Fine mapping a major QTL for flag leaf size and yield-related traits in rice

Leaf size is a major determinant of plant architecture and yield potential in crops. A previous study showed that the genomic region of chromosome 1 contains a major quantitative trait locus (QTL) for flag leaf size in a set of backcross recombinant inbred lines derived from two elite parental lines (Zhenshan 97 and 93-11). In the present study, the QTL (qFL1) was shown to explain a large proportion of the variation in flag leaf size (leaf length, width and area) in derived populations (BC(2)F(3) and BC(3)F(2)) in multiple environments. Using a large segregating population, we narrowed the location of qFL1 to a 31 kb region containing four predicted genes. Expression of one of these genes, OsFTL1, differed between leaves in near-isogenic lines carrying alleles of Zhenshan 97 and 93-11. qFL1 had a pleiotropic effect on flag leaf size and yield-related traits. Conditional QTL analysis of the derived population (BC(3)F(2)) supports the assertion that qFL1 is the QTL for flag leaf length and exhibits pleiotropy. Pyramiding of qFL1 with two known genes (GS3 and Wx) from 93-11 into Zhenshan 97 enlarged flag leaves, improved grain size and amylose content, and increased yield per plant, but slightly delayed heading date. These results provide a foundation for the functional characterization of the gene underlying the pleiotropic effects of qFL1 and for genetic improvement of the plant architecture and yield potential of rice.