Ectopic expression of OsNF-YA8,an endosperm-specific nuclear factor Y transcription-factor gene,causes vegetative and reproductive development defects in rice

Nuclear factor Y(NF-Y),a group of conserved transcription-factor complexes that consist of NF-YA,B,and C subunits,is essential for developmental regulation and for responses to environmental changes in eukaryotes.We previously found that some NF-Y genes,such as OsNF-YA8,were expressed specifically in the endosperm of rice.In the present study,overexpression of OsNF-YA8 in rice resulted in reduced plant height due to suppressed cell elongation in internodes.Gibberellin(GA)biosynthetic genes,including OsCPS1,OsGA20ox1,and OsGA20ox2,were down-regulated.OsNF-YA8 bound to the promoters of these genes to repress their expression.Endogenous GA content was decreased in OsNF-YA8 overexpressors,whose dwarf phenotype could be partially rescued by exogenous GA treatment.The findings suggested that ectopic expression of OsNF-YA8 causes defective GA biosynthesis in vegetative stage.Heading date in OsNF-YA8 overexpressors was delayed,especially under short-day conditions.OsNFYA8 bound to the promoter of Heading Date 3a(Hd3a),the florigen gene in rice,to negatively regulate flowering.Either ectopic activation or knockout of OsNF-YA8 impaired seed development,as indicated by reduced seed size and increased grain chalkiness.These results suggest that ectopic expression of the endosperm-specific OsNF-YA8 in rice disrupts both vegetative and reproductive development.

The Effect of Organ Temperature on Total Yield of Transplanted and Direct-Seeded Rice(Oryza sativa L.)

The canopy temperature of rice is an important index that directly reflects the growth and physiological state of rice,and affects the yield of rice plants to a great extent.The correlation between the temperatures of different rice organs and canopy in different growth stages and the grain yield is complex.The stability and universality of these correlations must be verified.We conducted a pot experiment using two rice varieties and two temperature treatments(high temperature treatment was carried out at the beginning of heading stage for 10 days).We measured rice organ temperature during seven stages of growth using a high-precision infrared thermal imager.Results showed that the optimal observation period for the rice canopy temperature was 13:00.Although the rice variety did not significantly impact the canopy or organ temperature(p>0.05),the different organs and canopy exhibited significantly different temperatures(p<0.05).The correlations between the leaf,stem,panicle,canopy–air temperature differences and seed setting rate,theoretical and actual yields were the strongest during the milk stage.Among them,the correlation coefficient betweenΔT_(s) and theoretical and actual yields was the highest,the relationship between theoretical yield(Y)andΔT_(s)(X)was Y=−5.6965X+27.778,R^(2)=0.9155.Compared withΔT_(l),ΔT_(p) andΔTc,ΔT_(s) was closely related to the main traits of plants.ΔT_(s) could better reflect the growth characteristics of rice thanΔT_(c),such as dry matter accumulation(r=−0.931),SPAD(r=0.699),N concentration(r=0.714),transpiration rate(r=−0.722).In conclusion,stem temperature was more important indicator than canopy temperature.Stem temperature is a better screening index for rice breeding and cultivation management in the future.

OsbZIP53 Negatively Regulates Immunity Response by Involving in Reactive Oxygen Species and Salicylic Acid Metabolism in Rice

The basic region/leucine zipper(bZIP)transcription factors play important roles in plant development and responses to abiotic and biotic stresses.OsbZIP53 regulates resistance to Magnaporthe oryzae in rice by analyzing APIP5-RNAi transgenic plants.To further investigate the biological functions of OsbZIP53,we generated osbzip53 mutants using CRISPR/Cas9 editing and also constructed OsbZIP53 over-expression transgenic plants.Comprehensive analysis of phenotypical,physiological,and transcriptional data showed that knocking-out OsbZIP53 not only improved disease resistance by inducing a hypersensitivity response in plants,but also regulated the immune response through the salicylic acid pathway.Specifically,disrupting OsbZIP53 increased H2O2 accumulation by promoting reactive oxygen species generation through up-regulation of several respiratory burst oxidase homologs(Osrboh genes)and weakened H2O2 degradation by directly targeting OsMYBS1.In addition,the growth of osbzip53 mutants was seriously impaired,while OsbZIP53 over-expression lines displayed a similar phenotype to the wild type,suggesting that OsbZIP53 has a balancing effect on rice immune response and growth.

Rice melatonin deficiency causes premature leaf senescence via DNA methylation regulation

In a study of DNA methylation changes in melatonin-deficient rice mutants,mutant plants showed premature leaf senescence during grain-filling and reduced grain yield.Melatonin deficiency led to transcriptional reprogramming,especially of genes involved in chlorophyll and carbon metabolism,redox regulation,and transcriptional regulation,during dark-induced leaf senescence.Hypomethylation of mCG and mCHG in the melatonin-deficient rice mutants was associated with the expression change of both protein-coding genes and transposable element-related genes.Changes in gene expression and DNA methylation in the melatonin-deficient mutants were compensated by exogenous application of melatonin.A decreased S-adenosyl-L-methionine level may have contributed to the DNA methylation variations in rice mutants of melatonin deficiency under dark conditions.

Combining QTL Mapping and Multi-Omics Identify Candidate Genes for Nutritional Quality Traits during Grain Filling Stage in Maize

The nutritional composition and overall quality of maize kernels are largely determined by the key chemical com-ponents:protein,oil,and starch.Nevertheless,the genetic basis underlying these nutritional quality traits during grainfilling remains poorly understood.In this study,the concentrations of protein,oil,and starch were studied in 204 recombinant inbred lines resulting from a cross between DH1M and T877 at four different stages post-pollination.All the traits exhibited considerable phenotypic variation.During the grain-filling stage,the levels of protein and starch content generally increased,whereas oil content decreased,with significant changes observed between 30 and 40 days after pollination.Quantitative trait locus(QTL)mapping was conducted and a total of 32 QTLs,comprising 14,12,and 6 QTLs for grain protein,oil,and starch content were detected,respectively.Few QTLs were consistently detectable across different time points.By integrating QTL analysis,glo-bal gene expression profiling,and comparative genomics,we identified 157,86,and 54 differentially expressed genes harboring nonsynonymous substitutions between the parental lines for grain protein,oil,and starch con-tent,respectively.Subsequent gene function annotation prioritized 15 candidate genes potentially involved in reg-ulating grain quality traits,including those encoding transcription factors(NAC,MADS-box,bZIP,and MYB),cell wall invertase,cellulose-synthase-like protein,cell division cycle protein,trehalase,auxin-responsive factor,and phloem protein 2-A13.Our study offers significant insights into the genetic architecture of maize kernel nutritional quality and identifies promising QTLs and candidate genes,which are crucial for the genetic enhance-ment of these traits in maize breeding programs.

Targeted mutagenesis of amino acid transporter genes for rice quality improvement using the CRISPR/Cas9 system

High grain protein content(GPC) reduces rice eating and cooking quality(ECQ). We generated OsAAP6 and OsAAP10 knockout mutants in three high-yielding japonica varieties and one japonica line using the CRISPR/Cas9 system. Mutation efficiency varied with genetic background in the T_0 generation, and GPC in the T_1 generation decreased significantly,owing mainly to a reduction in glutelin content. Amylose content was down-regulated significantly in some Osaap6 and all Osaap10 mutants. The increased taste value of these mutants was supported by Rapid Visco Analysis(RVA) profiles, which showed higher peak viscosity and breakdown viscosity and lower setback viscosity than the wild type. There were no significant deficiencies in agronomic traits of the mutants. Targeted mutagenesis of OsAAP6 and OsAAP10, especially OsAAP10, using the CRISPR/Cas9 system can rapidly reduce GPC and improve ECQ of rice, providing a new strategy for the breeding cultivars with desired ECQ.

Application of moderate nitrogen levels alleviates yield loss and grain quality deterioration caused by post-silking heat stress in fresh waxy maize

High temperature(HT)during grain filling is one of the most important environmental factors limiting maize yield and grain quality.Nitrogen(N)fertilizer is essential for maintaining normal plant growth and defense against environmental stresses.The effects of three N rates and two temperature regimes on the grain yield and quality of fresh waxy maize were studied using the hybrids Suyunuo 5(SYN5)and Yunuo 7(YN7)as materials.N application rates were 1.5,4.5,and 7.5 g plant-1,representing low,moderate,and high N levels(LN,MN,and HN,respectively).Mean day/night temperatures during the grain filling of spring-and summer-sown plants were 27.6/21.0°C and 28.6/20.0°C for ambient temperature(AT)and 35/21.0°C and 35/20.0°C for HT,respectively.On average,HT reduced kernel number,weight,yield,and moisture content by 29.8%,17.9%,38.7%,and 3.3%,respectively.Kernel number,weight,yield,moisture,and starch contents were highest under MN among the three N rates under both temperature regimes.HT reduced grain starch content at all N levels.HT increased grain protein content,which gradually increased with N rate.Mean starch granule size under MN was larger(10.9μm)than that under LN and HN(both 10.4μm)at AT.However,the mean size of starch granules was higher under LN(11.7μm)and lower under MN(11.2μm)at HT.Iodine binding capacity(IBC)was lowest under MN and highest under HN among the three N levels under both temperature regimes.In general,IBC at all N rates was increased by HT.Peak viscosity(PV)was gradually reduced with increasing N rate at AT.In comparison with LN,PV was increased by MN and decreased by HN at HT.Retrogradation percentage gradually increased with N rate at AT,but was lowest under MN among the three N rates at HT.LN+AT and MN+HT produced grain with high pasting viscosity and low retrogradation tendency.MN application could alleviate the negative effects of HT on the grain yield and quality of fresh waxy maize.

Effects of Early- and Late-Sowing on Starch Accumulation and Associated Enzyme Activities During Grain Filling Stage in Rice

The environmental temperature occurring during the grain filling stage is an important factoraffecting starch synthesis and accumulation in rice. We investigated starch accumulation, amylaseactivity and starch granule size distribution in two low-amylose japonica rice varieties, Nanjing 9108 andFujing 1606, grown in the field at different filling temperatures by manipulating sowing date. The two ricevarieties exhibited similar performances between two sowing dates. Total starch, amylose andamylopectin contents were lower at the early-filling stage of T1 treatment (Early-sowing) compared withthose at the same stage in T2 treatment (Late-sowing). In contrast, at the late-filling stage, when fieldtemperatures were generally decreasing, total starch and amylopectin contents in T1 were highercompared to those in T2. The ideal temperature for strong activity of ADP-glucose pyrophosphorylaseand soluble starch synthase was about 22℃. A higher temperature from the heading to maturity stagesin T1 increased the activities of starch branching enzyme and suppressed the activities of granule boundstarch synthetase and starch debranching enzyme. We found that rice produced larger-sized starchgranules under the T1 treatment. These results suggested that due to the early-sowing date, the hightemperature (30℃) occurring at the early-filling stage hindered starch synthesis and accumulation,however, the lower temperatures (22 ℃) at the late-filling stage allowed starch synthesis and accumulationto return to normal levels.

Cytological and molecular characteristics of delayed spike development in wheat under low temperature in early spring

Low temperature in early spring impairs wheat growth and grain yield.However,little is known about the cytological and molecular mechanisms underlying low temperature regulation of wheat spike development.Microstructure observation and transcriptome sequencing of wheat spikes under low temperature were conducted.Low temperature slowed spike development,reduced the yield-component parameters of wheat spikes at the harvest stage,delayed the formation of lateral spikelets and tissue development,and induced the early differentiation of terminal spikelets.Low temperature increased the content of abscisic acid and caused the upregulation of genes in the abscisic acid signaling pathway,including those encoding PP2 Cs,Sn RK2 s,and b ZIP transcription factors.Low temperature also induced the upregulation of 33 cold-responsive genes involved in wheat response to low-temperature stress and regulation of abscisic acid biosynthesis and metabolism of other substances.The wheat spike adapted to cold conditions by changing the expression levels of genes involved in spike morphogenesis,including the transcription-factor genes MADS6,ERF4,ERF78,WOX6,and NAC48.These findings suggest that low temperature in early spring delays wheat spike development by increasing abscisic acid content or affecting the expression of genes involved in morphogenesis.

Multi-environment QTL mapping of crown root traits in a maize RIL population

Crown root traits,including crown root angle(CRA),diameter(CRD),and number(CRN),are major determining factors of root system architecture,which influences crop production.In maize,the genetic mechanisms determining crown root traits in the field are largely unknown.CRA,CRD,and CRN were evaluated in a recombinant inbred line population in three field trials.High phenotypic variation was observed for crown root traits,and all measured traits showed significant genotype–environment interactions.Singleenvironment(SEA)and multi-environment(MEA)quantitative trait locus(QTL)analyses were conducted for CRA,CRD,and CRN.Of 46 QTL detected by SEA,most explained less than 10%of the phenotypic variation,indicating that a large number of minor-effect QTL contributed to the genetic component of these traits.MEA detected 25 QTL associated with CRA,CRD,and CRN,and 2 and 1 QTL were identified with significant QTL-by-environment interaction effects for CRA and CRD,respectively.A total of 26.1%(12/46)of the QTL identified by SEA were also detected by MEA,with many being detected in more than one environment.These findings contribute to our understanding of the phenotypic and genotypic patterns of crown root traits in different environments.The identified environment-specific QTL and stable QTL may be used to improve root traits in maize breeding.

Straw return influences the structure and functioning of arbuscular mycorrhizal fungal community in a rice-wheat rotation system

Straw return is a sustainable soil fertility-building practice,which can affect soil microbial communities.However,how straw return affects arbuscular mycorrhizal fungi(AMF)is not well explored.Here,we studied the impacts of different straw management treatments over eight years on the structure and functioning of AMF communities in a rice-wheat rotation system.The straw management treatments included no tillage with no straw(NTNS),rotary tillage straw return(RTSR),and ditch-buried straw return(DBSR).The community structure of AMF was characterized using high-throughput sequencing,and the mycorrhizal functioning was quantified using an in situ mycorrhizal-suppression treatment.Different straw management treatments formed unique AMF community structure,which was closely related to changes in soil total organic carbon,available phosphorus,total nitrogen,ammonium,and nitrate.When compared with NTNS,RTSR significantly increased Shannon diversity in 0–10 cm soil layer,while DBSR increased it in 10–20 cm soil layer;DBSR significantly increased hyphal length density in the whole ploughing layer(0–20 cm),but RTSR only increased it in the subsurface soil layer(10–20 cm).The mycorrhizal responses of shoot biomass and nutrient(N and P)uptake were positive under both straw return treatments(RTSR and DBSR),but negative under NTNS.The community composition of AMF was significantly correlated to hyphal length density,and the latter was further a positive predictor for the mycorrhizal responses of plant growth and nutrient uptake.These findings suggest that straw return can affect AMF community structure and functioning,and farmers should manage mycorrhizas to strengthen their beneficial effects on crop production.

Introgression of lac6/tl1/du13 improves the palatability of japonica rice

Amylose content(AC)is a crucial determinant of the eating and cooking quality(ECQ)of rice,with low AC varieties exhibiting a softer texture and greater stickiness-attributes that enhance palatability and are desirable in specific culinary contexts.To harness these traits,significant efforts have been made to manipulate AC to improve rice ECQ.Our research utilized the MutMap+approach to identify LAC6/TL1,a gene that is an allele of Du13,responsible for low AC.LAC6 encodes a C2H2 zinc finger protein,which specifically increases the splicing efficiency of the Wxb allele without affecting the Wxa allele.Functional studies of LAC6 revealed that its proper integration could rectify the undesirable AC phenotype,whereas mutations within this gene led to reduced AC and were associated with shorter grain length and decreased thousand-grain weight.Despite these drawbacks,such mutations positively impact rice palatability,presenting a trade-off between grain size and eating quality.To address the challenges posed by the reduced grain weight associated with LAC6 mutations,we developed a specific molecular marker for LAC6,which has been effectively used in breeding programs to select lac6/tl1/du13 homozygous individuals with larger grain size.Our findings demonstrate that the“small grain”trait associated with lac6/tl1/du13 can be effectively mitigated through combined phenotype-based and marker-assisted selection.This study highlights the potential of lac6/tl1/du13 as a valuable gene for breeding novel,high-quality soft rice varieties through targeted breeding strategies.

ESCRT-Ⅲ component OsSNF7.2 modulates leaf rolling by trafficking and endosomal degradation of auxin biosynthetic enzyme OsYUC8 in rice

The endosomal sorting complex required for transport(ESCRT)is highly conserved in eukaryotic cells and plays an essential role in the biogenesis of multivesicular bodies and cargo degradation to the plant vacuole or lysosomes.Although ESCRT components affect a variety of plant growth and development processes,their impact on leaf development is rarely reported.Here,we found that OsSNF7.2,an ESCRT-Ⅲ component,controls leaf rolling in rice(Oryza sativa).The Ossnf7.2 mutant rolled leaf 17(rl17)has adaxially rolled leaves due to the decreased number and size of the bulliform cells.OsSNF7.2is expressed ubiquitously in all tissues,and its protein is localized in the endosomal compartments.OsSNF7.2 homologs,including OsSNF7,OsSNF7.3,and OsSNF7.4,can physically interact with OsSNF7.2,but their single mutation did not result in leaf rolling.Other ESCRT complex subunits,namely OsVPS20,OsVPS24,and OsBRO1,also interact with OsSNF7.2.Further assays revealed that OsSNF7.2 interacts with OsYUC8 and aids its vacuolar degradation.Both Osyuc8and rl17 Osyuc8 showed rolled leaves,indicating that OsYUC8 and OsSNF7.2 function in the same pathway,conferring leaf development.This study reveals a new biological function for the ESCRT-Ⅲcomponents,and provides new insights into the molecular mechanisms underlying leaf rolling.

Histone deacetylase OsHDA706 increases salt tolerance via H4K5/K8 deacetylation of OsPP2C49 in rice

High salt is a major environmental factor that threatens plant growth and development.Increasing evidence indicates that histone acetylation is involved in plant responses to various abiotic stress;however,the underlying epigenetic regulatory mechanisms remain poorly understood.In this study,we revealed that the histone deacetylase OsHDA706 epigenetically regulates the expression of salt stress response genes in rice(Oryza sativa L.).OsHDA706 localizes to the nucleus and cytoplasm and OsHDA706 expression is significantly induced under salt stress.Moreover,oshda706 mutants showed a higher sensitivity to salt stress than the wild-type.In vivo and in vitro enzymatic activity assays demonstrated that OsHDA706 specifically regulates the deacetylation of lysines 5 and 8 on histone H4(H4K5and H4K8).By combining chromatin immunoprecipitation and mRNA sequencing,we identified the clade A protein phosphatase 2C gene,OsPP2C49,which is involved in the salt response as a direct target of H4K5 and H4K8 acetylation.We found that the expression of OsPP2C49 is induced in the oshda706 mutant under salt stress.Furthermore,the knockout of OsPP2C49 enhances plant tolerance to salt stress,while its overexpression has the opposite effect.Taken together,our results indicate that OsHDA706,a histone H4 deacetylase,participates in the salt stress response by regulating the expression of OsPP2C49 via H4K5 and H4K8 deacetylation.

Pijx confers broad-spectrum seedling and panicle blast resistance by promoting the degradation of ATP β subunit and OsRbohC-mediated ROS burst in rice

Rice blast,caused by the fungal pathogen Magnaporthe oryzae,is one of the most important diseases of rice.Utilization of blast-resistance genes is the most economical,effective,and environmentally friendly way to control the disease.However,genetic resources with broad-spectrum resistance(BSR)that is effective throughout the rice growth period are rare.In this work,using a genome-wide association study,we identify a new blast-resistance gene,Pijx,which encodes a typical CC-NBS-LRR protein.Pijx is derived from a wild rice species and confers BSR to M.oryzae at both the seedling and panicle stages.The functions of the resistant haplotypes of Pijx are confirmed by gene knockout and overexpression experiments.Mechanistically,the LRR domain in Pijx interacts with and promotes the degradation of the ATP synthase β subunit(ATPb)via the 26S proteasome pathway.ATPb acts as a negative regulator of Pijx-mediated panicle blast resistance,and interacts with OsRbohC to promote its degradation.Consistently,loss of ATPb function causes an increase in NAPDH content and ROS burst.Remarkably,when Pijx is introgressed into two japonica rice varieties,the introgression lines show BSR and increased yields that are approximately 51.59%and 79.31%higher compared with those of their parents in a natural blast disease nursery.In addition,we generate PPL^(Pijx Pigm) and PPL^(Pijx Piz-t) pyramided lines and these lines also have higher BSR to panicle blast compared with Pigm-or Piz-t-containing rice plants.Collectively,this study demonstrates that Pijx not only confers BSR to M.oryzae but also maintains high and stable rice yield,providing new genetic resources and molecular targets for breeding rice varieties with broad-spectrum blast resistance.

Two ABCI family transporters,OsABCI15 and OsABCI16,are involved in grain-filling in rice

Seed development is critical for plant reproduction and crop yield,with panicle seed-setting rate,grain-filling,and grain weight being key seed characteristics for yield improvement.However,few genes are known to regulate grain filling.Here,we identify two adenosine triphosphate(ATP)-binding cassette(ABC)I-type transporter genes,OsABCI15 and OsABCI16,involved in rice grain-filling.Both genes are highly expressed in developing seeds,and their proteins are localized to the plasma membrane and cytosol.Interestingly,knockout of OsABCI15 and OsABCI16 results in a significant reduction in seed-setting rate,caused predominantly by the severe empty pericarp phenotype,which differs from the previously reported low seed-setting phenotype resulting from failed pollination.Further analysis indicates that OsABCI15 and OsABCI16 participate in ion homeostasis and likely export ions between filial tissues and maternal tissues during grain filling.Importantly,overexpression of OsABCI15 and OsABCI16 enhances the seed-setting rate and grain yield in transgenic plants and decreases ion accumulation in brown rice.Moreover,the OsABCI15/16 orthologues in maize exhibit a similar role in kernel development,as demonstrated by their disruption in transgenic maize.Therefore,ourfindings reveal the important roles of two ABC transporters in cereal grain filling,highlighting their value in crop yield improvement.

Introgression of qPE9-1 allele,conferring the panicle erectness,leads to the decrease of grain yield per plant in japonica rice(Oryza sativa L.)

Panicle architecture is closely related to yield formation. The qPE9-1 gene has been proved to be widely used in high-yield rice cultivar developments, conferring erect panicle character in japonica rice. Recently, qPE9-1 has been successfully cloned; however, the genetic effect on grain yield per plant of the erect panicle allele qPE9-1 is controversial yet. In the present study, a drooping panicle parent Nongken 57, carrying qpe9-1 allele, was used as recurrent parent to successively backcross to a typical erect panicle line from the double haploid （DH） population （Wuyunjing 8/Nongken 57）, which was previously shown to carry qPE9-1 allele. Thus a pair of near-isogenic lines （NILs） was developed. The comparison of agronomic traits between the NILs showed that, when qpe9-1 was replaced by qPE9-1, the panicle architecture was changed from drooping to erect; moreover, the panicle length, plant height, 1000-grain weight and the tillers were significantly decreased, consequently resulting in the dramatic decrease of grain yield per plant by 30%. Therefore, we concluded that the qPE9-1 was a major factor controlling panicle architecture, and qPE9-1 had pleiotropic nature, with negative effects on grain yield per plant. This result strongly suggests that the erect panicle allele qPEg-1 should be used together with other favorable genes in the high-yield breeding practice. In addition, the effect of qPE9-1 on eating and cooking quality was also discussed in the present study.

Development of gene-tagged molecular markers for starch synthesis-related genes in rice

Improving grain quality is an important goal in breeding new elite rice varieties,requiring effective tools for the identification of target genotypes.Molecular marker-aided selection(MAS),combined with conventional breeding approaches,enables us to pre-cisely identify the individual genotypes that are associated with different grain quality features,which can dramatically improve the breeding efficiency.However,to date,the number of molecular markers used in MAS for grain quality improvement is still somewhat limited.In this study,based on our previous study that rice grain quality is strongly associated with starch synthesis in the endosperm,we developed 51 gene-tagged molecular markers according to sequence variations in 18 starch synthesis-related genes from 16 typical rice cultivars.These markers can discriminate the different alleles among rice germplasms.These novel markers will provide effective tools in improving grain quality via the breeding new elite rice varieties.

Brassinosteroids function in spikelet differentiation and degeneration in rice

Brassinosteroids(BRs) play crucial roles in many aspects of plant development. However, their function in spikelet differentiation and degeneration in rice(Oryza sativa L.) remains unclear. Here, we investigated the roles of these phytohormones in spikelet development in fieldgrown rice subjected to five different nitrogen(N)fertilization treatments during panicle differentiation. BR levels and expression of genes involved in BR biosynthesis and signal transduction were measured in spikelets. Pollen fertility and the number of differentiated spikelets were closely associated with 24-epicastasterone(24-epiCS) and 28-homobrassinolide(28-homoBL) levels in spikelets.Enhanced BR biosynthesis and signal transduction, in response to N treatment, enhanced spikelet differentiation, reduced spikelet degeneration, and increased grain yield. Increases in proton-pumping ATPase activity, ATPconcentration, energy charge, and antioxidant system(AOS) levels were consistent with 24-epiCS and28-homoBL concentrations. Exogenous application of 24-epiCS or 28-homoBL on young panicles induced a marked increase in endogenous 24-epiCS or 28-homoBL levels, energy charge, AOS levels, spikelet differentiation, and panicle weight. The opposite effects were observed following treatment with a BR biosynthesis inhibitor. Our findings indicate that, in rice, BRs mediate the effects of N fertilization on spikelet development and play a role in promoting spikelet development through increasing AOS levels and energy charge during panicle development.

OsbZIP76 interacts with OsNF-YBs and regulates endosperm cellularization in rice (Oryza sativa)

Following double fertilization,plant endosperm nuclei undergo syncytial divisions,followed by synchro-nous cellularization.Cellularization is a key event during endosperm development,but our understanding of its regulation is limited to Arabidopsis.In this study we show that OsbZIP76 regulates cellularization in rice(Oryza sativa).Activation of OsbZIP76 coincided with the initiation of cellularization,and its knockdown or knockout mutants exhibited precocious cellularization.Genes involved in en-dosperm development or starch biosynthesis were pre-maturely activated in the osbzip76 caryopsis.As a putative transcription factor,OsbZIP76 alone lacked transcriptional activation activity;however,it interacted with the nuclear factor Y(NF-Y)family transcription factors OsNF-YB9 and OsNF-YB1 in yeast and in planta.OsbZIP76 and OsNF-YB9 were predominantly expressed in the endosperm and the proteins colocalized.Seeds of osnf-yb1 and osbzip76 mu-tants showed reduced size and reduced apparent amylose content.The parent-of-origin-dependent expression of OsbZIP76 is variable in different rice accessions.In sum-mary,OsbZIP76 is an endosperm-expressed imprinted gene that regulates endosperm development in rice.