Gapless genome assembly of azalea and multi-omics investigation into divergence between two species with distinct f lower color

The genus Rhododendron(Ericaceae),with more than 1000 species highly diverse in f lower color,is providing distinct ornamental values and a model system for f lower color studies.Here,we investigated the divergence between two parental species with different f lower color widely used for azalea breeding.Gapless genome assembly was generated for the yellow-f lowered azalea,Rhododendron molle.Comparative genomics found recent proliferation of long terminal repeat retrotransposons(LTR-RTs),especially Gypsy,has resulted in a 125 Mb(19%)genome size increase in species-specific regions,and a significant amount of dispersed gene duplicates(13402)and pseudogenes(17437).Metabolomic assessment revealed that yellow f lower coloration is attributed to the dynamic changes of carotenoids/f lavonols biosynthesis and chlorophyll degradation.Time-ordered gene co-expression networks(TO-GCNs)and the comparison confirmed the metabolome and uncovered the specific gene regulatory changes underpinning the distinct f lower pigmentation.B3 and ERF TFs were found dominating the gene regulation of carotenoids/f lavonols characterized pigmentation in R.molle,while WRKY,ERF,WD40,C2H2,and NAC TFs collectively regulated the anthocyanins characterized pigmentation in the red-f lowered R simsii.This study employed a multi-omics strategy in disentangling the complex divergence between two important azaleas and provided references for further functional genetics and molecular breeding.

Haplotype-resolved genome assembly and allele- specific gene expression in cultivated ginger

Ginger(Zingiber officinale)is one of the most valued spice plants worldwide;it is prized for its culinary and folk medicinal applications and is therefore of high economic and cultural importance.Here,we present a haplotype-resolved,chromosome-scale assembly for diploid ginger anchored to 11 pseudochromosome pairs with a total length of 3.1 Gb.Remarkable structural variation was identified between haplotypes,and two inversions larger than 15Mb on chromosome 4 may be associated with ginger infertility.We performed a comprehensive,spatiotemporal,genome-wide analysis of allelic expression patterns,revealing that most alleles are coordinately expressed.The alleles that exhibited the largest differences in expression showed closer proximity to transposable elements,greater coding sequence divergence,more relaxed selection pressure,and more transcription factor binding site differences.We also predicted the transcription factors potentially regulating 6-gingerol biosynthesis.Our allele-aware assembly provides a powerful platform for future functional genomics,molecular breeding,and genome editing in ginger.

Chromosome-scale assembly and evolution of the tetraploid Salvia splendens (Lamiaceae) genome

Polyploidization plays a key role in plant evolution,but the forces driving the fate of homoeologs in polyploid genomes,i.e.,paralogs resulting from a whole-genome duplication(WGD)event,remain to be elucidated.Here,we present a chromosome-scale genome assembly of tetraploid scarlet sage(Salvia splendens),one of the most diverse ornamental plants.We found evidence for three WGD events following an older WGD event shared by most eudicots(theγevent).A comprehensive,spatiotemporal,genome-wide analysis of homoeologs from the most recent WGD unveiled expression asymmetries,which could be associated with genomic rearrangements,transposable element proximity discrepancies,coding sequence variation,selection pressure,and transcription factor binding site differences.The observed differences between homoeologs may reflect the first step toward sub-and/or neofunctionalization.This assembly provides a powerful tool for understanding WGD and gene and genome evolution and is useful in developing functional genomics and genetic engineering strategies for scarlet sage and other Lamiaceae species.