Development of plant cytosine base editors with the Cas12a system

Base editors of the Cas9 system have been widely used for precise nucleotide substitution in crops. In this study, Cas12a was applied to construct plant cytosine base editors(CBEs). The main elements of Cas12aCBEs were engineered and their efficiency was evaluated in stably transformed rice cells. An optimized ttCas12a-hyA3Bctd editor, consisting of a LbCas12a variant carrying catalytic inactive D832A and temperature-tolerance D156R double mutations, a truncated human APOBEC3B deaminase, a human RAD51 single-stranded DNA-binding domain, and double copies of UGI, outperformed other Cas12aCBEs in base editing efficiency. In T0transgenic rice plants, ttCas12a-hyA3Bctd edited an average of42.01% and a maximum of 68.75% of lines at six genomic targets. A-to-G conversions were generated in rice by an adenine base editor with a similar architecture to the optimized CBE. Our results provide preliminary evidence for the feasibility of robust and efficient plant Cas12a base editing systems, which could be useful for precise crop breeding.

Increasing fidelity and efficiency by modifying cytidine base-editing systems in rice

The efficiency of plant cytidine base-editing systems is limited, and unwanted mutations frequently occur in transgenic plants. We increased the cytidine editing frequency and fidelity of the plant base editor 3(BE3) and targeted activation-induced cytidine deaminase(CDA)(target-AID) systems by coexpressing three copies of free uracil–DNA glycosylase(UDG) inhibitor(UGI). The editing efficiency of the improved BE3 and CDA systems reached as high as 88.9% and 85.7%, respectively, in regenerated rice plants, with a very low frequency of unwanted mutations. The low editing frequency of the BE3 system in the GC context could be overcome by the modified CDA system. These results provide a highfidelity and high-efficiency solution for rice genomic base editing.

Pt-Re/rGO bimetallic catalyst for highly selective hydrogenation of cinnamaldehyde to cinnamylalcohol

In the present work, a series of Pt-based catalysts, alloyed with a second metal, i.e., Re, Sn, Er, La, and Y, and supported on activated carbon, ordered mesoporous carbon, N-doped mesoporous carbon or reduced graphene oxide(rGO), have been developed for selective hydrogenation of cinnamaldehyde to cinnamylalcohol. Re and rGO were proved to be the most favorable metal dopant and catalyst support, respectively. Pt_(50) Re_(50)/rGO showed the highest cinnamylalcohol selectivity of 89% with 94% conversion of cinnamaldehyde at the reaction conditions of 120 °C, 2.0 MPaH_2 and 4 h.

Prime editing-mediated precise knockin of protein tag sequences in the rice genome

Dear Editor,Accurately labeling proteins in living plant cells has long been a challenge and can be addressed by targeted insertion of tag sequences in a given locus.Recent optimized plant prime editors(PEs)enable efficient programmable installation of small insertions or deletions,including insertions of short sequences(Li et al.,2022a,2022b;Jiang et al.,2022;Xu et al.,2022;Zong et al.,2022;Zou et al.,2022).To investigate whether prime editing can be used to tag endogenous proteins in rice,we made use of the enpPE2 system described in our previous report(Li et al.,2022b).

Genome editing mediated by SpCas9 variants with broad non-canonical PAM compatibility in plants

Streptococcus pyogenes Cas9(SpCas9)is the most widely used genome editing tool in plants.The editing induced by SpCas9 strictly requires a canonical NGG protospacer-adjacent motif(PAM),significantly limiting its scope of application.Recently,five SpCas9 variants,SpCas9-NRRH,SpCas9-NRCH,SpCas9-NRTH,SpG,and SPRY,were developed to recognize non-canonical PAMs in human cells.In this study,these variants were engineered for plant genome editing,and their targeted mutagenesis capabilities were comprehensively examined at various canonical and non-canonical PAM sites in rice(Oryza sativa)by stable transformation.Moreover,both cytosine base editors using a rat APOBEC1 or a human APO-BEC3a and adenine base editors using a directly evolved highly compatible TadA*-8e deaminase were developed from these SpCas9 variants.Our results demonstrated that the developed SpCas9 variantsbased base editors readily generated conversions between C.G and T.A in the target sites with noncanonical PAMs in transgenic rice lines.Collectively,the toolbox developed in this study substantially expands the scope of SpCas9-mediated genome editing and will greatly facilitate gene disruption and precise editing in plants.

Development of an efficient plant dual cytosine and adenine editor

An enhanced CDA-like(eCDAL)was established from Japanese lamprey CDA1-like 4 to achieve a high editing frequency in a broad region as a C-terminal cytosine base editors(CT-CBE).Then,a novel plant dual-base editor version1(pDuBE1)was developed by integrating TadA-8e into eCDAL.The editing efficiency of pDuBE1 could reach to 87.6%,with frequencies of concurrent A-to-G and C-to-T conversions as high as 49.7%in stably transformed plant cells.Our results showed that pDuBE1 could mediate robust dual editing in plant genome,providing a powerful manipulation tool for precise crop breeding and screening platforms for in planta direct evolution.

Development of Plant Prime-Editing Systems for Precise Genome Editing

Prime-editing systems have the capability to perform efficient and precise genome editing in human cells.In this study,we first developed a plant prime editor 2(pPE2)system and test its activity by generating a targeted mutation on an HPT^(-ATG) reporter in rice.Our results showed that the pPE2 system could induce programmable editing at different genome sites.In transgenic T0 plants,pPE2-generated mutants occurred with 0%–31.3%frequency,suggesting that the efficiency of pPE2 varied greatly at different genomic sites and with prime-editing guide RNAs of diverse structures.To optimize editing efficiency,guide RNAs were introduced into the pPE2 system following the PE3 and PE3b strategy in human cells.However,at the genomic sites tested in this study,pPE3 systems generated only comparable or even lower editing frequencies.Furthemore,we developed a surrogate pPE2 system by incorporating the HPT^(-ATG) reporter to enrich the prime-edited cells.The nucleotide editing was easily detected in the resistant calli transformed with the surrogate pPE2 system,presumably due to the enhanced screening efficiency of edited cells.Taken together,our results indicate that plant prime-editing systems we developed could provide versatile and flexible editing in rice genome.

Atomically precise metal-chalcogenide semiconductor molecular nanoclusters with high dispersibility:Designed synthesis and intracluster photocarrier dynamics

A comprehensive understanding of excited-state dynamics of semiconductor quantum dots or nanomaterials at the atomic or molecular level is of scientific importance.Pure inorganic(or non-covalently protected)seimiconductor molecular nanoclusters with atomically precise structure are contributive to establish accurate correlation of excited-state dynamics with their composition/structure,however,the related studies are almost blank because of unresolved solvent dispersion issue.Herein,we designedly created the largest discrete chalcogenide seimiconductor molecular nanoclusters(denoted P2-CuMSnS,M=In or/and Ga)with great dispersibility,and revealed an interesting intracluster“core–shell”charge transfer relaxation dynamics.A systematic red shift in absorption spectra with the gradual substitution of In by Ga was experimentally and computationally investigated,and femtosecond transient absorption measurements further manifested there were three ultrafast processes in excited-state dynamics of P2 nanoclusters with the corresponding amplitudes directed by composition variation.Current results hold the great promise of the solution-processible applications of semiconductor-NC-based quantum dots and facilitate the development of atomically precise nano-chemistry.

Surface protection method for the magnetic core using covalent organic framework shells and its application in As(Ⅲ)depth removal from acid wastewater

Fe_(3)O_(4)-based materials are widely used for magnetic separation from wastewater.However,they often suffer from Fe-leaching behavior under acidic conditions,decreasing their ac-tivity and limiting sustainable practical applications.In this study,covalent organic frame-works(COFs)were used as the shell to protect the Fe_(3)O_(4) core,and the Fe_(3)O_(4)@COF core-shell composites were synthesized for As(Ⅲ)removal from acid wastewater.The imine-linked COFs can in situ grow on the surface of the Fe_(3)O_(4) core layer by layer with[COFs/Fe_(3)O_(4)]mol ratio of up to 2∶1.The Fe-leaching behavior was weakened over a wide pH range of 1-13.Moreover,such composites keep their magnetic characteristic,making them favorable for nanomaterial separation.As(Ⅲ)batch adsorption experiments results indicated that,when COFs are used as the shell for the Fe_(3)O_(4) core,a balance between As(Ⅲ)removal efficiencies and the thickness of the COF shell exists.Higher As(Ⅲ)removal efficiencies are obtained when the[COFs/Fe_(3)O_(4)]mol ratios were<1.5∶1,but thicker COF shells were not beneficial for As(Ⅲ)removal.Such composites also exhibited better As(Ⅲ)removal performances in the pH range of 1-7.Over a wide pH range,the zeta potential of Fe_(3)O_(4)@COF core-shell compos-ites becomes more positive,which benefits the capture of negative arsenic ions.In addition,thinner surface COFs were favorable for mass transfer and facilitating the reaction of Fe and As elements.Our study highlights the promise of using COFs in nanomaterial surface protection and achieving As(Ⅲ)depth removal under acidic conditions.