qGW11a/OsCAT8,encoding an amino acid permease,negatively regulates grain size and weight in rice

Grain size is a key factor influencing grain weight in rice.In this study,a chromosome segment substitution line(CSSL9-17)was identified,that exhibits a significant reduction in both grain size and weight compared to its donor parent 93-11.Further investigation identified two quantitative trait loci(QTL)on chromosome 11,designated qGW11a and qGW11b,which contribute to 1000-grain weight with an additive effect.LOC_Os11g05690,encoding the amino acid permease OsCAT8,is the target gene of qGW11a.Overexpression of OsCAT8 resulted in decreased grain weight,while OsCAT8 knockout mutants exhibited increased grain weight.The 287-bp located within the OsCAT8 promoter region of 93-11 negatively regulates its activity,which is subsequently correlated with an increase in grain size and weight.These results suggest that OsCAT8 functions as a negative regulator of grain size and grain weight in rice.

Wide grain 4,encoding an alpha-tubulin,regulates grain size by affecting cell expansion in rice

Rice is one of the three most important food crops in the world.Increasing rice yield is an effective way to ensure food security.Grain size is a key factor affecting rice yield;however,the genetic and molecular mechanisms regulating grain size have not been fully investigated.In this study,we identified a rice mutant,wide grain 4-D(wg4-D),that exhibited a significant increase in grain width and a decrease in grain length.Histological analysis demonstrated that WG4 affects cell expansion thereby regulating grain size.MutMap-based gene mapping and complementary transgenic experiments revealed that WG4 encodes an alpha-tubulin,OsTubA1.A SNP mutation in WG4 affected the arrangement of cortical microtubules and caused a wide-grain phenotype.WG4 is located in nuclei and cytoplasm and expressed in various tissues.Our results provide insights into the function of tubulin in rice and identifies novel targets the regulation of grain size in crop breeding.

A natural allele of TAW1 contributes to high grain number and grain yield in rice

Grain number per panicle (GNP) is a complex trait controlled by quantitative trait loci (QTL),directly determining grain yield in rice.Identifying GNP-associated QTL is desirable for increasing rice yield.A rice chromosome segment substitution line (CSSL),F771,which showed increased panicle length and GNP,was identified in a set of CSSLs derived from a cross between two indica cultivars,R498 (recipient) and WY11327 (donor).Genetic analysis showed that the panicle traits in F771 were semidominant and controlled by multiple QTL.Six QTL were consistently identified by QTL-seq analysis.Among them,the major QTL q PLN10 for panicle length and GNP was localized to a 121-kb interval between markers N802 and N909 on chromosome 10.Based on quantitative real-time PCR and sequence analysis,TAWAWA1(TAW1),a known regulator of rice inflorescence architecture,was identified as the candidate gene for q PLN10.A near-isogenic line,NIL-TAW1,was developed to evaluate its effects.In comparison with the recurrent parent R498,NIL-TAW1 showed increased panicle length (14.0%),number of secondary branches (20.9%) and GNP (22.0%),and the final grain yield per plant of NIL-TAW1 was increased by18.6%.Transgenic experiments showed that an appropriate expression level of TAW1 was necessary for panicle development.Haplotype analysis suggested that the favorable F771-type (Hap 13) of TAW1was introduced from aus accessions and had great potential value in high-yield breeding both in indica and japonica varieties.Our results provide a promising genetic resource for rice grain yield improvement.

OsSPL18 controls grain weight and grain number in rice

Grain weight and grain number are two important traits directly determining grain yield in rice. To date,a lot of genes related to grain weight and grain number have been identified; however, the regulatory mechanism underlying these genes remains largely unknown. In this study, we studied the biological function of OsSPL18 during grain and panicle development in rice. Knockout (KO) mutants of OsSPL18exhibited reduced grain width and thickness, panicle length and grain number, but increased tiller number. Cytological analysis showed that OsSPL18 regulates the development of spikelet hulls by affecting cell proliferation. qRT-PCR and GUS staining analyses showed that OsSPL18 was highly expressed in developing young panicles and young spikelet hulls, in agreement with its function in regulating grain and panicle development. Transcriptional activation experiments indicated that OsSPL18is a functional transcription factor with activation domains in both the N-terminus and C-terminus, and both activation domains are indispensable for its biological functions. Quantitative expression analysis showed that DEP1, a major grain number regulator, was significantly down-regulated in OsSPL18 KO lines.Both yeast one-hybrid and dual-luciferase (LUC) assays showed that OsSPL18 could bind to the DEP1promoter, suggesting that OsSPL18 regulates panicle development by positively regulating the expression of DEP1. Sequence analysis showed that OsSPL18 contains the OsmiR156k complementary sequence in the third exon; 5?RLM-RACE experiments indicated that OsSPL18 could be cleaved by OsmiR156k. Taken together, our results uncovered a new OsmiR156k-OsSPL18-DEP1 pathway regulating grain number in rice.

Loss of Gn1a/OsCKX2 confers heavy-panicle rice with excellent lodging resistance

Significant achievements have been made in breeding programs for the heavy-panicle-type(HPT)rice(Oryza sativa) in Southwest China. The HPT varieties now exhibit excellent lodging resistance,allowing them to overcome the greater pressures caused by heavy panicles. However, the genetic mechanism of this lodging resistance remains elusive. Here, we isolated a major quantitative trait locus, Panicle Neck Diameter 1(PND1), andidentified the causal gene as GRAIN NUMBER 1 A/CYTOKININ OXIDASE 2(Gn1 A/Os CKX2). The null gn1 a allele from rice line R498(gn1 aR498) improved lodging resistance through increasing the culm diameter and promoting crown root development.Loss-of-function of Gn1 a/Os CKX2 led to cytokinin accumulation in the crown root tip and accelerated the development of adventitious roots. Gene pyramiding between the null gn1 aR498 allele with two gain-of-function alleles, STRONG CULM 2(SCM2)and SCM3, further improved lodging resistance.Moreover, Gn1 a/Os CKX2 had minimal influence on overall rice quality. Our research thus highlights the distinct genetic components of lodging resistance of HPT varieties and provides a strategy for tailormade crop improvement of both yield and lodging resistance in rice.

A single nucleotide substitution at 5'-UTR of GSN1 represses its translation and leads to an increase of grain length in rice

Rice grain size is an important trait that affects rice yield and quality, and thus the identification of genes related to grain size is of great significance for improving rice yield and quality. Many genes related to grain size, such as DEP1(Huang et al., 2009),GW5(Liu et al., 2017).

Characterization and Fine Mapping of GLABROUS RICE 2 in Rice

Glabrous rice exhibits glabrous leaves and hulls because neither of these structures have trichomes on their surfaces. Glabrous rice varieties have become an important germplasm resource in the rice industry because they have considerable packaging efficiency and can reduce skin itching and dust during harvesting, drying, and packing （Shim et al., 2012; Zhang et al., 2012）.

Deletion of a Dna K protein gene causes seedling green-revertible albino by retarding chloroplast development in rice

Green-revertible albino mutants are important sources for studying chloroplast structure, chloroplast development, chlorophyll biosynthesis, and plant photo- synthesis. In the present study, we characterized a green- revertible albino mutant gra（k）, which was obtained from the tissue-cultured rice Kitaake. The mutant gra（k） exhib- ited albino on its first three leaves. The leaf color started to turn green at the four-leaf stage. The chlorophyll contents were deeply reduced at the seedling stage, and the chloroplast development was delayed in gra（k）. The green- revertible albino （gra） phenotype of the mutant gra（k） was temperature dependent. The main agronomic traits, including plant height, tilling number per plant, seed set- ting rate, and thousand-grain weight, slightly decreased in gra（k） comparing to those in the wild-type Kitaake. Genetic analysis showed that the gra phenotype was con- trolled by a single recessive nucleic gene. By using 5,168 recessive F2 individuals derived from the cross of gra（k） × Jodan, the locus of the gene Gra（k） was delimited in a DNA region of 200 kb between the makers B-31 and P11 on chromosome 5. Sequencing analysis indicated that the three functionally annotated genes, LOC_Os05g23700, LOC_Os05g23720, and LOC_Os05g23740, were all deleted in the 200 kb region in the mutant gra（k）. Trans- genic test revealed that the gra（k） plants over-expressing LOC_Os05g23740CDS were restored to normal green as the wild-type Kitaake. Our results proved that the deletion of the DnaK protein gene LOC_Os05g23740 （encoding the chaperon protein OsHsp70CP1） led to the gra phenotype in the mutant gra（k）.

Improving the efficiency of hybrid combination preparation in rice breeding by a modified flowering stimulant

The utilization of hybrid vigor is an important breakthrough in the history of rice breeding.To select the best hybrid combinations,breeders manually perform extensive testing of hybridizations between restorer and sterile lines,which is a laborious and time-consuming process.Here,we report that a modified flowering stimulant containing methyl jasmonate(MeJA),6-benzylamine adenine and kinetin effectively promotes the flowering and seed set of male-sterile rice lines.Different concentrations of the ingredients were tested to identify an optimal formulation.Seed quality evaluation indicated that hybrid seeds from plants sprayed with the flowering stimulant had a higher germination rate than seeds from plants prepared by glume-cutting.In summary,the modified flowering stimulant described in this study may help reduce the labor requirement associated with hybrid rice breeding and improve yield and efficiency.

Characterization and Fine Mapping of a Novel Vegetative Senescence Lethal Mutant Locus in Rice

Mutants showing spontaneous cell death in the absence of pathogen attack are called lesion mimic mutants （lmm） （Lorrain et al., 2003）. These mutants usually exhibit typical hypersensitive responses （HRs） within or around the lesion spots, which are frequently observed in plants challenged with avirulent pathogens （Lorrain et al., 2003）. A number of these mutants have been characterized in rice （Zeng et al., 2004）, Arabidopsis （Guo et al., 2013）, maize （Wang et al., 2013） and barley （Persson et al., 2008）. Most lmm show enhanced resistance to various pathogens （Huang et al., 2011）, because HR is usually accompanied with enhanced defense responses, such as reactive oxygen species （ROS） activation （Qiao et al., 2010） and increased expression of pathogenesis-related genes （Lorrain et al., 2003）. Additionally, most lmm exhibit defects in growth and development due to the disordered physiolog- ical and molecular processes caused by the lesion spots. Thus, lmm are powerful tools for the study of the molecular mech- anisms of cell death, plant development and disease resistance （Lorrain et al., 2003; Babu et al., 2011）.