Towards cultivar-oriented gene discovery for better crops

The continued expansion of the world population,increasingly inconsistent climate and shrinking agricultural resources present major challenges to crop breeding.Fortunately,the increasing ability to discover and manipulate genes creates new opportunities to develop more productive and resilient cultivars.Many genes have been described in papers as being beneficial for yield increase.However,few of them have been translated into increased yield on farms.In contrast,commercial breeders are facing gene decidophobia,i.e.,puzzled about which gene to choose for breeding among the many identified,a huge chasm between gene discovery and cultivar innovation.The purpose of this paper is to draw attention to the shortfalls in current gene discovery research and to emphasise the need to align with cultivar innovation.The methodology dictates that genetic studies not only focus on gene discovery but also pay good attention to the genetic backgrounds,experimental validation in relevant environments,appropriate crop management,and data reusability.The close of the gaps should accelerate the application of molecular study in breeding and contribute to future global food security.

A wheat integrative regulatory network from large-scale complementary functional datasets enables trait-associated gene discovery for crop improvement

Gene regulation is central to all aspects of organism growth,and understanding it using large-scale functional datasets can provide a whole view of biological processes controlling complex phenotypic traits in crops.However,the connection between massive functional datasets and trait-associated gene discovery for crop improvement is still lacking.In this study,we constructed a wheat integrative gene regulatory network(wGRN)by combining an updated genome annotation and diverse complementary functional datasets,including gene expression,sequence motif,transcription factor(TF)binding,chromatin accessibility,and evolutionarily conserved regulation.wGRN contains 7.2 million genome-wide interactions covering 5947 TFs and 127439 target genes,which were further verified using known regulatory relationships,condition-specific expression,gene functional information,and experiments.We used wGRN to assign genome-wide genes to 3891 specific biological pathways and accurately prioritize candidate genes associated with complex phenotypic traits in genome-wide association studies.In addition,wGRN was used to enhance the interpretation of a spike temporal transcriptome dataset to construct high-resolution networks.We further unveiled novel regulators that enhance the power of spike phenotypic trait prediction using machine learning and contribute to the spike phenotypic differences among modern wheat accessions.Finally,we developed an interactive webserver,wGRN(http://wheat.cau.edu.cn/wGRN),for the community to explore gene regulation and discover trait-associated genes.Collectively,this community resource establishes the foundation for using large-scale functional datasets to guide trait-associated gene discovery for crop improvement.

A telomere-to-telomere gap-free reference genome of watermelon and its mutation library provide important resources for gene discovery and breeding

Watermelon,Citrullus lanatus,is the world's third largest fruit crop.Reference genomes with gaps and a narrow genetic base hinder functional genomics and genetic improvement of watermelon.Here,we report the assembly of a telomere-to-telomere gap-free genome of the elite watermelon inbred line G42 by incorporating high-coverage and accurate long-read sequencing data with multiple assembly strategies.All 11 chromosomes have been assembled into single-contig pseudomolecules without gaps,representing the highest completeness and assembly quality to date.The G42 reference genome is 369321829 bp in length and contains 24205 predicted protein-coding genes,with all 22 telomeres and 11 centromeres characterized.Furthermore,we established a pollen-EMS mutagenesis protocol and obtained over 200000M1 seeds from G42.In a sampling pool,48 monogenic phenotypic mutations,selected from 223M1and 78 M2 mutants with morphological changes,were confirmed.The average mutation density was 1 SNP/1.69Mband1 indel/4.55 Mb per M1 plant and 1SNP/1.08Mb and 1 indel/6.25 Mb per M2 plant.Taking advantage of the gap-free G42 genome,8039 mutations from 32 plants sampled from M1 and M2 families were identified with 100%accuracy,whereas only 25% of the randomly selected mutations identified using the 97103v2 reference genome could be confirmed.Using this library and the gap-free genome,two genes responsible for elongated fruit shape and male sterility(CiMs1)were identified,both caused by a single basechange from G to A.The validated gap-free genome and its EMS mutation library provide invaluable resources for functional genomics and genetic improvement of watermelon.

Hitchhiking Effect Mapping: A New Approach for Discovering Agronomic Important Genes

Besides the natural selection, the crops cultivated today have experienced two episodes of strong artificial selection, domestic and modern breeding. Domestication led to giant genetic structure differentiation between cultivars and their wild species, while modern breeding made further genetic structure differentiation between the modern varieties and the landraces. In a population, diversity of the loci under strong selection is significantly lower than that of other loci. At the same time, diversity in the genomic regions flanking these selected loci also declines in the process of selection. This phenomenon is called hitchhiking effects or selection sweep in genetics. Genomic regions with selection sweep （haplotype block） could be detected after draft genome scanning （genome typing） with molecular markers in a number of released varieties or natural populations. Marker/trait association analysis in these regions would detect the loci （or QTLs） even the favored alleles （genes） in breeding or natural adaptation. Fine scanning of these genomic regions would help to determine the sizes of haplotype blocks and to discover the key genes, thereby providing very valuable information for isolation of the key genes and molecular design of new varieties. Establishment of high density genetic linkage maps in the major crops and availability of high throughput genotyping platform make it possible to discover agronomic important genes through marker/trait association analysis. On the basis of available publications, we give a brief introduction of the hitchhiking effect mapping approach in this paper using plant height, 1 000-grain weight, and phosphorus-deficiency tolerance as examples in wheat.

Identification of Genes Associated with Clubroot Resistance in Chinese Cabbage

The transcriptome-wide gene expression was compared between susceptible and resistant Chinese cabbage cultivars to identify genes that contributed to clubroot resistance. A higher number of differentially expressed genes were detected in susceptible cultivars than in resistant cultivars. Fifty-six genes involved in cell wall modification, hormone signaling, root marphogenesis, nematodes response and cell proliferation were uniquely expressed in the resistant cultivars. Among them, 27 genes were involved in cell wall modification and hormone signaling, indicating that genes in these two types might play a vital role in the defense response to pathogen infection.

Shaping Taste: The Molecular Discovery of Rice Genes Improving Grain Size, Shape and Quality

Modern-day human life is absolutely dependent upon the food that we derive from our crop plants. We eat grains, fruits, roots, tubers and other structures, all of which are constructed via coordinated organ growth. Whilst plant organ identity is first established in apical meristems （vegetative and floral shoot meristems and root meristems）, and in other meristematic regions, the final size and shape of organs are defined by subsequent coordination of organ expansion in longitudinal and transverse axes.

SoySNP618K array:A high-resolution single nucleotide polymorphism platform as a valuable genomic resource for soybean genetics and breeding

Innovations in genomics have enabled the development of low-cost,high-resolution,single nucleotide polymorphism(SNP)genotyping arrays that accelerate breeding progress and support basic research in crop science.Here,we developed and validated the Soy SNP618 K array(618,888 SNPs)for the important crop soybean.The SNPs were selected from whole-genome resequencing data containing 2,214 diverse soybean accessions;29.34%of the SNPs mapped to genic regions representing 86.85%of the 56,044annotated high-confidence genes.Identity-by-state analyses of 318 soybeans revealed 17 redundant accessions,highlighting the potential of the Soy SNP618 K array in supporting gene bank management.The patterns of population stratification and genomic regions enriched through domestication were highly consistent with previous findings based on resequencing data,suggesting that the ascertainment bias in the Soy SNP618 K array was largely compensated for.Genome-wide association mapping in combination with reported quantitative trait loci enabled fine-mapping of genes known to influence flowering time,E2 and Gm PRR3 b,and of a new candidate gene,Gm VIP5.Moreover,genomic prediction of flowering and maturity time in 502 recombinant inbred lines was highly accurate(>0.65).Thus,the Soy SNP618 K array is a valuable genomic tool that can be used to address many questions in applied breeding,germplasm management,and basic crop research.

Vegetable biology and breeding in the genomics era

Vegetable crops provide a rich source of essential nutrients for humanity and represent critical economic values to global rural societies. However, genetic studies of vegetable crops have lagged behind major food crops, such as rice, wheat and maize,thereby limiting the application of molecular breeding. In the past decades, genome sequencing technologies have been increasingly applied in genetic studies and breeding of vegetables. In this review, we recapitulate recent progress on reference genome construction, population genomics and the exploitation of multi-omics datasets in vegetable crops. These advances have enabled an in-depth understanding of their domestication and evolution, and facilitated the genetic dissection of numerous agronomic traits, which jointly expedites the exploitation of state-of-the-art biotechnologies in vegetable breeding. We further provide perspectives of further directions for vegetable genomics and indicate how the ever-increasing omics data could accelerate genetic, biological studies and breeding in vegetable crops.

Design and construction of microbial cell factories based on systems biology

Environmental sustainability is an increasingly important issue in industry.As an environmentally friendly and sustainable way,constructing microbial cell factories to produce all kinds of valuable products has attracted more and more attention.In the process of constructing microbial cell factories,systems biology plays a crucial role.This review summarizes the recent applications of systems biology in the design and construction of microbial cell factories from four perspectives,including functional genes/enzymes discovery,bottleneck pathways identification,strains tolerance improvement and design and construction of synthetic microbial consortia.Systems biology tools can be employed to identify functional genes/enzymes involved in the biosynthetic pathways of products.These discovered genes are introduced into appropriate chassis strains to build engineering microorganisms capable of producing products.Subsequently,systems biology tools are used to identify bottleneck pathways,improve strains tolerance and guide design and construction of synthetic microbial consortia,resulting in increasing the yield of engineered strains and constructing microbial cell factories successfully.

Exploiting Natural Variation in Tomato to Define Pathway Structure and Metabolic Regulation of Fruit Polyphenolics in the Lycopersicum Complex

While the structures of plant primary metabolic pathways are generally well defined and highly conserved across species,those defining specialized metabolism are less well characterized and more highly variable across species.In this study,we investigated polyphenolic metabolism in the lycopersicum complex by characterizing the underlying biosynthetic and decorative reactions that constitute the metabolic network of polyphenols across eight different species of tomato.For this purpose,GC-MS-and LC-MS-based metabolomics of different tissues of Solatium lycopersicum and wild tomato species were carried out,in concert with the evaluation of cross-hybridized microarray data for MapMan-based transcriptomic analysis,and publicly available RNA-sequencing data for annotation of biosynthetic genes.The combined data were used to compile species-specific metabolic networks of polyphenolic metabolism,allowing the establishment of an entire pan-species biosynthetic framework as well as annotation of the functions of decoration enzymes involved in the formation of metabolic diversity of the flavonoid pathway.The combined results are discussed in the context of the current understanding of tomato flavonol biosynthesis as well as a global view of metabolic shifts during fruit ripening.Our results provide an example as to how large-scale biology approaches can be used for the definition and refinement of large specialized metabolism pathways.

Functional Genomics of Wood Quality and Properties

Genomics promises to enrich the investigations of biology and biochemistry. Current advancements in genomics have major implications for genetic improvement in animals, plants, and microorganisms, and for our understanding of cell growth, development, differentiation, and communication. Significant progress has been made in the understanding of plant genomics in recent years, and the area continues to progress rapidly. Functional genomics offers enormous potential to tree improvement and the understanding of gene expression in this area of science worldwide. In this review we focus on functional genomics of wood quality and properties in trees, mainly based on progresses made in genomics study of Pinus and Populus. The aims of this review are to summarize the current status of functional genomics including: (1) Gene discovery; (2) EST and genomic sequencing; (3) From EST to functional genomics; (4) Approaches to functional analysis; (5) Engineering lignin biosynthesis; (6) Modification of cell wall biogenesis; and (7) Molecular modelling. Functional genomics has been greatly invested worldwide and will be important in identifying candidate genes whose function is critical to all aspects of plant growth, development, differentiation, and defense. Forest biotechnology industry will significantly benefit from the advent of functional genomics of wood quality and properties.