No abstract

Passionfruit (Passiflora edulis) is widely cultivated in tropical and subtropical regions around the world. Several viruses of the genus Potyvirus pose serious threat to passion fruit production. The origin, dispersal and evolution of these potyviruses, however, are poorly understood. Here, we investigated the genetic structure of telosma mosaic virus (TelMV), a potyvirus that infects passionfruit in East and Southeast Asia, after a survey of its incidence in passionfruit plants of China. The phylogeny inferred from 140 nucleotide sequences of the coat protein (CP) gene of TelMV, including 96 determined in this study, separated this virus into 4 clades. TelMV isolates from passionfruit were placed into Clade 1–3, while those from other plant species into Clade 4. Interestingly, TelMV isolates of passionfruit from Thailand were found in all the three clades of Clade 1–3, but those from China and Vietnam were found exclusively in Clade 1. Nevertheless, TelMV isolates within Clade 1 tended to cluster according to their geographical origin. Geographical populations from Thailand, Taiwan and Hainan islands of China showed significant genetic differences with one another and with those from Guangxi, Fujian, Guangdong, Yunnan and Jiangsu provinces of China. Altogether, these data suggest that several distinct TelMV clades had arisen from the passionfruit of Thailand, but only one of which was dispersed. In expanding its distribution, this clade of TelMV has undergone geography-associated evolution. Further studies on this hypothesis may shed new insights into mechanisms underlying the emergence of potyviral diseases in passionfruit plants.

The mlr-dependent biodegradation plays an essential role in the natural attenuation of microcystins (MCs) in eutrophic freshwater ecosystems. However, their evolutionary origin is still unclear due to the lack of mlr gene cluster sequences. In this study, a Sphingopyxis sp. strain X20 with high MC-degrading ability was isolated, and the mlrA gene activity was verified by heterologous expression. The whole sequence of the mlr gene cluster in strain X20 was obtained through PCR and thermal asymmetric interlaced (TAIL)-PCR, and then used for evolutionary origin analyses together with the sequences available in GenBank. Phylogenetic analyses of mlr gene clusters suggested that the four mlr genes had the same origin and evolutionary history. Genomic island analyses showed that there is a genomic island on the genome of sphingomonads that is capable of degrading MCs, on which the mlr gene cluster anchors. The concentrated distribution of the mlr gene cluster in sphingomonads implied that these genes have likely been present in the sphingomonads gene pool for a considerable time. Therefore, the mlr gene cluster may have initially entered into the genome of sphingomonads together with the genomic island by a horizontal gene transfer event, and then become inherited by some sphingomonads. The species other than sphingomonads have likely acquired mlr genes from sphingomonads by recently horizontal gene transfer due to the sporadic distribution of MC-degrading species and the mlr genes in them. Our results shed new light on the evolutionary origin of the mlr cluster and thus facilitate the interpretation of characteristic distribution of the mlr gene in bacteria and the understanding of whole mlr pathway.

The complete chloroplast sequence of the Anoectochilus roxburghii, a popular traditional Chinese medicine for the treatment of cancer, was determined in this study. The chloroplast genome (cpDNA)^ was 152,802 bp in length, containing a pair of inverted repeats of 52,728 bp separated by a large single-copy region and a small single-copy region of 82,641 bp and 17,433 bp, respectively. The chloroplast genome encodes 116 predicted functional genes, including 81 protein-coding genes, four ribosomal RNA genes, and 31 transfer RNA genes, 25 of which are duplicated in the inverted repeat regions. The cpDNA is GC-rich (36.9%).