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25 October 2020, Volume 42 Issue 05
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  • Articles
    Allelochemicals of Panax notoginseng and their effects on various plants and rhizosphere microorganisms
    Yi-Jun Qiao, Cheng-Zhen Gu, Hong-Tao Zhu, Dong Wang, Meng-Yue Zhang, Yi-Xuan Zhang, Chong-Ren Yang, Ying-Jun Zhang
    2020, 42(05):  323-333.  doi:10.1016/j.pld.2020.04.003
    Abstract ( 80 )   HTML ( )   PDF (18814KB) ( 75 )   Save
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    Panax notoginseng (Araliaceae) is an important ginseng herb with various health benefits and a history of cultivation in southwestern China over 400 years. In recent years P. notoginseng has faced serious continuous-cropping obstacles due to its large-scale cultivation. In this study, we aim to explore the allelochemicals of P. notoginseng and their interactions with various plants and rhizosphere microorganisms. The chemical constituents of the soil cultivated with 3-year-old P. notoginseng were studied by column chromatography, spectroscopic and GC-MS analyses. We identified 13 volatile components and isolated six triterpenes (1-4, 6-7) and one anthraquinone (5). Compounds 1-7 were tested for their effects on seed germination and root elongation in P. notoginseng, corn, wheat, turnip, water spinach and Arabidopsis thaliana. We also examined the effect of compounds 1-7 on the growth of ten rhizosphere microorganisms of P. notoginseng. At a concentration of 1.0 μg mL-1, compounds 3 and 5-7 caused the death of P. notoginseng root cells and compounds 2, 6 and 7 induced the death of root cells of A. thaliana. Compounds 1-5 and 7 inhibited elongation of A. thaliana root tip cells at a concentration of 10.0 μg mL-1. Moreover, at a concentration of 0.1 mg mL-1, compounds 3, 4, 6 and 7 inhibited the growth of probiotics and promoted the growth of pathogens of P. notoginseng. These results suggest that these isolated ursane-type triterpenoid acids and anthraquinone are potential allelochemicals that contribute to continuous-cropping obstacles of P. notoginseng.
    The complete plastome sequences of five Aponogeton species (Aponogetonaceae): Insights into the structural organization and mutational hotspots
    Virginia M. Mwanzia, Ding-Xuan He, Andrew W. Gichira, Yan Li, Boniface K. Ngarega, Mwihaki J. Karichu, Peris W. Kamau, Zhi-Zhong Li
    2020, 42(05):  334-342.  doi:10.1016/j.pld.2020.02.002
    Abstract ( 51 )   HTML ( )   PDF (7618KB) ( 39 )   Save
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    Members of the aquatic plant genus Aponogeton are widely used commercially in aquariums because of their variable leaf shape and unique inflorescences. However, due to extensive similarity between species in this genus, morphological characters are generally inadequate for taxonomic classification. Currently, molecular makers available for taxonomic and phylogenetic studies of Aponogeton are limited. One approach to clarifying relationships between species in these complex groups is to use divergence hotspot regions within the genome. Here, we sequenced and analyzed the plastomes of five Aponogeton species collected from China, Zambia, and Kenya, and subsequently screened these plastomes for divergent DNA hotspots. The five plastomes are circular structures with sizes ranging from 154,167 bp to 154,860 bp. The Large and the Small Single Copies are separated by two Inverted Repeats. One hundred and thirteen unique genes were identified including 79 protein-coding, 30 tRNA, and four rRNA genes. We found that the most abundant repeats in all but one species were mononucleotide repeats (A/T) and that there were 23 potential RNA ending sites. Interestingly, a ~3 kb inversion, which includes the accD gene, was detected within the Asian species of Aponogeton. The inversion may be related to more frequent exchanges between this region and the nuclear genome. Furthermore, we detected mutational hotspot sites among the five Aponogeton species. Three of these hotspots are intergenic spacer regions (accD-psaI, rbcL-accD and trnH-GUG-psbA) that might be suitable for use as barcodes to resolve intrageneric relationships. We also identified four highly variable protein-coding genes (ccsA, rpl22, rps16 and ycf1) may be used as barcodes to resolve the higher-level phylogenies. Our study will provide valuable molecular resources for the taxonomic and phylogenomic study of the complex genus Aponogeton.
    Genetic diversity and population structure of Camellia huana (Theaceae), a limestone species with narrow geographic range, based on chloroplast DNA sequence and microsatellite markers
    Shuang Li, Shang-Li Liu, Si-Yu Pei, Man-Man Ning, Shao-Qing Tang
    2020, 42(05):  343-350.  doi:10.1016/j.pld.2020.06.003
    Abstract ( 60 )   HTML ( )   PDF (5043KB) ( 36 )   Save
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    Camellia huana is an endangered species with a narrow distribution in limestone hills of northern Guangxi and southern Guizhou provinces, China. We used one chloroplast DNA (cpDNA) fragment and 12 pairs of microsatellite (simple sequence repeat; SSR) markers to assess the genetic diversity and structure of 12 C. huana populations. A total of 99 alleles were detected for 12 polymorphic loci, and eight haplotypes and nine polymorphic sites were detected within 5200 bp of cpDNA. C. huana populations showed a low level of genetic diversity (n=8, Hd=0.759, Pi=0.00042 for cpDNA, NA=3.931, HE=0.466 for SSRs), but high genetic differentiation between populations (FST=0.2159 for SSRs, FST=0.9318 for cpDNA). This can be attributed to the narrow distribution and limestone habitat of C. huana. STRUCTURE analysis divided natural C. huana populations into two groups, consistent with their geographical distribution. Thus, we suggest that five natural C. huana populations should be split into two units to be managed effectively.
    Preliminary study on Cd accumulation characteristics in Sansevieria trifasciata Prain
    Xiong Li, Yongping Yang
    2020, 42(05):  351-355.  doi:10.1016/j.pld.2020.05.001
    Abstract ( 20 )   HTML ( )   PDF (3293KB) ( 14 )   Save
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    Phytoremediation techniques to clean heavy metal pollution soil depend on identifying plant species that can act as phytoremediators. One important approach to screening potential phytoremediators is to evaluate characteristics of heavy metal accumulation. In this study, we performed firsthand analysis of Cd tolerance and accumulation characteristics of three Sansevieria trifasciata cultivars by pot experiment. Plant growth results showed that all three S. trifasciata cultivars can tolerate 50 mg kg-1 soil Cd concentration. After growth under 50 mg kg-1 soil Cd concentration for 4 months, the Cd bioconcentration factors in the shoots of S. ‘Trifasciata’, S. trifasciata ‘Laurentii’, and S. trifasciata ‘Silver Hahnii’ were 1.26, 1.30, and 1.19, while those in the roots were 12.53, 11.43, and 5.45, respectively. This result reveals the considerably low translocation factors of 0.10, 0.12, and 0.22 for S. ‘Trifasciata’, S. trifasciata ‘Laurentii’, and S. trifasciata ‘Silver Hahnii’, respectively. These results suggest that all three S. trifasciata cultivars had high Cd absorption capacities but low Cd translocation capacities. In combination with total Cd accumulation distribution and plant growth characteristics, S. trifasciata can be designed as a phytostabilizer in Cd-contaminated soils in its cultivation regions. Meanwhile, the mechanism of high Cd tolerance and accumulation characteristics in the roots of S. trifasciata should be explored. This study provides new resources for dealing with Cd-contaminated soils and exploring Cd tolerance and accumulation mechanisms in plants.
    Extreme plastid RNA editing may confound phylogenetic reconstruction: A case study of Selaginella (lycophytes)
    Xin-Yu Du, Jin-Mei Lu, De-Zhu Li
    2020, 42(05):  356-361.  doi:10.1016/j.pld.2020.06.009
    Abstract ( 52 )   HTML ( )   PDF (810KB) ( 22 )   Save
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    Cytidine-to-uridine (C-to-U) RNA editing is common in coding regions of organellar genomes throughout land plants. In most cases RNA editing alters translated amino acids or creates new start codons, potentially confounds phylogenetic reconstructions. In this study, we used the spike moss genus Selaginella (lycophytes), which has the highest frequency of RNA editing, as a model to test the effects of extreme RNA editing on phylogenetic reconstruction. We predicted the C-to-U RNA editing sites in coding regions of 18 Selaginella plastomes, and reconstructed the phylogenetic relationships within Selaginella based on three data set pairs consisted of plastome or RNA-edited coding sequences, first and second codon positions, and translated amino acid sequences, respectively. We predicted between 400 and 3100 RNA editing sites of 18 Selaginella plastomes. The numbers of RNA editing sites in plastomes were highly correlated with the GC content of first and second codon positions, but not correlated with the GC content of plastomes as a whole. Contrast phylogenetic analyses showed that there were substantial differences (e.g., the placement of clade B in Selaginella) between the phylogenies generated by the plastome and RNA-edited data sets. This empirical study provides evidence that extreme C-to-U RNA editing in the coding regions of organellar genomes alters the sequences used for phylogenetic reconstruction, and might even confound phylogenetic reconstruction. Therefore, RNA editing sites should be corrected when plastid or mitochondrial genes are used for phylogenetic studies, particularly in those lineages with abundant organellar RNA editing sites, such as hornworts, quillworts, spike mosses, and some seed plants.
    Similar mycorrhizal fungal communities associated with epiphytic and lithophytic orchids of Coelogyne corymbosa
    Jiao Qin, Wei Zhang, Shi-Bao Zhang, Ji-Hua Wang
    2020, 42(05):  362-369.  doi:10.1016/j.pld.2020.07.005
    Abstract ( 45 )   HTML ( )   PDF (12512KB) ( 10 )   Save
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    Mycorrhizal fungi are essential for the growth and development of both epiphytic (growing on trees) and lithophytic (growing on rocks) orchids. Previous studies indicate that in lowland tropical areas, orchid mycorrhizal fungal compositions are correlated with the life form (i.e., epiphytic, lithophytic, or terrestrial) of their host plants. We therefore tested if a similar correlation exists in an orchid distributed at higher elevations. Coelogyne corymbosa is an endangered ornamental orchid species that can be found as a lithophyte and epiphyte in subtropical to subalpine areas. Based on high-throughput sequencing of the fungal internal transcribed spacer 2 (ITS2)-rDNA region of mycorrhizae of C. corymbosa, we detected 73 putative mycorrhizal fungal Operational Taxonomic Units (OTUs). The OTUs of two dominant lineages (Cantharellales and Sebacinales) detected from C. corymbosa are phylogenetically different from those of other species within the genus Coelogyne, indicating that different orchid species prefer specific mycorrhizal fungi. We also found that the Non-metric multidimensional scaling (NMDS) plots of orchid mycorrhizal fungi were not clustered with life form, the variations among orchid mycorrhizal fungal communities of different life forms were not significant, and most of the OTUs detected from epiphytic individuals were shared by the lithophytic plants, suggesting that orchid mycorrhizal associations of C. corymbosa were not affected by life form. These findings provide novel insights into mycorrhizal associations with endangered ornamental orchids.
    A hybrid sterile locus leads to the linkage drag of interspecific hybrid progenies
    Mianmian Wang, Jun Yang, Jinpeng Wan, Dayun Tao, Jiawu Zhou, Diqiu Yu, Peng Xu
    2020, 42(05):  370-375.  doi:10.1016/j.pld.2020.07.003
    Abstract ( 20 )   HTML ( )   PDF (2832KB) ( 5 )   Save
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    Interspecific hybridization plays an important role in rice breeding by broadening access to desirable traits such as disease resistance and improving yields. However, interspecific hybridization is often hindered by hybrid sterility, linkage drag, and distorted segregation. To mine for favorable genes from Oryza glaberrima, we cultivated a series of BC4 introgression lines (ILs) of O. glaberrima in the japonica rice variety background (Dianjingyou 1) in which the IL-2769 (BC4F10) showed longer sterile lemmas, wider grains and spreading panicles compared with its receptor parent, suggesting that linkage drag may have occurred. Based on the BC5F2 population, a hybrid sterility locus, S20, a long sterile lemma locus, G1-g, and a new grain width quantitative trait locus (QTL), qGW7, were mapped in the linkage region about 15 centimorgan (cM) from the end of the short arm of chromosome 7. The hybrid sterility locus S20 from O. glaberrima eliminated male gametes of Oryza sativa, and male gametes carrying the alleles of O. sativa in the heterozygotes were aborted completely. In addition, the homozygotes presented a genotype of O. glaberrima, and homozygous O. sativa were not produced. Surprisingly, the linked traits G1-g and qGW7 showed similar segregation distortion. These results indicate that S20 was responsible for the linkage drag. As a large number of detected hybrid sterility loci are widely distributed on rice chromosomes, we suggest that hybrid sterility loci are the critical factors for the linkage drag in interspecific and subspecific hybridization of rice.
    DNA barcoding and molecular phylogeny of Dumasia (Fabaceae: Phaseoleae) reveals a cryptic lineage
    Kai-Wen Jiang, Rong Zhang, Zhong-Fu Zhang, Bo Pan, Bin Tian
    2020, 42(05):  376-385.  doi:10.1016/j.pld.2020.07.007
    Abstract ( 50 )   HTML ( )   PDF (14850KB) ( 22 )   Save
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    Dumasia taxonomy and classification have long been problematic. Species within this genus have few morphological differences and plants without flowers or fruits are difficult to accurately identify. In this study, we evaluated the ability of six DNA barcoding sequences, one nuclear (ITS) and five chloroplast regions (trnH-psbA, matK, rbcL, trnL-trnF, psbB-psbF), to efficiently identify Dumasia species. Most single markers or their combinations identify obvious barcoding gaps between intraspecific and interspecific genetic variation. Most combined analyses including ITS showed good species resolution and identification efficiency. We therefore suggest that ITS alone or a combination of ITS with any cpDNA marker are most suitable for DNA barcoding of Dumasia. The phylogenetic analyses clearly indicated that Dumasia yunnanensis is not monophyletic and is separated as two independent branches, which may result from cryptic differentiation. Our results demonstrate that molecular data can deepen the comprehension of taxonomy of Dumasia and provide an efficient approach for identification of the species.
    Distribution patterns of clonal plants in the subnival belt of the Hengduan Mountains, SW China
    Yongqian Gao, Jinxuan Zheng, Xiangqun Lin, Fan Du
    2020, 42(05):  386-392.  doi:10.1016/j.pld.2020.06.006
    Abstract ( 24 )   HTML ( )   PDF (1460KB) ( 15 )   Save
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    Clonal reproduction (i.e., production of potentially independent offspring by vegetative growth) is thought to provide plants with reproductive assurance. Thus, studying the evolution of clonal reproduction in local floras is crucial for our understanding of the adaptive mechanisms plants deploy in stressful environments such as alpine regions. In this study, we characterized clonal plant species in the subnival belt of the Hengduan Mountains (a global biodiversity hotspot with extreme environmental conditions in southwest China), in order to determine the effects of sex system, growth form, and elevational distribution on clonality. We compiled clonality data of angiosperm species belonging to 41 families in the subnival belt of the Hengduan Mountains using published information. Of the 793 species recorded in the region, 47.92% (380 species) are clonal species. Both sex system and growth form had significant effects on the occurrence of clonal reproduction: unisexual species (79.79%) were more likely to be clonal than bisexual species (43.63%), and herbaceous species (51.04%) were more likely to be clonal than woody species (16.67%). Compared with non-alpine-endemic species (44.60%), alpine-endemic species (58.33%) showed a significantly higher proportion of clonal reproduction. Further logistic regression analysis showed a positive association between incidence of clonality and elevational range, indicating that species distributed at high elevations are more likely to be clonal. Furthermore, the elevational gradients in clonality were contingent on sex system or growth form. This study reveals that plants in the subnival belt of the Hengduan Mountains might optimize their probability of reproduction through clonal reproduction, a finding that adds to our growing understanding of plant's adaptations to harsh alpine environments.
    Twenty years of Chinese vascular plant novelties, 2000 through 2019
    Cheng Du, Shuai Liao, David E. Boufford, Jinshuang Ma
    2020, 42(05):  393-398.  doi:10.1016/j.pld.2020.08.004
    Abstract ( 54 )   HTML ( )   PDF (4837KB) ( 33 )   Save
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    From 2000 to 2019, 11,895 new names or new additions to the Chinese vascular flora were proposed by 4226 individuals (4086 articles and 140 books), as documented in the Chinese Plant Names Index (CPNI). During those 20 years, 4407 new taxa of vascular plants were described from China, including 7 new families, 132 new genera, 3543 new species, 68 new subspecies, 497 new varieties and 160 new forms. Additionally, 3562 new combinations and names at new rank and 306 new replacement names were also proposed. Among these various new names were 150 invalid names and 108 illegitimate names, including some that have not been resolved. Six hundred and forty three vascular plants were reported as new to China, while 2349 names were reduced to synonyms of 1406 taxa. The data show that the Chinese flora increased in size at the rate of about 200 taxa annually during those years. Despite the increased attention given to biodiversity in recent years, the evidence indicates that a large number of species in China have yet to be discovered. Further basic investigation of the Chinese flora is needed. Additionally, in the past two decades only 8.5% of the newly published species have been based on molecular evidence, but in the past five years such data have increased significantly, reaching about 20%. Molecular data will undoubtedly become increasingly significant in the discovery of new species in the coming years. Yunnan, Guangxi, Sichuan, Xizang and Taiwan were important sources of new discoveries, with more than 3300 new taxa and records from these five provinces. By area, Taiwan and Hainan, two islands in southern China, have the highest density of newly discovered species. Regional plant surveys are still needed, especially in areas in the southwest and on the southern islands.