Molecular Mechanisms of Quantitative Genetics Revealed By Cloning and Systems Analysis of 474 Genes Controlling Fiber Length in Cotton and 1,501 Genes Controlling Grain Yield in Maize

Quantitative traits are paramount to all living organisms, including plants, animals and humans. While quantitative genetics has been studied for over 100 years, little is known of its underlying molecular mechanisms. A total of 474 genes controlling cotton fiber length (GFL) and 1,501 genes controlling maize grain yield (ZmGY) were cloned using a high-throughput gene and QTL cloning system. The functions and effects of the genes were confirmed through field trials. The GFL genes each have an effect on fiber length ranging from 2.6% to 7.9% and the ZmGY genes each have an effect on grain yield ranging from 14.8% to 61.0%. Of the 474 GFL genes, 11.4% increased and 88.6% decreased cotton fiber length when turned on or up-regulated. Of the 1,501 ZmGY genes, 26.7% increased and 73.3% decreased maize grain yield when turned on or up-regulated. These results not only provide a first line of evidence that quantitative traits are indeed controlled by numerous genes with minor effects such as cotton fiber length, as hypothesized in classical quantitative genetics, but also discovered that some of the genes have major effects such as the ZmGY genes. Moreover, systems analysis of the genes has discovered several novel molecular mechanisms of quantitative genetics, thus providing new concepts and new strategy to study and manipulate traits underlying quantitative genetics. Based on these findings, a gene-based breeding system that is far more powerful than the marker- or genomics-assisted breeding has been proposed, which will enable more effectively manipulating quantitative traits in plant breeding.