GCN4 motifs in the promoter region might contribute to high expression of OsAAP6 in endosperm. The presence of several cis-regulatory elements involved in the abscisic acid, methyl jasmonate-, and gibberellin- responsiveness, gives indication of abscisic acid-, methyl jasmonate-, and gibberellin- dependent regulation. According to promoter and expression analyses, abiotic and biotic stresses can alter OsAAP6 transcripts. Co-expression analysis derived several candidate genes including 8 transcription factors and 6 protein kinases that probably linked to the GPC in rice. This is significant as there have been no previous reports regarding the involvement of these transcription factors and protein kinases in GPC. According to biological process enrichment analysis, metabolic process was the most highly overrepresented categories in the co-expressed genes. The information reported herein could lay a foundation for quality improvement efforts for major crops.