Genetic Variability and Evolutionary Dynamics of Papaya Ringspot Virus and Papaya Leaf Distortion Mosaic Virus Infecting Feral Papaya in Hainan Island.

The commercialized genetically modified (GM) papaya cultivars have protected papaya from the devastating disease caused by papaya ringspot virus (PRSV). However, papaya leaf distortion mosaic virus (PLDMV), which causes similar infection symptoms but is serologically distinct from PRSV, was found as a competitive threat to the papaya industry. Our study surveyed the occurrence of PRSV and PLDMV as well as the transgenic markers of the 35S promoter from cauliflower mosaic virus (CaMV 35S) and the neomycin phosphotransferase II (NPT II) gene in feral papaya plants, which were found frequently growing outside of cultivated papaya fields on Hainan Island. In total, 123 feral papayas, comprising 62 (50.4%) GM plants and 61 (49.6%) non-GM ones, were sampled. Among them, 23 (18.7%) were positive for PRSV, 49 (39.8%) were positive for PLDMV, including 5 plants co-infected by PRSV and PLDMV, and 56 (45.5%) plants were free of either virus. In traditional papaya growing regions, we detected fewer PRSV-infected plants (2 in 33, 6%) than in other regions (21 in 90, 23%). But overall, whether transgenic or not made no significance in PRSV incidence (P=0.230), with 9 PRSV-infected plants among 62 GM papayas and 14 among 61 non-GM papayas. Phylogenetic and genetic differentiation analysis showed a clear correlation between PRSV and PLDMV populations and their geographical origins. Negative selection was estimated for the selected gene regions of both viruses. Notably, PLDMV has deviated from neutral evolution and experienced population expansion, exhibiting increased genetic diversity and is becoming the predominant threat to papaya in Hainan.

Profiles of Cytokinins Metabolic Genes and Endogenous Cytokinins Dynamics during Shoot Multiplication In Vitro of Phalaenopsis.

Shoot multiplication induced by exogenous cytokinins (CKs) has been commonly used in Phalaenopsis micropropagation for commercial production. Despite this, mechanisms of CKs action on shoot multiplication remain unclear in Phalaenopsis. In this study, we first identified key CKs metabolic genes, including six isopentenyltransferase (PaIPTs), six cytokinin riboside 5' monophosphate phosphoribohydrolase (PaLOGs), and six cytokinin dehydrogenase (PaCKXs), from the Phalaenopsis genome. Then, we investigated expression profiles of these CKs metabolic genes and endogenous CKs dynamics in shoot proliferation by thidiazuron (TDZ) treatments (an artificial plant growth regulator with strong cytokinin-like activity). Our data showed that these CKs metabolic genes have organ-specific expression patterns. The shoot proliferation in vitro was effectively promoted with increased TDZ concentrations. Following TDZ treatments, the highly expressed CKs metabolic genes in micropropagated shoots were PaIPT1, PaLOG2, and PaCKX4. By 30 days of culture, TDZ treatments significantly induced CK-ribosides levels in micropropagated shoots, such as tZR and iPR (2000-fold and 200-fold, respectively) as compared to the controls, whereas cZR showed only a 10-fold increase. Overexpression of PaIPT1 and PaLOG2 by agroinfiltration assays resulted in increased CK-ribosides levels in tobacco leaves, while overexpression of PaCKX4 resulted in decreased CK-ribosides levels. These findings suggest de novo biosynthesis of CKs induced by TDZ, primarily in elevation of tZR and iPR levels. Our results provide a better understanding of CKs metabolism in Phalaenopsis micropropagation.

Complete mitochondrial genome of Angelica dahurica and its implications on evolutionary analysis of complex mitochondrial genome architecture in Apiaceae.

Angelica dahurica is a kind of Chinese traditional herbs with economic and ornament value, widely distributed in China. Despite its significance, there have been limited comprehensive investigations on the genome of A. dahurica, particularly regarding mitochondrial genomes. To investigate the conversion between mitochondrial genome and chloroplast genome, a complete and circular mitochondrial genome was assembled using Oxford Nanopore Technologies (ONT) long reads. The mitochondrial genome of A. dahurica had a length of 228,315 base pairs (bp) with 45.06% GC content. The mitochondrial genome encodes 56 genes, including 34 protein-coding genes, 19 tRNA genes and 3 rRNA genes. Moreover, we discovered that 9 homologous large fragments between chloroplast genome and mitochondrial genome based on sequence similarity. This is the first report for A. dahurica mitochondrial genome, which could provide an insight for communication between plastid genome, and also give a reference genome for medicinal plants within the Angelica family.