Development of organelle single nucleotide polymorphism (SNP) markers and their application for the identification of cytoplasmic inheritance patterns in Pyropia yezoensis (Bangiales,Rhodophyta)

The genus Pyropia contains several important cultivated species.Genetic research in nori species has mainly focused on the cell nucleus,with few studies on organelles(chloroplast and mitochondria).Due to the high copy numbers of organelles in cells,which influence the development and traits of algae,it is necessary to study their genetic mechanism.In this study,the marine red alga Pyropia yezoensis,an important economic macroalga,was selected as the study object.To investigate organelle(chloroplast and mitochondria)inheritance in P.yezoensis,the wild type RZ(maternal strain)was crossed with the red mutant HT(paternal strain)and 30 color-sectors from 11 F1 gametophytic blades were examined.The complete chloroplast and mitochondrial genomes of the red mutant(HT)were assembled for the first time.One reliable and stable single nucleotide polymorphism(SNP)loci filtrated by bioinformatics analysis was used as a molecular marker for chloroplast and mitochondrial DNA,respectively,in subsequent experiments.PCR amplification and sequence analysis showed that the haplotypes of color-sectors detected were consistent with those of the maternal parent,confirming that both chloroplast and mitochondrial genomes were inherited maternally in P.yezoensis.The inheritance pattern of organelles in P.yezoensis can be used to guide the hybridization and breeding of nori.Additionally,the organelle SNP markers developed in this study can be applied in subsequent genetic research.

Construction of high-density genetic linkage map of Pyropia yezoensis(Bangiales,Rhodophyta)and identifi cation of red color trait QTLs in the thalli

Pyropia yezoensis is an important macroalga because of its extensive global distribution and economic importance.Color is an important trait in the thalli of P.yezoensis,it is also an effective marker to identify the hybridization in genetic breeding.In this study,a high-density genetic linkage map was constructed based on high-throughput single nucleotide polymorphism(SNP)markers,and used for analyzing the quantitative trait loci(QTLs)of red color trait in the thalli of P.yezoensis.The conchospore undergoes meiosis to develop into an ordered tetrad,and each cell has a haploid phenotype and can grow into a single individual.Based on this theory,F1 haploid population was used as the mapping population.The map included 531 SNP markers,394.57 cM long on average distance of 0.74 cM.Collinear analysis of the genetic linkage map and the physical map indicated that the coverage between the two maps was 79.42%.Furthermore,QTL mapping identified six QTLs for the chromosomal regions associated with the red color trait of the thalli.The value of phenotypic variance explained(PVE)by an individual QTL ranged from 4.71%-63.11%.And QTL qRed-1-1,with a PVE of 63.11%,was considered the major QTL.Thus,these data may provide a platform for gene and QTL fine mapping,and marker-assisted breeding in P.yezoensis in the future.

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.

A bestrophin-like protein modulates the proton motive force across the thylakoid membrane in Arabidopsis

During photosynthesis, photosynthetic electron transport generates a proton motive force （pmf） across the thylakoid membrane, which is used for ATP biosynthesis via ATP synthase in the chloroplast. The pmf is composed of an electric potential （△φ） and an osmotic component （△pH）. Partitioning between these components in chloroplasts is strictly regulated in response to fluctuating environments. However, our knowledge of the molecular mechanisms that regulate pmf partitioning is limited. Here, we report a bestrophin-like protein （AtBest）, which is critical for pmf partitioning. While the △pH component was slightly reduced in atbest, the △φ component was much greater in this mutant than in the wild type, resulting in less efficient activation of nonphotochemical quenching （NPQ） upon both illumination and a shift from low light to high light. Although no visible phenotype was observed in the atbest mutant in the greenhouse, this mutant exhibited stronger photoinhibition than the wild type when grown in the field. AtBest belongs to the bestrophin family proteins, which are believed to function as chloride （Cl^-） channels. Thus, our findings reveal an important Cl^- channel required for ion transport and homeo- stasis across the thylakoid membrane in higher plants. These processes are essential for fine-tuning photosynthesis under fluctuating environmental conditions.