The genome evolution and domestication of tropical fruit mango

High-quality reference genome of cowpea beetle Callosobruchus maculatus

Callosobruchus maculatus is one of the most competitive stored grain pests, which causes a great loss to agricultural economy. However, due to an inadequacy of high-quality reference genome, the molecular mechanisms for olfactory and hypoxic adaptations to stored environments are unknown and require to be revealed urgently, which will contribute to the detection and prevention of the invasive pests C. maculatus. Here, we presented a high-quality chromosome-level genome of C. maculatus based on Illumina, Nanopore and Hi-C sequencing data. The total size was 1.2 Gb, and 65.17% (797.47 Mb) of it was identified to be repeat sequences. Among assembled chromosomes, chromosome 10 was considered the X chromosome according to the evidence of reads coverage and homologous genes among species. The current version of high-quality genome provides preferable data resources for the adaptive evolution research of C. maculatus.

Population structure and genetic diversity of mango (Mangifera indica L.) germplasm resources as revealed by single-nucleotide polymorphism markers

Introduction

Mango is a vital horticultural fruit crop, and breeding is an essential strategy to enhance ongoing sustainability. Knowledge regarding population structure and genetic diversity in mango germplasm is essential for crop improvement.

Methods

A set of 284 mango accessions from different regions of the world were subjected to high-throughput sequencing and specific-locus amplified fragment (SLAF) library construction to generate genomic single-nucleotide polymorphism (SNP).

Results

After filtering, raw data containing 539.61 M reads were obtained. A total of 505,300 SLAFs were detected, of which, 205,299 were polymorphic. Finally, 29,136 SNPs were employed to dissect the population structure, genetic relationships, and genetic diversity. The 284 mango accessions were divided into two major groups: one group consisted mainly of mango accessions from Australia, the United States, Cuba, India, Caribbean, Israel, Pakistan, Guinea, Burma, China, and Sri Lanka, which belonged to the Indian type (P1); the other group contained mango accessions from the Philippines, Thailand, Indonesia, Vietnam, Cambodia, Malaysia, and Singapore, which belonged to Southeast Asian type (P2). Genetic diversity, principal component analysis (PCA), and population structure analyses revealed distinct accession clusters. Current results indicated that the proposed hybridization occurred widely between P1 and P2.

Discussion

Most of the accessions (80.99%) were of mixed ancestry, perhaps including multiple hybridization events and regional selection, which merits further investigation.

Genetic mosaic of the Mediterranean fig: comprehensive genomic insights from a gene bank collection

High-depth whole-genome resequencing of 53 diverse fig tree genotypes yielded a rich dataset of genetic variants. We successfully identified 5,501,460 single-nucleotide polymorphisms (SNPs) and 1,228,537 insertions and deletions (InDels), providing a high-density and excellent-quality genetic map of the fig tree. We also performed a detailed population structure analysis, dividing the 53 genotypes into three geographical groups and assessing their genetic diversity and divergence. Analysis of structural variants (SVs) and copy number variations (CNVs) revealed their potential functional impact, particularly in plant-pathogen interaction and secondary metabolism. Metabolomic fingerprinting of fig genotypes uncovered extensive variation in primary metabolites and polyphenolic compounds, highlighting the influence of genotype on fruit quality traits such as nutritional content and bioactive compound composition. The genome-wide association study (GWAS) identified critical SNPs associated with fruit quality and morphological features. The discovery of significant candidate genes, such as AGL62, GDSL, and COBRA-like protein 4 genes, offers promising targets for marker-assisted selection and genome editing approaches to improve fig fruit morphological and quality traits. This extensive genomic analysis of fig trees enhances our understanding of the genetic basis of important agronomic traits and provides a rich resource for future research in this economically and nutritionally significant fruit.

Genomic diversity, population structure, and genome-wide association reveal genetic differentiation and trait improvements in mango

Mango (Mangifera indica L.) has been widely cultivated as a culturally and economically significant fruit tree for roughly 4000 years. Despite its rich history, little is known about the crop's domestication, genomic variation, and the genetic loci underlying agronomic traits. This study employs the whole-genome re-sequencing of 224 mango accessions sourced from 22 countries, with an average sequencing depth of 16.37×, to explore their genomic variation and diversity. Through phylogenomic analysis, M. himalis J.Y. Liang, a species grown in China, was reclassified into the cultivated mango group known as M. indica. Moreover, our investigation of mango population structure and differentiation revealed that Chinese accessions could be divided into two distinct gene pools, indicating the presence of independent genetic diversity ecotypes. By coupling genome-wide association studies with analyses of genotype variation patterns and expression patterns, we identified several candidate loci and dominant genotypes associated with mango flowering capability, fruit weight, and volatile compound production. In conclusion, our study offers valuable insights into the genetic differentiation of mango populations, paving the way for future agronomic improvements through genomic-assisted breeding.

Identification and Comprehensive Analysis of OFP Genes for Fruit Shape Influence in Mango

OVATE family proteins (OFPs) are a class of plant-specific proteins with a conserved OVATE domain that play fundamental roles in fruit development and plant growth. Mango (Mangifera indica L.) is an economically important subtropical fruit tree characterized by a diverse array of fruit shapes and sizes. Despite extensive research on OFPs across various species, there remains a scarcity of information regarding OFPs in mango. Here, we have successfully identified 25 OFP genes (MiOFPs) in mango, each of which exhibits the conserved OVATE domains. The MiOFP gene exhibit a range of 2-6 motifs, with all genes containing both motif 1 and motif 2. Phylogenetic analysis on 97 OFPs (including 18 AtOFPs, 24 SlOFPs, 25 MiOFPs, and 30 OsOFPs) indicated that MiOFPs could be divided into three main clades: clade I, II, and III. Comparative morphological analysis identified significant variations in fruit longitudinal diameter, fruit transverse diameter, and fruit shape index between two distinct shaped mango cultivars ('Hongxiangya' and 'Jingpingmang') at DAP5, DAP7, and DAP10 stages. The subsequent examination of paraffin sections revealed distinct patterns of cell elongation. The majority of MiOFP genes exhibited predominantly expressed in developing organs, specifically flowers and immature fruits, while displaying distinct expression patterns. RNA-Seq analysis revealed significant disparities in the expression levels of several OFP genes, including MiOFP5, MiOFP11, MiOFP21, MiOFP22, MiOFP23, and MiOFP25, between the two mango cultivars. These findings suggest that these six genes may play a crucial role for fruit shape in mango, especially the MiOFP22. The findings of this study have established a basis for future investigations into MiOFPs in mango, offering a solid foundation for further research in this field.

Identification of the ERF gene family of Mangifera indica and the defense response of MiERF4 to Xanthomonas campestris pv. mangiferaeindicae

An important regulatory role for ethylene-responsive transcription factors (ERFs) is in plant growth and development, stress response, and hormone signaling. However, AP2/ERF family genes in mango have not been systematically studied. In this study, a total of 113 AP2/ERF family genes were identified from the mango genome and phylogenetically classified into five subfamilies: AP2 (28 genes), DREB (42 genes), ERF (33 genes), RAV (6 genes), and Soloist (4 genes). Of these, the ERF family, in conjunction with Arabidopsis and rice, forms a phylogenetic tree divided into seven groups, five of which have MiERF members. Analysis of gene structure and cis-elements showed that each MiERF gene contains only one AP2 structural domain, and that MiERF genes contain a large number of cis-elements associated with hormone signaling and stress response. Collinearity tests revealed a high degree of homology between MiERFs and CsERFs. Tissue-specific and stress-responsive expression profiling revealed that MiERF genes are primarily involved in the regulation of reproductive growth and are differentially and positively expressed in response to external hormones and pathogenic bacteria. Physiological results from a gain-of-function analysis of MiERF4 transiently overexpressed in tobacco and mango showed that transient expression of MiERF4 resulted in decreased colony count and callose deposition, as well as varying degrees of response to hormonal signals such as ETH, JA, and SA. Thus, MiERF4 may be involved in the JA/ETH signaling pathway to enhance plant defense against pathogenic bacteria. This study provides a basis for further research on the function and regulation of MiERF genes and lays a foundation for the selection of disease-resistant genes in mango.

Computational analysis and expression profiling of two-component system (TCS) gene family members in mango (Mangifera indica) indicated their roles in stress response

The two-component system (TCS) gene family is among the most important signal transduction families in plants and is involved in the regulation of various abiotic stresses, cell growth and division. To understand the role of TCS genes in mango (Mangifera indica ), a comprehensive analysis of TCS gene family was carried out in mango leading to identification of 65 MiTCS genes. Phylogenetic analysis divided MiTCSs into three groups (histidine kinases, histidine-containing phosphotransfer proteins, and response regulators) and 11 subgroups. One tandem duplication and 23 pairs of segmental duplicates were found within the MiTCSs . Promoter analysis revealed that MiTCSs contain a large number of cis -elements associated with environmental stresses, hormone response, light signalling, and plant development. Gene ontology analysis showed their involvement in various biological processes and molecular functions, particularly signal transduction. Protein-protein interaction analysis showed that MiTCS proteins interacted with each other. The expression pattern in various tissues and under many stresses (drought, cold, and disease) showed that expression levels varied among various genes in different conditions. MiTCSs 3D structure predictions showed structural conservation among members of the same groups. This information can be further used to develop improved cultivars and will serve as a foundation for gaining more functional insights into the TCS gene family.

A chromosome-scale genome of Rhus chinensis Mill. provides new insights into plant-insect interaction and gallotannins biosynthesis

Rhus chinensis Mill., an economically valuable Anacardiaceae species, is parasitized by the galling aphid Schlechtendalia chinensis, resulting in the formation of the Chinese gallnut (CG). Here, we report a chromosomal-level genome assembly of R. chinensis, with a total size of 389.40 Mb and scaffold N50 of 23.02 Mb. Comparative genomic and transcriptome analysis revealed that the enhanced structure of CG and nutritional metabolism contribute to improving the adaptability of R. chinensis to S. chinensis by supporting CG and galling aphid growth. CG was observed to be abundant in hydrolysable tannins (HT), particularly gallotannin and its isomers. Tandem repeat clusters of dehydroquinate dehydratase/shikimate dehydrogenase (DQD/SDH) and serine carboxypeptidase-like (SCPL) and their homologs involved in HT production were determined as specific to HT-rich species. The functional differentiation of DQD/SDH tandem duplicate genes and the significant contraction in the phenylalanine ammonia-lyase (PAL) gene family contributed to the accumulation of gallic acid and HT while minimizing the production of shikimic acid, flavonoids, and condensed tannins in CG. Furthermore, we identified one UDP glucosyltransferase (UGT84A), three carboxylesterase (CXE), and six SCPL genes from conserved tandem repeat clusters that are involved in gallotannin biosynthesis and hydrolysis in CG. We then constructed a regulatory network of these genes based on co-expression and transcription factor motif analysis. Our findings provide a genomic resource for the exploration of the underlying mechanisms of plant-galling insect interaction and highlight the importance of the functional divergence of tandem duplicate genes in the accumulation of secondary metabolites.

Cold-stress induced metabolomic and transcriptomic changes in leaves of three mango varieties with different cold tolerance

BACKGROUND

Mango (Mangifera indica L.) is grown in Hainan, Guangdong, Yunnan, Sichuan, and Fujian provinces and Guanxi autonomous region of China. However, trees growing in these areas suffer severe cold stress during winter, which affects the yield. To this regard, data on global metabolome and transcriptome profiles of leaves are limited. Here, we used combined metabolome and transcriptome analyses of leaves of three mango cultivars with different cold stress tolerance, i.e. Jinhuang (J)-tolerant, Tainung (T) and Guiremang No. 82 (G)-susceptible, after 24 (LF), 48 (MF) and 72 (HF) hours of cold.

RESULTS

A total of 1,323 metabolites belonging to 12 compound classes were detected. Of these, amino acids and derivatives, nucleotides and derivatives, and lipids accumulated in higher quantities after cold stress exposure in the three cultivars. Notably, Jinhuang leaves showed increasing accumulation trends of flavonoids, terpenoids, lignans and coumarins, and alkaloids with exposure time. Among the phytohormones, jasmonic acid and abscisic acid levels decreased, while N6-isopentenyladenine increased with cold stress time. Transcriptome analysis led to the identification of 22,526 differentially expressed genes. Many genes enriched in photosynthesis, antenna proteins, flavonoid, terpenoid (di- and sesquiterpenoids) and alkaloid biosynthesis pathways were upregulated in Jihuang leaves. Moreover, expression changes related to phytohormones, MAPK (including calcium and H2O2), and the ICE-CBF-COR signalling cascade indicate involvement of these pathways in cold stress responses.

CONCLUSION

Cold stress tolerance in mango leaves is associated with regulation of primary and secondary metabolite biosynthesis pathways. Jasmonic acid, abscisic acid, and cytokinins are potential regulators of cold stress responses in mango leaves.

TCOD: an integrated resource for tropical crops

Tropical crops are vital for tropical agriculture, with resource scarcity, functional diversity and extensive market demand, providing considerable economic benefits for the world's tropical agriculture-producing countries. The rapid development of sequencing technology has promoted a milestone in tropical crop research, resulting in the generation of massive amount of data, which urgently needs an effective platform for data integration and sharing. However, the existing databases cannot fully satisfy researchers' requirements due to the relatively limited integration level and untimely update. Here, we present the Tropical Crop Omics Database (TCOD, https://ngdc.cncb.ac.cn/tcod), a comprehensive multi-omics data platform for tropical crops. TCOD integrates diverse omics data from 15 species, encompassing 34 chromosome-level de novo assemblies, 1 255 004 genes with functional annotations, 282 436 992 unique variants from 2048 WGS samples, 88 transcriptomic profiles from 1997 RNA-Seq samples and 13 381 germplasm items. Additionally, TCOD not only employs genes as a bridge to interconnect multi-omics data, enabling cross-species comparisons based on homology relationships, but also offers user-friendly online tools for efficient data mining and visualization. In short, TCOD integrates multi-species, multi-omics data and online tools, which will facilitate the research on genomic selective breeding and trait biology of tropical crops.

MiMYB10 transcription factor regulates biosynthesis and accumulation of carotenoid involved genes in mango fruit

Carotenoids are essential and beneficial substances for both plant and human health. Identifying the regulatory network of these pigments is necessary for improving fruit quality and commodity value. In this study, we performed integrative analyses of transcriptome data from two different type fruits, ripening peel color at green ('Neelum' mango) and red ('Irwin' mango). Specifically, we found that MiMYB10 transcription level was highly associated with mango peel color. Further, silencing MiMYB10 homologous gene in tomato fruits resulted in lower carotenoid and anthocyanin content. Electrophoretic mobility shift assays and dual-luciferase clarified that MiMYB10 regulates the carotenoid biosynthesis gene MiPDS (phytoene desaturase gene) in a direct manner. On the other hand, MiMYB10 activates the expression of carotenoid biosynthesis genes (PSY, Z-ISO, CRTISO, LCYE) and chlorophyll degradation gene (SGR1), promoting the accumulation of carotenoid, accelerating chlorophyll degradation, and controlling peel color. In summary, this study identified important roles of MiMYB10 in pigment regulatory and provided new options for breeding strategies aiming to improve fruit quality.

Novel Tri-Segmented Rhabdoviruses: A Data Mining Expedition Unveils the Cryptic Diversity of Cytorhabdoviruses

Cytorhabdoviruses (genus Cytorhabdovirus, family Rhabdoviridae) are plant-infecting viruses with enveloped, bacilliform virions. Established members of the genus Cytorhabdovirus have unsegmented single-stranded negative-sense RNA genomes (ca. 10-16 kb) which encode four to ten proteins. Here, by exploring large publicly available metatranscriptomics datasets, we report the identification and genomic characterization of 93 novel viruses with genetic and evolutionary cues of cytorhabdoviruses. Strikingly, five unprecedented viruses with tri-segmented genomes were also identified. This finding represents the first tri-segmented viruses in the family Rhabdoviridae, and they should be classified in a novel genus within this family for which we suggest the name "Trirhavirus". Interestingly, the nucleocapsid and polymerase were the only typical rhabdoviral proteins encoded by those tri-segmented viruses, whereas in three of them, a protein similar to the emaravirus (family Fimoviridae) silencing suppressor was found, while the other predicted proteins had no matches in any sequence databases. Genetic distance and evolutionary insights suggest that all these novel viruses may represent members of novel species. Phylogenetic analyses, of both novel and previously classified plant rhabdoviruses, provide compelling support for the division of the genus Cytorhabdovirus into three distinct genera. This proposed reclassification not only enhances our understanding of the evolutionary dynamics within this group of plant rhabdoviruses but also illuminates the remarkable genomic diversity they encompass. This study not only represents a significant expansion of the genomics of cytorhabdoviruses that will enable future research on the evolutionary peculiarity of this genus but also shows the plasticity in the rhabdovirus genome organization with the discovery of tri-segmented members with a unique evolutionary trajectory.

Haplotype-resolved genome of heterozygous African cassava cultivar TMEB117 (Manihot esculenta)

Cassava (Manihot esculenta Crantz) is a vital tropical root crop providing essential dietary energy to over 800 million people in tropical and subtropical regions. As a climate-resilient crop, its significance grows as the human population expands. However, yield improvement faces challenges from biotic and abiotic stress and limited breeding. Advanced sequencing and assembly techniques enabled the generation of a highly accurate, nearly complete, haplotype-resolved genome of the African cassava cultivar TMEB117. It is the most accurate cassava genome sequence to date with a base-level accuracy of QV > 64, N50 > 35 Mbp, and 98.9% BUSCO completeness. Over 60% of the genome comprises repetitive elements. We predicted over 45,000 gene models for both haplotypes. This achievement offers valuable insights into the heterozygosity genome organization of the cassava genome, with improved accuracy, completeness, and phased genomes. Due to its high susceptibility to African Cassava Mosaic Virus (ACMV) infections compared to other cassava varieties, TMEB117 provides an ideal reference for studying virus resistance mechanisms, including epigenetic variations and smallRNA expressions.

Genome-wide identification of CaARR-Bs transcription factor gene family in pepper and their expression patterns under salinity stress

In plants, ARRs-B transcription factors play a crucial role in regulating cytokinin signal transduction, abiotic stress resistance, and plant development. A number of adverse environmental conditions have caused severe losses for the pepper (Capsicum annuum L.)-a significant and economically important vegetable. Among the transcription factors of the type B-ARRs family, multiple members have different functions. In pepper, only a few members of the ARRs-B family have been reported and characterized. The current study aimed to characterize ARRs-B transcription factors in C. annuum, including phylogenetic relationships, gene structures, protein motif arrangement, and RT-qPCR expression analyses and their role in salinity stress. In total, ten genes encode CaARRs-B transcription factors (CaARR1 to CaARR10) from the largest subfamily of type-B ARRs were identified in C. annum. The genome-wide analyses of the CaARRs-B family in C. annuum were performed based on the reported ARRs-B genes in Arabidopsis. An analysis of homologous alignments of candidate genes, including their phylogenetic relationships, gene structures, conserved domains, and qPCR expression profiles, was conducted. In comparison with other plant ARRs-B proteins, CaARRs-B proteins showed gene conservation and potentially specialized functions. In addition, tissue-specific expression profiles showed that CaARRs-B genes were differentially expressed, suggesting functionally divergent. CaARRs-B proteins had a typical conserved domain, including AAR-like (pfam: PF00072) and Myb DNA binding (pfam: PF00249) domains. Ten of the CaARRs-B genes were asymmetrically mapped on seven chromosomes in Pepper. Additionally, the phylogenetic tree of CaARRs-B genes from C. annuum and other plant species revealed that CaARRs-B genes were classified into four clusters, which may have evolved conservatively. Further, using quantitative real-time qRT-PCR, the study assessed the expression patterns of CaARRs-B genes in Capsicum annuum seedlings subjected to salt stress. The study used quantitative real-time qRT-PCR to examine CaARRs-B gene expression in Capsicum annuum seedlings under salt stress. Roots exhibited elevated expression of CaARR2 and CaARR9, while leaves showed decreased expression for CaARR3, CaARR4, CaARR7, and CaARR8. Notably, no amplification was observed for CaARR10. This research sheds light on the roles of CaARRs-B genes in pepper's response to salinity stress. These findings enrich our comprehension of the functional implications of CaARRs-B genes in pepper, especially in responding to salinity stress, laying a solid groundwork for subsequent in-depth studies and applications in the growth and development of Capsicum annuum.

Comparative genomics profiling revealed multi-stress responsive roles of the CC-NBS-LRR genes in three mango cultivars

The nucleotide-binding site-leucine-rich repeat (NBS-LRR) gene family is the largest group of disease resistance (R) genes in plants and is active in response to viruses, bacteria, and fungi usually involved in effector-triggered immunity (ETI). Pangenome-wide studies allow researchers to analyze the genetic diversity of multiple species or their members simultaneously, providing a comprehensive understanding of the evolutionary relationships and diversity present among them. The draft pan-genome of three Mangifera indica cultivars (Alphonso, Hong Xiang Ya, and Tommy atkins) was constructed and Presence/absence variants (PAVs) were filtered through the ppsPCP pipeline. As a result, 2823 genes and 5907 PAVs from H. Xiang Ya, and 1266 genes and 2098 PAVs from T. atkins were added to the reference genome. For the identification of CC-NBS-LRR (CNL) genes in these mango cultivars, this draft pan-genome study has successfully identified 47, 27, and 36 members in Alphonso, H. Xiang Ya, and T. atkins respectively. The phylogenetic analysis divided MiCNL proteins into four distinct subgroups. All MiCNL genes are unevenly distributed on chromosomes. Both tandem and segmental duplication events played a significant role in the expansion of the CNL gene family. These genes contain cis-elements related to light, stress, hormone, and development. The analysis of protein-protein interactions (PPI) revealed that MiCNL proteins interacted with other defense-responsive proteins. Gene Ontology (GO) analysis indicated that MiCNL genes play a role in defense mechanisms within the organism. The expression level of the identified genes in fruit peel was observed under disease and cold stress which showed that Mi_A_CNL13 and 14 were up-regulated while Mi_A_CNL15, 25, 30, 31, and 40 were down-regulated in disease stress. On the other hand, Mi_A_CNL2, 14, 41, and 45 were up-regulated and Mi_A_CNL47 is down-regulated in cold stress. Subsequently, the Random Forest (RF) classifier was used to assess the multi-stress response of MiCNLs. It was found that Mi_A_CNL14 is a gene that responds to multiple stress conditions. The CNLs have similar protein structures which show that they are involved in the same function. The above findings provide a foundation for a deeper understanding of the functional characteristics of the mango CNL gene family.

Combined transcriptome and metabolome analysis reveal that the white and yellow mango pulp colors are associated with carotenoid and flavonoid accumulation, and phytohormone signaling

Mango (Mangifera indica L.) is a widely appreciated tropical fruit for its rich color and nutrition. However, knowledge on the molecular basis of color variation is limited. Here, we studied HY3 (yellowish-white pulp) and YX4 (yellow pulp), reaped with 24 h gap from the standard harvesting time. The carotenoids and total flavonoids increased with the advance of harvest time (YX4 > HY34). Transcriptome sequencing showed that higher expressions of the core carotenoid biosynthesis genes and flavonoid biosynthesis genes are correlated to their respective contents. The endogenous indole-3-acetic acid and jasmonic acid contents decreased but abscisic acid and ethylene contents increased with an increase in harvesting time (YX4 > HY34). Similar trends were observed for the corresponding genes. Our results indicate that the color differences are related to carotenoid and flavonoid contents, which in turn are influenced by phytohormone accumulation and signaling.

Exogenous glutathione maintains the postharvest quality of mango fruit by modulating the ascorbate-glutathione cycle

Background

Mango fruit is prone to decay after harvest and premature senescence, which significantly lowers its quality and commercial value.

Methods

The mango fruit (Mangifera indica L.cv. Guixiang) was treated with 0 (control), 2, 5, and 8 mM of reduced glutathione (GSH) after harvest. The fruit was stored at 25 ± 1 °C for 12 days to observe the changes in the antioxidant capacity and postharvest quality.

Results

Compared with the control, the 5 mM GSH treatment significantly decreased the weight loss by 44.0% and 24.4%, total soluble solids content by 25.1% and 4.5%, and soluble sugar content by 19.0% and 27.0%. Conversely, the 5 mM GSH treatment increased the firmness by 25.9% and 30.7% on days 4 and 8, respectively, and the titratable acidity content by 115.1% on day 8. Additionally, the 5 mM GSH treatment decreased the malondialdehyde and hydrogen peroxide contents and improved the antioxidant capacity of mango fruit by increasing the superoxide dismutase and peroxidase activities and upregulating the expression of the encoding genes. Meanwhile, the higher levels of monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase enzyme activities and gene expressions accelerated the AsA-GSH cycle, thereby increasing the accumulation of AsA and GSH and maintaining the redox balance.

Conclusions

Overall, the experimental results suggest that 5 mM GSH maintains high antioxidant capacity and postharvest quality of mangoes and can use as an effective preservation technique for postharvest mangoes.

The Effect of Methodological Considerations on the Construction of Gene-Based Plant Pan-genomes

Pan-genomics is an emerging approach for studying the genetic diversity within plant populations. In contrast to common resequencing studies that compare whole genome sequencing data with a single reference genome, the construction of a pan-genome (PG) involves the direct comparison of multiple genomes to one another, thereby enabling the detection of genomic sequences and genes not present in the reference, as well as the analysis of gene content diversity. Although multiple studies describing PGs of various plant species have been published in recent years, a better understanding regarding the effect of the computational procedures used for PG construction could guide researchers in making more informed methodological decisions. Here, we examine the effect of several key methodological factors on the obtained gene pool and on gene presence-absence detections by constructing and comparing multiple PGs of Arabidopsis thaliana and cultivated soybean, as well as conducting a meta-analysis on published PGs. These factors include the construction method, the sequencing depth, and the extent of input data used for gene annotation. We observe substantial differences between PGs constructed using three common procedures (de novo assembly and annotation, map-to-pan, and iterative assembly) and that results are dependent on the extent of the input data. Specifically, we report low agreement between the gene content inferred using different procedures and input data. Our results should increase the awareness of the community to the consequences of methodological decisions made during the process of PG construction and emphasize the need for further investigation of commonly applied methodologies.

Genome-Wide Identification of the WD40 Gene Family in Tomato (Solanum lycopersicum L.)

WD40 proteins are a superfamily of regulatory proteins widely found in eukaryotes that play an important role in regulating plant growth and development. However, the systematic identification and characterization of WD40 proteins in tomato (Solanum lycopersicum L.) have not been reported. In the present study, we identified 207 WD40 genes in the tomatoes genome and analyzed their chromosomal location, gene structure and evolutionary relationships. A total of 207 tomato WD40 genes were classified by structural domain and phylogenetic tree analyses into five clusters and 12 subfamilies and were found to be unevenly distributed across the 12 tomato chromosomes. We identified six tandem duplication gene pairs and 24 segmental duplication pairs in the WD40 gene family, with segmental duplication being the major mode of expansion in tomatoes. Ka/Ks analysis revealed that paralogs and orthologs of WD40 family genes underwent mainly purifying selection during the evolutionary process. RNA-seq data from different tissues and developmental periods of tomato fruit development showed tissue-specific expression of WD40 genes. In addition, we constructed four coexpression networks according to the transcriptome and metabolome data for WD40 proteins involved in fruit development that may be related to total soluble solid formation. The results provide a comprehensive overview of the tomato WD40 gene family and will provide valuable information for the validation of the function of tomato WD40 genes in fruit development.

High resolution mapping of QTLs for fruit color and firmness in Amrapali/Sensation mango hybrids

Introduction

Mango (Mangifera indica L.), acclaimed as the 'king of fruits' in the tropical world, has historical, religious, and economic values. It is grown commercially in more than 100 countries, and fresh mango world trade accounts for ~3,200 million US dollars for the year 2020. Mango is widely cultivated in sub-tropical and tropical regions of the world, with India, China, and Thailand being the top three producers. Mango fruit is adored for its taste, color, flavor, and aroma. Fruit color and firmness are important fruit quality traits for consumer acceptance, but their genetics is poorly understood.

Methods

For mapping of fruit color and firmness, mango varieties Amrapali and Sensation, having contrasting fruit quality traits, were crossed for the development of a mapping population. Ninety-two bi-parental progenies obtained from this cross were used for the construction of a high-density linkage map and identification of QTLs. Genotyping was carried out using an 80K SNP chip array.

Results and discussion

Initially, we constructed two high-density linkage maps based on the segregation of female and male parents. A female map with 3,213 SNPs and male map with 1,781 SNPs were distributed on 20 linkages groups covering map lengths of 2,844.39 and 2,684.22cM, respectively. Finally, the integrated map was constructed comprised of 4,361 SNP markers distributed on 20 linkage groups, which consisted of the chromosome haploid number in Mangifera indica (n =20). The integrated genetic map covered the entire genome of Mangifera indica cv. Dashehari, with a total genetic distance of 2,982.75 cM and an average distance between markers of 0.68 cM. The length of LGs varied from 85.78 to 218.28 cM, with a mean size of 149.14 cM. Phenotyping for fruit color and firmness traits was done for two consecutive seasons. We identified important consistent QTLs for 12 out of 20 traits, with integrated genetic linkages having significant LOD scores in at least one season. Important consistent QTLs for fruit peel color are located at Chr 3 and 18, and firmness on Chr 11 and 20. The QTLs mapped in this study would be useful in the marker-assisted breeding of mango for improved efficiency.

The Involvement of the Laccase Gene Cglac13 in Mycelial Growth, Germ Tube Development, and the Pathogenicity of Colletotrichum gloeosporioides from Mangoes

Colletotrichum gloeosporioides is one of the most serious diseases that causes damage to mangoes. Laccase, a copper-containing polyphenol oxidase, has been reported in many species with different functions and activities, and fungal laccase could be closely related to mycelial growth, melanin and appressorium formation, pathogenicity, and so on. Therefore, what is the relationship between laccase and pathogenicity? Do laccase genes have different functions? In this experiment, the knockout mutant and complementary strain of Cglac13 were obtained through polyethylene glycol (PEG)-mediated protoplast transformation, which then determined the related phenotypes. The results showed that the knockout of Cglac13 significantly increased the germ tube formation, and the formation rates of appressoria significantly decreased, delaying the mycelial growth and lignin degradation and, ultimately, leading to a significant reduction in the pathogenicity in mango fruit. Furthermore, we observed that Cglac13 was involved in regulating the formation of germ tubes and appressoria, mycelial growth, lignin degradation, and pathogenicity of C. gloeosporioides. This study is the first to report that the function of laccase is related to the formation of germ tubes, and this provides new insights into the pathogenesis of laccase in C. gloeosporioides.

Postharvest light-induced flavonoids accumulation in mango (Mangifera indica L.) peel is associated with the up-regulation of flavonoids-related and light signal pathway genes

INTRODUCTION

Flavonoids are important secondary metabolites in plants and light is a crucial environmental factor regulating flavonoids biosynthesis. However, effect of light on the different flavonoids compositions accumulation in mango and the relevant molecular mechanism still need to be clarified.

METHODS

In this study, green-mature fruits of red mango cultivar 'Zill' were subjected to postharvest light treatment, and fruit peel color, total soluble solids content, total organic acid, and firmness of flesh were measured. The flavonoids metabolites profile, and the expression of flavonoids-related genes and light signal pathway genes were also analyzed.

RESULTS

Results showed that light treatment promoted the red coloration of fruit peel and increased the total soluble solids content and firmness of flesh. The concentration of flavonols, proanthocyanidins and anthocyanins, and expression of key flavonoids biosynthetic genes including MiF3H, MiFLS, MiLAR, MiANS, MiUFGT1, and MiUFGT3 were significantly induced by light. The MYBs regulating flavonols and proanthocyanidins, i.e. MiMYB22 and MiMYB12, as well as the key light signal pathway transcription factors (TFs) MiHY5 and MiHYH, were identified in mango. The transcription of MiMYB1, MiMYB12, MiMYB22, MiHY5 and MiHYH was up-regulated by light.

DISCUSSION

Our results provide a postharvest technology to improve mango fruit appearance quality, and are helpful to reveal the molecular mechanism of light-induced flavonoids biosynthesis in mango.

MangoBase: A Genomics Portal and Gene Expression Atlas for Mangifera indica

Mango (Mangifera indica L.) (2n = 40) is a member of the Anacardiaceae family, which was domesticated at least 4000 years ago in Asia. Mangoes are delicious fruits with great nutritional value. They are one of the major fruit crops worldwide, cultivated in more than 100 countries, with a production of more than 40 million tons. Recently the genome sequences of several mango varieties have been released, but there are no bioinformatics platforms dedicated to mango genomics and breeding to host mango omics data. Here, we present MangoBase, a web portal dedicated to mango genomics, which provides multiple interactive bioinformatics tools, sequences, and annotations to analyze, visualize, and download omics data related to mango. Additionally, MangoBase includes a gene expression atlas with 12 datasets and 80 experiments representing some of the most significant mango RNA-seq experiments published to this date. These experiments study mango fruit ripening in several cultivars with different pulp firmness and sweetness or peel coloration, and other experiments also study hot water postharvest treatment, infection with C. gloeosporioides, and the main mango tree organ tissues.

A proposed metric set for evaluation of genome assembly quality

Quality control is essential for genome assemblies; however, a consensus has yet to be reached on what metrics should be adopted for the evaluation of assembly quality. N50 is widely used for contiguity measurement, but its effectiveness is constantly in question. Prevailing metrics for the completeness evaluation focus on gene space, yet challenging areas such as tandem repeats are commonly overlooked. Achieving correctness has become an indispensable dimension for quality control, while prevailing assembly releases lack scores reflecting this aspect. We propose a metric set with a set of statistic indexes for effective, comprehensive evaluation of assemblies and provide a score of a finished assembly for each metric, which can be utilized as a benchmark for achieving high-quality genome assemblies.

Bamboo charcoal mediated plant secondary metabolites biosynthesis in tomato against South American tomato pinworm (Tuta absoluta)

Introduction

The south American tomato pinworm (Tuta absoluta), an invasive insect pest species, has established itself in more than 33 Chinese prefectures, where it is mainly damaging tomato crops. Immediate efforts have been initiated to find strategies to control this pest. Studies have shown that biochar (BC) amendment to soil can enhance plant growth and resistance to herbivory.

Methods

First, we quantified the morphological performance of tomato plants grown in different coconut bran and bamboo charcoal (v/v) combinations and selected the most beneficial one. Then we checked the T. absoluta survival on the tomato plants grown in the selected bamboo charcoal combination. Finally, we studied the leaf metabolite accumulation and gene expression changes in tomato plants after growing in the selected bamboo charcoal combination.

Results

We found that the 30:1 ratio of bamboo charcoal and coconut bran is the most beneficial to tomato growth as its amendment to soil increased tomato plant height, stem thickness, and chlorophyll content, whereas, the T. absoluta survival decreased. The metabolome profiles of BC tomato leaves showed an increased accumulation of flavonoids, terpenoids, and phenolic acids compared to CK. Transcriptome sequencing resulted in the identification of 244 differentially expressed genes. Most of the upregulated genes were associated with stress-related hub proteins, flavonoid biosynthesis, MAPK and phytohormone signaling, and terpenoid biosynthesis. Additionally, the expression of many genes related to signaling and defense was changed in response to the bamboo charcoal amendment.

Discussion

We conclude that bamboo charcoal induces biosynthesis of flavonoids, terpenoids, and phenolic acids, which improve plant growth and tolerance against T. absoluta, thus reducing the survival of destructive pests.

Genome assembly of wild loquat (Eriobotrya japonica) and resequencing provide new insights into the genomic evolution and fruit domestication in loquat

Wild loquats (Eriobotrya japonica Lindl.) provide remarkable genetic resources for studying domestication and breeding improved varieties. Herein, we generate the first high-quality chromosome-level genome assembly of wild loquat, with 45 791 predicted protein-coding genes. Analysis of comparative genomics indicated that loquat shares a common ancestor with apple and pear, and a recent whole-genome duplication event occurred in loquat prior to its divergence. Genome resequencing showed that the loquat germplasms can be distinctly classified into wild and cultivated groups, and the commercial cultivars have experienced allelic admixture. Compared with cultivated loquats, the wild loquat genome showed very few selected genomic regions and had higher levels of genetic diversity. However, whole-genome scans of selective sweeps were mainly related to fruit quality, size, and flesh color during the domestication process. Large-scale transcriptome and metabolome analyses were further performed to identify differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) in wild and cultivated loquats at various fruit development stages. Unlike those in wild loquat, the key DEGs and DAMs involved in carbohydrate metabolism, plant hormone signal transduction, flavonoid biosynthesis, and carotenoid biosynthesis were significantly regulated in cultivated loquats during fruit development. These high-quality reference genome, resequencing, and large-scale transcriptome/metabolome data provide valuable resources for elucidating fruit domestication and molecular breeding in loquat.

Jasmonic acid enhances osmotic stress responses by MYC2-mediated inhibition of protein phosphatase 2C1 and response regulators 26 transcription factor in tomato

The jasmonic acid (JA) signaling pathway is involved in the plant response to drought stress. JA and other hormones synergistically regulate the drought response in plants. However, the molecular mechanism underlying this synergism remains poorly defined. In the present study, transcriptome analyses of guard cells and quantitative PCR experiments revealed that MYC2 negatively regulated the negative regulator of ABA signaling, SlPP2C1, and the type-B response regulator in the cytokinin pathway, SlRR26, and this negative regulation was direct. SlRR26 overexpression reduced drought tolerance in transgenic tomatoes, whereas slrr26^cr lines were more tolerant to drought. SlRR26 negatively modulated reactive oxygen species levels in stomata and stomatal closure through RobhB. Moreover, SlRR26 overexpression counteracted JA-mediated stomatal closure, suggesting that SlRR26 played a negative role in the JA-mediated drought response. These findings suggest that MYC2 plays a key role in JA-regulated stomatal closure under drought stress by inhibiting SlPP2C1 and SlRR26.

Advances in sequencing and key character analysis of mango (Mangifera indica L.)

Mango (Mangifera indica L.) is an important fruit crop in tropical and subtropical countries associated with many agronomic and horticultural problems, such as susceptibility to pathogens, including powdery mildew and anthracnose, poor yield and quality, and short shelf life. Conventional breeding techniques exhibit significant limitations in improving mango quality due to the characteristics of long ripening, self-incompatibility, and high genetic heterozygosity. In recent years, much emphasis has been placed on identification of key genes controlling a certain trait through genomic association analysis and directly breeding new varieties through transgene or genotype selection of offspring. This paper reviews the latest research progress on the genome and transcriptome sequencing of mango fruit. The rapid development of genome sequencing and bioinformatics provides effective strategies for identifying, labeling, cloning, and manipulating many genes related to economically important traits. Preliminary verification of the functions of mango genes has been conducted, including genes related to flowering regulation, fruit development, and polyphenol biosynthesis. Importantly, modern biotechnology can refine existing mango varieties to meet the market demand with high economic benefits.

Genome-Wide Analysis and Expression of Cyclic Nucleotide-Gated Ion Channel (CNGC) Family Genes under Cold Stress in Mango (Mangifera indica)

The 'king of fruits' mango (Mangifera indica) is widely cultivated in tropical areas and has been threatened by frequent extreme cold weather. Cyclic nucleotide-gated ion channel (CNGC) genes have an important function in the calcium-mediated development and cold response of plants. However, few CNGC-related studies are reported in mango, regardless of the mango cold stress response. In this study, we identified 43 CNGC genes in mango showing tissue-specific expression patterns. Five MiCNGCs display more than 3-fold gene expression induction in the fruit peel and leaf under cold stress. Among these, MiCNGC9 and MiCNGC13 are significantly upregulated below 6 °C, suggesting their candidate functions under cold stress. Furthermore, cell membrane integrity was damaged at 2 °C in the mango leaf, as shown by the content of malondialdehyde (MDA), and eight MiCNGCs are positively correlated with MDA contents. The high correlation between MiCNGCs and MDA implies MiCNGCs might regulate cell membrane integrity by regulating MDA content. Together, these findings provide a valuable guideline for the functional characterization of CNGC genes and will benefit future studies related to cold stress and calcium transport in mango.

Differential effects of low and high temperature stress on pollen germination and tube length of mango (Mangifera indica L.) genotypes

Mango flowering is highly sensitive to temperature changes. In this research, the maximum values of pollen germination rate (PGR), pollen tube length (PTL) and their cardinal temperatures (Tmin, Topt and Tmax) were estimated by using quadratic equation and modified bilinear model under the conditions of 14-36 °C. The pollen germination rate in four mango varieties ranged from 29.1% ('Apple mango') to 35.5% ('Renong No. 1'); the length of pollen tube ranged from 51.2 μm ('Deshehari') to 56.6 μm ('Jinhuang'). The cardinal temperatures ranges (Tmin, Topt and Tmax) of pollen germination were 20.3-22.8 °C, 26.7-30.6 °C and 30.4-34.3 °C, respectively; similarly, cardinal temperatures (Tmin, Topt and Tmax) of pollen tube growth were 20.3-21.2 °C, 27.9-32.1 °C and 30.2-34.4 °C respectively. Of those, 'Renong No. 1' could maintain relatively high pollen germination rate even at 30 °C, however, 'Deshehari' had the narrowest adaptive temperature range. These results were further confirmed by changes of superoxide dismutase, catalase activity and malondialdehyde content. These results showed that mango flowering was highly sensitive to temperature changes and there were significant differences in pollen germination rate and pollen tube length among different varieties. Current research results were of great significance for the introduction of new mango varieties in different ecological regions, the cultivation and management of mango at the flowering stage and the breeding of new mango varieties.

Advances in Physiological, Transcriptomic, Proteomic, Metabolomic, and Molecular Genetic Approaches for Enhancing Mango Fruit Quality

Mango (Mangifera indica L.) is a nutritionally important fruit of high nutritive value, delicious in taste with an attractive aroma. Due to their antioxidant and therapeutic potential, mango fruits are receiving special attention in biochemical and pharmacognosy-based studies. Fruit quality determines consumer's acceptance, and hence, understanding the physiological, biochemical, and molecular basis of fruit development, maturity, ripening, and storage is essential. Transcriptomic, metabolomic, proteomic, and molecular genetic approaches have led to the identification of key genes, metabolites, protein candidates, and quantitative trait loci that are associated with enhanced mango fruit quality. The major pathways that determine the fruit quality include amino acid metabolism, plant hormone signaling, carbohydrate metabolism and transport, cell wall biosynthesis and degradation, flavonoid and anthocyanin biosynthesis, and carotenoid metabolism. Expression of the polygalacturonase, cutin synthase, pectin methyl esterase, pectate lyase, β-galactosidase, and ethylene biosynthesis enzymes are related to mango fruit ripening, flavor, firmness, softening, and other quality processes, while genes involved in the MAPK signaling pathway, heat shock proteins, hormone signaling, and phenylpropanoid biosynthesis are associated with diseases. Metabolomics identified volatiles, organic acids, amino acids, and various other compounds that determine the characteristic flavor and aroma of the mango fruit. Molecular markers differentiate the mango cultivars based on their geographical origins. Genetic linkage maps and quantitative trait loci studies identified regions in the genome that are associated with economically important traits. The review summarizes the applications of omics techniques and their potential applications toward understanding mango fruit physiology and their usefulness in future mango breeding.

The evolutionary patterns, expression profiles, and genetic diversity of expanded genes in barley

Gene duplication resulting from whole-genome duplication (WGD), small-scale duplication (SSD), or unequal hybridization plays an important role in the expansion of gene families. Gene family expansion can also mediate species formation and adaptive evolution. Barley (Hordeum vulgare) is the world's fourth largest cereal crop, and it contains valuable genetic resources due to its ability to tolerate various types of environmental stress. In this study, 27,438 orthogroups in the genomes of seven Poaceae were identified, and 214 of them were significantly expanded in barley. The evolutionary rates, gene properties, expression profiles, and nucleotide diversity between expanded and non-expanded genes were compared. Expanded genes evolved more rapidly and experienced lower negative selection. Expanded genes, including their exons and introns, were shorter, they had fewer exons, their GC content was lower, and their first exons were longer compared with non-expanded genes. Codon usage bias was also lower for expanded genes than for non-expanded genes; the expression levels of expanded genes were lower than those of non-expanded genes, and the expression of expanded genes showed higher tissue specificity than that of non-expanded genes. Several stress-response-related genes/gene families were identified, and these genes could be used to breed barley plants with greater resistance to environmental stress. Overall, our analysis revealed evolutionary, structural, and functional differences between expanded and non-expanded genes in barley. Additional studies are needed to clarify the functions of the candidate genes identified in our study and evaluate their utility for breeding barley plants with greater stress resistance.

The Current Developments in Medicinal Plant Genomics Enabled the Diversification of Secondary Metabolites' Biosynthesis

Medicinal plants produce important substrates for their adaptation and defenses against environmental factors and, at the same time, are used for traditional medicine and industrial additives. Plants have relatively little in the way of secondary metabolites via biosynthesis. Recently, the whole-genome sequencing of medicinal plants and the identification of secondary metabolite production were revolutionized by the rapid development and cheap cost of sequencing technology. Advances in functional genomics, such as transcriptomics, proteomics, and metabolomics, pave the way for discoveries in secondary metabolites and related key genes. The multi-omics approaches can offer tremendous insight into the variety, distribution, and development of biosynthetic gene clusters (BGCs). Although many reviews have reported on the plant and medicinal plant genome, chemistry, and pharmacology, there is no review giving a comprehensive report about the medicinal plant genome and multi-omics approaches to study the biosynthesis pathway of secondary metabolites. Here, we introduce the medicinal plant genome and the application of multi-omics tools for identifying genes related to the biosynthesis pathway of secondary metabolites. Moreover, we explore comparative genomics and polyploidy for gene family analysis in medicinal plants. This study promotes medicinal plant genomics, which contributes to the biosynthesis and screening of plant substrates and plant-based drugs and prompts the research efficiency of traditional medicine.

Genome assembly and association tests identify interacting loci associated with vigor, precocity, and sex in interspecific pistachio rootstocks

Understanding the basis of hybrid vigor remains a key question in crop breeding and improvement, especially for rootstock development where F1 hybrids are extensively utilized. Full-sibling UCB-1 F1 seedling rootstocks are widely planted in commercial pistachio orchards that are generated by crossing 2 highly heterozygous outbreeding parental trees of Pistacia atlantica (female) and P. integerrima (male). This results in extensive phenotypic variability, prompting costly removal of low-yielding small trees. To identify the genetic basis of this variability, we assembled chromosome-scale genome assemblies of the parental trees of UCB-1. We genotyped 960 UCB-1 trees in an experimental orchard for which we also collected multiyear phenotypes. We genotyped an additional 1,358 rootstocks in 6 commercial pistachio orchards and collected single-year tree-size data. Genome-wide single marker association tests identified loci associated with tree size and shape, sex, and precocity. In the experimental orchard, we identified multiple trait-associated loci and a strong candidate for ZZ/ZW sex chromosomes. We found significant marker associations unique to different traits and to early vs late phenotypic measures of the same trait. We detected 2 loci strongly associated with rootstock size in commercial orchards. Pseudo-testcross classification of markers demonstrated that the trait-associated alleles for each locus were segregating in the gametes of opposite parents. These 2 loci interact epistatically to generate the bimodal distribution of tree size with undesirable small trees observed by growers. We identified candidate genes within these regions. These findings provide a foundational resource for marker development and genetic selection of vigorous pistachio UCB-1 rootstock.

Genome-Wide Characterization, Identification and Expression Profile of MYB Transcription Factor Gene Family during Abiotic and Biotic Stresses in Mango (Mangifera indica)

Mango (Mangifera indica) is an economically important fruit tree, and is cultivated in tropical, subtropical, and dry-hot valley areas around the world. Mango fruits have high nutritional value, and are mainly consumed fresh and used for commercial purposes. Mango is affected by various environmental factors during its growth and development. The MYB transcription factors participates in various physiological activities of plants, such as phytohormone signal transduction and disease resistance. In this study, 54 MiMYB transcription factors were identified in the mango genome (371.6 Mb). A phylogenetic tree was drawn based on the amino acid sequences of 222 MYB proteins of mango and Arabidopsis. The phylogenetic tree showed that the members of the mango MYB gene family were divided into 7 group, including Groups 1, -3, -4, -5, -6, -8, and -9. Ka/Ks ratios generally indicated that the MiMYBs of mango were affected by negative or positive selection. Quantitative real-time PCR showed that the transcription levels of MiMYBs were different under abiotic and biotic stresses, including salicylic acid, methyl jasmonate, and H₂O₂ treatments, and Colletotrichum gloeosporioides and Xanthomonas campestris pv. mangiferaeindicae infection, respectively. The transcript levels of MiMYB5, -35, -36, and -54 simultaneously responded positively to early treatments with salicylic acid, methyl jasmonate, and H₂O_2. The transcript level of MiMYB54 was activated by pathogenic fungal and bacterial infection. These results are beneficial for future interested researchers aiming to understand the biological functions and molecular mechanisms of MiMYB genes.

The barley DIR gene family: An expanded gene family that is involved in stress responses

Gene family expansion plays a central role in adaptive divergence and, ultimately, speciation is influenced by phenotypic diversity in different environments. Barley (Hordeum vulgare) is the fourth most important cereal crop in the world and is used for brewing purposes, animal feed, and human food. Systematic characterization of expanded gene families is instrumental in the research of the evolutionary history of barley and understanding of the molecular function of their gene products. A total of 31,750 conserved orthologous groups (OGs) were identified using eight genomes/subgenomes, of which 1,113 and 6,739 were rapidly expanded and contracted OGs in barley, respectively. Five expanded OGs containing 20 barley dirigent genes (HvDIRs) were identified. HvDIRs from the same OG were phylogenetically clustered with similar gene structure and domain organization. In particular, 7 and 5 HvDIRs from OG0000960 and OG0001516, respectively, contributed greatly to the expansion of the DIR-c subfamily. Tandem duplication was the driving force for the expansion of the barley DIR gene family. Nucleotide diversity and haplotype network analysis revealed that the expanded HvDIRs experienced severe bottleneck events during barley domestication, and can thus be considered as potential domestication-related candidate genes. The expression profile and co-expression network analysis revealed the critical roles of the expanded HvDIRs in various biological processes, especially in stress responses. HvDIR18, HvDIR19, and HvDIR63 could serve as excellent candidates for further functional genomics studies to improve the production of barley products. Our study revealed that the HvDIR family was significantly expanded in barley and might be involved in different developmental processes and stress responses. Thus, besides providing a framework for future functional genomics and metabolomics studies, this study also identified HvDIRs as candidates for use in improving barley crop resistance to biotic and abiotic stresses.

Genome-wide identification of the mango CONSTANS (CO) family and functional analysis of two MiCOL9 genes in transgenic Arabidopsis

CONSTANS/CONSTANS-like (CO/COL) transcription factors play a vital role in the photoperiodic flowering pathway. However, the biological functions of COL genes in mango are unclear. In this study, we identified 31 COL genes from the 'Jin Huang' mango genome and divided them into three groups according to the specific gene structure and protein domain characteristics. These 31 MiCOL genes were heterogeneously distributed on 14 chromosomes. Expression pattern analysis showed that most MiCOL genes were mainly expressed in leaves and stems and during the floral induction period, followed by the floral differentiation period. The expression of COL genes was induced by drought and salt stress, but the expression patterns of different genes were different, which may suggest that MiCOL genes are involved in the abiotic stress response of mango. Under salt and drought conditions, two MiCOL9 genes can improve the resistance of Arabidopsis by improving the scavenging ability of ROS and proline accumulation and reducing the MDA content. Additionally, overexpression of MiCOL9 genes significantly inhibited flowering in transgenic Arabidopsis. This work provides an important foundation for understanding the biological roles of mango COL genes in plant growth, development and stress responses.

Genome analysis of Phrixothrix hirtus (Phengodidae) railroad worm shows the expansion of odorant-binding gene families and positive selection on morphogenesis and sex determination genes

Among bioluminescent beetles of the Elateroidea superfamily, Phengodidae is the third largest family, with 244 bioluminescent species distributed only in the Americas, but is still the least studied from the phylogenetic and evolutionary points of view. The railroad worm Phrixothrix hirtus is an essential biological model and symbolic species due to its bicolor bioluminescence, being the only organism that produces true red light among bioluminescent terrestrial species. Here, we performed partial genome assembly of P. hirtus, combining short and long reads generated with Illumina sequencing, providing the first source of genomic information and a framework for comparative analyses of the bioluminescent system in Elateroidea. This is the largest genome described in the Elateroidea superfamily, with an estimated size of ∼3.4 Gb, displaying 32 % GC content, and 67 % transposable elements. Comparative genomic analyses showed a positive selection of genes and gene family expansion events of growths and morphogenesis gene products, which could be associated with the atypical anatomical development and morphogenesis found in paedomorphic females and underdeveloped males. We also observed gene family expansion among distinct odorant-binding receptors, which could be associated with the pheromone communication system typical of these beetles, and retrotransposable elements. Common genes putatively regulating bioluminescence production and control, including two luciferase genes corresponding to lateral lanterns green-emitting and head lanterns red-emitting luciferases with 7 exons and 6 introns, and genes potentially involved in luciferin biosynthesis were found, indicating that there are no clear differences about the presence or absence of gene families associated with bioluminescence in Elateroidea.

Expression Profiling of Four Mango FT/TFL1-Encoding Genes under Different Fruit Load Conditions, and Their Involvement in Flowering Regulation

Plant flowering is antagonistically modulated by similar FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1) proteins. In mango (Mangifera indica L.), flowering is induced by cold temperatures, unless the tree is juvenile or the adult tree had a high fruit load (HFL) in the summer. Here, we studied the effects of juvenility and fruit load on the expression of four MiFT/TFL1 genes cloned from the mango ‘Shelly’ cultivar. Ectopic expression of MiFT1 in Arabidopsis resulted in early flowering, whereas over-expression of MiFT2 and the two cloned MiTFL1 genes repressed flowering. Moreover, juvenility was positively correlated with higher transcript levels of MiFT2 and both MiTFL1s. In trees with a low fruit load, leaf MiFT1 expression increased in winter, whereas HFL delayed its upregulation. MiFT2 expression was upregulated in both leaves and buds under both fruit load conditions. Downregulation of both MITFL1s in buds was associated with a decrease in regional temperatures under both conditions; nevertheless, HFL delayed the decrease in their accumulation. Our results suggest that cold temperature has opposite effects on the expression of MiFT1 and the MiTFL1s, thereby inducing flowering, whereas HFL represses flowering by both suppressing MiFT1 upregulation and delaying MiTFL1s downregulation. The apparent flowering-inhibitory functions of MiFT2 are discussed.

Identification of early quassinoid biosynthesis in the invasive tree of heaven (Ailanthus altissima) confirms evolutionary origin from protolimonoids

The tree of heaven, Ailanthus altissima (MILL.) SWINGLE, is a globally invasive plant known to secrete allelopathic metabolites called quassinoids. Quassinoids are highly modified triterpenoids. So far, nothing has been known about the biochemical basis of quassinoid biosynthesis. Here, based on transcriptome and metabolome data of Ailanthus altissima, we present the first three steps of quassinoid biosynthesis, which are catalysed by an oxidosqualene cyclase and two cytochrome P450 monooxygenases, resulting in the formation of the protolimonoid melianol. Strikingly, these steps are identical to the first steps of the biosynthesis of limonoids, structurally different triterpenoids from sister plant families within the same order Sapindales. Our results are therefore not only important to fully understand the biosynthesis of complex triterpenoids in plants, but also confirm the long-standing hypothesis that quassinoids and limonoids share an evolutionary origin. In addition, our transcriptome data for Ailanthus altissima will be beneficial to other researchers investigating the physiology and ecology of this invasive tree.

Genomic and Bioinformatic Resources for Perennial Fruit Species

In the post-genomic era, data management and development of bioinformatic tools are critical for the adequate exploitation of genomics data. In this review, we address the actual situation for the subset of crops represented by the perennial fruit species. The agronomical singularity of these species compared to plant and crop model species provides significant challenges on the implementation of good practices generally not addressed in other species. Studies are usually performed over several years in non-controlled environments, usage of rootstock is common, and breeders heavily rely on vegetative propagation. A reference genome is now available for all the major species as well as many members of the economically important genera for breeding purposes. Development of pangenome for these species is beginning to gain momentum which will require a substantial effort in term of bioinformatic tool development. The available tools for genome annotation and functional analysis will also be presented.

Jackfruit genome and population genomics provide insights into fruit evolution and domestication history in China

As the largest known tree-borne fruit in the world, jackfruit (Artocarpus heterophyllus) is an important cultivated crop in tropical regions of South and Southeast Asia. The species has been cultivated in China for more than 1000 years, but the history of its introduction to the country remains unclear. We assembled a high-quality chromosome-level genome of jackfruit into 985.63 Mb with scaffold N50 of 32.81 Mb. We analyzed whole-genome resequencing data of 295 landraces to investigate the domestication history in China and agronomic trait evolution of jackfruit. Population structure analysis revealed that jackfruits of China could be traced back to originate from Southeast Asia and South Asia independently. Selection signals between jackfruit and its edible congener, cempedak (Artocarpus integer), revealed several important candidate genes associated with fruit development and ripening. Moreover, analyses of selective sweeps and gene expression revealed that the AhePG1 gene may be the major factor in determining fruit texture. This study not only resolves the origins of jackfruit of China, but also provides valuable genomic resources for jackfruit breeding improvement and offers insights into fruit size evolution and fruit texture changes.

Genomic insights into the evolution of plant chemical defense

Plant trait evolution can be impacted by common mechanisms of genome evolution, including whole-genome and small-scale duplication, rearrangement, and selective pressures. With the increasing accessibility of genome sequencing for non-model species, comparative studies of trait evolution among closely related or divergent lineages have supported investigations into plant chemical defense. Plant defensive compounds include major chemical classes, such as terpenoids, alkaloids, and phenolics, and are used in primary and secondary plant functions. These include the promotion of plant health, facilitation of pollination, defense against pathogens, and responses to a rapidly changing climate. We discuss mechanisms of genome evolution and use examples from recent studies to impress a stronger understanding of the link between genotype and phenotype as it relates to the evolution of plant chemical defense. We conclude with considerations for how to leverage genomics, transcriptomics, metabolomics, and functional assays for studying the emergence and evolution of chemical defense systems.

The Manchurian Walnut Genome: Insights into Juglone and Lipid Biosynthesis

BACKGROUND

Manchurian walnut (Juglans mandshurica Maxim.) is a tree with multiple industrial uses and medicinal properties in the Juglandaceae family (walnuts and hickories). J. mandshurica produces juglone, which is a toxic allelopathic agent and has potential utilization value. Furthermore, the seed of J. mandshurica is rich in various unsaturated fatty acids and has high nutritive value.

FINDINGS

Here, we present a high-quality chromosome-scale reference genome assembly and annotation for J. mandshurica (n = 16) with a contig N50 of 21.4 Mb by combining PacBio high-fidelity reads with high-throughput chromosome conformation capture data. The assembled genome has an estimated sequence size of 548.7 Mb and consists of 657 contigs, 623 scaffolds, and 40,453 protein-coding genes. In total, 60.99% of the assembled genome consists of repetitive sequences. Sixteen super-scaffolds corresponding to the 16 chromosomes were assembled, with a scaffold N50 length of 33.7 Mb and a BUSCO complete gene percentage of 98.3%. J. mandshurica displays a close sequence relationship with Juglans cathayensis, with a divergence time of 13.8 million years ago. Combining the high-quality genome, transcriptome, and metabolomics data, we constructed a gene-to-metabolite network and identified 566 core and conserved differentially expressed genes, which may be involved in juglone biosynthesis. Five CYP450 genes were found that may contribute to juglone accumulation. NAC, bZip, NF-YA, and NF-YC are positively correlated with the juglone content. Some candidate regulators (e.g., FUS3, ABI3, LEC2, and WRI1 transcription factors) involved in the regulation of lipid biosynthesis were also identified.

CONCLUSIONS

Our genomic data provide new insights into the evolution of the walnut genome and create a new platform for accelerating molecular breeding and improving the comprehensive utilization of these economically important tree species.

The chromosome-level genome for Toxicodendron vernicifluum provides crucial insights into Anacardiaceae evolution and urushiol biosynthesis

The lacquer tree (Toxicodendron vernicifluum (Stokes) F.A. Barkley) is an important tree with economic, industrial, and medicinal values. Here, we generated the reference genome of T. vernicifluum at the chromosome level with 491.93 Mb in size, in which 98.26% of the assembled contigs were anchored onto 15 pseudochromosomes with the scaffold N50 of 32.97 Mb. Comparative genomic analysis revealed the gene families related to urushiol biosynthesis were expanded, contributing to the ecological fitness and biological adaptability of the lacquer tree. We combined multi-omics data to identify genes that encode key enzymes in the T. vernicifluum urushiol and lignin biosynthetic pathways. Furthermore, the unique active metabolites, such as butin and fisetin, in cultivar lacquers were identified by metabolism profiling. Our work would provide crucial insights into metabolite synthesis such as urushiol and lignin, meanwhile offer a basis for further exploration of the cultivation and breeding of T. vernicifluum and other Anacardiaceae members.

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We provide the first chromosome-level genome for Toxicodendron vernicifluum

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We explore the phylogenetic position of lacquer tree

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We identify genes involved in the urushiol and lignin biosynthetic pathways

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Analysis of the unique active metabolites in cultivar lacquers by LC-MS/MS is reported

Unlocking plant metabolic diversity: A (pan)-genomic view

Plants produce a remarkable diversity of structurally and functionally diverse natural chemicals that serve as adaptive compounds throughout their life cycles. However, unlocking this metabolic diversity is significantly impeded by the size, complexity, and abundant repetitive elements of typical plant genomes. As genome sequencing becomes routine, we anticipate that links between metabolic diversity and genetic variation will be strengthened. In addition, an ever-increasing number of plant genomes have revealed that biosynthetic gene clusters are not only a hallmark of microbes and fungi; gene clusters for various classes of compounds have also been found in plants, and many are associated with important agronomic traits. We present recent examples of plant metabolic diversification that have been discovered through the exploration and exploitation of various genomic and pan-genomic data. We also draw attention to the fundamental genomic and pan-genomic basis of plant chemodiversity and discuss challenges and future perspectives for investigating metabolic diversity in the coming pan-genomics era.

Genome-wide SNP and InDel analysis of three Philippine mango species inferred from whole-genome sequencing

Background

The Philippines is among the top 10 major exporters of mango worldwide. However, genomic studies of Philippine mangoes remain largely unexplored and lacking. Here, we sequenced the whole genome of the three Philippine mango species, namely, Mangifera odorata (Huani), Mangifera altissima (Paho), and Mangifera indica “Carabao” variety using Illumina HiSeq 2500, to identify and analyze their genome-wide variants (SNPs and InDels).

Results

The high confidence variants were identified by successfully mapping 93–95% of the quality-filtered reads to the Alphonso and Tommy Atkins mango reference genomes. Using these two currently available mango genomes, most variants were observed in M. odorata (4,353,063 and 4,277,287), followed by M. altissima (3,392,763 and 3,449,917), and lastly, M. indica Carabao (2,755,267 and 2,852,480). Approximately 50, 46, and 38% of the variants were unique in the three Philippine mango genomes. The analysis of variant effects and functional annotation across the three mango species revealed 56,982 variants with high-impact effects mapped onto 37,746 genes, of which 25% were found to be novel. The affected mango genes include those with potential economic importance such as 6945 genes for defense/resistance/immune response, 323 genes for fruit development, and 338 genes for anthocyanin production.

Conclusions

To date, this is the first sequencing effort to comprehensively analyze genome-wide variants essential for the development of genome-wide markers specific to these mango species native to the Philippines. This study provides an important genomic resource that can be used for the genetic improvement of mangoes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00326-3.

Complete mitochondrial genomes of three Mangifera species, their genomic structure and gene transfer from chloroplast genomes

Background

Among the Mangifera species, mango (Mangifera indica) is an important commercial fruit crop. However, very few studies have been conducted on the Mangifera mitochondrial genome. This study reports and compares the newly sequenced mitochondrial genomes of three Mangifera species.

Results

Mangifera mitochondrial genomes showed partial similarities in the overall size, genomic structure, and gene content. Specifically, the genomes are circular and contain about 63–69 predicted functional genes, including five ribosomal RNA (rRNA) genes and 24–27 transfer RNA (tRNA) genes. The GC contents of the Mangifera mitochondrial genomes are similar, ranging from 44.42–44.66%. Leucine (Leu) and serine (Ser) are the most frequently used, while tryptophan (Trp) and cysteine (Cys) are the least used amino acids among the protein-coding genes in Mangifera mitochondrial genomes. We also identified 7–10 large chloroplast genomic fragments in the mitochondrial genome, ranging from 1407 to 6142 bp. Additionally, four intact mitochondrial tRNAs genes (tRNA-Cys, tRNA-Trp, tRNA-Pro, and tRNA-Met) and intergenic spacer regions were identified. Phylogenetic analysis based on the common protein-coding genes of most branches provided a high support value.

Conclusions

We sequenced and compared the mitochondrial genomes of three Mangifera species. The results showed that the gene content and the codon usage pattern of Mangifera mitochondrial genomes is similar across various species. Gene transfer from the chloroplast genome to the mitochondrial genome were identified. This study provides valuable information for evolutionary and molecular studies of Mangifera and a basis for further studies on genomic breeding of mango.