Kernel lysine content does not increase in some maize opaque2 mutants

The recessive mutant allele of the opaque2 gene (o2) alters the endosperm protein pattern and increases the kernel lysine content of maize (Zea mays L.). In this study, sequencing results showed that the o2 mutant was successfully introgressed into 12 elite normal maize inbred lines by marker assisted selection (MAS). The average genetic similarity between these normal inbred lines and their o2 near-isogenic lines (NILs) was more than 95%. Kernel lysine content increased significantly in most of o2 NILs lines relative to normal elite inbreds, but remained unchanged in the genetic backgrounds Dan598o2 and Liao2345o2. Moreover, the kernel characteristics of these two o2 NILs did not differ from the other inbred lines. The results of lysine content analysis in the F1 hybrids between Liao2345o2 and Dan598o2 and other o2 NILs demonstrated that gene(s) other than opaque2 may control kernel lysine content in these two o2 NILs. The results of zein analysis showed that 22-kD α-zein synthesis was reduced or absent, and the 19-kD α-zein synthesis was greatly reduced compared with the recurrent parents in most o2 NILs except for Dan598o2 and Liao2345o2. Our results indicate that gene(s) other than opaque2 may play more important roles in zein synthesis and kernel lysine content in some maize genetic backgrounds.