Asymmetric cell divisions in plant development
Asymmetric cell divisions define plant development. High-throughput genomic and modelling approaches can elucidate their regulation, which in turn could enable the engineering of plant traits such as stomatal density, lateral root development and wood formation. Asymmetric divisions are formative divisions that generate daughter cells of distinct identity. These divisions are coordinated by either extrinsic (‘niche-controlled’) or intrinsic regulatory mechanisms and are fundamentally important in plant development.
A recent review in Annals of Botany describes how asymmetric cell divisions are regulated during development and in different cell types in both the root and the shoot of plants. It further highlights ways in which omics and modelling approaches have been used to elucidate these regulatory mechanisms. For example, the regulation of embryonic asymmetric divisions is described, including the first divisions of the zygote, formative vascular divisions and divisions that give rise to the root stem cell niche. Asymmetric divisions of the root cortex endodermis initial, pericycle cells that give rise to the lateral root primordium, procambium, cambium and stomatal cells are also discussed. The authors provide a perspective on the role of other hormones or regulatory molecules in asymmetric divisions, the presence of segregated determinants and the usefulness of modelling approaches in understanding network dynamics within these very special cells.
Kajala, Kaisa, Priya Ramakrishna, Adam Fisher, Dominique C. Bergmann, Ive De Smet, Rosangela Sozzani, Dolf Weijers, and Siobhan M. Brady. Omics and modelling approaches for understanding regulation of asymmetric cell divisions in arabidopsis and other angiosperm plants. (2014) Annals of Botany 113(7): 1083-1105.
Bats are responsible for pollinating several species of plants. A new paper in Annals of Botany reports for the first time bat-pollination of a species in the genus Tillandsia.
Bromeliaceae is a species-rich neotropical plant family, of which Tillandsia is the most diverse genus and includes more than a third of all bromeliad species. The flowers of some species show characteristics typical for pollination by nocturnal animals, particularly bats and moths. The authors find that nectar production is restricted to the night hours, and the most frequent visitor and the only pollinator is the nectarivorous bat Anoura geoffroyi. This is the first report of chiropterophily within the genus Tillandsia, and the results suggest an ongoing evolutionary switch from pollination by birds or moths to bats.
Aguilar-Rodríguez, P.A., Krömer, T., García-Franco, J.G., Knauer, A., & Kessler, M. (2014) First record of bat-pollination in the species-rich genus Tillandsia (Bromeliaceae). Annals of Botany, 113 (6): 1047-1055. doi: 10.1093/aob/mcu031
(Sorry, we’ll try to make next year’s Halloween special much scarier than this.)
Hydrometeorology and ecophysiology of cloud forests
Tropical montane cloud forests (TMCFs) are characterized by a unique set of biological and hydroclimatic features, including frequent and/or persistent fog, cool temperatures, and high biodiversity and endemism. These forests are one of the most vulnerable ecosystems to climate change given their small geographic range, high endemism and dependence on a rare microclimatic envelope. The frequency of atmospheric water deficits for some cloud forests is likely to increase in the future, but the consequences for the integrity and distribution of these ecosystems are uncertain. In order to investigate plant and ecosystem responses to climate change, we need to know how cloud forest species function in response to current climate, which factors shape function and ecology most and how these will change into the future.
A recent review in Annals of Botany focuses on recent ecophysiological research of cloud forest plants to establish a link between hydrometeorological conditions and vegetation distribution, functioning and survival. The hydraulic characteristics of cloud forest trees are discussed, together with the prevalence and ecological consequences of foliar uptake of fog water, a key process that allows efficient acquisition of water during cloud immersion periods, minimizing water deficits and favouring survival of species prone to drought-induced hydraulic failure.
Fog occurrence is the single most important microclimatic feature affecting the distribution and function of cloud forest plants. Plants in cloud forests are very vulnerable to drought (possessing a small hydraulic safety margin), and the presence of fog and water uptake minimizes the occurrence of tree water deficits and thus favours the survival of cloud forest trees where such deficits may occur. Characterizing the interplay between microclimatic dynamics and plant water relations is key to foster more realistic projections about climate change effects on cloud forest function and distribution.
Oliveira, R.S., Eller, C. B., Bittencourt, P.R., and Mulligan, M. (2014). The hydroclimatic and ecophysiological basis of cloud forest distributions under current and projected climates. Annals of Botany, 113(6): 909-920. doi: 10.1093/aob/mcu060
Frequency-dependent pollinator discrimination acts against female plants in the gynodioecious Geranium maculatum
Gynodioecy, the co-occurrence of female and hermaphroditic individuals, is thought to be an intermediate step between hermaphroditism and separate sexes, a major transition in flowering plants. This paper suggests that suggest that pollinator discrimination negatively affects females’ relative fitness when they are rare. Thus the initial spread of females in a population, the first step in the evolution of gynodioecy, may be made more difficult due to pollinator discrimination.
Factors affecting stress tolerance in recalcitrant embryonic axes from seeds of four Quercus (Fagaceae) species native to the USA or China
Oaks (Quercus species) are often considered ‘foundation’ components of temperate and/or subtropical forest ecosystems. However, the populations of some species are declining and there is considerable urgency to develop ex situ conservation strategies. In this study, the storage physiology of seeds within Quercus was explored in order to determine factors that affect survival during cryopreservation and to provide a quantitative assessment of seed recalcitrance to support future studies of this complex trait.
Multiple origins of circumboreal taxa in Pyrola (Ericaceae), a group with a Tertiary relict distribution
Two major categories of Northern Hemisphere intercontinental disjunctions are Tertiary relict disjunctions and circumboreal distributions. Tertiary relict disjunctions tend to be older and involve groups from warm temperate to sub-tropical regions, reflecting the warm climates of the Tertiary epoch. Conversely, circumboreal distributions typically involve cold temperate to Arctic-Alpine species, and tend to be younger, reflecting the recent development of these biomes due to global cooling over the past 5 million years. This paper reconstructs the biogeographic history of Pyrola based on a clear phylogenetic analysis and to explore how the genus attained its circumboreal distribution.
Maintenance of species cohesion despite ongoing hybridization
The maintenance of species cohesion despite ongoing gene exchange via natural hybridization in plants is a phenomenon attracting increasing research attention. Natural hybridization can create bridges for gene flow, offering a platform for adaptive evolution by introducing variation and novel traits into populations, potentially resulting in introgression and admixture of genotypes. With advances in genetic technologies, researchers have been able to uncover greater complexity within hybrid populations and we can now delve deeper into how interspecific gene exchange can be ongoing despite the presence of strong reproductive barriers.
When species cohesion is maintained despite ongoing natural hybridization, many questions are raised about the evolutionary processes operating in the species complex. A recent study in Annals of Botany examines the extensive natural hybridization between the Australian native shrubs Lomatia myricoides and L. silaifolia (Proteaceae). These species exhibit striking differences in morphology and ecological preferences, exceeding those found in most studies of hybridization to date. The results show that morphological and ecological distinctions between plant species can be maintained despite ongoing gene flow via natural hybridization. Localized gene flow and introgression are expected to be ongoing between L. myricoides and L. silaifolia and their hybrids wherever they occur in sympatry, due to the permeability of this species barrier.
McIntosh, E. J., Rossetto, M., Weston, P. H., & Wardle, G. M. (2014) Maintenance of strong morphological differentiation despite ongoing natural hybridization between sympatric species of Lomatia (Proteaceae). Annals of Botany, 113 (5): 861-872. doi: 10.1093/aob/mct314
Nuclear microsatellite markers (nSSRs), genotyping methods and morphometric analyses were used to uncover patterns of hybridization and the role of gene flow in morphological differentiation between sympatric species.
The complexity of hybridization patterns differed markedly between sites, however, signals of introgression were present at all sites. One site provided evidence of a large hybrid swarm and the likely presence of multiple hybrid generations and backcrosses, another site a handful of early generational hybrids and a third site only traces of admixture from a past hybridization event. The presence of cryptic hybrids and a pattern of morphological bimodality amongst hybrids often disguised the extent of underlying genetic admixture.
Distinct parental habitats and phenotypes are expected to form barriers that contribute to the rapid reversion of hybrid populations to their parental character state, due to limited opportunities for hybrid/intermediate advantage. Furthermore, strong genomic filters may facilitate continued gene flow between species without the danger of assimilation. Stochastic fire events facilitate temporal phenological isolation between species and may partly explain the bi-directional and site-specific patterns of hybridization observed. Furthermore, the findings suggest that F1 hybrids are rare, and backcrosses may occur rapidly following these initial hybridization events.
Paleopolyploidy in the flax genus, Linum
Polyploidy, the duplication of whole genomes, is an important evolutionary force that is especially prevalent in plants. Recent study has revealed that all angiosperms have undergone at least two rounds of ancient whole-genome duplication in addition to several younger, lineage-specific events. These events are thought to have been very important in the evolutionary diversification of flowering plants.
Cultivated flax (Linum usitatissimum) is known to have undergone a whole-genome duplication around 5–9 million years ago. The aim of a recent study in Annals of Botany was to investigate whether other whole-genome duplication events have occurred in the evolutionary history of cultivated flax. Knowledge of such whole-genome duplications will be important in understanding the biology and genomics of cultivated flax.
Sveinsson, S., McDill, J., Wong, G. K., Li, J., Li, X., Deyholos, M. K., & Cronk, Q. C. (2014) Phylogenetic pinpointing of a paleopolyploidy event within the flax genus (Linum) using transcriptomics. Annals of Botany, 113(5), 753-761. doi: 10.1093/aob/mct306
Transcriptomes of 11 Linum species were sequenced using the Illumina platform. The short reads were assembled de novo and the DupPipe pipeline was used to look for signatures of polyploidy events from the age distribution of paralogues. In addition, phylogenies of all paralogues were assembled within an estimated age window of interest. These phylogenies were assessed for evidence of a paleopolyploidy event within the genus Linum.
A previously unknown paleopolyploidy event that occurred 20–40 million years ago was discovered and shown to be specific to a clade within Linum containing cultivated flax (L. usitatissimum) and other mainly blue-flowered species. The finding was supported by two lines of evidence. First, a significant change of slope (peak) was shown in the age distribution of paralogues that was phylogenetically restricted to, and ubiquitous in, this clade. Second, a large number of paralogue phylogenies were retrieved that are consistent with a polyploidy event occurring within that clade.
The results show the utility of multi-species transcriptomics for detecting whole-genome duplication events and demonstrate that that multiple rounds of polyploidy have been important in shaping the evolutionary history of flax. Understanding and characterizing these whole-genome duplication events will be important for future Linum research.
ADH1 and carbohydrate metabolism in seeds of rice
Rice (Oryza sativa) has the rare ability to germinate and elongate a coleoptile under oxygen-deficient conditions, which include both hypoxia and anoxia. It has previously been shown that Alcohol Dehydrogenase 1 (ADH1) is required for cell division and cell elongation in the coleoptile of submerged rice seedlings by means of studies using a rice ADH1-deficient mutant, reduced adh activity (rad).
A recent paper in Annals of Botany aims to understand how low ADH1 in rice affects carbohydrate metabolism in the embryo and endosperm, and lactate and alanine synthesis in the embryo during germination and subsequent coleoptile growth in submerged seedlings.
Even in a submerged environment containing substantial amounts of dissolved oxygen, a reduction in ADH (as brought about by an ADH1 mutation) reduces seedling viability, changes the balance between the end-products of glycolysis and decreases sugar concentrations in the endosperm and embryo. Exogenous sugar did not improve the growth or survival of the ADH1 mutant, indicating that sugar processing in the embryo was probably the limiting factor. However, how low ADH activity affects the endosperm deserves further experimental attention. The endosperm is well suited for investigations of sugar production and transport because of its simple composition and metabolism.
Takahashi, H., Greenway, H., Matsumura, H., Tsutsumi, N., & Nakazono, M. (2014) Rice alcohol dehydrogenase 1 promotes survival and has a major impact on carbohydrate metabolism in the embryo and endosperm when seeds are germinated in partially oxygenated water. Annals of Botany, 113 (5): 851-859. doi: 10.1093/aob/mct305
The September issue of CBE—Life Sciences Education is a Special Focus edition on plant science education:
Plant Behavior. CBE Life Sci Educ September 2, 2014 13:363-368; doi:10.1187/cbe.14-06-0100
Plants are a huge and diverse group of organisms ranging from microscopic marine phytoplankton to enormous terrestrial trees. Stunning, and yet some of us take plants for granted. In this plant issue of LSE, WWW.Life Sciences Education focuses on a botanical topic that most people, even biologists, do not think about—plant behavior.
Book Review: Plant Biology for Young Children. CBE Life Sci Educ September 2, 2014 13:369-370; doi:10.1187/cbe.14-06-0093
My Life as a Plant is an activity book targeted toward helping young children see the importance, relevance, and beauty of plants in our daily lives. The book succeeds at introducing children to plant biology in a fun, inquiry-based, and appropriately challenging way.
Understanding Early Elementary Children’s Conceptual Knowledge of Plant Structure and Function through Drawings. CBE Life Sci Educ September 2, 2014 13:375-386; doi:10.1187/cbe.13-12-0230
We present the results of an early elementary study (K–1) that used children’s drawings to examine children’s understanding of plant structure and function.
Effects of a Research-Infused Botanical Curriculum on Undergraduates’ Content Knowledge, STEM Competencies, and Attitudes toward Plant Sciences. CBE Life Sci Educ September 2, 2014 13:387-396; doi:10.1187/cbe.13-12-0231
This research-infused botanical curriculum increased students’ knowledge and awareness of plant science topics, improved their scientific writing, and enhanced their statistical knowledge.
Connections between Student Explanations and Arguments from Evidence about Plant Growth. CBE Life Sci Educ September 2, 2014 13:397-409; doi:10.1187/cbe.14-02-0028
In an analysis of 22 middle and high school student interviews, we found that many students reinterpret the hypotheses and results of standard investigations of plant growth to match their own understandings. Students may benefit from instructional strategies that scaffold their explanations and inquiry about how plants grow.
Beyond Punnett Squares: Student Word Association and Explanations of Phenotypic Variation through an Integrative Quantitative Genetics Unit Investigating Anthocyanin Inheritance and Expression in Brassica rapa Fast Plants. CBE Life Sci Educ September 2, 2014 13:410-424; doi:10.1187/cbe.13-12-0232
This study explores shifts in student word association and explanations of phenotypic variation through an integrative quantitative genetics unit using Brassica rapa Fast Plants.
Optimizing Learning of Scientific Category Knowledge in the Classroom: The Case of Plant Identification. CBE Life Sci Educ September 2, 2014 13:425-436; doi:10.1187/cbe.13-11-0224
The software program Visual Learning—Plant Identification offers a solution to problems in category learning, such as plant identification. It uses well-established learning principles, including development of perceptual expertise in an active-learning format, spacing of practice, interleaving of examples, and testing effects to train conceptual learning.
Attention “Blinks” Differently for Plants and Animals. CBE Life Sci Educ September 2, 2014 13:437-443; doi:10.1187/cbe.14-05-0080
We use an established paradigm in visual cognition, the “attentional blink,” to demonstrate that our attention is captured more slowly by plants than by animals. This suggests fundamental differences in how the visual system processes plants, which may contribute to plant blindness considered broadly.
Lagoons, coral atolls and coconut palm dispersal (Viewpoint)
When coconut palms are the subject of a scientific report, the introductory paragraphs can mention only a few of the multiple uses that make this pan-tropical crop invaluable to thousands of smallholder farmers. A comment on the beauty and familiar appearance of coconut palms is hard to resist, and may be illustrated by a picture showing the graceful stems, supporting a crown of fronds, curving over a tropical lagoon, into which the ripe fruit can fall and float. The difficulty of dealing with a long-lived monocotyledon of unknown origin that cannot be vegetatively propagated may also be mentioned.
The original home of the coconut palm, Cocos nucifera, and the extent of its natural dispersal are not known. Proponents of a South American origin must explain why it is not indigenous there and why it shows greatest diversity in southern Asia. Conversely, proponents of an Asian origin must explain why there are no Asian Cocoseae and why the closest botanical relative to Cocos is in South America. Both hypotheses share the common problems of how, when, where and in what directions long-distance dispersal occurred.
Harries, H.C., & Clement, C.R. (2013) Long-distance dispersal of the coconut palm by migration within the coral atoll ecosystem. Annals of Botany, 113 (4): 565-570. doi: 10.1093/aob/mct293
Effects of nitrogen on ω-gliadins in wheat grain
Wheat is the most important food crop in the temperate world, being used to produce bread, pasta, noodles and a range of other baked goods and foods. The ability to produce this wide range of products is largely determined by the grain storage proteins (prolamins), which form a viscoelastic network, called gluten, in dough formed from wheat flour. The classification into gliadins and glutenins has proved to be remarkably durable, but does not reflect the true molecular and evolutionary relationships of the proteins.
The ω-gliadin storage proteins of wheat are of interest in relation to their impact on grain processing properties and their role in food allergy, particularly the ω-5 sub-group and wheat-dependent exercise-induced anaphylaxis. The ω-gliadins are also known to be responsive to nitrogen application. A recent study published in Annals of Botany compares the effects of cultivar and nitrogen availability on the synthesis and deposition of ω-gliadins in wheat grown under field conditions in the UK, including temporal and spatial analyses at the protein and transcript levels.
The results show that wheat ω-gliadins vary in amount and composition between cultivars, and in their response to nitrogen supply. Their spatial distribution is also affected by nitrogen supply, being most highly concentrated in the sub-aleurone cells of the starchy endosperm under higher nitrogen availability.
Wan, Y., Gritsch, C.S., Hawkesford, M.J., & Shewry, P.R. (2014) Effects of nitrogen nutrition on the synthesis and deposition of the ω-gliadins of wheat. Annals of Botany, 113(4), 607-615. doi: 10.1093/aob/mct291