Tangren Cheng

The genome of Prunus mume

Prunus mume (mei), which was domesticated in China more than 3,000 years ago as ornamental plant and fruit, is one of the first genomes among Prunus subfamilies of Rosaceae been sequenced. Here, we assemble a 280M genome by combining 101-fold next-generation sequencing and optical mapping data. We further anchor 83.9% of scaffolds to eight chromosomes with genetic map constructed by restriction-site-associated DNA sequencing. Combining P. mume genome with available data, we succeed in reconstructing nine ancestral chromosomes of Rosaceae family, as well as depicting chromosome fusion, fission and duplication history in three major subfamilies. We sequence the transcriptome of various tissues and perform genome-wide analysis to reveal the characteristics of P. mume, including its regulation of early blooming in endodormancy, immune response against bacterial infection and biosynthesis of flower scent. The P. mume genome sequence adds to our understanding of Rosaceae evolution and provides important data for improvement of fruit trees.

Genetic control of juvenile growth and botanical architecture in an ornamental woody plant, Prunus mume Sieb. et Zucc. as revealed by a high-density linkage map.

Mei, Prunus mume Sieb. et Zucc., is an ornamental plant popular in East Asia and, as an important member of genus Prunus, has played a pivotal role in systematic studies of the Rosaceae. However, the genetic architecture of botanical traits in this species remains elusive. This paper represents the first genome-wide mapping study of quantitative trait loci (QTLs) that affect stem growth and form, leaf morphology and leaf anatomy in an intraspecific cross derived from two different mei cultivars. Genetic mapping based on a high-density linkage map constricted from 120 SSRs and 1,484 SNPs led to the detection of multiple QTLs for each trait, some of which exert pleiotropic effects on correlative traits. Each QTL explains 3-12% of the phenotypic variance. Several leaf size traits were found to share common QTLs, whereas growth-related traits and plant form traits might be controlled by a different set of QTLs. Our findings provide unique insights into the genetic control of tree growth and architecture in mei and help to develop an efficient breeding program for selecting superior mei cultivars.

High-density genetic map construction and identification of a locus controlling weeping trait in an ornamental woody plant (Prunus mume Sieb. et Zucc)

High-density genetic map is a valuable tool for fine mapping locus controlling a specific trait especially for perennial woody plants. In this study, we firstly constructed a high-density genetic map of mei (Prunus mume) using SLAF markers, developed by specific locus amplified fragment sequencing (SLAF-seq). The linkage map contains 8,007 markers, with a mean marker distance of 0.195 cM, making it the densest genetic map for the genus Prunus. Though weeping trees are used worldwide as landscape plants, little is known about weeping controlling gene(s) (Pl). To test the utility of the high-density genetic map, we did fine-scale mapping of this important ornamental trait. In total, three statistic methods were performed progressively based on the result of inheritance analysis. Quantitative trait loci (QTL) analysis initially revealed that a locus on linkage group 7 was strongly responsible for weeping trait. Mutmap-like strategy and extreme linkage analysis were then applied to fine map this locus within 1.14 cM. Bioinformatics analysis of the locus identified some candidate genes. The successful localization of weeping trait strongly indicates that the high-density map constructed using SLAF markers is a worthy reference for mapping important traits for woody plants.

Genome-wide identification, characterisation and expression analysis of the MADS-box gene family in Prunus mume.

MADS-box genes encode transcription factors that play crucial roles in plant development, especially in flower and fruit development. To gain insight into this gene family in Prunus mume, an important ornamental and fruit plant in East Asia, and to elucidate their roles in flower organ determination and fruit development, we performed a genome-wide identification, characterisation and expression analysis of MADS-box genes in this Rosaceae tree. In this study, 80 MADS-box genes were identified in P. mume and categorised into MIKC, Mα, Mβ, Mγ and Mδ groups based on gene structures and phylogenetic relationships. The MIKC group could be further classified into 12 subfamilies. The FLC subfamily was absent in P. mume and the six tandemly arranged DAM genes might experience a species-specific evolution process in P. mume. The MADS-box gene family might experience an evolution process from MIKC genes to Mδ genes to Mα, Mβ and Mγ genes. The expression analysis suggests that P. mume MADS-box genes have diverse functions in P. mume development and the functions of duplicated genes diverged after the duplication events. In addition to its involvement in the development of female gametophytes, type I genes also play roles in male gametophytes development. In conclusion, this study adds to our understanding of the roles that the MADS-box genes played in flower and fruit development and lays a foundation for selecting candidate genes for functional studies in P. mume and other species. Furthermore, this study also provides a basis to study the evolution of the MADS-box family.

Genome-Wide Analysis of the AP2/ERF Gene Family in Prunus mume

The APETALA 2/ethylene-responsive element binding factor (AP2/ERF) transcription factors play important roles in plant development and responses to stress. Although the entire genomes of four Rosaceae species have been fully sequenced, no genome-wide analysis of AP2/ERF gene family has yet been reported in the Rosaceae family. In this study, 116 AP2/ERF genes were identified from Chinese plum (Prunus mume). Based on the number of AP2/ERF domains, these PmAP2/ERF genes were classified into three families (AP2, ERF, and RAV) along with a single member. The ERF family was subdivided into 11 groups. Of those, 22 and 41 PmAP2/ERF genes were involved in segmental and tandem duplications, respectively. Putative orthologs in Arabidopsis were identified for 73 PmAP2/ERF genes following synteny analysis. Transcriptome sequencing analysis showed that expression of PmAP2/ERF genes was widely variable.

Genome-Wide Characterization and Linkage Mapping of Simple Sequence Repeats in Mei (Prunus mume Sieb. et Zucc.)

Because of its popularity as an ornamental plant in East Asia, mei (Prunus mume Sieb. et Zucc.) has received increasing attention in genetic and genomic research with the recent shotgun sequencing of its genome. Here, we performed the genome-wide characterization of simple sequence repeats (SSRs) in the mei genome and detected a total of 188,149 SSRs occurring at a frequency of 794 SSR/Mb. Mononucleotide repeats were the most common type of SSR in genomic regions, followed by di- and tetranucleotide repeats. Most of the SSRs in coding sequences (CDS) were composed of tri- or hexanucleotide repeat motifs, but mononucleotide repeats were always the most common in intergenic regions. Genome-wide comparison of SSR patterns among the mei, strawberry (Fragaria vesca), and apple (Malus×domestica) genomes showed mei to have the highest density of SSRs, slightly higher than that of strawberry (608 SSR/Mb) and almost twice as high as that of apple (398 SSR/Mb). Mononucleotide repeats were the dominant SSR motifs in the three Rosaceae species. Using 144 SSR markers, we constructed a 670 cM-long linkage map of mei delimited into eight linkage groups (LGs), with an average marker distance of 5 cM. Seventy one scaffolds covering about 27.9% of the assembled mei genome were anchored to the genetic map, depending on which the macro-colinearity between the mei genome and Prunus T×E reference map was identified. The framework map of mei constructed provides a first step into subsequent high-resolution genetic mapping and marker-assisted selection for this ornamental species.

Genome-wide DNA polymorphisms in two cultivars of mei ( Prunus mume sieb. et zucc.)

BackgroundMei (Prunus mume Sieb. et Zucc.) is a famous ornamental plant and fruit crop grown in East Asian countries. Limited genetic resources, especially molecular markers, have hindered the progress of mei breeding projects. Here, we performed low-depth whole-genome sequencing of Prunus mume ‘Fenban’ and Prunus mume ‘Kouzi Yudie’ to identify high-quality polymorphic markers between the two cultivars on a large scale.ResultsA total of 1464.1 Mb and 1422.1 Mb of ‘Fenban’ and ‘Kouzi Yudie’ sequencing data were uniquely mapped to the mei reference genome with about 6-fold coverage, respectively. We detected a large number of putative polymorphic markers from the 196.9 Mb of sequencing data shared by the two cultivars, which together contained 200,627 SNPs, 4,900 InDels, and 7,063 SSRs. Among these markers, 38,773 SNPs, 174 InDels, and 418 SSRs were distributed in the 22.4 Mb CDS region, and 63.0% of these marker-containing CDS sequences were assigned to GO terms. Subsequently, 670 selected SNPs were validated using an Agilent’s SureSelect solution phase hybridization assay. A subset of 599 SNPs was used to assess the genetic similarity of a panel of mei germplasm samples and a plum (P. salicina) cultivar, producing a set of informative diversity data. We also analyzed the frequency and distribution of detected InDels and SSRs in mei genome and validated their usefulness as DNA markers. These markers were successfully amplified in the cultivars and in their segregating progeny.ConclusionsA large set of high-quality polymorphic SNPs, InDels, and SSRs were identified in parallel between ‘Fenban’ and ‘Kouzi Yudie’ using low-depth whole-genome sequencing. The study presents extensive data on these polymorphic markers, which can be useful for constructing high-resolution genetic maps, performing genome-wide association studies, and designing genomic selection strategies in mei.

Whole-Transcriptome Analysis of Differentially Expressed Genes in the Vegetative Buds, Floral Buds and Buds of Chrysanthemum morifolium

Background Chrysanthemum morifolium is an important floral crop that is cultivated worldwide. However, due to a lack of genomic resources, very little information is available concerning the molecular mechanisms of flower development in chrysanthemum. Results The transcriptomes of chrysanthemum vegetative buds, floral buds and buds were sequenced using Illumina paired-end sequencing technology. A total of 15.4 Gb of reads were assembled into 91,367 unigenes with an average length of 739 bp. A total of 43,137 unigenes showed similarity to known proteins in the Swissprot or NCBI non-redundant protein databases. Additionally, 25,424, 24,321 and 13,704 unigenes were assigned to 56 gene ontology (GO) categories, 25 EuKaryotic Orthologous Groups (KOG) categories, and 285 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, respectively. A total of 1,876 differentially expressed genes (DEGs) (1,516 up-regulated, 360 down-regulated) were identified between vegetative buds and floral buds, and 3,300 DEGs (1,277 up-regulated, 1,706 down-regulated) were identified between floral buds and buds. Many genes encoding important transcription factors (e.g., AP2, MYB, MYC, WRKY, NAC and CRT) as well as proteins involved in carbohydrate metabolism, protein kinase activity, plant hormone signal transduction, and the defense responses, among others, were considerably up-regulated in floral buds. Genes involved in the photoperiod pathway and flower organ determination were also identified. These genes represent important candidate genes for molecular cloning and functional analysis to study flowering regulation in chrysanthemum. Conclusion This comparative transcriptome analysis revealed significant differences in gene expression and signaling pathway components between the vegetative buds, floral buds and buds of Chrysanthemum morifolium. A wide range of genes was implicated in regulating the phase transition from vegetative to reproductive growth. These results should aid researchers in the study of flower-time regulation, breeding and molecular biology in chrysanthemum.

Identification and expression analysis of the SQUAMOSA promoter-binding protein (SBP)-box gene family in Prunus mume

SQUAMOSA promoter-binding protein (SBP)-box family genes encode plant-specific transcription factors that play crucial roles in plant development, especially flower and fruit development. However, little information on this gene family is available for Prunus mume, an ornamental and fruit tree widely cultivated in East Asia. To explore the evolution of SBP-box genes in Prunus and explore their functions in flower and fruit development, we performed a genome-wide analysis of the SBP-box gene family in P. mume. Fifteen SBP-box genes were identified, and 11 of them contained an miR156 target site. Phylogenetic and comprehensive bioinformatics analyses revealed that different groups of SBP-box genes have undergone different evolutionary processes and varied in their length, structure, and motif composition. Purifying selection has been the main selective constraint on both paralogous and orthologous SBP-box genes. In addition, the sequences of orthologous SBP-box genes did not diverge widely after the split of P. mume and Prunus persica. Expression analysis of P. mume SBP-box genes revealed their diverse spatiotemporal expression patterns. Three duplicated SBP-box genes may have undergone subfunctionalization in Prunus. Most of the SBP-box genes showed high transcript levels in flower buds and young fruit. The four miR156-nontargeted genes were upregulated during fruit ripening. Together, these results provide information about the evolution of SBP-box genes in Prunus. The expression analysis lays the foundation for further research on the functions of SBP-box genes in P. mume and other Prunus species, especially during flower and fruit development.

A Model Framework for Identifying Genes that Guide the Evolution of Heterochrony

Heterochrony, the phylogenic change in the time of developmental events or rate of development, has been thought to play an important role in producing phenotypic novelty during evolution. Increasing evidence suggests that specific genes are implicated in heterochrony, guiding the process of developmental divergence, but no quantitative models have been instrumented to map such heterochrony genes. Here, we present a computational framework for genetic mapping by which to characterize and locate quantitative trait loci (QTLs) that govern heterochrony described by four parameters, the timing of the inflection point, the timing of maximum acceleration of growth, the timing of maximum deceleration of growth, and the length of linear growth. The framework was developed from functional mapping, a dynamic model derived to map QTLs for the overall process and pattern of development. By integrating an optimality algorithm, the framework allows the so-called heterochrony QTLs (hQTLs) to be tested and quantified. Specific pipelines are given for testing how hQTLs control the onset and offset of developmental events, the rate of development, and duration of a particular developmental stage. Computer simulation was performed to examine the statistical properties of the model and demonstrate its utility to characterize the effect of hQTLs on population diversification due to heterochrony. By analyzing a genetic mapping data in rice, the framework identified an hQTL that controls the timing of maximum growth rate and duration of linear growth stage in plant height growth. The framework provides a tool to study how genetic variation translates into phenotypic innovation, leading a lineage to evolve, through heterochrony.