Yield potential, plant height and heading date are three classes of traits that determine the productivity of many crop plants. Here we show that the quantitative trait locus (QTL) Ghd7, isolated from an elite rice hybrid and encoding a CCT domain protein, has major effects on an array of traits in rice, including number of grains per panicle, plant height and heading date. Enhanced expression of Ghd7 under long-day conditions delays heading and increases plant height and panicle size. Natural mutants with reduced function enable rice to be cultivated in temperate and cooler regions. Thus, Ghd7 has played crucial roles for increasing productivity and adaptability of rice globally.

Rice yield and heading date are two distinct traits controlled by quantitative trait loci (QTLs). The dissection of molecular mechanisms underlying rice yield traits is important for developing high-yielding rice varieties. Here, we report the cloning and characterization of Ghd8, a major QTL with pleiotropic effects on grain yield, heading date, and plant height. Two sets of near isogenic line populations were developed for the cloning of Ghd8. Ghd8 was narrowed down to a 20-kb region containing two putative genes, of which one encodes the OsHAP3 subunit of a CCAAT-box binding protein (HAP complex); this gene was regarded as the Ghd8 candidate. A complementary test confirmed the identity and pleiotropic effects of the gene; interestingly, the genetic effect of Ghd8 was dependent on its genetic background. By regulating Ehd1, RFT1, and Hd3a, Ghd8 delayed flowering under long-day conditions, but promoted flowering under short-day conditions. Ghd8 up-regulated MOC1, a key gene controlling tillering and branching; this increased the number of tillers, primary and secondary branches, thus producing 50% more grains per plant. The ectopic expression of Ghd8 in Arabidopsis caused early flowering by 10 d-a situation similar to the one observed by its homolog AtHAP3b, when compared to wild-type under long-day conditions; these findings indicate the conserved function of Ghd8 and AtHAP3b in flowering in Arabidopsis. Our results demonstrated the important roles of Ghd8 in rice yield formation and flowering, as well as its opposite functions in flowering between rice and Arabidopsis under long-day conditions.

Changes in human lifestyle and food consumption have resulted in a large increase in the incidence of type-2 diabetes, obesity, and colon disease, especially in Asia. These conditions are a growing threat to human health, but consumption of foods high in resistant starch (RS) can potentially reduce their incidence. Strategies to increase RS in rice are limited by a lack of knowledge of its molecular basis. Through map-based cloning of a RS locus in indica rice, we have identified a defective soluble starch synthase gene (SSIIIa) responsible for RS production and further showed that RS production is dependent on the high expression of the Waxy a (Wx a ) allele, which is prevalent in indica varieties. The resulting RS has modified granule structure; high amylose, lipid, and amylose-lipid complex; and altered physicochemical properties. This discovery provides an opportunity to increase RS content of cooked rice, especially in the indica varieties, which predominates in southern Asia.diabetes | resistant starch biosynthesis | soluble starch synthase | granule-bound starch synthase | amylose-lipid complex I ncreases in the incidence of type-2 diabetes are being observed throughout the world. This increase is thought to be due to changes in both diet and lifestyle (1, 2) and is increasingly apparent in Asia. Consumption of foods high in resistant starch (RS) can help to control type-2 diabetes, because its slow digestion and absorption by the small intestine decreases postprandial glucose and insulin responses (3). Foods high in RS also potentially protect against pathogen infection, diarrhea, inflammatory bowel disease, colon cancer, and chronic renal and hepatic diseases. Consumption of RS can increase satiety and reduce calorie intake to help weight management (3). Thus, improvement of the amounts and properties of RS in foods is an important goal.Rice (Oryza sativa L.) is consumed by more than half the world's population (4), and for many, it is the primary source of nutrients and carbohydrates for energy. Consumption of 18-20 g of RS (5, 6) is recommended per day for health benefits, but hot cooked rice typically contains <3% RS (7). Rice varieties or mutants with improved RS have been identified, such as Goami No. 2, Gongmi No. 3, RS111, and Jiangtangdao 1 (7-10).A high-RS, high-amylose transgenic rice line has been developed by suppressing the expression of starch branching enzymes (SBEs) (11) and a mutation of SBEIIb cosegregated with RS content in rice (8). In other cereals, down-regulation of soluble starch synthase (SS) SSIIa and of SBE results in greater RS in barley (12, 13) and wheat (14)(15)(16)(17)(18)(19)(20). Because the molecular basis underlying RS production is largely unknown, discovery of new RS genes is vital both for the elucidation of RS biosynthesis and for the breeding of high-RS varieties. We therefore screened a mutagenized population of the hybrid-rice restorer line R7954 for mutants with high RS in hot cooked rice. This strategy was designed to identify new RS genes of practical value ...