Genetic relationship and pedigree of Chinese watermelon varieties based on diversity of perfect SNPs

Watermelon(Citrullus lanatus)is one of the world’s most important fruit crops,and China produces the most watermelons in the world.Recently,a watermelon variome consisting of 414 key resequenced accessions was reported.However,the genetic relationships and pedigree of Chinese watermelon varieties in the seed market remain unclear.In this study,241 evenly distributed perfect single nucleotide polymorphisms(SNPs)derived from the watermelon variome were selected for variety identification.The diversity of 247 Chinese watermelon varieties was identified based on their SNP genotypes.The 247 watermelon varieties were clustered into five subpopulations:the East Asian ecotype,intermediate ecotype,small fruit with red flesh ecotype,small fruit with yellow flesh ecotype,and American ecotype.We further established the pedigree of four subpopulations,of which JingXinNo.1,ZaoChunHongYu,HuangXiaoYu and XiaoLan,and Sugarlee were the main doner of the East Asian ecotype,small fruit with red flesh ecotype,small fruit with yellow flesh ecotype,and American ecotype,respectively.Thirty-two core SNPs were selected and applied in watermelon variety identification.They were also validated by the Kompetitive allele-specific PCR(KASPar)platform.The present study furthered our understanding of the genetic relationships and pedigree of watermelon varieties in China,and will help to manage the plant variety protection in watermelon.

Comparison of DUS testing and SNP fingerprinting for variety identification in cucumber

Variety identification plays an important role in protecting the intellectual property of varieties,ensuring seed quality,and encouraging breeding innovation.Currently,morphological evaluation in the field,such as distinctness,uniformity,and stability(DUS)testing,and DNA fingerprinting in the laboratory using molecular markers are two dominant methods used for variety identification.Few studies have compared the results of these approaches,and the relationship between the two methods is obscure.In this study,134 dominant cucumber varieties were evaluated using 50 DUS testing traits and genotyped by 40 single nucleotide polymorphisms(SNPs).The 40 SNPs were developed in our previous study and arewell suited for variety identification.In the DUS testing,significant positive or negative correlations among 50 DUS traits were observed,and 20 core traits,including 15 fruit traits,were further selected to increase field inspection efficiency.This suggested that fruit shape plays an important role in variety identification.The ratio of fruit length/diameter was themost important trait,explaining 9.2%of the phenotypic variation.In the DNA fingerprinting test,the 40 SNPs were highly polymorphic and could distinguish all of the 134 cucumber varieties,and 14 core SNPs were selected to improve the identification rate.Interestingly,the population structure analysis of 134 cucumber varieties by phenotypic data in the DUS test was in accordance with the genotypic data from the DNA fingerprinting,indicating that all varieties could be divided into the same four subgroups:European type,North China type,South China type,and hybrids of the North China and South China types.Moreover,linear correlativity of distinguishment for each pair of varieties was observed between the DUS test and the DNA fingerprinting.These results indicated that these two methods have good application in future research,especially for the scaled-up analysis of hundreds of varieties.

Identification of long noncoding RNAs involved in resistance to downy mildew in Chinese cabbage

Brassica downy mildew,a severe disease caused by Hyaloperonospora brassicae,can cause enormous economic losses in Chinese cabbage(Brassica rapa L.ssp.pekinensis)production.Although some research has been reported recently concerning the underlying resistance to this disease,no studies have identified or characterized long noncoding RNAs involved in this defense response.In this study,using high-throughput RNA sequencing,we analyzed the disease-responding mRNAs and long noncoding RNAs in two resistant lines(T12–19 and 12–85)and one susceptible line(91–112).Clustering and Gene Ontology analysis of differentially expressed genes(DEGs)showed that more DEGs were involved in the defense response in the two resistant lines than in the susceptible line.Different expression patterns and proposed functions of differentially expressed long noncoding RNAs among T12–19,12–85,and 91–112 indicated that each has a distinct disease response mechanism.There were significantly more cis-and trans-functional long noncoding RNAs in the resistant lines than in the susceptible line,and the genes regulated by these RNAs mostly participated in the disease defense response.Furthermore,we identified a candidate resistance-related long noncoding RNA,MSTRG.19915,which is a long noncoding natural antisense transcript of a MAPK gene,BrMAPK15.Via an agroinfiltration-mediated transient overexpression system and virus-induced gene silencing technology,BrMAPK15 was indicated to have a greater ability to defend against pathogens.MSTRG.19915-silenced seedlings showed enhanced resistance to downy mildew,probably because of the upregulated expression of BrMAPK15.This research identified and characterized long noncoding RNAs involved in resistance to downy mildew,laying a foundation for future in-depth studies of disease resistance mechanisms in Chinese cabbage.

Genome-wide analysis of changes in miRNA and target gene expression reveals key roles in heterosis for chinese cabbage biomass

Heterosis is a complex phenomenon in which hybrids show better phenotypic characteristics than their parents do.Chinese cabbage(Brassica rapa L.spp.pekinensis)is a popular leafy crop species,hybrids of which are widely used in commercial production;however,the molecular basis of heterosis for biomass of Chinese cabbage is poorly understood.We characterized heterosis in a Chinese cabbage hybrid cultivar and its parental lines from the seedling stage to the heading stage;marked heterosis of leaf weight and biomass yield were observed.Small RNA sequencing revealed 63 and 50 differentially expressed microRNAs(DEMs)at the seedling and early-heading stages,respectively.The expression levels ofthe majority of miRNA clusters in the hybrid were lower than the mid-parent values(MPVs).Using degradome sequencing,we identi fied 1,819 miRNA target genes.Gene ontology(GO)analyses demonstrated that the target genes ofthe MPV-DEMs and low parental expression level dominance(ELD)miRNAs were signi ficantly enriched in leaf morphogenesis,leaf development,and leaf shaping.Transcriptome analysis revealed that the expression levels of photosynthesis and chlorophyll synthesis-related MPV-DEGs(differentially expressed genes)were signi ficantly different in the F_(1) hybrid compared to the parental lines,resulting in increased photosynthesis capacity and chlorophyll content in the former.Furthermore,expression of genes known to regulate leaf development was also observed at the seedling stage.Arabidopsis plants overexpressing BrGRF4.2 and bra-miR396 presented increased and decreased leaf sizes,respectively.These results provide new insight into the regulation of target genes and miRNA expression patterns in leaf size and heterosis for biomass of B.rapa.

A Genomic Variation Map Provides Insights into the Genetic Basis of Spring Chinese Cabbage (Brassica rapa ssp.pekinensis)Selection

Chinese cabbage is the most consumed leafy crop in East Asian countries.However,premature bolting induced by continuous low temperatures severely decreases the yield and quality of the Chinese cabbage, and therefore restricts its planting season and geographic distribution.In the past 40years,spring Chinese cabbage with strong winterness has been selected to meet the market demand.Here,we report a genome variation map of Chinese cabbage generated from the resequencing data of 194 geographically diverse accessions of three ecotypes.In-depth analyses of the selection sweeps and genome-wide patterns revealed that spring Chinese cabbage was selected from a specific population of autumn Chinese cabbage around the area of Shandong peninsula in northern China.We identified 23 genomic loci that underwent intensive selection,and further demonstrated by gene expression and haplotype analyses that the incorporation of elite alleles of VERNALISATION INSENTIVE 3.1(BrVIN3.1)and FLOWER LOCUS C 1(BrFLC1)is a determinant genetic source of variation during selection.Moreover,we showed that the quantitative response of BrVIN3.1 to cold due to the sequence variations in the cis elements of the BrVlN3.1 promoter significantly contributes to bolting-time variation in Chinese cabbage.Collectively, our study provides valuable insights into the genetic basis of spring Chinese cabbage selection and will facilitate the breeding of bolting-resistant Varieties by molecular-marker-assisted selection,transgenic or gene editingapproaches.