Generation of low-cadmium rice germplasms via knockout of OsLCD using CRISPR/Cas9

The OsLCD gene,which has been implicated in cadmium (Cd) accumulation in rice,might be a useful target for CRISPR/Cas9 editing.However,the effects of Os LCD gene editing on Cd accumulation,plant growth,and yield traits remain unknown.Here,we used CRISPR/Cas9to generate oslcd single mutants from indica and japonica rice cultivars.We also generated osnramp5 single mutants and oslcd osnramp5 double mutants in the indica background.When grown in Cd-contaminated paddy soils,all oslcd single mutants accumulated less Cd than the wild types (WTs).Consistent with this,oslcd single mutants grown in Cd-contaminated hydroponic culture accumulated significantly less Cd in the shoots as compared to WTs.This decrease in accumulation probably resulted from the reduction of Cd translocation under Cd stress.Oxidative damage also decreased,and plant growth increased in all oslcd single mutant seedlings as compared to WTs in the presence of Cd.Plant growth and most yield traits,as well essential element concentrations in rice seedling shoots,brown rice,and rice straw,were similar between oslcd single mutants and WTs.In the presence of Cd,Cd concentrations in the brown rice and shoots of oslcd osnramp5 double mutants were significantly decreased compared with WTs as well as osnramp single mutants.Our results suggested that OsL CD knockout may reduce Cd accumulation alone or in combination with other knockout mutations in a variety of rice genotypes;unlike Os Nramp5 mutations,Os LCD knockout did not reduce essential element contents.Therefore,Os LCD knockout might be used to generate low-Cd rice germplasms.

Using PyC modified 3D carbon fiber to reinforce UHTC under low temperature sintering without pressure

Finding the optimum balance between strength and toughness,as well as acquiring reliable thermal shock resistance and oxidation resistance,has always been the most concerned topic in the discussion of ultra-high temperature ceramic composites.Herein,PyC modified 3D carbon fiber is used to reinforce ultra-high temperature ceramic(UHTC).The macroscopic block composite with large size is successfully fabricated through low temperature sintering at 1300℃without pressure.The prepared PyC modified 3D C_(f)/ZrC-SiC composites simultaneously possess excellent physical and chemical stability under the synergistic effect of PyC interface layer and low temperature 1/2 sintering without pressure.The fracture toughness is increased in magnitude to 13.05±1.72 MPa·m^(1/2)accompanied by reliable flexural strength of 251±27 MPa.After rapid thermal shock spanning from room temperature(RT)to 1200℃,there are no visible surface penetrating cracks,spalling,or structural fragmentation.The maximum critical temperature difference reaches 875℃,which is nearly three times higher than that of traditional monolithic ceramics.The haunting puzzle of intrinsic brittleness and low damage tolerance are resolved fundamentally.Under the protection of PyC interface layer,the carbon fibers around oxide layer and matrix remain structure intact after static oxidation at 1500℃for 30 min.The oxide layer has reliable physical and chemical stability and resists the erosion from fierce oxidizing atmosphere,ensuring the excellent oxidation resistance of the composites.In a sense,the present work provides promising universality in designability and achievement of 3D carbon fiber reinforced ceramic composites.

Comparative physiological and transcriptomic analyses illuminate common mechanisms by which silicon alleviates cadmium and arsenic toxicity in rice seedlings

The inessential heavy metal/loids cadmium(Cd)and arsenic(As),which often co-occur in polluted paddy soils,are toxic to rice.Silicon(Si)treatment is known to reduce Cd and As toxicity in rice plants.To better understand the shared mechanisms by which Si alleviates Cd and As stress,rice seedlings were hydroponically exposed to Cd or As,then treated with Si.The addition of Si significantly ameliorated the inhibitory effects of Cd and As on rice seedling growth.Si supplementation decreased Cd and As translocation from roots to shoots,and significantly reduced Cd-and As-induced reactive oxygen species generation in rice seedlings.Transcriptomics analyses were conducted to elucidate molecular mechanisms underlying the Si-mediated response to Cd or As stress in rice.The expression patterns of the differentially expressed genes in Cd-or As-stressed rice roots with and without Si application were compared.The transcriptomes of the Cd-and As-stressed rice roots were similarly and profoundly reshaped by Si application,suggesting that Si may play a fundamental,active role in plant defense against heavy metal/loid stresses by modulating whole genome expression.We also identified two novel genes,0s01g0524500 and 0s06g0514800,encoding a myeloblastosis(MYB)transcription factor and a thionin,respectively,which may be candidate targets for Si to alleviate Cd and As stress in rice,as well as for the generation of Cd-and/or As-resistant plants.This study provides valuable resources for further clarification of the shared molecular mechanisms underlying the Si-mediated alleviation of Cd and As toxicity in rice.

Comparative transcriptomics provide new insights into the mechanisms by which foliar silicon alleviates the effects of cadmium exposure in rice

Silicon(Si)has been shown to alleviate Cd stress in rice.Here,we investigated the beneficial effects of foliar Si in an indica rice Huanghuazhan(HHZ).Our results showed that foliar Si in-creases the dry weight and decreases Cd translocation in Cd-exposed rice at the grain-filling stage only,implying that the filling stage is critical for foliar Si to reduce Cd accumulation.We also investigated the transcriptomics in flag leaves(FLs),spikelets(SPs),and node Is(NIs)of Cd-exposed HHZ after foliar Si application at the filling stage.Importantly,the gene expression profiles associated with the Si-mediated alleviation of Cd stress were tissue spe-cific,while shared pathways were mediated by Si in Cd-exposed rice tissues.Furthermore,after the Si treatment of Cd-exposed rice,the ATP-binding cassette(ABC)-transporters were mostly upregulated in FL and SP,while the bivalent cation transporters were mostly down-regulated in FL and NI,possibly helping to reduce Cd accumulation.The genes associated with essential nutrient transporters,carbohydrate and secondary metabolite biosynthesis,and cytochrome oxidase activity were mostly upregulated in Cd-exposed FL and SP,which may help to alleviate oxidative stress and improve plant growth under Cd exposure.Inter-estingly,genes responsible for signal transduction were negatively regulated in FL,but pos-itively regulated in SP,by foliar Si.Our results provide transcriptomic evidence that foliar Si plays an active role in alleviating the effects of Cd exposure in rice.In particular,foliar Si may alter the expression pattern of genes associated with transport,biosynthesis and metabolism,and oxidation reduction.