ELE restrains empty glumes from developing into lemmas

Although there is evident homology among reproductive organs when comparing Poaceae （grass） and eudicots, the identity of grass specific organs, such as lodicules, palea, lemma, and glumes has been the subject of a vast and largely inconclusive discussion. Here we provide some direct evidence to support the idea that the empty glumes of rice （Oryza sativa） are counterparts of lemmas. We show that the development of empty glumes is regulated by ELE （elongated empty glume）, which belongs to a plant specific novel gene family. Mutations at the ELE locus cause elongated empty glumes, which mimic the lemmas and have the epidermal morphology of lemmas with four or five vascular bundles. As a nuclear-localized gene, ELE is specifically expressed at the empty glumes of immature spikelets, and its ectopic expression causes many floral development defects, including lemma-like palea, extra palea-like structures, elongated lodicules, extra stamens and stigmas. Our result suggests that empty glumes are lemmas of the sterile florets located at the lateral side of the rice spikelet, and ELE acts as a regulator restraining its growth to maintain its small size in wild-type plants.

Rice AGL1 determines grain size and sterile lemma identity

The grass spikelet is a unique inflorescence structure that determines grain size.Although many genetic factors have been well characterized for grain size and glume development,the underlying molecular mechanisms in rice are far from established.Here,we isolated rice gene,AGL1 that controlled grain size and determines the fate of the sterile lemma.Loss of function of AGL1 produced larger grains and reduced the size of the sterile lemma.Larger grains in the agl1 mutant were caused by a larger number of cells that were longer and wider than in the wild type.The sterile lemma in the mutant spikelet was converted to a rudimentary glume-like organ.Our findings showed that the AGL1(also named LAX1)protein positively regulated G1 expression,and negatively regulated NSG1 expression,thereby affecting the fate of the sterile lemma.Taken together,our results revealed that AGL1 played a key role in negative regulation of grain size by controlling cell proliferation and expansion,and supported the opinion that rudimentary glume and sterile lemma in rice are homologous organs.

Ectopic expression of VRT-A2 underlies the origin of Triticum polonicum and Triticum petropavlovskyi with long outer glumes and grains

Polish wheat (Triticum polonicum) is a unique tetraploid wheat species characterized by an elongated outer glume. The genetic control of the long-glume trait by a single semi-dominant locus, P1 (from Polish wheat), was established more than 100 years ago, but the underlying causal gene and molecular nature remain elusive. Here, we report the isolation of VRT-A2, encoding an SVP-clade MADS-box transcription factor, as the P1 candidate gene. Genetic evidence suggests that in T. polonicum, a naturally occurring sequence rearrangement in the intron-1 region of VRT-A2 leads to ectopic expression of VRT-A2 in floral organs where the long-glume phenotype appears. Interestingly, we found that the intron-1 region is a key ON/OFF molecular switch for VRT-A2 expression, not only because it recruits transcriptional repressors, but also because it confers intron-mediated transcriptional enhancement. Genotypic analyses using wheat accessions indicated that the P1 locus is likely derived from a single natural mutation in tetraploid wheat, which was subsequently inherited by hexaploid T. petropavlovskyi. Taken together, our findings highlight the promoter-proximal intron variation as a molecular basis for phenotypic differentiation, and thus species formation in Triticum plants.

Machine vision inspection of rice seed based on Hough transform

A machine vision system was developed to inspect the quality of rice seeds. Five varieties of Jinyou402, Shanyou10, Zhongyou207, Jiayou and IIyou were evaluated. The images of both sides of rice seed with black background and white background were acquired with the image processing system for identifying external features of rice seeds. Five image sets consisting of 600 original images each were obtained. Then a digital image processing algorithm based on Hough transform was developed to inspect the rice seeds with incompletely closed glumes. The algorithm was implemented with all image sets using a Matlab 6.5 procedure. The results showed that the algorithm achieved an average accuracy of 96% for normal seeds, 92% for seeds with fine fissure and 87% for seeds with incompletely closed glumes. The algorithm was proved to be applicable to different seed varieties and insensitive to the color of the background.

Research Progress on Mechanized Mixed Sowing Seed Production Technology of Hybrid Rice

Hybrid rice planting has been widely popularized and applied in the world. However, the high cost of seed production and the complicated procedures have become a bottleneck in the development of hybrid rice. The research progress on mixed sowing seed production techniques of hybrid rice was introduced from the aspects of rice resources creation, breeding, sowing seed technology research and cost benefit analysis. The production technology of the new mixed seeding combina- tion ＂Xinhunyou 6＂ was investigated, including the research and validation of benta- zon treatment period and dosage, mixing ratio of male and female parents, and the comparative test of different different sowing methods, which revealed that the mechanization technology of seed production of hybrid rice was mature and feasible and would be one of the most important development trend of technological devel- opment of hybrid rice production.

Fosmid library construction and screening for the maize mutant gene Vestigial glume 1

The maize mutant gene Vestigial glume 1(Vg1) has been fine-mapped to a narrow region by map-based cloning and the candidate gene for Vg1 spanned 19.5 kb. Here we report Vg1 genomic fosmid library construction and screening. The fosmid library of Vg1 consisted of574,000 clones with an average insert size of 36.4 kb, representing 7.9-fold coverage of the maize genome. Fosmid stability assays indicated that clones were stable during propagation in the fosmid system. Using Vg1 candidate gene-specific primers, a positive clone was successfully identified. This discovery will pave the way for identifying the function of Vg1 in maize development.

Identification and Gene Mapping of a multi-floret spikelet 1 (mfs1) Mutant Associated with Spikelet Development in Rice

In this study, a rice spikelet mutant, multi-floret spikelet 1 （mfsl）, which was derived from ethylmethane sulfonate （EMS）- treated Jinhui 10 （Oryza sativa L. ssp. indica） exhibited pleiotropic defects in spikelet development. The mfsl spikelet displayed degenerated the empty glume, elongated the rachilla, the extra lemma-like organ and degraded the palea. Additionally, mfsl flowers produced varied numbers of inner floral organs. The genetic analysis revealed that the mutational trait was controlled by a single recessive gene. With 401 recessive individuals from the F2 segregation population, the MFS1 gene was finally mapped on chromosome 5, an approximate 350 kb region. The present study will be useful for cloning and functional analysis of MFS1, which would facilitate understanding of the molecular mechanism involved in spikelet development in rice.

Phenotypic characterization of a rice mutant Oryza sativa extraordinary glume 1(Oseg 1)and its genetic analysis

A rice mutant with Yaponica 9522 cultivar background Oryza sativa extraordinary glume 1 （Oseg 1） was identified from the M2 mutant pool mutagenized by ^60Co γ-ray. Compared with wild type plants, Oseg 1 developed longer empty glumes and rudimentary glumes. In some Oseg 1 mutants, the number of stamens of flowers was reduced and leaf-like lodicules occurred, and excessive lemma/palea-like organ could be observed in some mutant spikelets. This indicated that OsEG1 could regulate the development of rudimentary glumes, empty glumes, lemma/palea, lodicules, and stamens. Genetic analysis indicated that Oseg 1 came from a single recessive genetic locus. To clone OsEG1 gene, F2 population was constructed by a cross between Oseg 1 （Japonica） and Guangluai4 （Indica）. Using map-based cloning approach, OsEG1 was mapped on chromosome 4, between INDEL marker OS407 and WHM0466 with genetic distance of 2.0 cm and 1.0 cm, respectively. These results are useful for further cloning and functional analysis of the OsEG1 gene.

Molecular mapping and candidate gene analysis of the semi-dominant gene Vestigial glume1 in maize

The glume is an organ of the maize spikelet and plays important roles in anther and kernel development.Vestigial glume1(Vg1)is a classic mutant associated with ligule and glume development.Here we report the phenotypic characterization,fine mapping,and candidate gene analysis of the Vg1 mutant.Vg1 is a semi-dominant and pleiotropic gene,and also affects plant height,ear height,and tassel length.Vg1 ligule degeneration begins at the first leaf,and the Vg1 tassel and ear can be distinguished from those of wild-type plants when their lengths reach respectively 55 mm and 51 mm.Using a BC3 mapping population of 11,445 plants,we delimited the Vg1 functional site to an interval of 7.4 kb,flanked by the markers InDelLM and CRM6.A putative cyclopropane fatty-acid synthase gene(ZmCPA-FAS1)was hypothesized to underlie the mutant phenotype.We detected a Helitron insertion in the sixth intron of ZmCPAFAS1.Its presence caused abnormal alternative splicing of ZmCPA-FAS1 that conferred new characteristics on the Vg1 mutant.These findings are a basis for further discovery of the molecularmechanism underlying glume development and a potential guide formaize breeding of small-glume varieties,especially sweet corn breeding.

OsPEX1,a leucine-rich repeat extensin protein,functions in the regulation of caryopsis development and quality in rice

Rice caryopses are enclosed by outer glumes.The size and dimension of the outer glume are the main determinants of caryopsis size.However,it is unclear whether caryopsis development is completely dependent on the size of the glume,or whether it can grow and expand autonomously despite the constraint of glume enclosure.We report the identification of a mutant line that produces normal-sized glumes with smaller mature caryopses that do not fill the entire glume cavity.The caryopsis phenotype in the pex1 mutant is caused by a reduction in cell size.Os PEX1,a leucine-rich repeat extensin gene,was highly expressed in the developing caryopsis.Overexpression of Os PEX1 driven by a constitutive promoter recapitulated the mutant phenotype,showing that the small-caryopsis phenotype is caused by overexpression of the Os PEX1 gene.Free amino acids,including several essential amino acids,and crude protein were increased in pex1 relative to the wild type,endowing pex1 with improved nutritional quality.Our results suggest that caryopsis development can be genetically uncoupled from maternally controlled glume development and that Os PEX1 might be a new resource for improving nutritional quality of rice cultivars.

The C2H2 zinc-finger protein LACKING RUDIMENTARY GLUME 1 regulates spikelet development in rice

Rice(Oryza sativa)spikelets are a unique inflorescence structure and their development directly determines grain size and yield.Although many genes related to spikelet development have been reported,the molecular mechanisms underlying this process have not been fully elucidated.In this study,we identified a new recessive rice mutant,lacking rudimentary glume 1(lrg1).The lrg1 spikelets only formed one rudimentary glume,which,along with the sterile lemmas,was homeotically transformed into lemma-like organs and acquired lemma identity.The transition from the spikelet to the floral meristem was delayed in the lrg1 mutant,resulting in the formation of an ectopic lemma-like organ between the sterile lemma and the terminal floret.In addition,we found that the abnormal lrg1 grain phenotype resulted from the alteration of cell numbers and the hull size.LRG1 encodes a ZOS4-06-C2H2 zinc-finger protein with the typical EAR motifs,and is expressed in all organs and tissues.LRG1 localizes to the nucleus and can interact with the TOPLESS-RELATED PROTEINs(TPRs)to repress the expressions of their downstream target genes.Taken together,our results reveal that LRG1 plays an important role in the regulation of spikelet organ identity and grain size.