GEMMA CUP-ASSOCIATED MYB1, an Ortholog of Axillary Meristem Regulators,Is Essential in Vegetative Reproduction in Marchantia polymorpha

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Induction of Multichotomous Branching by CLAVATA Peptide in Marchantia polymorpha

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An Early Arising Role of the MicroRNA156/529-SPL Module in Reproductive Development Revealed by the Liverwort Marchantia polymorpha

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A pseudomolecule‐scale genome assembly of the liverwort Marchantia polymorpha

Marchantia polymorpha has recently become a prime model for cellular, evo‐devo, synthetic biological, and evolutionary investigations. We present a pseudomolecule‐scale assembly of the M. polymorpha genome, making comparative genome structure analysis and classical genetic mapping approaches feasible. We anchored 88% of the M. polymorpha draft genome to a high‐density linkage map resulting in eight pseudomolecules. We found that the overall genome structure of M. polymorpha is in some respects different from that of the model moss Physcomitrella patens. Specifically, genome collinearity between the two bryophyte genomes and vascular plants is limited, suggesting extensive rearrangements since divergence. Furthermore, recombination rates are greatest in the middle of the chromosome arms in M. polymorpha like in most vascular plant genomes, which is in contrast with P. patens where recombination rates are evenly distributed along the chromosomes. Nevertheless, some other properties of the genome are shared with P. patens. As in P. patens, DNA methylation in M. polymorpha is spread evenly along the chromosomes, which is in stark contrast with the angiosperm model Arabidopsis thaliana, where DNA methylation is strongly enriched at the centromeres. Nevertheless, DNA methylation and recombination rate are anticorrelated in all three species. Finally, M. polymorpha and P. patens centromeres are of similar structure and marked by high abundance of retroelements unlike in vascular plants. Taken together, the highly contiguous genome assembly we present opens unexplored avenues for M. polymorpha research by linking the physical and genetic maps, making novel genomic and genetic analyses, including map‐based cloning, feasible.     

Migration of prospindle before the first asymmetric division in germinating spore of Marchantia polymorpha

The development of the plant body starts with spore germination in bryophytes. In many cases, the first division of the spore occurs after germination and cell elongation of the spore. In Marchantia polymorpha, asymmetric division occurs upon spore germination to generate two daughter cells: the larger one retains the ability to divide and develops into the thallus via sporeling or protonema, while the smaller one maintains tip growth and differentiates into the first rhizoid, providing a scaffold for initial development. Although spore germination of M. polymorpha was described in the 19th century, the intracellular processes of the first asymmetric division of the spore have not been well characterized. In this study, we used live-cell imaging analyses to elucidate microtubule dynamics during the first asymmetric division concomitantly with germination. In particular, we demonstrated that the preprophase band was not formed in the spore and that the bipolar prospindle, which is a microtubule structure surrounding the nucleus during prophase, migrated from the center to the periphery in the spore, suggesting that it was the earliest visible sign of cell polarity. We also showed that the occurrence of asymmetric division depended on actin filaments. Our findings regarding the first division of the spore in M. polymorpha will lead to a better model for cell-autonomous asymmetric division in plants.     

The maturation and aging trajectory of Marchantia polymorpha at single-cell resolution

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Oil Body Formation in Marchantia polymorpha Is Controlled by MpC1HDZ and Serves as a Defense against Arthropod Herbivores

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Identification of the sex-determining factor in the liverwort Marchantia polymorpha reveals unique evolution of sex chromosomes in a haploid system

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Regulation of Asexual Reproduction of the Planarians Dugesia tigrina

We studied asexual reproduction of planarians under the natural and artificial photoperiodic conditions. It was shown that light inhibits the fission of planarians, while darkness stimulates it. The diurnal dynamics of the fission of planarians demonstrated a circadian rhythm. This rhythm is stable, which is expressed when the conditions are experimentally changed: constant darkness, unnatural rhythm of light-darkness succession). However, this stability is affected at the time zone change. The planarians are adapted to new conditions and begin to fission at once in correspondence with the new diurnal regime.     

地钱生殖托形态结构新观察及其对有性生殖的适应

用显微观察技术对苔类植物地钱（Marchantia polymorpha）生殖托的形态结构进行了研究,本研究的新观察包括：（1）生殖托具有明显的背腹分化,被认为是叶状体为适应有性生殖而高度特化的直立枝;（2）雌托盘的9～11个指状裂瓣中边缘两个稍不同,除了两个边缘裂瓣外的其他裂瓣间具雌苞。托柄具有背腹之分,雌托柄背面具光合组织,并向两侧扩展形成纵沟,雌托柄的腹面具2条被鳞片重叠覆盖相互平行的纵沟,内具假根;（3）与雌托柄不同,雄托柄外观平滑,背面无光合组织及纵沟。观察发现,伞状的雌托能滞留水分,并沿雌托柄的纵沟缓慢释放连续的水流,游动精子沿着纵沟内的水流到达雌托下面的颈卵器。上述观察表明地钱生殖托的结构是对有性生殖的一种适应,这有助于我们理解地钱受精作用的机理。     

Inactivation of Cdc42 in embryonic brain results in hydrocephalus with ependymal cell defects in mice

The establishment of a polarized cellular morphology is essential for a variety of processes including neural tube morphogenesis and the development of the brain. Cdc42 is a Ras-related GTPase that plays an essential role in controlling cell polarity through the regulation of the actin and microtubule cytoskeleton architecture. Previous studies have shown that Cdc42 plays an indispensable role in telencephalon development in earlier embryo developmental stage (before E12.5). However, the functions of Cdc42 in other parts of brain in later embryo developmental stage or in adult brain remain unclear. Thus, in order to address the role of Cdc42 in the whole brain in later embryo developmental stage or in adulthood, we used Cre/loxP technology to generate two lines of tissuespecific Cdc42-knock-out mice. Inactivation of Cdc42 was achieved in neuroepithelial cells by crossing Cdc42/ flox mice with Nestin- Cre mice and resulted in hydrocephalus, causing death to occur within the postnatal stage. Histological analyses of the brains from these mice showed that ependymal cell differentiation was disrupted, resulting in aqueductal stenosis. Deletion of Cdc42 in the cerebral cortex also induced obvious defects in interkinetic nuclear migration and hypoplasia. To further explore the role of Cdc42 in adult mice brain, we examined the effects of knocking-out Cdc42 in radial glial cells by crossing Cdc42/fl ox mice with human glial fi brillary acidic protein (GFAP)-Cre mice. Inactivation of Cdc42 in radial glial cells resulted in hydrocephalus and ependymal cell denudation. Taken together, these results highlight the importance of Cdc42 for ependymal cell differentiation and maintaining, and suggest that these functions likely contribute to the essential roles played by Cdc42 in the development of the brain.     

The Role of Seed and Vegetative Reproduction in Plant Recruitment and Demography in Tallgrass Prairie

Recruitment, establishment and survivorship of seed- and vegetatively-derived shoots were quantified biweekly in annually burned and infrequently burned tallgrass prairie to investigate the contributions of seed and vegetative reproduction to the maintenance and dynamics of tallgrass prairie plant populations, the demography of seedlings and ramets, and the influence of fire on the demography of grasses and forbs. Clonally produced grass and forb ramets comprised >99%of all established shoots present at the end of the growing season, whereas established seedlings accounted for <1%,emphasizing the rarity of successful seedling establishment and the importance of vegetative reproduction in driving the annual regeneration and dynamics of aboveground plant populations in tallgrass prairie. Most recruitment from vegetative reproduction occurred early in the growing season and was higher in annually burned than infrequently burned sites, although low levels of new stem recruitment occurred continuously throughout the growing season. Peak recruitment on annually burned prairie coincided with peak recruitment of the dominant C₄ grasses Andropogon gerardii and Sorghastrum nutans prior to prescribed spring fire, with a second peak in recruitment occurring following fire. On infrequently burned prairie, grass and forb recruitment was highest in early April and declined steadily through May. The naturalized C₃ grass, Poa pratensis, was responsible for most of the early recruitment on unburned sites, whereas A. gerardii contributed most to recruitment later in May. Infrequently burned prairie was dominated by these two grasses and contained a larger forb component than annually burned prairie. The principal demographic effect of fire was on ramet natality rather than mortality. Fire regime, plant functional group, or timing of cohort emergence before or after fire did not affect ramet survivorship. C₄ grass shoots that emerged early and were damaged by fire showed similar survivorship patterns to tillers that emerged after fire. Differences in species composition between annually burned and infrequently burned prairie are driven by fire effects on vegetative reproduction and appear to be related principally to the effect of fire and detritus accumulation on the development of belowground vegetative meristems of C₄ grasses and their emergence dynamics.     

Resistance and capacity in the thallus of Marchantia polymorpha

Calculations of the resistance r and capacity c of cell membrances and the resistancer ₁ of cell interiors of a community of cells in Marchantia polymorpha L. thalli are presented. These parameters of a multicellular system were determined by the adaptation of methods employed for the calculation of the resistance and capacity of single cells. The obtained results indicate that such a procedure is justified. A generally accepted resistance-capacity model of the cell was used as a basis for the determination of r, c, and r₁ (representing membrane resistance, membrane capacity, and resistance of cell interior, respectively). The calculations were based on measurements of impedance and phase shift within the frequency range of 5 Hz-1000 Hz. Stainless steel plates were employed as the measuring electrodes; polarization resistance and capacity were determined by separate measurements. The calculations confirmed the assumption that the parameters r, c, and r₁ were constant within the investigated frequency range.
The calculations of resistance and capacity for 25 plants were constant within the investigated frequency range. The calculations of resistance and capacity for 25 plants were carried out by four different methods and they yielded results of the order of : r = 0.45 kΩ± 0.15 kΩ, r₁= 1.0 kΩ± 0.45 kΩ, c = 11 μF ± 3.5 μF. Circular diagrams of impedance also confirmed the validity of the accepted model within the frequency range of 25–300 Hz.     

一个植物无性生殖遗传规律的发现

为了固定植物杂种优势,克服杂交水稻必需年年制种,杂种只能利用一次等缺点,本研究进行了固定水稻杂种与遗传育种研究。考察了30个野生稻种,其中西非长雄蕊野生稻80-001(AgAg,O.longistaminata)受到重视,为根茎繁殖,大花药、长柱头、花粉粒小而均匀,但自交不亲和。用长野80-001与亚洲栽培稻(O.sativa,AA)杂交,在杂种F2、F3出现了农艺性状整齐一致并能连续遗传的群体,并称此为群体分离和固定杂种。这种群体分离和固定杂种不符合孟德尔氏生物有性生殖遗传规律,故称此为植物无性生殖规律,表达该规律的遗传模式是F1=F2=F3……=F n,F1≌F2=F3……=F n。这一发现揭示了植物无性生殖遗传规律,填补了植物无性生殖遗传空白,且应用于植物育种能固定种间、亚种间、品种间的杂种优势,节约2/3以上的育种时间、人力、物力,是一个植物快速育种的新途径。选育的粳稻中新一号(粳稻84-15/喜峰F2)(93)京审粮字第9号、籼稻杂交稻一号(90-3027/坊迪F2),已通过北京市和海南省审定推广。     

黄土高原三种耐干藓营养繁殖的季节差异及机理

苔藓植物在园林绿化、水土保持等方面的应用日益增加,目前藓类植物营养繁殖的影响因素鲜见报道,限制了其应用研究。本研究以黄土高原常见的耐干藓(扭口藓、土生对齿藓、短叶对齿藓)为对象,研究了3种藓春、夏、秋、冬季营养繁殖能力(以活力指数表征)差异及其叶绿素、可溶性糖、可溶性蛋白质、丙二醛(MDA)含量等生理指标变化,探索了耐干藓营养繁殖的季节差异与其生理特征之间的关系。结果表明: 1)藓类繁殖具有明显的季节差异,3种藓夏季活力指数均低于其他3个季节,平均较秋、冬、春季分别下降56.1%、48.4%、10.1%;相同季节的活力指数具有明显的年际变化。2)3种藓繁殖能力具有明显的种间差异,以短叶对齿藓最高,扭口藓最低,且后者的繁殖能力季节和年际变化最大。3)3种藓不同季节生理特征差异显著,其中夏季MDA含量高于其他季节,可溶性糖和可溶性蛋白质含量低于其他季节。4)耐干藓的营养繁殖季节变化主要与可溶性糖含量有关。本研究明确了藓类营养繁殖能力随季节变化的规律,指出可溶性糖含量是影响藓类营养繁殖的关键因素,可为藓类植物保护和人工培养提供科学依据。