Individual Maize Chromosomes in the C3 Plant Oat Can Increase Bundle Sheath Cell Size and Vein Density

C-4 photosynthesis has evolved in at least 66 lineages within the angiosperms and involves alterations to the biochemistry, cell biology, and development of leaves. The characteristic Kranz anatomy of most C-4 leaves was discovered in the 1890s, but the genetic basis of these traits remains poorly defined. Oat x maize addition lines allow the effects of individual maize (Zea mays; C-4) chromosomes to be investigated in an oat (Avena sativa; C-3) genetic background. Here, we have determined the extent to which maize chromosomes can introduce C-4 characteristics into oat and have associated any C-4-like changes with specific maize chromosomes. While there is no indication of a simultaneous change to C-4 biochemistry, leaf anatomy, and ultrastructure in any of the oat x maize addition lines, the C-3 oat leaf can be modified at multiple levels. Maize genes encoding phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, and the 2'-oxoglutarate/malate transporter are expressed in oat and generate transcripts of the correct size. Three maize chromosomes independently cause increases in vein density, and maize chromosome 3 results in larger bundle sheath cells with increased cell wall lipid deposition in oat leaves. These data provide proof of principle that aspects of C-4 biology could be integrated into leaves of C-3 crops.