Molecular Mechanisms Underlying Increase in Lysine Content of Waxy Maize through the Introgression of the opaque2 Allele

The opaque2 (o2) mutation in maize is associated with high lysine content in endosperm and good nutritional value. To improve the nutritional quality of waxy maize, the o2 allele was introgressed into the wxwx line using marker-assisted backcrossing selection technology. The lysine content of o2o2wxwx lines was higher than that of the wxwx line. To reveal the mechanism of increasing lysine content through introgression of the o2 in waxy maize, the transcriptome on kernels (18th day after pollination) of the o2o2wxwx and parent lines was analyzed using RNA-sequencing (RNA-Seq). The RNA-Seq analysis revealed 49 differentially expressed genes (DEGs). Functional analysis showed that these DEGs were mostly related to the catalytic activity and metabolic processes. The O2 gene regulated multiple metabolic pathways related to biological processes (BP) and molecular function (MP) during waxy maize endosperm development. In particular, in the o2o2wxwx lines, the two genes that encode the EF-1α and LHT1 were up-regulated, but the gene that encodes sulfur-rich proteins was down-regulated, raising the grain lysine content. These findings are of great importance for understanding the molecular mechanism underlying the lysine content increase due to o2 allele introgression into waxy maize.