Maize Dek33 encodes a pyrimidine reductase in riboflavin biosynthesis essential for oilbody formation and ABA biosynthesis during seed development.

The maize (Zea mays) classic kernel mutant defective kernel 33 (dek33) produced defective and occasionally viviparous kernel phenotype. In this study, we cloned Dek33 by positional cloning and found that it encodes the pyrimidine reductase in riboflavin biosynthesis. In dek33, a single base mutation (G-to-A) in the C-terminal COG3236 domain caused a premature stop codon (TGA), producing a weak mutant allele with significant reduction of truncated DEK33 protein and riboflavin content. The dek33 mutation significantly affected oilbody formation and suppressed endoreduplication. The dek33 mutation also disrupted ABA biosynthesis, resulting in less ABA content, which might be responsible for the viviparous embryo. In addition, our results indicated that the COG3236 domain is important for the protein stability of DEK33. The yeast two-hybrid experiment identified several proteins that interact with DEK33, including RGLG2 and SnRK1, suggesting possible post-translational regulation to DEK33 stability. The interaction between DEK33 and these proteins was further confirmed by luciferase complementation image assay. This study provided a weak mutant allele to explore cellular responses due to impaired riboflavin biosynthesis during seed development. Our findings indicated that the COG3236 domain might be an essential regulatory structure for DEK33 stability in maize.