Heterologous Expression and Characterization of Tea (Camellia sinensis) Polyamine Oxidase Homologs and Their Involvement in Stresses.

Polyamine oxidase (PAO) is a key enzyme maintaining polyamine homeostasis, which affects plant physiological activities. Until now, the gene members and function of PAOs in tea (Camellia sinenesis) have not been fully identified. Here, through the expression in Escherichia coli and Nicotiana benthamiana, we identified six genes annotated as CsPAO in tea genome and transcriptome and determined their enzyme reaction modes and gene expression profiles in tea cultivar 'Yinghong 9'. We found that CsPAO1,2,3 could catalyze spermine, thermospermine, and norspermidine, and CsPAO2,3 could catalyze spermidine in the back-conversion mode, which indicated that the precursor of γ-aminobutyric acid might originate from the oxidation of putrescin but not spermidine. We further investigated the changes of CsPAO activity with temperature and pH and their stability. Kinetic parameters suggested that CsPAO2 was the major PAO modifying polyamine composition in tea, and it could be inactivated by ß-hydroxyethylhydrazine and aminoguanidine. Putrescine content and CsPAO2 expression were high in tea flowers. CsPAO2 responded to wound, drought, and salt stress; CsPAO1 might be the main member responding to cold stress; anoxia induced CsPAO3. We conclude that in terms of phylogenetic tree, enzyme characteristics, and expression profile, CsPAO2 might be the dominant CsPAO in the polyamine degradation pathway.

First Report of Powdery Mildew on Rosa cymosa Caused by Podosphaera pannosa in Guizhou Province, China.

Rosa cymosa is a traditional Chinese medicine and an ornamental plant in China (Fan et al. 2020). In April 2022, powdery mildew symptoms were observed on R. cymosa in Guiyang, Guizhou Province, China. The incidence was approximately 5% among all observed one hundred R. cymosa plants. On average, 20% of the twig tips per diseased R. cymosa plant were affected. Powdery mildew colonies covered the adaxial and abaxial surfaces of leaves. Infected young leaves rolled up along the main vein. Stems and mature leaves occasionally had signs of powdery mildew. The hyphae were straight to flexuous, branched, septate, 3 to 6 µm in width. Conidiophores were erect, straight or somewhat flexuous, and 100 to 235 µm long. Foot cells (n = 30) were cylindrical or subcylindrical, straight or somewhat flexuous, and measured 20 to 48 µm (length) × 4.5 to 5.5 µm (width). Foot cells were followed by one to two shorter cells (n = 30) that measured 8 to 12 µm (length) × 4.5 to 5.8 µm (width). The shorter cells were followed by a chain of four to eight conidia. The conidia (n = 50) were hyaline, cylindrical to ovoid, with fibrosin bodies, and measured 20 to 28 µm (length) × 10.5 to 16.5 µm (width). No chasmothecia were observed on the surface of diseased leaves. For molecular identification, the ribosomal DNA internal transcribed spacer (ITS) was amplified and sequenced using primers ITS1/ITS4 (White et al. 1990). The obtained 508-bp ITS sequence was deposited in GenBank (Accession No. ON316871). The subsequent phylogeny grouped the ITS sequence within a clade of Podosphaera pannosa sequences. Based on both morphological and phylogenetic characteristics, the powdery mildew pathogen was identified as P. pannosa (Braun et al. 2002). The voucher specimen (Accession No. GZNU-RCPP/0804/2022) were deposited at the School of Life Sciences, Guizhou Normal University, China. Pathogenicity was assessed by gently pressing naturally diseased leaves onto young leaves of three healthy, potted 2-year-old R. cymosa plants, with three non-inoculated plants as controls. Powdery mildew symptoms were observed on all inoculated plants after incubation for 10 days at 21°C, 75% relative humidity, and 12 h/12 h light/dark cycle in a greenhouse. The control plants remained symptomless. The re-isolated powdery mildew colonies on inoculated leaves were morphologically identical to those observed on the original diseased leaves, fulfilling Koch's postulates. Podosphaera pannosa has been described as the most frequent species causing powdery mildew on the Rosaceae family, particularly on Rosa spp. and Prunus spp. (Hubert et al. 2012; Félix-Gastélum et al. 2014). The occurrence of powdery mildew on R. cymosa caused by P. pannosa could pose a potential disease threat to other Rosa crops or Prunus spp.

The complete chloroplast genome sequence of garden cress (Lepidium sativum L.) and its phylogenetic analysis in Brassicaceae family.

Garden cress, Lepidium sativum L., is not only an important vegetable which is cultivated in the entire world, but also a widely used folk medicine for the treatment of hyperactive airways disorders. However, as a member of Brassicaceae, few studies have been carried out on its phylogenetic relationship with other Brassicaceae members. Herein, the complete chloroplast (cp) genome of garden cress wa deciphered by the combination of Illumina Hiseq and PacBio Hiseq Platform after extracting of its cp DNA. The cp genome showed a typically quadripartite cycle with 154997 bp, including a pair of inverted repeats (IRa and IRb) of 26491 bp intersected by a large single copy (LSC) region of 84007 bp and a small single copy (SSC) region of 18008 bp. Totally, 128 unique genes were assembled in this cp genome, including 83 protein genes, 37 tRNAs and 8 rRNAs. A total of 73 simple sequence repeats (SSRs) with a length of at least 10 bp were detected. Phylogenetic analysis based on 30 cp genome of Brassicaceae family showed that the L. sativum was closely related to L. virginicum. This study provides important information for future evolution, genetic and molecular biology studies of L. sativum.

The complete chloroplast genome sequence of Dendrobium thyrsiflorum (Orchidaceae) and its phylogenetic analysis.

Dendrobium thyrsiflorum Rchb.f., a native species to China, is widely used as an important garden flower and a traditional Chinese medicine. Herein, the complete chloroplast (cp) genome of D. thyrsiflorum was deciphered by high-throughput sequencing. The cp genome exhibited a typical quadripartite cycle of 151,686 bp in length, comprising of a pair of inverted repeats (IRa and IRb) of 26,293 bp which were intersected by a large single copy (LSC) region of 84,749 bp and a small single copy (SSC) region of 14,351 bp. A total of 126 genes were de novo assembled in this cp genome, including 78 protein genes, 40 tRNA genes and 8 rRNA genes. Among these genes, 86 genes (22 tRNAs and 64 coding genes) were single copy, the rest were two-copy genes, and the average of GC content of the whole genome is 37.55%. Phylogenetic trees showed that the D. thyrsiflorum was closely related to D. devonianum. This study provides molecular information for future evolution, genetic and molecular biology studies of Dendrobium.