Rice leaf inclination2, a VIN3-1ike protein, regulates leaf angle through modulating cell division of the collar

As an important agronomic trait, inclination of leaves is crucial Ior crop architecture and grain yields. 10 understand the molecular mechanism controlling rice leaf angles, one rice leaf inclination2 （1c2, three alleles） mutant was identified and functionally characterized. Compared to wild-type plants, lc2 mutants have enlarged leaf angles due to increased cell division in the adaxial epidermis of lamina joint. The LC2 gene was isolated through positional cloning, and encodes a vernalization insensitive 3-like protein. Complementary expression of LC2 reversed the enlarged leaf angles of lc2 plants, confirming its role in controlling leaf inclination. LC2 is mainly expressed in the lamina joint during leaf development, and particularly, is induced by the phytohormones abscisic acid, gibberellic acid, auxin, and brassinosteroids. LC2 is localized in the nucleus and defects of LC2 result in altered expression of cell division and hormone-responsive genes, indicating an important role of LC2 in regulating leaf inclination and mediating hormone effects.

LSCHL4 from Japonica Cultivar, Which Is Allelic to NAL 1, Increases Yield of Indica Super Rice 93-11

The basic premise of high yield in rice is to improve leaf photosynthetic efficiency and coordinate the sourcesink relationship in rice plants. Quantitative trait loci （QTLs） related to morphological traits and chlorophyll content of rice leaves were detected at the stages of heading to maturity, and a major QTL （qLSCHL4） related to flag leaf shape and chlorophyll content was detected at both stages in recombinant inbred lines constructed using the indica rice cultivar 93-11 and the japonica rice cultivar Nipponbare. Map-based cloning and expression analysis showed that LSCHL4 is allelic to NAL1, a gene previously reported in narrow leaf mutant of rice. Overexpression lines transformed with vector carrying LSCHL4 from Nipponbare and a near-isogenic line of 93-11 （NIL-9311） had significantly increased leaf chlorophyll content, enlarged flag leaf size, and improved panicle type. The average yield of NIL-9311 was 18.70% higher than that of 93-11. These results indicate that LSCHL4 had a pleiotropic function. Exploring and pyramiding more high-yield alleles resem- bling LSCHL4 for super rice breeding provides an effective way to achieve new breakthroughs in raising rice yield and generate new ideas for solving the problem of global food safety.

Natural variation in the promoter of OsHMA3 contributes to differential grain cadmium accumulation between Indica and Japonica rice

Rice is a major source of cadmium(Cd) intake for Asian people. Indica rice usually accumulates more Cd in shoots and grains than Japonica rice. However, underlying genetic bases for differential Cd accumulation between Indica and Japonica rice are still unknown. In this study, we cloned a quantitative trait locus(QTL) grain Cd concentration on chromosome 7(GCC7) responsible for differential grain Cd accumulation between two rice varieties by performing QTL analysis and map-based cloning. We found that the two GCC7 alleles, GCC7PA64s and GCC793-11, had different promoter activity of OsHMA3,leading to different OsHMA3 expression and different shoot and grain Cd concentrations. By analyzing the distribution of different haplotypes of GCC7 among diverse rice accessions, we discovered that the high and low Cd accumulation alleles, namely GCC793-11 and GCC7PA64s, were preferentially distributed in Indica and Japonica rice,respectively. We further showed that the GCC7PA64sallele can be used to replace the GCC793-11 allele in the super cultivar 93-11 to reduce grain Cd concentration without adverse effect on agronomic traits. Our results thus reveal that the QTL GCC7 with sequence variation in the OsHMA3 promoter is an important determinant controlling differential grain Cd accumulation between Indica and Japonica rice.

Genetic Analysis and Gene-Mapping of Two Reduced-Culm-Number Mutants in Rice

In the present study, In order to systematically dissect the genetic mechanism of rice （Oryza satlva L.） tilling for the super rice ideotype and the model system of branching development, two ethyl methane suifonate-induced rice reduced-culm-number（rcn） mutants from the progeny of Nippobare （O. satlva ssp. japonica）, namely rcn8 and rcn9, were used. Their maximum tillers were both less than 4. in addition, rcn9 had another major feature of rust-spotted leaves. Allelic tests between these two mutants and seven other recessive few-tiller mutants revealed that they were previously unknown loci. Genetic analysis showed that the rcn traits were all controlled by a pair of different recessive genes, designated as RCN8and RCNg, respectively. Two F2 populations derived from crosses between the rcn8 or rcn9 mutants and 93-11 were constructed. Linkage analysis using two rcn F2 mapping populations with published simple sequence repeat markers demonstrated that the RCN8 and RCN9 genes were mapped on the long arm of chromosome 1 （119.6 cM） and the short arm of chromosome 6 （63.6 cM）, respectively. The results of the present study are beneficial to map-based cloning and functional analysis of the RCN8 and RCN9 genes.

Recent Progress on Rice Genetics in China

Through thousands of years of evolution and cultivation, tremendously rich genetic diversity has been accumulated in rice （Oryza sativa L.）, developing a large germplasm pool from which people can select varieties with morphologies of Interest and other important agronomic traits. With the development of modern genetics, scientists have paid more attention to the genetic value of these elite varieties and germplasms, and such rich rice resources provide a good foundation for genetic research in China. Approximately 100 000 accessions of radiation-, chemical- or insertion-induced mutagenesis have been generated since the 1980s, and great progress has been made on rice molecular genetics. So far at least 16 variant/mutant genes Including MOC1, BC1, SKC1, and Rfgenes have been isolated and characterized in China. These achievements greatly promote the research on functional genomics, understanding the mechanism of plant development and molecular design breeding of rice in China. Here we review the progress of three aspects of rice genetics in China： moving forward at the molecular level, genetic research on elite varieties and germplasms, and new gene screening and genetic analysis using mutants. The prospects of rice genetics are also discussed.

Reduction of OsFLW7 expression enhanced leaf area and grain production in rice

Increasing rice production is important to ensure food security in China. Exploring yield potential and identifying genes beneficial to yield are important goals in the modern rice breeding. Generally, controlling leaf morphology, increasing photosynthesis efficiency and modulating the ＂sink-source＂ relationship can pro- mote the breeding of high-yield rice as well as other cereal crops . The morphology of the leaf includes length, width and degree of curl after its emergence from the meristem and is determined by the establishment of polariW along the adaxial-abaxial, ventral-dorsal and medial-lateral axes and regulated at genetic, hormonal and environmental levels . Rice leaf morphology varies widely among rice subspecies and cultivars. Quantitative trait loci （QTLs） affecting leaf shape commonly have pleiotropic effects on rice yield , which are more useful than mutant genes for studying the molecular mechanism of leaf shape regulation and their application to rice breeding.