Genome assembly and resequencing analyses provide new insights into the evolution, domestication and ornamental traits of crape myrtle

Crape myrtle(Lagerstroemia indica)is a globally used ornamental woody plant and is the representative species of Lagerstroemia.However,studies on the evolution and genomic breeding of L.indica have been hindered by the lack of a reference genome.Here we assembled the first high-quality genome of L.indica using PacBio combined with Hi-C scaffolding to anchor the 329.14-Mb genome assembly into 24 pseudochromosomes.We detected a previously undescribed independent whole-genome triplication event occurring 35.5 million years ago in L.indica following its divergence from Punica granatum.After resequencing 73 accessions of Lagerstroemia,the main parents of modern crape myrtle cultivars were found to be L.indica and L.fauriei.During the process of domestication,genetic diversity tended to decrease in many plants,but this was not observed in L.indica.We constructed a high-density genetic linkage map with an average map distance of 0.33 cM.Furthermore,we integrated the results of quantitative trait locus(QTL)using genetic mapping and bulk segregant analysis(BSA),revealing that the major-effect interval controlling internode length(IL)is located on chr1,which contains CDL15,CRG98,and GID1b1 associated with the phytohormone pathways.Analysis of gene expression of the red,purple,and white flower-colour flavonoid pathways revealed that differential expression of multiple genes determined the flower colour of L.indica,with white flowers having the lowest gene expression.In addition,BSA of purple-and green-leaved individuals of populations of L.indica was performed,and the leaf colour loci were mapped to chr12 and chr17.Within these intervals,we identified MYB35,NCED,and KAS1.Our genome assembly provided a foundation for investigating the evolution,population structure,and differentiation of Myrtaceae species and accelerating the molecular breeding of L.indica.

Transcriptome and chemical analyses identify candidate genes associated with flower color shift in a natural mutant of Chrysanthemum × morifolium

Flower color variation in Chrysanthemum×morifolium is an important horticultural trait.This study identifies a natural bud sprout mutant of chrysanthemum cultivar Hanluhong(HLH)which normally produces red flowers.In the mutant(hlh),the tip of the petals turn golden yellow and gradually turn yellow from tip to the base.After two years of consecutive propagation through cuttings,the mutant traits were stable.Here,the contents of carotenoids and anthocyanidins were determined by HPLC-MS/MS.Compared to HLH,the hlh displayed significantly higher contents of lutein.Then we comparatively analyzed the transcriptome of the ray florets tissues during three flower developmental stages.Higher number of stage specific DEGs were found in mutant cultivar as compared to wild type.About 200 DEGs were filtered related to the metabolism of flavonoids,carotenoids,terpenoids,and anthocyanins.Combined with weighted gene co-expression network analysis(WGCNA)and qRT-PCR verification,CHI,DFR,ANS and CCD4 genes involved in anthocyanins biosynthesis and carotenoids degradation were identified as candidate genes.Among the transcription factors,MYB,bHLH and WD40 members showed significant expression variations between the two cultivars.These results improve our understanding of flower color variation especially red and yellow color transition in chrysanthemum.

Current perspectives on shoot branching regulation

Shoot branching is regulated by the complex interactions among hormones, development, and environmental factors. Recent studies into the regulatory mechanisms of shoot branching have focused on strigolactones,which is a new area of investigation in shoot branching regulation. Elucidation of the function of the D53 gene has allowed exploration of detailed mechanisms of action of strigolactones in regulating shoot branching. In addition,the recent discovery that sucrose is key for axillary bud release has challenged the established auxin theory, in which auxin is the principal agent in the control of apical dominance. These developments increase our understanding of branching control and indicate that regulation of shoot branching involves a complex network. Here, we first summarize advances in the systematic regulatory network of plant shoot branching based on current information. Then we describe recent developments in the synthesis and signal transduction of strigolactones.Based on these considerations, we further summarize the plant shoot branching regulatory network, including long distance systemic signals and local gene activity mediated by strigolactones following perception of external environmental signals, such as shading, in order to provide a comprehensive overview of plant shoot branching.