CPTA treatment reveals potential transcription factors associated with carotenoid metabolism in flowers of Osmanthus fragrans

Osmanthus fragrans is one of the top ten traditional flowers in China.It is divided into three different groups according to its color.α-Carotene and β-carotene are the main determinants to distinguish the color differences between three groups.However,the dominant genes and transcription factors involved in carotenoid metabolism remain unclear.CPTA treatment(0.7mmol·L−1)remarkably promoted lycopene,α-carotene and β-carotene contents in flowers.Transcriptome sequencing analysis revealed that CPTA treatment could trigger chain reactions in carotenoid metabolism pathway genes.Four up-regulated and 10 down-regulated transcription factors which have close association with carotenoid variation were significantly induced by CPTA treatment.The up-regulated TFs such as MYB43,MYB123,HSF,were further subjected to transcript expression determination in different cultivars with drastic colors.Among them,transcript expression of four up-regulated TFs coincided with the carotenoid accumulation in different cultivars.We selected up-regulated OfMYB43 to verify its function,which is related to stress tolerance and transcriptional regulation.Transient overexpression of OfMYB43 in O.fragrans flowers showed that it could remarkably promote the expression of PDS,ZISO,LCYE and CCD4,leading to increased accumulation of β-branch carotenoids.OfMYB43 was a potential positive regulator of carotenoid biosynthesis in O.fragrans flowers.This study provides insight into the molecular mechanism of carotenoid metabolism in O.fragrans.

Comparative transcriptome analysis of different heat stress responses between self-root grafting line and heterogeneous grafting line in rose

Rose is sensitive to high temperature which will make the rose go into a semi-dormancy state.Grafting is an excellent way to enhance rose heat tolerance.Here,heat-tolerant Rosa multiflora‘Huanong Wuci 1'(W)and heat-sensitive Rosa chinensis‘Old Blush’(X)were selected as experimental materials.The RNA-seq technique was used to investigate the transcriptomes of self-root grafting line(XX0),heterogeneous grafting line(XW0),self-root grafting line under 6 h heat stress(XX6),and heterogeneous grafting line under 6 h heat stress(XW6).Under high temperature stress,multiple signaling pathways were activated,moreover,a large number of transcription factors and functional genes were induced,especially the HSFs and HSPs with remarkably upregulated expression levels.The GO analysis showed that the differences in the expressions of the genes related to fatty acids and carbohydrates were observed between self-root grafting line and heterogeneous grafting line.In addition,14 P450s were differentially expressed,and one lectin gene was up-regulated in XW0 vs XW6,but down-regulated in XX0 vs XX6.Considering physiological and biochemical traits such as relative electrolyte leakage,SOD activity,proline,and total soluble sugars,DEGs involved in these processes may be key factors to resist high temperature.The present study provides an insight into the complex mechanism underlying grafting in response to heat stress.Our results indicate that grafting is an effective way to improve rose heat resistance.

Whole-genome resequencing of Osmanthus fragrans provides insights into flower color evolution

Osmanthus fragrans is a well-known ornamental plant that has been domesticated in China for 2500 years.More than 160 cultivars have been found during this long period of domestication,and they have subsequently been divided into four cultivar groups,including the Yingui,Jingui,Dangui,and Sijigui groups.These groups provide a set of materials to study genetic evolution and variability.Here,we constructed a reference genome of O.fragrans‘Liuyejingui’in the Jingui group and investigated its floral color traits and domestication history by resequencing a total of 122 samples,including 119 O.fragrans accessions and three other Osmanthus species,at an average sequencing depth of 15×.The population structure analysis showed that these 119 accessions formed an apparent regional cluster.The results of linkage disequilibrium(LD)decay analysis suggested that varieties with orange/red flower color in the Dangui group had undergone more artificial directional selection;these varieties had the highest LD values among the four groups,followed by the Sijigui,Jingui,and Yingui groups.Through a genome-wide association study,we further identified significant quantitative trait loci and genomic regions containing several genes,such as ethylene-responsive transcription factor 2 and Arabidopsis pseudoresponse regulator 2,that are positively associated with petal color.Moreover,we found a frameshift mutation with a 34-bp deletion in the first coding region of the carotenoid cleavage dioxygenase 4 gene.This frameshift mutation existed in at least one site on both alleles in all varieties of the Dangui group.The results from this study shed light on the genetic basis of domestication in woody plants,such as O.fragrans.