The Evolving Role of Botanical Gardens and Natural Areas:A Floristic Case Study from Royal Botanical Gardens,Canada

As leaders calling for the conservation of the world’s plants,botanical gardens protect plants within living collections.Many also study,manage and restore plants in natural habitats.Royal Botanical Gardens(Ontario,Canada) has integrated both horticultural and natural heritage in its mission for decades.Envisioned by municipal leaders in the 1920s as a combination of nature sanctuaries and civic gardens,RBG now includes forests,wetlands and other habitats,gardens and built spaces.Today RBG is Canada’s largest botanical garden on the basis of area.In the 1950s RBG began to inventory plant diversity.The checklist of spontaneous vascular plants now exceeds 1 170 species,of which 752 are native.This is 37% of Ontario’s native vascular plants and 19% of the native vascular flora of Canada.The RBG nature sanctuaries are among the richest locations in Canada for species-level diversity.We examine the history of floristic exploration within RBG and compare plant species-area relationships among protected natural areas in Ontario.This comparison supports the contention that the nature sanctuaries,and in particular Cootes Paradise,could be considered an important area for plants in Canada,and relative to the nation’s flora,a biodiversity hotspot.The fact that a candidate vascular plant hotspot for Canada lies within a major botanical garden presents opportunities for raising public awareness of the importance of plant diversity,as well as focusing attention on the scientific and conservation biology needs of communities and individual species in this area.     

Receptor-Like Kinases in Plant Innate Immunity

Plants employ a highly effective surveillance system to detect potential pathogens, which is critical for the success of land plants in an environment surrounded by numerous microbes. Recent efforts have led to the identification of a number of immune receptors and components of immune receptor complexes. It is now clear that receptor-like kinases （RLKs） and receptor-like proteins （RLPs） are key pattern-recognition receptors （PRRs） for microbe- and plant-derived molecular patterns that are associated with pathogen invasion. RLKs and RLPs involved in immune signaling belong to large gene families in plants and have undergone lineage specific expansion. Molecular evolution and population studies on phytopathogenic molecular signatures and their receptors have provided crucial insight into the co-evolution between plants and pathogens.     

BUD2, encoding an S-adenosylmethionine decarboxylase, is required for Arabidopsis growth and development

Polyamines are implicated in regulating various developmental processes in plants, but their exact roles and how they govern these processes still remain elusive. We report here an Arabidopsis bushy and dwarf mutant, bud2, which results from the complete deletion of one member of the small gene family that encodes S-adenosylmethionine decarboxylases （SAMDCs） necessary for the formation of the indispensable intermediate in the polyamine biosynthetic pathway. The bud2 plant has enlarged vascular systems in inflorescences, roots, and petioles, and an altered homeostasis ofpolyamines. The double mutant of bud2 and samdcl, a knockdown mutant of another SAMDC member, is embryo lethal, demonstrating that SAMDCs are essential for plant embryogenesis. Our results suggest that polyamines are required for the normal growth and development of higher plants.     

Arabidopsis Thylakoid Formation 1 Is a Critical Regulator for Dynamics of PSII-LHCII Complexes in Leaf Senescence and Excess Light

In higher plants, photosystem II （PSII） is a large pigment-protein supramolecular complex composed of the PSII core complex and the plant-specific peripheral light-harvesting complexes （LHCil）. PSli-LHCII complexes are highly dynamic in their quantity and macro-organization to various environmental conditions. In this study, we reported a critical factor, the Arabidopsis Thylakoid Formation 1 （THF1） protein, which controls PSII-LHCII dynamics during dark- induced senescence and light acclimation. Loss-of-function mutations in THF1 lead to a stay-green phenotype in path- ogen-infected and senescent leaves. Both LHCII and PSll core subunits are retained in dark-induced senescent leaves of thfl, indicative of the presence of PSII-LHCII complexes. Blue native （BN）-polyacrylamide gel electrophoresis （PAGE） and immunoblot analysis showed that, in dark- and high-light-treated thfl leaves, a type of PSII-LHCII megacomplex is selec- tively retained while the stability of PSII-LHCII supercomplexes significantly decreased, suggesting a dual role of THF1 in dynamics of PSII-LHCII complexes. We showed further that THF1 interacts with Lhcb proteins in a pH-dependent manner and that the stay-green phenotype of thfl relies on the presence of LHCII complexes. Taken together, the data suggest that THF1 is required for dynamics of PSII-LHCII supramolecular organization in higher plants.     

The response of peatlands to climate warming: A review

Peatlands hold a large portion of the Earth’s terrestrial organic carbon and serve as important pools in the global carbon cycle. Due to their strong feedbacks, peatlands are one of the most important ecosystems with respect to climate warming. This paper reviews the effects of climate warming on peatland ecosystems. Climate warming will shift the point in time when vascular peatland plants flower and reach maximum biomass to an earlier date. Flower production for some plants will increase, but how the phenology of peatland bryophytes will react is still unknown. Climate warming may increase productivity of peatlands, especially ombrotrophic Sphagnum bogs, but in the long run the negative effects from decreased water availability may prevail. Climate warming will change the basic characteristics of peatlands: their wetness and the related cold environment and nutrient shortage. By increased mineralization and nitrogen and phosphorus availability, climate warming will facilitate the growth of vascular plants. This will suppress endangered plant species (which usually grow in low-productive, phosphorus-limited habitats) and lead to a change in vegetation composition and a decrease in peatland biodiversity. Climate warming will change the competitive balance between bryophytes and between Sphagnum and vascular plants. Climate warming in the Late Pleistocene facilitated the initiation of peatland formation, but most current experiments show an obvious tendency for climate warming to drive many peatlands to regressive succession with a shift in dominance from Sphagnum to vascular plants. This change in vegetation will increase the flux of CH₄ and possibly also CO₂. The effect of accelerated peat decay as a result of climate warming will vary between types of peatlands. Since climate warming will generally enhance peat respiration more than net primary production, more and more peatlands will become carbon sources rather than carbon sinks, which will aggravate climate warming by positive feedback. Finally, this paper addresses some problems with current manipulative experimental studies on peatland response to climate warming and makes suggestions for further studies.     

The response of peatlands to climate warming: A review

Peatlands hold a large portion of the Earth’s terrestrial organic carbon and serve as important pools in the global carbon cycle. Due to their strong feedbacks, peatlands are one of the most important ecosystems with respect to climate warming. This paper reviews the effects of climate warming on peatland ecosystems. Climate warming will shift the point in time when vascular peatland plants flower and reach maximum biomass to an earlier date. Flower production for some plants will increase, but how the phenology of peatland bryophytes will react is still unknown. Climate warming may increase productivity of peatlands, especially ombrotrophic Sphagnum bogs, but in the long run the negative effects from decreased water availability may prevail. Climate warming will change the basic characteristics of peatlands: their wetness and the related cold environment and nutrient shortage. By increased mineralization and nitrogen and phosphorus availability, climate warming will facilitate the growth of vascular plants. This will suppress endangered plant species (which usually grow in low-productive, phosphorus-limited habitats) and lead to a change in vegetation composition and a decrease in peatland biodiversity. Climate warming will change the competitive balance between bryophytes and between Sphagnum and vascular plants. Climate warming in the Late Pleistocene facilitated the initiation of peatland formation, but most current experiments show an obvious tendency for climate warming to drive many peatlands to regressive succession with a shift in dominance from Sphagnum to vascular plants. This change in vegetation will increase the flux of CH₄ and possibly also CO₂. The effect of accelerated peat decay as a result of climate warming will vary between types of peatlands. Since climate warming will generally enhance peat respiration more than net primary production, more and more peatlands will become carbon sources rather than carbon sinks, which will aggravate climate warming by positive feedback. Finally, this paper addresses some problems with current manipulative experimental studies on peatland response to climate warming and makes suggestions for further studies.     

New Strigolactone Analogs as Plant Hormones with Low Activities in the Rhizosphere

Strigolactones （SLs） are known not only as plant hormones, but also as rhizosphere signals for establishing symbiotic and parasitic interactions. The design of new specific SL analogs is a challenging goal in understanding the basic plant biology and is also useful to control plant architectures without favoring the development of parasitic plants. Two different molecules （23 （3＇-methyI-GR24）, 31 （thia-3＇-methyl-debranone-like molecule）） already described, and a new one （AR36）, for which the synthesis is presented, are biologically compared with the well-known GR24 and the recently identified CISA-1. These different structures emphasize the wide range of parts attached to the D-ring for the bioactivity as a plant hormone. These new compounds possess a common dimethylbutenolide motif but their structure varies in the ABC part of the molecules： 23 has the same ABC part as GR24, while 31 and AR36 carry, respectively, an aromatic ring and an acyclic carbon chain. Detailed information is given for the bioactivity of such derivatives in strigolactone synthesis or in perception mutant plants （pea rmsl and rms4, Arabidopsis max2 and, max4） for different hormonal functions along with their action in the rhizosphere on arbuscular mycorrhizal hyphal growth and parasitic weed germination.     

From Proteomics to Structural Studies of Cytosolic/MitochondriaI-Type Thioredoxin Systems in Barley Seeds

Thioredoxins （Trx） are ubiquitous proteins that participate in thiol disulfide reactions via two active site cysteine residues, allowing Trx to reduce disulfide bonds in target proteins. Recent progress in proteome analysis has resulted in identification of a wide range of potential target proteins for Trx, indicating that Trx plays a key role in several aspects of cell metabolism. In contrast to other organisms, plants contain multiple forms of Trx that are classified based on their primary structures and sub-cellular localization. The reduction of cytosolic and mitochondrial types of Trx is dependent on NADPH and catalyzed by NADPH-dependent thioredoxin reductase （NTR）. In barley, two isoforms each of Trx and NTR have been identified and investigated using proteomics, gene expression, and structural studies. This review outlines the diverse roles suggested for cytosolic/mitochondrial-type Trx systems in cereal seeds and summarizes the current knowledge of the barley system including recent data on function, regulation, interactions, and structure. Directions for future research are discussed.     

Sequence Diversity and Enzyme Activity of Ferric-Chelate Reductase LeFRO1 in Tomato

Ferric-chelate reductase which functions in the reduction of ferric to ferrous iron on root surface is a critical protein for iron ho- meostasis in strategy I plants. LeFROI is a major ferric-chelate reductase involved in iron uptake in tomato. To identify the natural variations of LeFRO1 and to assess their effect on the ferric-chelate reductase activity, we cloned the coding sequences of LeFRO1 from 16 tomato varieties collected from different regions, and detected three types of LeFRO1 （LeFRO1MM, LeFRO1Ailsa and LeFRO1Monita） with five amino acid variations at the positions 21, 24, 112, 195 and 582. Enzyme activity assay revealed that the three types of LeFRO1 possessed different ferric-chelate reductase activity （LeFRO1AiISa 〉 LeFRO1MM 〉 LeFRO1M~nita）. The 112th amino acid residue Ala of LeFRO1 is critical for maintaining the high activity of ferric-chelate reductase, because modification of this amino acid resulted in a significant reduction of enzyme activity. Further, we showed that the combination of the amino acid residue lie at the site 24 with Lys at the site 582 played a positive role in the enzyme activity of LeFRO1. In conclusion, the findings are helpful to understand the natural adaptation mechanisms of plants to iron-limiting stress, and may provide new knowledge to select and manipulate LeFRO1 for improving the iron deficiency tolerance in tomato.     

Abiotic and Biotic Stresses and Changes in the Lignin Content and Composition in Plants

Lignin is a polymer of phenylpropanoid compounds formed through a complex biosynthesis route,represented by a metabolic grid for which most of the genes involved have been sequenced in several plants,mainly in the model-plants Arabidopsis thaliana and Populus.Plants are exposed to different stresses,which may change lignin content and composition.In many cases,particularly for plant-microbe interactions,this has been suggested as defence responses of plants to the stress.Thus,understanding how a stressor modulates expression of the genes related with lignin biosynthesis may allow us to develop study-models to increase our knowledge on the metabolic control of lignin deposition in the cell wall.This review focuses on recent literature reporting on the main types of abiotic and biotic stresses that alter the biosynthesis of lignin in plants.     

Construction and Application of Efficient Ac-Ds Transposon Tagging Vectors in Rice

Transposons are effective mutagens alternative to T-DNA for the generation of insertional mutants in many plant species including those whose transformation is inefficient. The current strategies of transposon tagging are usually slow and labor-intensive and yield low frequency of tagged lines. We have constructed a series of transposon tagging vectors based on three approaches： （i） AcTPase controlled by glucocorticoid binding domain/VP16 acidic activation domain/Gal4 DNA-binding domain （GVG） chemical-inducible expression system; （ii） deletion of AcTPase via Cre-lox site-specific recombination that was initially triggered by Ds excision; and （iii） suppression of early transposition events in transformed rice callus through a dual-functional hygromycin resistance gene in a novel Ds element （HPT-Ds）, We tested these vectors in transgenic rice and characterized the transposition events. Our results showed that these vectors are useful resources for functional genomics of rice and other crop plants. The vectors are freely available for the community,     

Arabidopsis FtsZ2-1 and FtsZ2-2 Are Functionally Redundant,But FtsZ-Based Plastid Division Is Not Essential for Chloroplast Partitioning or Plant Growth and Development

FtsZ1 and FtsZ2 are phylogenetically distinct families of FtsZ in plants that co-localize to mid-plastid rings and facilitate division of chloroplasts. In plants, altered levels of either FtsZ1 or FtsZ2 cause dose-dependent defects in chloroplast division; thus, studies on the functional relationship between FtsZgenes require careful manipulation of FtsZ levels in vivo. To define the functional relationship between the two FtsZ2 genes in Arabidopsis thaliana, FtsZ2-1 and FtsZ2-2, we expressed FtsZ2-1 in an ftsZ2-2 null mutant, and vice versa, and determined whether the chloroplast division defects were rescued in plants expressing different total levels of FtsZ2. Full rescue was observed when either the FtsZ2-1 or FtsZ2-2 level approximated total FtsZ2 levels in wild-type （WT）. Additionally, FtsZ2-2 interacts with ARC6, as shown previously for FtsZ2- 1. These data indicate that FtsZ2-1 and FtsZ2-2 are functionally redundant for chloroplast division in Arabidopsis. To rigorously validate the requirement of each FtsZ family for chloroplast division, we replaced FtsZ1 with FtsZ2 in vivo, and vice versa, while maintaining the FtsZ level in the transgenic plants equal to that of the total level in WT. Chloroplast division defects were not rescued, demonstrating conclusively that FtsZ1 and FtsZ2 are non-redundant for maintenance of WT chloroplast numbers. Finally, we generated ftsZtriple null mutants and show that plants completely devoid of FtsZ protein are viable and fertile. As plastids are presumably essential organelles, these findings suggest that an FtsZ-independent mode of plastid partitioning may occur in higher plants.     

Mechanisms for flowering plants to benefit arthropod natural enemies of insect pests： Prospects for enhanced use in agriculture

Reduction of noncrop habitats, intensive use of pesticides and high levels of disturbance associated with intensive crop production simplify the farming landscape and bring about a sharp decline of biodiversity. This, in turn, weakens the biological control ecosystem service provided by arthropod natural enemies. Strategic use of flowering plants to enhance plant biodiversity in a well-targeted manner can provide natural enemies with food sources and shelter to improve biological control and reduce dependence on chemical pesticides. This article reviews the nutritional value of various types of plant-derived food for natural enemies, possible adverse effects on pest management, and the practical application of flowering plants in orchards, vegetables and field crops, agricultural systems where most research has taken place. Prospects for more effective use of flowering plants to maximize biological control of insect pests in agroecosystem are good but depend up on selection of optimal plant species based on information on the ecological mechanisms by which natural enemies are selectively favored over pest species.     

Between a Rock and a Dry Place： The Water-Stressed Moss

The earliest land plants faced a suite of abiotic stresses largely unknown to their aquatic algal ancestors. The descendants of these plants evolved two general mechanisms for survival in the relatively arid aerial environment. While the vascular plants or ＇tracheophytes＇ developed tissue specializations to transport and retain water, the other main lineages of land plants, the bryophytes, retained a simple, nonvascular morphology. The bryophytes--mosses, hornworts, and liverworts--continually undergo a co-equilibration of their water content with the surrounding environment and rely to a great extent on intrinsic cellular mechanisms to mitigate damage due to water stress. This short review will focus on the cellular and molecular responses to dehydration and rehydration in mosses, and offer insights into general plant responses to water stress.     

Endogenous Small RNA Clusters in Plants

In plants, small RNAs（sRNAs） usually refer to non-coding RNAs（ncRNAs） with lengths of 20–24 nucleotides. sRNAs are involved in the regulation of many essential processes related to plant development and environmental responses. sRNAs in plants are mainly grouped into microRNAs（miRNAs） and small interfering RNAs（siRNAs）, and the latter can be further classified into trans-acting siRNAs（ta-siRNAs）, repeat-associated siRNAs（ra-siRNAs）, natural anti-sense siRNAs（nat-siRNAs）, etc. Many sRNAs exhibit a clustered distribution pattern in the genome. Here, we summarize the features and functions of cluster-distributed sRNAs, aimed to not only provide a thorough picture of sRNA clusters（SRCs） in plants, but also shed light on the identification of new classes of functional sRNAs.