of Botany,Chinese Academy Of Sciences
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Phylogenomics, plastome degradation and mycoheterotrophy evolution of Neottieae (Orchidaceae), with emphasis on the systematic position and Loess Plateau-Changbai Mountains disjunction of Diplandrorchis
No full textBackground Mycoheterotrophy is a unique survival strategy adapted to dense forests and has attracted biologists' attention for centuries. However, its evolutionary origin and related plastome degradation are poorly understood. The tribe Neottieae contains various nutrition types, i.e., autotrophy, mixotrophy, and mycoheterotrophy. Here, we present a comprehensive phylogenetic analysis of the tribe based on plastome and nuclear ITS data. We inferred the evolutionary shift of nutrition types, constructed the patterns of plastome degradation, and estimated divergence times and ancestral ranges. We also used an integration of molecular dating and ecological niche modeling methods to investigate the disjunction between the Loess Plateau and Changbai Mountains in Diplandrorchis, a mycoheterotrophic genus endemic to China that was included in a molecular phylogenetic study for the first time. Results Diplandrorchis was imbedded within Neottia and formed a clade with four mycoheterotrophic species. Autotrophy is the ancestral state in Neottieae, mixotrophy independently originated at least five times, and three shifts from mixotrophy to mycoheterotrophy independently occurred. The five mixotrophic lineages possess all plastid genes or lost partial/all ndh genes, whereas each of the three mycoheterotroph lineages has a highly reduced plastome: one lost part of its ndh genes and a few photosynthesis-related genes, and the other two lost almost all ndh, photosynthesis-related, rpo, and atp genes. These three mycoheterotrophic lineages originated at about 26.40 Ma, 25.84 Ma, and 9.22 Ma, respectively. Diplandrorchis had presumably a wide range in the Pliocene and migrated southward in the Pleistocene. Conclusions The Pleistocene climatic fluctuations and the resultant migration resulted in the Loess Plateau-Changbai Mountains disjunction of Diplandrorchis. In the evolution of mycoheterotrophic lineages, the loss of plastid-encoded genes and plastome degradation are staged and irreversible, constraining mycoheterotrophs to inhabit understories with low light levels. Accordingly, the rise of local forests might have promoted the origin of conditions in which mycoheterotrophy is advantageous
The retention dynamics of early-spring N input in a temperate forest ecosystem: Implications for winter N deposition
No full textIn N-limited temperate regions of China, rates of atmospheric N deposition remain high during winter due to industrial development and energy consumption. Winter-deposited N accumulates and is then released after snowmelt. However, little is known about the retention dynamics of early-spring N input in temperate forest ecosystems. We applied 15N isotopic tracer after snowmelt, and then quantified 15N dynamics in litter, soils, microbes and vascular plants over the following growing season in a warm temperate forest of northern China. In early spring (7 days after 15N addition), approximately 80% of applied 15N was retained in the ecosystem. The 15N recovery was the highest in litter, followed by soils and microbes, with only trivial acquisition in vascular plants. After early spring, there was little change in total 15N recovery over the following season, which indicated that the temperate forest ecosystem had high potential for the retention of early-spring N input. The 15N levels gradually declined in litter and microbes, while they were gradually increased in the vascular plants. In late fall, substantial 15N tracer retained in litter and was resorbed from senescing tissues to roots. Evergreen coniferous trees presented higher 15N acquisition than deciduous broad-leaved trees. Our results suggest that substantial early-spring N input can be retained in warm temperate forest ecosystems. The findings highlight the importance of litter and plants in sustaining early-spring exogenous N resources, inferring the need to considering winter N deposition for a better understanding of N cycling in temperate ecosystems
Elevated [CO2] raises the temperature optimum of photosynthesis and thus promotes net photosynthesis of winter wheat and rice
No full textAtmospheric CO2 concentration ([CO2]) has increased by 49% since the pre-industrial era, and this increase will continue. Photosynthesis has long been recognized as one of the most temperature-sensitive processes, while far less is known about how elevated [CO2] (e[CO2]) affect crop photosynthesis response to short-term temperature increase. To reveal the effect, we measured gas exchange of winter wheat and rice with various leaf temperatures (T-L) under different [CO2] conditions (ambient, +120 mu mol mol(-1) in wheat, +160 mu mol mol(-1) in rice, and +200 mu mol mol(-1) in both) using open-top chamber facility. Analysis of the measurements showed that e[CO2] generally increased net photosynthesis (P-n) by 10-40% across various T-L at different developmental stages. The temperature sensitivity of P-n was negatively correlated with T-L. Elevated [CO2] raised the temperature optimum (T-opt) of P-n by 1.8-5.6 degrees C for wheat and 2.2-4.8 degrees C for rice, resulting in a wider range of T-L that can promote P-n. The responses of stomatal conductance, the maximum rate of carboxylation and the ratio of intercellular to growth environment [CO2] to T-opt are not only crop-specific but also stage-dependent. Furthermore, there is a divergence in the relationships between photosynthetic parameters for wheat and rice at T-opt. We conclude that e[CO2] raises T-opt of leaf photosynthesis and thus promotes P-n of winter wheat and rice in a humid subtropical climate. Further research on the coordination of leaf hydraulic and photosynthetic parameters in upland wheat and irrigated rice, as well as their response to e[CO2] should be made in the context of climate change
Immigration dynamics of tropical and subtropical Southeast Asian limestone karst floras
No full textEx situ origins and dispersal of taxa have played important roles in the assembly of island-like biodiversity hotspots. Insular limestone karsts in Southeast Asia are hotspots of biodiversity and endemism, but the immigration processes of their unique floras are still poorly known. Here, we used Gesneriaceae as a proxy to investigate the immigration dynamics of tropical and subtropical Southeast Asian karst floras. We present the most comprehensive phylogenetic analysis of the Old World gesneriads to date based on twelve loci. By estimating divergence times and reconstructing ancestral states (habitat, soil type and range), we found that immigration into subtropical Southeast Asian karst floras first occurred in the Early Miocene, with two peaks in the Early-Middle Miocene and the Pliocene-Early Pleistocene, whereas immigration into tropical Southeast Asian karsts initiated in the Late Eocene, with two peaks in the Late Oligocene and the Late Miocene. We also discover that Southeast Asian karst biodiversity comprises immigrant pre-adapted lineages and descendants from local acid soil ancestors, although niche shift from acid soil to karst in tropical Southeast Asian islands was lacking. This study advances our understanding of the historical assembly of Southeast Asian karst floras
Exogenous Arachidonic Acid Affects Fucoxanthin Biosynthesis and Photoprotection in Phaeodactylum tricornutum
No full textFucoxanthin is an oxygenated carotenoid component that has been reported to play important roles in anti-oxidation, anti-obesity and anti-cancer in the human body. Fucoxanthin-chlorophyll protein (FCP) complexes participate in light harvesting and photoprotection in diatom. In order to better understand the change of fucoxanthin content and its role in photoprotection, the growth, fucoxanthin biosynthesis and photosynthetic phenotypes were studied in the diatom Phaeodactylum tricornutum under the treatment of exogenous arachidonic acid (AA). Our results demonstrated that even low concentration of AA at 0.1 mg/L strongly induced fucoxanthin accumulation in algal cells to a maximum of 1.1 mg/g dry weight (DW), which was 36.6% higher than that in the untreated ones. By principal component analysis (PCA), we also identified a close correlation between fucoxanthin accumulation and the expression of genes involved in fucoxanthin biosynthesis, especially phytoene synthase (PSY), suggesting that AA change the metabolism of fucoxanthin by inducing carotenoid metabolic enzymes at the transcriptional level. Furthermore, we found that the exogenous application of AA affected non-photochemical quenching (NPQ) and photoinhibition, which resulted from the changed diadinoxanthin (DD) and diatoxanthin (DT) cycle, and thus played an important role in photoprotection
Phylogenomic conflict analyses in the apple genus Malus s.l. reveal widespread hybridization and allopolyploidy driving diversification, with insights into the complex biogeographic history in the Northern Hemisphere
No full textPhylogenomic evidence from an increasing number of studies has demonstrated that different data sets and analytical approaches often reconstruct strongly supported but conflicting relationships. In this study, 785 single-copy nuclear genes and 75 complete plastomes were used to infer the phylogenetic relationships and estimate the historical biogeography of the apple genus Malus sensu lato, an economically important lineage disjunctly distributed in the Northern Hemisphere and involved in known and suspected hybridization and allopolyploidy events. The nuclear phylogeny recovered the monophyly of Malus s.l. (including Docynia); however, the genus was supported to be biphyletic in the plastid phylogeny. An ancient chloroplast capture event in the Eocene in western North America best explains the cytonuclear discordance. Our conflict analysis demonstrated that ILS, hybridization, and allopolyploidy could explain the widespread nuclear gene tree discordance. One deep hybridization event (Malus doumeri) and one recent event (Malus coronaria) were detected in Malus s.l. Furthermore, our historical biogeographic analysis integrating living and fossil data supported a widespread East Asian-western North American origin of Malus s.l. in the Eocene, followed by several extinction and dispersal events in the Northern Hemisphere. We also propose a general workflow for assessing phylogenomic discordance and biogeographic analysis using deep genome skimming data sets
Rice Cell Division Cycle 20s are required for faithful chromosome segregation and cytokinesis during meiosis
No full textChromosome segregation must be under strict regulation to maintain chromosome euploidy and stability. Cell Division Cycle 20 (CDC20) is an essential cell cycle regulator that promotes the metaphase-to-anaphase transition and functions in the spindle assembly checkpoint, a surveillance pathway that ensures the fidelity of chromosome segregation. Plant CDC20 genes are present in multiple copies, and whether CDC20s have the same functions in plants as in yeast and animals is unclear, given the potential for divergence or redundancy among the multiple copies. Here, we studied all three CDC20 genes in rice (Oryza sativa) and constructed two triple mutants by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9-mediated genome editing to explore their roles in development. Knocking out all three CDC20 genes led to total sterility but did not affect vegetative development. Loss of the three CDC20 proteins did not alter mitotic division but severely disrupted meiosis as a result of asynchronous and unequal chromosome segregation, chromosome lagging, and premature separation of chromatids. Immunofluorescence of tubulin revealed malformed meiotic spindles in microsporocytes of the triple mutants. Furthermore, cytokinesis of meiosis I was absent or abnormal, and cytokinesis II was completely prevented in all mutant microsporocytes; thus, no tetrads or pollen formed in either cdc20 triple mutant. Finally, the subcellular structures and functions of the tapetum were disturbed by the lack of CDC20 proteins. These findings demonstrate that the three rice CDC20s play redundant roles but are indispensable for faithful meiotic chromosome segregation and cytokinesis, which are required for the production of fertile microspores. Loss of all three rice Cell Division Cycle 20 genes caused male sterility, meiotic chromosome missegregation, aberrant spindle morphology, loss of meiotic cytokinesis, and disrupted tapetal function
Fire-prone Rhamnaceae with South African affinities in Cretaceous Myanmar amber
No full textThe rapid Cretaceous diversification of flowering plants remains Darwin's 'abominable mystery' despite numerous fossil flowers discovered in recent years. Wildfires were frequent in the Cretaceous and many such early flower fossils are represented by charcoalified fragments, lacking complete delicate structures and surface textures, making their similarity to living forms difficult to discern. Furthermore, scarcity of information about the ecology of early angiosperms makes it difficult to test hypotheses about the drivers of their diversification, including the role of fire in shaping flowering plant evolution. We report the discovery of two exquisitely preserved fossil flower species, one identical to the inflorescences of the extant crown-eudicot genus Phylica and the other recovered as a sister group to Phylica, both preserved as inclusions together with burned plant remains in Cretaceous amber from northern Myanmar (similar to 99 million years ago). These specialized flower species, named Phylica piloburmensis sp. nov. and Eophylica priscastellata gen. et sp. nov., exhibit traits identical to those of modern taxa in fire-prone ecosystems such as the fynbos of South Africa, and provide evidence of fire adaptation in angiosperms