652 VOLUME 46 | NUMBER 4 | JUNE 2014 NATURE GENETICS The drive toward more sustainable agriculture has raised the profile of crop plant nutrient-use efficiency. Here we show that a major rice nitrogen-use efficiency quantitative trait locus (qNGR9) is synonymous with the previously identified gene DEP1 (DENSE AND ERECT PANICLES 1). The different DEP1 alleles confer different nitrogen responses, and genetic diversity analysis suggests that DEP1 has been subjected to artificial selection during Oryza sativa spp. japonica rice domestication. The plants carrying the dominant dep1-1 allele exhibit nitrogen- insensitive vegetative growth coupled with increased nitrogen uptake and assimilation, resulting in improved harvest index and grain yield at moderate levels of nitrogen fertilization. The DEP1 protein interacts in vivo with both the Ga (RGA1) and Gb (RGB1) subunits, and reduced RGA1 or enhanced RGB1 activity inhibits nitrogen responses. We conclude that the plant G protein complex regulates nitrogen signaling and modulation of heterotrimeric G protein activity provides a strategy for environmentally sustainable increases in rice grain yield. Our ability to feed the world’s current population is, in part, a result of the Green Revolution, which was based on the adoption of semi-dwarf cereals that had an increased harvest index; however, the increase in grain yields required substantial increases in nitrogen fertilization levels 1,2 . Unfortunately, these increases in nitrogen fertilizer applications also resulted in what are now well-documented deleterious impacts on the environment 3 . Therefore, the continued growth of the human population and the imminent threat of global climate change represent a major challenge for increasing grain yields without simultaneously exacerbating the degradation of the natural environment 4 . Thus, there is an urgent need to develop crops that show improved nitrogen-use efficiency 5 . However, current understanding of the genetic basis of rice nitrogen-use efficiency remains at the level of the identification of a number of quantitative trait loci (QTLs), with no understanding of the nature of the genes presumed to underlie them 6–9 . Rice varieties exhibit substantial genetic variation with respect to plant height and tiller number at different nitrogen fertilization levels (Supplementary Table 1). For example, the vegetative growth of O. sativa spp. indica variety Nanjing6 (NJ6) is highly responsive to nitrogen, with plant height and tiller number being strongly correlated with nitrogen input level (Fig. 1a and Supplementary Table 2). Conversely, the vegetative growth of the japonica variety Qianzhonglang2 (QZL2) is largely unresponsive to nitrogen fertili- zation level, with plants grown with low nitrogen input having plant height and tiller numbers that are essentially the same as those of plants grown with high nitrogen input (Fig. 1b and Supplementary Table 2). These differences are associated with the consistently supe- rior harvest index (the ratio between grain weight and above-ground biomass at maturity) of QZL2 (Supplementary Table 2). Among a set of 226 recombinant inbred lines (RILs) bred from a QZL2 × NJ6 intercross hybrid progenitor, one line (RIL-D22) exhibited marked nitrogen responses with respect to plant height and tiller number (Fig. 1c–e) and another (RIL-D04) behaved in a nitrogen-unresponsive manner that was similar to QZL2 (Fig. 1f and Supplementary Table 2). Genetic analysis of a recurrent backcross (BC 2 F 2 ) population having RIL-D22 as the donor parent and QZL2 as the recurrent parent identi- fied qNGR9 as a major QTL for nitrogen-mediated growth responses and mapped this QTL to chromosome 9 (Fig. 1g). By positional cloning and genetic complementation, we found that qNGR9 is synonymous with DEP1 (DENSE AND ERECT PANICLE 1), a gene that has been shown previously to regulate rice panicle archi- tecture 10–12 (Supplementary Note). A variant dep1 allele found in the Italian rice cultivar Balilla con- fers an increased number of grains per panicle (and a consequent increase in grain yield that is characteristic of many japonica rice varieties) 10 . We developed near-isogenic lines (NILs) carrying DEP1 (from NJ6, called NIL-DEP1) and dep1-1 (from QZL2, called NIL–dep1-1) (Supplementary Fig. 1) and found that although the NIL-DEP1 line exhibited a vegetative growth response to nitrogen Heterotrimeric G proteins regulate nitrogen-use efficiency in rice Hongying Sun 1,6 , Qian Qian 2,6 , Kun Wu 1,6 , Jijing Luo 3,6 , Shuansuo Wang 1,6 , Chengwei Zhang 1 , Yanfei Ma 1 , Qian Liu 1 , Xianzhong Huang 1 , Qingbo Yuan 1 , Ruixi Han 1 , Meng Zhao 1,4 , Guojun Dong 2 , Longbiao Guo 2 , Xudong Zhu 2 , Zhiheng Gou 5 , Wen Wang 5 , Yuejin Wu 4 , Hongxuan Lin 3 & Xiangdong Fu 1 1 The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, National Centre for Plant Gene Research, Beijing, China. 2 The State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, China. 3 The State Key Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China. 4 Institute of Technical Biology and Agriculture Engineering, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China. 5 The State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China. 6 These authors contributed equally to this work. Correspondence should be addressed to X.F. (xdfu@genetics.ac.cn). Received 31 October 2012; accepted 19 March 2014; published online 28 April 2014; doi:10.1038/ng.2958 LETTERS npg © 2014 Nature America, Inc. All rights reserved.