Comparative transcriptome profiling reveals the mechanism of increasing lysine and tryptophan content through pyramiding opaque2, opaque16 and waxy1 genes in maize

To explore the molecular mechanism behind maize grain quality and use of different gene stacking to im- prove the nutritional quality of grain, marker-assisted selection (MAS) was used to select three recessive mutant lines containing o2o16wx, along with the double-recessive mutant lines containing o2o16, o2wx, and o16wx. The resulting seeds were taken for transcriptome sequencing analysis 18 days after pollination (DAP). Results: Compared with the recurrent parent genes, in the lysine synthesis pathway, the gene pyramiding lines (o2o16wx, o2wx, and o16wx) revealed that the gene encoding aspartate kinase (AK) was up-regulated and promoted lysine synthesis. In the lysine degradation pathway, 'QCL8010_1' (o2o16wx) revealed that the gene encoding saccharopine dehydrogenase (LKR/SDH) was down-regulated. In addition, the gene pyramid- ing lines (o2o16wx, o2o16, and o16wx) indicated that the gene encoding 2-oxoglutarate dehydrogenase E1 component (OGDH) was down-regulated, inhibiting the degradation of lysine. In the tryptophan synthesis pathway, the genes encoding anthranilate synthase (AS), anthranilate synthase (APT), and tryptophan syn- thase (TS) were up-regulated (in o2o16wx, o2o16, o2wx, and o16wx), and promote tryptophan synthesis. In the tryptophan degradation pathway, it was revealed that the genes encoding indole-3-producing oxidase (IAAO) and indole-3-pyruvate monooxygenase (YUCCA) were down-regulated. These results provide a ref- erence for revealing the mechanism of the o2, o16, and wx with different gene pyramiding to improve grain quality in maize.