The Genetic Architecture of Leaf Stable Carbon Isotope Composition inZea maysand the Effect of Transpiration Efficiency on Elemental Accumulation

ABSTRACT With increased demand on freshwater resources for agriculture, it is imperative that more water-use efficient crops are developed. Leaf stable carbon isotope composition, δ 13 C, is a proxy for transpiration efficiency and a possible tool for breeders, but the underlying mechanisms effecting δ 13 C in C 4 plants are not known. It has been suggested that differences in specific leaf area, which potentially reflects variation in internal CO 2 diffusion, can impact leaf δ 13 C. However, at this point the relationship has not been tested in maize. Furthermore, although it is known that water movement is important for elemental uptake, it is not clear how manipulation of transpiration for increased water-use efficiency may impact nutrient accumulation. Here we characterize the underlying genetic architecture of leaf δ 13 C and test its relationship to specific leaf area and the ionome in four biparental populations of maize. Five significant QTL for leaf δ 13 C were identified, including both novel QTL as well as some that were identified previously in maize kernels. One of the QTL regions contains an Erecta-like gene, the ortholog of which has been shown to regulate transpiration efficiency and leaf δ 13 C in Arabidopsis . Our data does not support a relationship between δ 13 C and specific leaf area, and of the 19 elements analyzed, only a weak correlation between molybdenum and δ 13 C was detected. Together these data begin to build a genetic understanding of leaf δ 13 C in maize and suggest the potential to improve plant water use without significantly influencing elemental homeostasis. Article Summary Quantitative genetics approaches were used to investigate the genetic architecture of leaf stable carbon isotope discrimination (δ 13 C) in maize. Developing a better understanding of leaf δ 13 C could facilitate its use in breeding for reduced transpirational water loss. Several genomic regions were identified that contribute to the variation observed in leaf δ 13 C. Furthermore, contrary to what has been observed in other species, leaf δ 13 C was not correlated with specific leaf area. Finally, a leaf ionomic analysis indicates that a reduction in transpiration, and thus mass flow, would not result in a decrease in nutrient accumulation.