Molecular Mechanisms Regulating Heterosis: Systems Analysis of 981 ZmHET Genes Controlling Grain Yield Heterosis in Maize, Zea mays L.

Heterosis or hybrid vigor is one of the most economically important biological phenomenon. Use of heterosis in agriculture helps feed and clothe billions of people in the world. The utilization of heterosis has not only led to dramatic yield increases in crops, including maize, rice, sorghum and other crops, but also dramatically enhanced crop adaptation to climate change and abiotic and biotic stresses relative to non-hybrid varieties, due to its significantly increased plant vigor. Nevertheless, the molecular mechanisms underlying heterosis remain unclear. Shortage of such knowledge is significantly limiting our understanding and the most effective uses of heterosis in agriculture. We have cloned 981 genes controlling maize grain yield heterosis, named ZmHET, using a new gene cloning system. All of the genes have been validated and their contributions to grain yield heterosis have been determined by turning on or up-regulating each of the genes in the genetic backgrounds of eight maize F₁ hybrid and inbred parent combinations. Each of the ZmHET genes was found to contribute to grain yield mid-parent heterosis by 32.5% to 252.1%. However, 128 (13.0%) of them resulted in increased heterosis while 853 (87.0%) led to decreased heterosis when turned on or up-regulated. Moreover, we have analyzed the 981 ZmHET genes in a systematic manner and the results have revealed several new and exciting discoveries on the molecular mechanisms regulating grain yield heterosis in maize. This provides new concepts, knowledge and strategies to effectively use and manipulate grain yield heterosis in crop breeding and production.