The integrated genomics of crop domestication and breeding.

As a major event in human civilization, wild plants were successfully domesticated to be crops, largely owing to continuing artificial selection. Here, we summarize new discoveries made during the past decade in crop domestication and breeding. The construction of crop genome maps and the functional characterization of numerous trait genes provide foundational information. Approaches to read, interpret, and write complex genetic information are being leveraged in many plants for highly efficient de novo or re-domestication. Understanding the underlying mechanisms of crop microevolution and applying the knowledge to agricultural productions will give possible solutions for future challenges in food security.

Pan-Genome of Wild and Cultivated Soybeans.

Soybean is one of the most important vegetable oil and protein feed crops. To capture the entire genomic diversity, it is needed to construct a complete high-quality pan-genome from diverse soybean accessions. In this study, we performed individual de novo genome assemblies for 26 representative soybeans that were selected from 2,898 deeply sequenced accessions. Using these assembled genomes together with three previously reported genomes, we constructed a graph-based genome and performed pan-genome analysis, which identified numerous genetic variations that cannot be detected by direct mapping of short sequence reads onto a single reference genome. The structural variations from the 2,898 accessions that were genotyped based on the graph-based genome and the RNA sequencing (RNA-seq) data from the representative 26 accessions helped to link genetic variations to candidate genes that are responsible for important traits. This pan-genome resource will promote evolutionary and functional genomics studies in soybean.

The WD40 domain-containing protein Ehd5 positively regulates flowering in rice (Oryza sativa).

Heading date (flowering time), which greatly influences regional and seasonal adaptability in rice (Oryza sativa), is regulated by many genes in different photoperiod pathways. Here, we characterized a heading date gene, Early heading date 5 (Ehd5), using a modified bulked segregant analysis method. The ehd5 mutant showed late flowering under both short-day and long-day conditions, as well as reduced yield, compared to the wild type. Ehd5, which encodes a WD40 domain-containing protein, is induced by light and follows a circadian rhythm expression pattern. Transcriptome analysis revealed that Ehd5 acts upstream of the flowering genes Early heading date 1 (Ehd1), RICE FLOWERING LOCUS T 1 (RFT1), and Heading date 3a (Hd3a). Functional analysis showed that Ehd5 directly interacts with Rice outermost cell-specific gene 4 (Roc4) and Grain number, plant height, and heading date 8 (Ghd8), which might affect the formation of Ghd7-Ghd8 complexes, resulting in increased expression of Ehd1, Hd3a, and RFT1. In a nutshell, these results demonstrate that Ehd5 functions as a positive regulator of rice flowering and provide insight into the molecular mechanisms underlying heading date.

CropGS-Hub: a comprehensive database of genotype and phenotype resources for genomic prediction in major crops.

The explosive amount of multi-omics data has brought a paradigm shift both in academic research and further application in life science. However, managing and reusing the growing resources of genomic and phenotype data points presents considerable challenges for the research community. There is an urgent need for an integrated database that combines genome-wide association studies (GWAS) with genomic selection (GS). Here, we present CropGS-Hub, a comprehensive database comprising genotype, phenotype, and GWAS signals, as well as a one-stop platform with built-in algorithms for genomic prediction and crossing design. This database encompasses a comprehensive collection of over 224 billion genotype data and 434 thousand phenotype data generated from >30 000 individuals in 14 representative populations belonging to 7 major crop species. Moreover, the platform implemented three complete functional genomic selection related modules including phenotype prediction, user model training and crossing design, as well as a fast SNP genotyper plugin-in called SNPGT specifically built for CropGS-Hub, aiming to assist crop scientists and breeders without necessitating coding skills. CropGS-Hub can be accessed at https://iagr.genomics.cn/CropGS/.

A point mutation in the meiotic crossover formation gene HEI10/TFS2 leads to thermosensitive genic sterility in rice.

Thermosensitive genic female sterility (TGFS) is a promising property to be utilized for hybrid breeding. Here, we identified a rice TGFS line, tfs2, through an ethyl methyl sulfone (EMS) mutagenesis strategy. This line showed sterility under high temperature and became fertile under low temperature. Few seeds were produced when the tfs2 stigma was pollinated, indicating that tfs2 is female sterile. Gene cloning and genetic complementation showed that a point mutation from leucine to phenylalanine in HEI10 (HEI10tfs2), a crossover formation protein, caused the TGFS trait of tfs2. Under high temperature, abnormal univalents were formed, and the chromosomes were unequally segregated during meiosis, similar to the reported meiotic defects in oshei10. Under low temperature, the number of univalents was largely reduced, and the chromosomes segregated equally, suggesting that crossover formation was restored in tfs2. Yeast two-hybrid assays showed that HEI10 interacted with two putative protein degradation-related proteins, RPT4 and SRFP1. Through transient expression in tobacco leaves, HEI10 were found to spontaneously aggregate into dot-like foci in the nucleus under high temperature, but HEI10tfs2 failed to aggregate. In contrast, low temperature promoted HEI10tfs2 aggregation. This result suggests that protein aggregation at the crossover position contributes to the fertility restoration of tfs2 under low temperature. In addition, RPT4 and SRFP1 also aggregated into dot-like foci, and these aggregations depend on the presence of HEI10. These findings reveal a novel mechanism of fertility restoration and facilitate further understanding of HEI10 in meiotic crossover formation.

Temperature and light reverse the fertility of rice P/TGMS line ostms19 via reactive oxygen species homeostasis.

P/TGMS (Photo/thermo-sensitive genic male sterile) lines are crucial resources for two-line hybrid rice breeding. Previous studies revealed that slow development is a general mechanism for sterility-fertility conversion of P/TGMS in Arabidopsis. However, the difference in P/TGMS genes between rice and Arabidopsis suggests the presence of a distinct P/TGMS mechanism in rice. In this study, we isolated a novel P/TGMS line, ostms19, which shows sterility under high-temperature conditions and fertility under low-temperature conditions. OsTMS19 encodes a novel pentatricopeptide repeat (PPR) protein essential for pollen formation, in which a point mutation GTA(Val) to GCA(Ala) leads to ostms19 P/TGMS phenotype. It is highly expressed in the tapetum and localized to mitochondria. Under high temperature or long-day photoperiod conditions, excessive ROS accumulation in ostms19 anthers during pollen mitosis disrupts gene expression and intine formation, causing male sterility. Conversely, under low temperature or short-day photoperiod conditions, ROS can be effectively scavenged in anthers, resulting in fertility restoration. This indicates that ROS homeostasis is critical for fertility conversion. This relationship between ROS homeostasis and fertility conversion has also been observed in other tested rice P/TGMS lines. Therefore, we propose that ROS homeostasis is a general mechanism for the sterility-fertility conversion of rice P/TGMS lines.

Armadillo repeat only protein GS10 negatively regulates brassinosteroid signaling to control rice grain size.

Grain yield and grain quality are major determinants in modern breeding controlled by many quantitative traits loci (QTLs) in rice (Oryza sativa). However, the mechanisms underlying grain shape and quality are poorly understood. Here, we characterize a QTL for grain size and grain quality via map-based cloning from wild rice (W1943), GS10 (Grain Size on Chromosome 10), which encodes a protein with 6 tandem armadillo repeats. The null mutant gs10 shows slender and narrow grains with altered cell size, which has a pleiotropic effect on other agronomical traits. Functional analysis reveals that GS10 interacts with TUD1 (Taihu Dwarf1) and is epistatic to OsGSK2 (glycogen synthase kinase 2) through regulating grain shape and lamina joint inclination, indicating it is negatively involved in brassinosteroid (BR) signaling. Pyramiding gs10 and the grain size gene GW5 into cultivar GLA4 substantially improved grain shape and appearance quality. Natural variation analysis revealed that gs10 from the wild rice Oryza rufipogon W1943 is a rare allele across the rice population. Collectively, these findings advance our understanding of the underlying mechanism of grain shape and provide the beneficial allele of gs10 for future rice breeding and genetic improvement.

FKF1b controls reproductive transition associated with adaptation to geographical distribution in maize.

Maize (Zea mays subspecies mays) is an important commercial crop across the world, and its flowering time is closely related to grain yield, plant cycle and latitude adaptation. FKF1 is an essential clock-regulated blue-light receptor with distinct functions on flowering time in plants, and its function in maize remains unclear. In this study, we identified two FKF1 homologs in the maize genome, named ZmFKF1a and ZmFKF1b, and indicated that ZmFKF1a and ZmFKF1b independently regulate reproductive transition through interacting with ZmCONZ1 and ZmGI1 to increase the transcription levels of ZmCONZ1 and ZCN8. We demonstrated that ZmFKF1b underwent artificial selection during modern breeding in China probably due to its role in geographical adaptation. Furthermore, our data suggested that ZmFKF1bHap_C7 may be an elite allele, which increases the abundance of ZmCONZ1 mRNA more efficiently and adapt to a wider range of temperature zone than that of ZmFKF1bHap_Z58 to promote maize floral transition. It extends our understanding of the genetic diversity of maize flowering. This allele is expected to be introduced into tropical maize germplasm to enrich breeding resources and may improve the adaptability of maize at different climate zones, especially at temperate region.

Low temperature compensates for defective tapetum initiation to restore the fertility of the novel TGMS line ostms15.

In rice breeding, thermosensitive genic male sterility (TGMS) lines based on the tms5 locus have been extensively employed. Here, we reported a novel rice TGMS line ostms15 (Oryza sativa ssp. japonica ZH11) which show male sterility under high temperature and fertility under low temperature. Field evaluation from 2018 to 2021 revealed that its sterility under high temperature is more stable than that of tms5 (ZH11), even with occasional low temperature periods, indicating its considerable value for rice breeding. OsTMS15 encodes an LRR-RLK protein MULTIPLE SPOROCYTE1 (MSP1) which was reported to interact with its ligand to initiate tapetum development for pollen formation. In ostms15, a point mutation from GTA (Val) to GAA (Glu) in its TIR motif of the LRR region led to the TGMS phenotype. Cellular observation and gene expression analysis showed that the tapetum is still present in ostms15, while its function was substantially impaired under high temperature. However, its tapetum function was restored under low temperature. The interaction between mOsTMS15 and its ligand was reduced while this interaction was partially restored under low temperature. Slow development was reported to be a general mechanism of P/TGMS fertility restoration. We propose that the recovered protein interaction together with slow development under low temperature compensates for the defective tapetum initiation, which further restores ostms15 fertility. We used base editing to create a number of TGMS lines with different base substitutions based on the OsTMS15 locus. This work may also facilitate the mechanistic investigation and breeding of other crops.

Natural variation of ZmLNG1 alters organ shapes in maize.

The development of a series of elite maize hybrids has greatly increased crop yield in the past decades. Parental lines of these hybrids usually come from different heterotic groups and contain many genetic differences. Identifications of important quantitative trait genes in the elite hybrids can extend our understanding of heterosis and also help to guide genetic improvement. Here, we mapped a major quantitative trait locus using a linkage population from an elite maize hybrid Zhengdan958 and identified ZmLNG1 as the causative gene controlling multiple morphologic traits in maize. A 6-kb deletion in one parental line of the hybrid leads to the fusion of ZmLNG1 with its nearby gene. The fusion event prevents the C-terminal of ZmLNG1 from interacting with ZmTON1, which resulted in the change of plant architecture. Further experiments demonstrated that ZmLNG1 could act as a mediator to connect ZmTON1 and ZmOFPs, which belong to another type of plant morphological regulatory proteins, thereby affecting the phosphorylation level of ZmOFPs. These results demonstrate the importance of ZmLNG1 in forming the TON1-TRM-PP2A complex and provide a model for the regulation of plant organ morphology by TON1-recruiting motifs (TRMs) and Ovate family proteins (OFPs).

The nitrate transporter OsNPF7.9 mediates nitrate allocation and the divergent nitrate use efficiency between indica and japonica rice.

Nitrate allocation in Arabidopsis (Arabidopsis thaliana) represents an important mechanism for mediating plant environmental adaptation. However, whether this mechanism occurs or has any physiological/agronomic importance in the ammoniphilic plant rice (Oriza sativa L.) remains unknown. Here, we address this question through functional characterization of the Nitrate transporter 1/Peptide transporter Family (NPF) transporter gene OsNPF7.9. Ectopic expression of OsNPF7.9 in Xenopus oocytes revealed that the gene encodes a low-affinity nitrate transporter. Histochemical and in-situ hybridization assays showed that OsNPF7.9 expresses preferentially in xylem parenchyma cells of vasculature tissues. Transient expression assays indicated that OsNPF7.9 localizes to the plasma membrane. Nitrate allocation from roots to shoots was essentially decreased in osnpf7.9 mutants. Biomass, grain yield, and nitrogen use efficiency (NUE) decreased in the mutant dependent on nitrate availability. Further analysis demonstrated that nitrate allocation mediated by OsNPF7.9 is essential for balancing rice growth and stress tolerance. Moreover, our research identified an indica-japonica divergent single-nucleotide polymorphism occurring in the coding region of OsNPF7.9, which correlates with enhanced nitrate allocation to shoots of indica rice, revealing that divergent nitrate allocation might represent an important component contributing to the divergent NUE between indica and japonica subspecies and was likely selected as a favorable trait during rice breeding.

A retrotransposon insertion in MUTL-HOMOLOG 1 affects wild rice seed set and cultivated rice crossover rate.

Wild rice (Oryza rufipogon) has a lower panicle seed setting rate (PSSR) and gamete fertility than domesticated rice (Oryza sativa), but the genetic mechanisms of this phenomenon remain unknown. Here, we cloned a null allele of OsMLH1, an ortholog of MutL-homolog 1 to yeast and mammals, from wild rice O. rufipogon W1943 and revealed a 5.4-kb retrotransposon insertion in OsMLH1 is responsible for the low PSSR in wild rice. In contrast to the wild-type, a near isogenic line NIL-mlh1 exhibits defective crossover (CO) formation during meiosis, resulting in reduced pollen viability, partial embryo lethality, and low PSSR. Except for the mutant of mismatch repair gene postmeiotic segregation 1 (Ospms1), all other MutL mutants from O. sativa indica subspecies displayed male and female semi-sterility similar to NIL-mlh1, but less severe than those from O. sativa japonica subspecies. MLH1 and MLH3 did not contribute in an additive fashion to fertility. Two types of MutL heterodimers, MLH1-PMS1 and MLH1-MLH3, were identified in rice, but only the latter functions in promoting meiotic CO formation. Compared to japonica varieties, indica cultivars had greater numbers of CO events per meiosis. Our results suggest that low fertility in wild rice may be caused by different gene defects, and indica and japonica subspecies have substantially different CO rates responsible for the discrepancy between the fertility of mlh1 and mlh3 mutants.

Deleterious mutations are characterized by higher genomic heterozygosity than other genic variants in plant genomes.

Deleterious mutations can reduce the fitness of crop varieties, which limits the plant breeding efficacy. While crop deleterious mutations have been extensively examined, most studies focused on one specific crop with different analyzing methods, which hinders unveiling shared genomic characteristics of deleterious mutations across diverse crops. Here we used standardized approaches to characterize the deleterious mutations in genomes of domesticated inbreeding (i.e., rice, soybean, and tomato) and clonally propagated crops (i.e., grape and pineapple). We found that deleterious mutations are commonly targeted by purifying selection, and are over-presented in a nearly fixed derived allele frequency in the course of plant domestication. Further, a generally negative correlation between genetic load and the artificial selection strength is observed. Importantly, we consistently uncovered the higher derived genomic heterozygosity for deleterious mutations compared to other genic variants. This study broadens our understanding of the evolution of deleterious mutations in plant genomes.

Deep-learning-based automatic evaluation of rice seed germination rate.

BACKGROUND: Rice is an important food crop plant in the world and is also a model plant for genetics and breeding research. The germination rate is an important indicator that measures the performance of rice seeds. Currently, solutions involving image processing techniques have substantial challenges in the identification of seed germination. The detection of rice seed germination without human intervention involves challenges because the rice seeds are small and densely distributed. RESULTS: In this article, we develop a convolutional neural network (YOLO-r) that can detect the germination status of rice seeds and automatically evaluate the total number of germinations. Image partition, the Transformer encoder, a small target detection layer, and CDIoU loss are exploited in YOLO-r to improve the detection accuracy. A total of 21 429 seeds were collected, which have different phenotypic characteristics in length, shape, and color. The results show that the mean average precision of YOLO-r is 0.9539, which is higher than the compared models. Moreover, the average detection time per image of YOLO-r was 0.011 s, which meets the real-time requirements. The experimental results demonstrate that YOLO-r is robust to complex situations such as water stains, impurities, awns, adhesion, and so on. The results also show that the mean absolute error of the predicted germination rate mainly exists within 0.1. CONCLUSIONS: Numerous experimental studies have demonstrated that YOLO-r can predict rice germination rate in a fast, easy, and accurate manner. © 2022 Society of Chemical Industry.

A comparison between anterolateral thigh perforator flap and abdominal pedicle flap in repair of hand injuries and tissue defects.

The purpose of this study was to compare the outcome of anterolateral thigh perforator flap and abdominal pedicled flap repair for treating traumatic tissue defects of the hand. A total of 140 patients with hand trauma tissue defects were randomly divided (random number table) into Group A and Group B, with 70 cases in each group. Group A was given anterolateral thigh perforator flap repair, while Group B was given abdominal pedicled flap repair. The healing time of wounds in Group A was noted to be shorter than that in Group B (p<0.001). At one week after surgery, VAS score, serum IL-6 and TNF-α levels in Group A were 4 times lower than those in Group B (p<0.001 for all). Anterolateral thigh perforator flap repair works more effectively on traumatic tissue defects of the hands than abdominal pedicled flap repair. It reduces pain, shortens wound healing time, and lowers serum IL-6 and TNF-α levels.

Mutation of glucose-methanol-choline oxidoreductase leads to thermosensitive genic male sterility in rice and Arabidopsis.

Thermosensitive genic male sterility (TGMS) lines serve as the major genetic resource for two-line hybrid breeding in rice. However, their unstable sterility under occasional low temperatures in summer highly limits their application. In this study, we identified a novel rice TGMS line, ostms18, of cultivar ZH11 (Oryza sativa ssp. japonica). ostms18 sterility is more stable in summer than the TGMS line carrying the widely used locus tms5 in the ZH11 genetic background, suggesting its potential application for rice breeding. The ostms18 TGMS trait is caused by the point mutation from Gly to Ser in a glucose-methanol-choline (GMC) oxidoreductase; knockout of the oxidoreductase was previously reported to cause complete male sterility. Cellular analysis revealed the pollen wall of ostms18 to be defective, leading to aborted pollen under high temperature. Further analysis showed that the tapetal transcription factor OsMS188 directly regulates OsTMS18 for pollen wall formation. Under low temperature, the flawed pollen wall in ostms18 is sufficient to protect its microspore, allowing for development of functional pollen and restoring fertility. We identified the orthologous gene in Arabidopsis. Although mutants for the gene were fertile under normal conditions (24°C), fertility was significantly reduced under high temperature (28°C), exhibiting a TGMS trait. A cellular mechanism integrated with genetic mutations and different plant species for fertility restoration of TGMS lines is proposed.

Fine-tuning grain amylose contents by genome editing of Waxy cis-regulatory region in rice.

Rice grain amylose contents (ACs) is a key quantitative trait influencing eating and cooking quality. Regulating the expression level of Waxy, a key gene controlling ACs, and in turn fine-tuning the grain ACs, is an ideal approach to improve grain quality of rice varieties. Based on CRISPR/Cas9 genome editing technology, we designed eight targets in the cis-regulatory region of Wxa background, screened phenotypic changes of the transgenic lines and generated eight novel Waxy alleles with altered grain ACs. Among the eight alleles, we found that a 407-bp non-homologous substitution (NHS) in the 5'UTR-intron caused by genome editing regulated Waxy expression and decreased grain ACs by 2.9%. Moreover, embedding the 407-bp NHS into the cis-regulatory region of Wxb allele can also affect gene activity. Our work suggested the effect of 5'UTR-intron on Waxy gene expression regulation, and provided a potentially useful allele in breeding that can finely adjust rice grain ACs.

Genomic architecture of heterosis for yield traits in rice.

Increasing grain yield is a long-term goal in crop breeding to meet the demand for global food security. Heterosis, when a hybrid shows higher performance for a trait than both parents, offers an important strategy for crop breeding. To examine the genetic basis of heterosis for yield in rice, here we generate, sequence and record the phenotypes of 10,074 F2 lines from 17 representative hybrid rice crosses. We classify modern hybrid rice varieties into three groups, representing different hybrid breeding systems. Although we do not find any heterosis-associated loci shared across all lines, within each group, a small number of genomic loci from female parents explain a large proportion of the yield advantage of hybrids over their male parents. For some of these loci, we find support for partial dominance of heterozygous locus for yield-related traits and better-parent heterosis for overall performance when all of the grain-yield traits are considered together. These results inform on the genomic architecture of heterosis and rice hybrid breeding.

Ef-cd locus shortens rice maturity duration without yield penalty.

The contradiction between "high yielding" and "early maturing" hampers further improvement of annual rice yield. Here we report the positional cloning of a major maturity duration regulatory gene, Early flowering-completely dominant (Ef-cd), and demonstrate that natural variation in Ef-cd could be used to overcome the above contradictory. The Ef-cd locus gives rise to a long noncoding RNA (lncRNA) antisense transcript overlapping the OsSOC1 gene. Ef-cd lncRNA expression positively correlates with the expression of OsSOC1 and H3K36me3 deposition. Field test comparisons of early maturing Ef-cd near-isogenic lines with their wild types as well as of the derivative early maturing hybrids with their wild-type hybrids conducted under different latitudes determined that the early maturing Ef-cd allele shortens maturity duration (ranging from 7 to 20 d) without a concomitant yield penalty. Ef-cd facilitates nitrogen utilization and also improves the photosynthesis rate. Analysis of 1,439 elite hybrid rice varieties revealed that the 16 homozygotes and 299 heterozygotes possessing Ef-cd matured significantly earlier. Therefore, Ef-cd could be a vital contributor of elite early maturing hybrid varieties in balancing grain yield with maturity duration.

The Chimonanthus salicifolius genome provides insight into magnoliid evolution and flavonoid biosynthesis.

Chimonanthus salicifolius, a member of the Calycanthaceae of magnoliids, is one of the most famous medicinal plants in Eastern China. Here, we report a chromosome-level genome assembly of C. salicifolius, comprising 820.1 Mb of genomic sequence with a contig N50 of 2.3 Mb and containing 36 651 annotated protein-coding genes. Phylogenetic analyses revealed that magnoliids were sister to the eudicots. Two rounds of ancient whole-genome duplication were inferred in the C. salicifolious genome. One is shared by Calycanthaceae after its divergence with Lauraceae, and the other is in the ancestry of Magnoliales and Laurales. Notably, long genes with > 20 kb in length were much more prevalent in the magnoliid genomes compared with other angiosperms, which could be caused by the length expansion of introns inserted by transposon elements. Homologous genes within the flavonoid pathway for C. salicifolius were identified, and correlation of the gene expression and the contents of flavonoid metabolites revealed potential critical genes involved in flavonoids biosynthesis. This study not only provides an additional whole-genome sequence from the magnoliids, but also opens the door to functional genomic research and molecular breeding of C. salicifolius.