MicroRNAs in the moss Physcomitrella patens

Having diverged from the lineage that lead to flowering plants shortly after plants have established on land, mosses, which share fundamental processes with flowering plants but underwent little morphological changes by comparison with the fossil records, can be considered as an evolutionary informative place. Hence, they are especially useful for the study of developmental evolution and adaption to life on land. The transition to land exposed early plants to harsh physical conditions that resulted in key physiological and developmental changes. MicroRNAs (miRNAs) are an important class of small RNAs (sRNAs) that act as master regulators of development and stress in flowering plants. In recent years several groups have been engaged in the cloning of sRNAs from the model moss Physcomitrella patens. These studies have revealed a wealth of miRNAs, including novel and conserved ones, creating a unique opportunity to broaden our understanding of miRNA functions in land plants and their contribution to the latter??s evolution. Here we review the current knowledge of moss miRNAs and suggest approaches for their functional analysis in P. patens.     

The bryophytes Physcomitrium patens and Marchantia polymorpha as model systems for studying evolutionary cell and developmental biology in plants

Bryophytes are nonvascular spore-forming plants. Unlike in flowering plants, the gametophyte (haploid) generation of bryophytes dominates the sporophyte (diploid) generation. A comparison of bryophytes with flowering plants allows us to answer some fundamental questions raised in evolutionary cell and developmental biology. The moss Physcomitrium patens was the first bryophyte with a sequenced genome. Many cell and developmental studies have been conducted in this species using gene targeting by homologous recombination. The liverwort Marchantia polymorpha has recently emerged as an excellent model system with low genomic redundancy in most of its regulatory pathways. With the development of molecular genetic tools such as efficient genome editing, both P. patens and M. polymorpha have provided many valuable insights. Here, we review these advances with a special focus on polarity formation at the cell and tissue levels. We examine current knowledge regarding the cellular mechanisms of polarized cell elongation and cell division, including symmetric and asymmetric cell division. We also examine the role of polar auxin transport in mosses and liverworts. Finally, we discuss the future of evolutionary cell and developmental biological studies in plants.

A review of the cell biological and developmental mechanisms of bryophytes, including Physcomitrium patens and Marchantia polymorpha.     

Constraints and selection: insights from microsporogenesis in Asparagales

Developmental constraints have been proposed to interfere with natural selection in limiting the available set of potential adaptations. Whereas this concept has long been debated on theoretical grounds, it has been investigated empirically only in a few studies. In this article, we evaluate the importance of developmental constraints during microsporogenesis (male meiosis in plants), with an emphasis on phylogenetic patterns in Asparagales. Different developmental constraints were tested by character reshuffling or by simulated distributions. Among the different characteristics of microsporogenesis, only cell wall formation appeared as constrained. We show that constraints may also result from biases in the correlated occurrence of developmental steps (e.g., lack of successive cytokinesis when wall formation is centripetal). We document such biases and their potential outcomes, notably the establishment of intermediate stages, which allow development to bypass such constraints. These insights are discussed with regard to potential selection on pollen morphology.     

Theoretical analysis of mechanisms that generate the pigmentation pattern of animals

Mechanisms of animal skin pigment pattern formation have long been of interest to developmental and mathematical biologists. Although there has been a well-studied theoretical hypothesis-the reaction-diffusion system-that is able to reproduce the variety of skin patterns, a lack of molecular evidence has kept it just a hypothesis. In this review, we summarize the results of theoretical studies to date for researchers not familiar with their mathematical underpinnings, and we discuss future approaches that will more fully integrate mathematical models and experimental analyses.     

Portamento Rampicante - Volubile Provocato,in Alcune Piante,dal Trattamento Con Acido Gibberellico

Summary

In this communication reports are given on experiments and observations regarding treatment of several plants with Gibberellic acid and consequent manifestations of stem growth with twining-climbing behaviour. This phenomenon has been observed in plants which normally never present similar behaviour (Lactuca Scariola L.) and it has been provoked in plants genetically more or less predisposed (Phaseolus vulgaris L. cult. “aquila rossa” e Soja hispida Moench. cult. “Castelli” and “Giessner”). Normally climbing plants, as Ipomaea versicolor, has been treated for control.

In Phaseolus and in Soja the action of Gibberellic acid has been very considerable as plants thus treated have assumed all the characteristics of climbing growth. Photos and Tables clearly show the extent of such action.

In Ipomaea, in conformity with work hypothesis, we can clearly observe the meagre advantage in growth of internodes following tratment with Gibberellic Acid.

The purpose of these experiments, as is obvious, is to lay the bases for a physiological interpretation of climbing behaviour. It is clear by results obtained that, subordinately, at least, to certain qualitative structural manifestations, plants thrive with or without climbing behaviour according to whether their growth is more or less rapid and of different proportions. Increasing growth rapidity by tratment with Gibberellic Acid, we may obtain an twining growth phenomenon in plants genetically more or less predisposed towards said phenomenon, in those plants, that is, which in special environnmental conditions may sometimes, although exceptionally, manifest the tendency to climbing growth. This effect is obtained on plants in which we do not usually meet these phenomena but which, evidently, have the possibility of manifest them provided that am exceptional growth stimulas is operating.

From what above said we can deduce a first and simple work hypothesis, which will be the object of study in the near future, and which prospects the possibility that typically climbing plants owe their behaviour to the capacity of regulating their growth also in consequence of the formation of appropriate quantities of substances with gibberellinlike action and lacking some growth inhibiting condition. The same thing might be true for the plants which are climbing only on exceptional occasions, and a similar possibility might be given to the plant by particular external conditions in which the individual is formed, grows and develops.

Is is interesting also to observe that the analogy between climbing behaviour induced by Gibberellic Acid and natural one, extends also to leaf expansion behaviour and to other characteristics facts included in the field of etiolated plants.

Successive experiments will give us a deeper knowledge of this particular aspect of climbing behaviour and will define the conditions in which movements of shoot apex take place under the action of Gibberellic Acid and structural manifestations inherent, in comparison to those of naturally climbing plants.     

A comprehensive model for acrotonic,mesotonic and basitonic branchings in plants

Topological developmental models with local (position of internodes) and global (branch lengths) characteristics are proposed to investigate the relationships between fundamental branching patterns of plants such as acrotony, mesotony, and basitony, including the coincidence of different patterns on the same plant. Modification of the basic acrotony during the development by means of, (1) the final expected main axis length results in either basitony or an extension of acrotony over a shortened main axis, (2) the final expected lateral branch length yields either lateral unlimited sympodial branching or the absence of proximal branches. Combinations of these schemes can have variable quantitative expressions on main and lateral axes.As applications, progressive morphological changes introduced by monotonic variations of parameter values give an insight into the relationships between determinate and indeterminate growth, using Lycopersicon as an example. - A theoretical framework is proposed as a possible aid for formalizing plant typology.     

Effects of Nitric Oxide on Neuromuscular Properties of Developing Zebrafish Embryos

Nitric oxide is a bioactive signalling molecule that is known to affect a wide range of neurodevelopmental processes. However, its functional relevance to neuromuscular development is not fully understood. Here we have examined developmental roles of nitric oxide during formation and maturation of neuromuscular contacts in zebrafish. Using histochemical approaches we show that elevating nitric oxide levels reduces the number of neuromuscular synapses within the axial swimming muscles whilst inhibition of nitric oxide biosynthesis has the opposite effect. We further show that nitric oxide signalling does not change synapse density, suggesting that the observed effects are a consequence of previously reported changes in motor axon branch formation. Moreover, we have used in vivo patch clamp electrophysiology to examine the effects of nitric oxide on physiological maturation of zebrafish neuromuscular junctions. We show that developmental exposure to nitric oxide affects the kinetics of spontaneous miniature end plate currents and impacts the neuromuscular drive for locomotion. Taken together, our findings implicate nitrergic signalling in the regulation of zebrafish neuromuscular development and locomotor maturation.     

Phytoremediation of toxic trace elements in soil and water

Toxic heavy metals and metalloids, such as cadmium, lead, mercury, arsenic, and selenium, are constantly released into the environment. There is an urgent need to develop low-cost, effective, and sustainable methods for their removal or detoxification. Plant-based approaches, such as phytoremediation, are relatively inexpensive since they are performed in situ and are solar-driven. In this review, we discuss specific advances in plant-based approaches for the remediation of contaminated water and soil. Dilute concentrations of trace element contaminants can be removed from large volumes of wastewater by constructed wetlands. We discuss the potential of constructed wetlands for use in remediating agricultural drainage water and industrial effluent, as well as concerns over their potential ecotoxicity. In upland ecosystems, plants may be used to accumulate metals/metalloids in their harvestable biomass (phytoextraction). Plants can also convert and release certain metals/metalloids in a volatile form (phytovolatilization). We discuss how genetic engineering has been used to develop plants with enhanced efficiencies for phytoextraction and phytovolatilization. For example, metal-hyperaccumulating plants and microbes with unique abilities to tolerate, accumulate, and detoxify metals and metalloids represent an important reservoir of unique genes that could be transferred to fast-growing plant species for enhanced phytoremediation. There is also a need to develop new strategies to improve the acceptability of using genetically engineered plants for phytoremediation.

     

Theoretical and experimental approaches to understand morphogen gradients

Morphogen gradients, which specify different fates for cells in a direct concentration‐dependent manner, are a highly influential framework in which pattern formation processes in developmental biology can be characterized. A common analysis approach is combining experimental and theoretical strategies, thereby fostering relevant data on the dynamics and transduction of gradients. The mechanisms of morphogen transport and conversion from graded information to binary responses are some of the topics on which these combined strategies have shed light. Herein, we review these data, emphasizing, on the one hand, how theoretical approaches have been helpful and, on the other hand, how these have been combined with experimental strategies. In addition, we discuss those cases in which gradient formation and gradient interpretation at the molecular and/or cellular level may influence each other within a mutual feedback loop. To understand this interplay and the features it yields, it becomes essential to take system‐level approaches that combine experimental and theoretical strategies.     

L'evoluzione della cerchia legnosa in Quercus Pubescens W. Ein Quercus Ilex L. nel clima di Firenze

Summary

The evolution of the wood ring in Quercus pubescens W. and in Quercus Ilex L. in Florence (from June 1946 to June 1947).

The present study deals with the anatomical characters of the wood ring of Q. pubescens and of Q. Ilex. In both the specimens the wood of the stem and of the young branch has been investigated.

In both plants studied the cambial tissue of the stem starts dividing at the end of April, reaching its maximum activity from May to June.

On the contrary the cambium of the branch differentiates in Q. pubescens a month earlier (18 March-18 April) than in Q. Ilex (18 April-18 May). While in the branch of Q. Ilex a false ring can be seen corresponding to the autumn months, nothing of the kind is found in the branch of Q. pubescens; though it presents a false ring in the stem.

It is difficult to date clearly the period when the cambium stops its activity, but probably it happens at the end of August in the samples of the stem.

The leaf buds of Q. pubescens and of Q. Ilex open during April-May and the young branch is completely developed at the end of June. In both oaks some buds open in autumn, but the small branches are prevented to develop because of the cold.

No comparison can be made between the opening of the buds and the beginning of the cambial activity in the stem and in the branch.

Considering the evolution of these woods and their relationship to climatic factors, we can see that the cambial activity starts during a period of remarkable rainfall and of regular increase of temperature, and stops almost completely at the end of July, when temperature and dryness reach their highest values.

The autumn rainfall would favour again a cambial activity, but the values of the temperature, regularly decreasing, do not allow it.     

egl-4 acts through a transforming growth factor-beta/SMAD pathway in Caenorhabditis elegans to regulate multiple neuronal circuits in response to sensory cues

Sensory cues regulate several aspects of behavior and development in Caenorhabditis elegans, including entry into and exit from an alternative developmental stage called the dauer larva. Three parallel pathways, including a TGF-beta-like pathway, regulate dauer formation. The mechanisms by which the activities of these pathways are regulated by sensory signals are largely unknown. The gene egl-4 was initially identified based on its egg-laying defects. We show here that egl-4 has many pleiotropies, including defects in chemosensory behavior, body size, synaptic transmission, and dauer formation. Our results are consistent with a role for egl-4 in relaying sensory cues to multiple behavioral and developmental circuits in C. elegans. By epistasis analysis, we also place egl-4 in the TGF-beta-like branch and show that a SMAD gene functions downstream of egl-4 in multiple egl-4-regulated pathways, including chemosensation.     

The genes of plant signal transduction

Due to the enormous importance of plants as a source of both food and raw materials, an understanding of the control of their growth and development is imperative. Basic to this understanding is the identification of the genes that enable the plant to adapt to its environment while at the same time adhering to its basic developmental plan. The aims of this review are first to briefly summarize the various approaches that have been used to identify these plant signaling genes and second to give an overview of the genes that have been cloned so far and what these genes may tell us about the nature of signal transduction in plants.

The advent of modern molecular biology and molecular genetics has revolutionized our ability to unravel the complexities of plant signal transduction pathways. A whole battery of techniques are now available to identify the genes that control the plants development and ability to adapt to its environment.⁶⁵ Each technique has its own strengths and weaknesses and must be carefully selected by the researcher according to the question that he or she would like to ask.     

Plant Growth-Promoting Rhizobacteria-Mediated Adaptive Responses of Plants Under Salinity Stress

In this recent era, several approaches have been developed to alleviate the adverse effects of salinity stress in different plants. However, some of them are not eco-friendly. In this context, evolving sustainable approaches which enhance the productivity of saline soil without harming the environment are necessary. Many recent studies showed that plant growth-promoting rhizobacteria (PGPR) are known to confer salinity tolerance to plants. Salt-stressed plants inoculated with PGPR enhance the growth and productivity of crops by reducing oxidative damage, maintaining ionic homeostasis, enhancing antioxidant machinery, and regulating gene expressions. The PGPR also regulates the photosynthetic attributes such as net photosynthetic rate, chlorophyll, and carotenoid contents and enhances the salinity tolerance to plants. Moreover, PGPR has a great role in the enhancement of phytohormones and secondary metabolites synthesis in plants under salt stress. This review summarizes the current reports of the application of PGPR in plants under salt stress and discusses the PGPR-mediated mechanisms in plants of salt tolerance. This review also discusses the potential role of PGPR in cross-talk with phytohormones and secondary metabolites to alleviate salt stress and highlights the research gaps where further research is needed.

     

Virus-induced gene silencing in plants

Virus-induced gene silencing (VIGS) is a technology that exploits an RNA-mediated antiviral defense mechanism. In plants infected with unmodified viruses the mechanism is specifically targeted against the viral genome. However, with virus vectors carrying inserts derived from host genes the process can be additionally targeted against the corresponding mRNAs. VIGS has been used widely in plants for analysis of gene function and has been adapted for high-throughput functional genomics. Until now most applications of VIGS have been in Nicotiana benthamiana. However, new vector systems and methods are being developed that could be used in other plants, including Arabidopsis. Here we discuss practical and theoretical issues that are specific to VIGS rather than other gene "knock down" or "knockout" approaches to gene function. We also describe currently used protocols that have allowed us to apply VIGS to the identification of genes required for disease resistance in plants. These methods and the underlying general principles also apply when VIGS is used in the analysis of other aspects of plant biology.     

Mathematical Growth Analysis of Young Terminalia superba Plants in a Controlled Environment: Comparison of Growth Rhythms of the Principal Axis and of Axillary Branches

A Fourier analysis was used to study the marked variations inthe rate of shoot elongation and branch formation of young Terminaliasuperba plants. The growth of aerial parts of 3-month-old Terminaliaseedlings was measured daily during the following 7 months ofgrowth, and then weekly over a 15-month period of study. Measurementswere carried out in a controlled glasshouse at 27 °C and16 h photoperiod. The Fourier method clearly demonstrated thatthe main axis of young T. superba showed periodical regularvariations, with rest periods. This study revealed that theplagiotropic branch formation by apposition and elongation ofaxillary units was equally rhythmic and directly related tothe main shoot growth rhythm. However, the dates of outbreakof these new units on branches seemed relatively independentfrom variations in shoot growth rate. This developmental patternended in a characteristic and particular stratified branch systemin young Terminalia superba, comparable to the system shownby adult plants in their natural environment. Terminalia superba, Fourier analysis, growth rhythms     

Polyspermy in angiosperms: Its contribution to polyploid formation and speciation

Polyploidization has played a major role in the long‐term diversification and evolutionary success of angiosperms. Triploid formation among diploid plants, which is generally considered to be achieved by fertilization of an unreduced gamete with a reduced one, has been accepted as a means of polyploid production. In addition, it has been supposed that polyspermy also contributes to the triploid formation in maize, wheat, and some orchids; however, such a mechanism has been considered uncommon because reproducing the polyspermic situation and unambiguously investigating developmental profiles of polyspermic zygotes are difficult. To overcome these problems, rice polyspermic zygotes have been successfully produced by electrofusion of an egg cell with two sperm cells, and their developmental profiles have been monitored. The triploid zygotes progress through karyogamy and divide into two‐celled embryos via a typical bipolar mitotic division; the two‐celled embryos further develop into triploid plants, indicating that polyspermic plant zygotes, unlike those of animals, can develop normally. Furthermore, progenies consisting of triparental genetic materials have been successfully obtained in Arabidopsis through the pollination of two different kinds of male parents with a female parent. These different pieces of evidence for development and emergence of polyspermic zygotes in vitro and in planta suggest that polyspermy is a key event in polyploidization and species diversification.