Complete chloroplast genomes of five Cuscuta species and their evolutionary significance in the Cuscuta genus.

BACKGROUND: Cuscuta, a parasitic plant species in the Convolvulaceae family, grows in many countries and regions. However, the relationship between some species is still unclear. Therefore, more studies are needed to assess the variation of the chloroplast (cp) genome in Cuscuta species and their relationship with subgenera or sections, thus, providing important information on the evolution of Cuscuta species. RESULTS: In the present study, we identified the whole cp genomes of C. epithymum, C. europaea, C. gronovii, C. chinensis and C. japonica, and then constructed a phylogenetic tree of 23 Cuscuta species based on the complete genome sequences and protein-coding genes. The complete cp genome sequences of C. epithymum and C. europaea were 96,292 and 97,661 bp long, respectively, and lacked an inverted repeat region. Most cp genomes of Cuscuta spp. have tetragonal and circular structures except for C. epithymum, C. europaea, C. pedicellata and C. approximata. Based on the number of genes and the structure of cp genome and the patterns of gene reduction, we found that C. epithymum and C. europaea belonged to subgenus Cuscuta. Most of the cp genomes of the 23 Cuscuta species had single nucleotide repeats of A and T. The inverted repeat region boundaries among species were similar in the same subgenera. Several cp genes were lost. In addition, the numbers and types of the lost genes in the same subgenus were similar. Most of the lost genes were related to photosynthesis (ndh, rpo, psa, psb, pet, and rbcL), which could have gradually caused the plants to lose the ability to photosynthesize. CONCLUSION: Our results enrich the data on cp. genomes of genus Cuscuta. This study provides new insights into understanding the phylogenetic relationships and variations in the cp genome of Cuscuta species.

Molecular Processes of Dodder Haustorium Formation on Host Plant under Low Red/Far Red (R/FR) Irradiation.

Low R/FR irradiation can promote dodder haustorium formation on the host plant; however, the mechanisms underlying the process are still unknown. In this study, we compared the transcriptomic data during the formation of haustorium of Cuscuta chinensis on host plant Arabidopsisthaliana under low (R/FR = 0.1) versus high (R/FR = 0.2) R/FR irradiation at 12 h, 24 h and 72 h time points. The results show that low R/FR radiation significantly promoted the entanglement and haustorium formation. Transcriptome analysis showed that during the early stage of haustorium formation, low R/FR radiation significantly up-regulated ARR-A related genes and down-regulated peroxidase related genes compared with high R/FR radiation. Meanwhile, during the middle stage of haustorium formation, low R/FR treatment significantly increased the expression of genes related to pectinesterase (PE), polygalacturonase (PG) and pectin lyase (Pel) production, while, during the late stage of haustorium formation, peroxidase (Prx)-related genes were differentially expressed under different R/FR treatments. Overall, our findings show that a low R/FR ratio promotes the parasitism of C. chinensis through plant hormone signal transduction and cell wall degradation pathways. This study provides a basis for the control of parasitic plants.

Plant Virome Analysis by the Deep Sequencing of Small RNAs of Fritillaria thunbergii var. chekiangensis and the Rapid Identification of Viruses.

Thunberg fritillary (Fritillaria thunbergii), a perennial used in traditional Chinese herbal medicine, is a members of the family Liliaceae. The degeneration of germplasm is a severe problem in the production of Fritillaria thunbergii var. chekiangensis. However, no information about viral infections of F. thunbergii var. chekiangensis has been reported. In this study, we sequenced the small RNAs of F. thunbergii var. chekiangensis from leaves and bulbs, and viruses were identified using a phylogenetic analysis and BLAST search for sequence. In addition, multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) was used to rapidly detect viruses in this variety. Our study first reported that five viruses infected F. thunbergii var. chekiangensis. Among them, fritillary virus Y (FVY), lily mottle virus (LMoV), Thunberg fritillary mosaic virus (TFMV), and hop yellow virus (HYV) had been reported in F. thunbergii, while apple stem grooving virus was first reported in the genus Fritillaria. A multiplex RT-PCR method was developed to rapidly test the four viruses FVY, LMoV, TFMV, and HYV in F. thunbergii var. chekiangensis. Our results provide a better understanding of the infection of F. thunbergii var. chekiangensis by viruses and a basic reference for the better design of suitable control measures.