The kernel size-related quantitative trait locus qKW9 encodes a pentatricopeptide repeat protein that affects photosynthesis and grain filling.

In maize (Zea mays), kernel weight is an important component of yield that has been selected during domestication. Many genes associated with kernel weight have been identified through mutant analysis. Most are involved in the biogenesis and functional maintenance of organelles or other fundamental cellular activities. However, few quantitative trait loci (QTLs) underlying quantitative variation in kernel weight have been cloned. Here, we characterize a QTL,qKW9, associated with maize kernel weight. This QTL encodes a DYW motif pentatricopeptide repeat protein involved in C-to-U editing ofndhB, a subunit of the chloroplast NADH dehydrogenase-like complex. In a nullqkw9background, C-to-U editing ofndhBwas abolished, and photosynthesis was reduced, resulting in less maternal photosynthate available for grain filling. Characterization ofqKW9highlights the importance of optimizing photosynthesis for maize grain yield production. A pentatricopeptide repeat protein exerts a quantitative effect on maize kernel weight and size by affecting photosynthesis and grain filling.