All posts by AJ Cann

About AJ Cann

Alan Cann is a Senior Lecturer in the Department of Biology at the University of Leicester and Internet Consulting Editor for AoB.

Maintenance of plant species cohesion despite ongoing hybridization

Maintenance of species cohesion despite ongoing hybridization

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.

Polyploidy and the evolution of flax

Paleopolyploidy in the flax genus, Linum

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.

 

How rice germinates under water

ADH1 and carbohydrate metabolism in seeds of rice

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

 

Seeing the Forest and the Trees: Research on Plant Science Teaching and Learning

CBE Life Sci Educ 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.

 

The controversial origin of the coconut

Lagoons, coral atolls and coconut palm dispersal (Viewpoint)

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

 

A better understanding of wheat gluten

Effects of nitrogen on ω-gliadins in wheat grain

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

Pollen limitation and reduced reproductive success

Mating dynamics in Prunus virginiana

Mating dynamics in Prunus virginiana

A vast quantity of empirical evidence suggests that insufficient quantity or quality of pollen may lead to a reduction in fruit set, in particular for self-incompatible species. A recent study in Annals of Botany uses an integrative approach that combines field research with marker gene analysis to understand the factors affecting reproductive success in a widely distributed self-incompatible species, Prunus virginiana (Rosaceae).

The results show that even though P. virginiana is a widespread species, fragmented populations can experience significant reductions in fruit set and pollen limitation in the field. Detailed examination of one fragmented population suggests that these linitations may be explained by an increase in biparental inbreeding, correlated paternity and fine-scale genetic structure. The consistency of the field and fine-scale genetic analyses, and the consistency of the results within patches and across years, suggest that these are important processes driving pollen limitation in the fragment.

 

Suarez-Gonzalez, A., & Good, S.V. (2014) Pollen limitation and reduced reproductive success are associated with local genetic effects in Prunus virginiana, a widely distributed self-incompatible shrub. Annals of Botany, 113 (4): 595-605. doi: 10.1093/aob/mct289.

 

Plant evolution: The inevitability of C4 photosynthesis

Photosynthesis Although atmospheric carbon dioxide (CO2) levels are currently rising, the last 30 million years witnessed great declines in CO2, which has limited the efficiency of photosynthesis. Rubisco, the critical photosynthetic enzyme that catalyses the fixation of CO2 into carbohydrate, also reacts with oxygen when CO2 levels are low and temperatures are high. When this occurs, plants activate a process known as photorespiration, an energetically expensive set of reactions that release one molecule of CO2.

C4 photosynthesis is a clever solution to the problem of low atmospheric CO2. It is an internal plant carbon-concentrating mechanism that largely eliminates photorespiration: a ‘fuel-injection’ system for the photosynthetic engine. C4 plants differ from plants with the more typical ‘C3′ photosynthesis because they restrict Rubisco activity to an inner compartment, typically the bundle sheath, with atmospheric CO2 being fixed into a 4-carbon acid in the outer mesophyll. This molecule then travels to the bundle sheath, where it is broken down again, bathing Rubisco in CO2 and limiting the costly process of photorespiration.

The evolution of the C4 pathway requires many changes. These include the recruitment of multiple enzymes into new biochemical functions, massive shifts in the spatial distribution of proteins and organelles, and a set of anatomical modifications to cell size and structure. It is complex, and it is also highly effective: C4 plants include many of our most important and productive crops (maize, sorghum, sugarcane, millet) and are responsible for around 25% of global terrestrial photosynthesis. A new paper in eLife examines how this process may have evolved, first to correct an intercellular nitrogen imbalance, and only later evolved a central role in carbon fixation.

Understanding and forecasting the response of plants to climate change

Climate change effects on range and diversity of a fern

Climate change effects on range and diversity of a fern

Understanding and forecasting the response of plant species to climatic fluctuation is one of the top priorities for current biodiversity research because of the critical need to conserve and manage natural resources and biodiversity. Climate fluctuations are not a new phenomenon. Plants have responded to global, regional and local climate change via migration and/or adaptation since their origin. In turn, slow and/or little response to climate change (e.g. slow migration rate) increases the probability of local or global extinction. By constructing the spatio-temporal dynamics of plant response to climate change from the past, it may be possible to improve our ability to predict future changes in the range and distribution of species and their genetic diversity. Low diversity coincides with high climate change velocity.

Recently researchers have tried to untangle the response of plants to changing climates at the microevolutionary scale, by integrating species distribution models and statistical phylogeography. Combining these two techniques will not only overcome their individual limitations, but will also improve our understanding of the spatio-temporal population dynamics involved.

A recent paper in Annals of Botany uses species distribution modelling and population genetic analysis to assess how Asplenium fontanum, a fern species with high migration capacity, has responded to environmental change since the last ice-age and to predict possible future implications under global warming. The results show the importance of climatically stable areas for maintenance of populations and accumulation of genetic diversity, and indicate that such areas are vulnerable to extinction under future scenarios of climate change, resulting in possible permanent loss of historic genetic variation.

 

Bystriakova, N., Ansell, S.W., Russell, S.J., Grundmann, M., Vogel, J.C., & Schneider, H. Present, past and future of the European rock fern Asplenium fontanum: combining distribution modelling and population genetics to study the effect of climate change on geographic range and genetic diversity. (2014) Annals of Botany, 113(3), 453-465.
Climate change is expected to alter the geographic range of many plant species dramatically. Predicting this response will be critical to managing the conservation of plant resources and the effects of invasive species. The aim of this study was to predict the response of temperate homosporous ferns to climate change. Genetic diversity and changes in distribution range were inferred for the diploid rock fern Asplenium fontanum along a South–North transect, extending from its putative last glacial maximum (LGM) refugia in southern France towards southern Germany and eastern-central France. This study reconciles observations from distribution models and phylogeographic analyses derived from plastid and nuclear diversity. Genetic diversity distribution and niche modelling propose that genetic diversity accumulates in the LGM climate refugium in southern France with the formation of a diversity gradient reflecting a slow, post-LGM range expansion towards the current distribution range. Evidence supports the fern’s preference for outcrossing, contradicting the expectation that homosporous ferns would populate new sites by single-spore colonization. Prediction of climate and distribution range change suggests that a dramatic loss of range and genetic diversity in this fern is possible. The observed migration is best described by the phalanx expansion model. The results suggest that homosporous ferns reproducing preferentially by outcrossing accumulate genetic diversity primarily in LGM climate refugia and may be threatened if these areas disappear due to global climate change.

 

Reproduction and invasiveness in St. John’s wort

Reproduction and invasiveness in St. John’s wort

Reproduction and invasiveness in St. John’s wort

The relative ability of different plant taxa to invade new biogeographic regions successfully is dependent upon a number of biological and physical factors, one of which is the reproductive system, which directly influences population structure, gene flow and evolutionary potential. Considering seed formation, plants can reproduce through sex (selfing and outcrossing) or apomixis (asexual reproduction through seed.

St. John’s wort (Hypericum perforatum) is such an invasive species which is indigenous to central and eastern Europe; it is self-compatible and can reproduce through sex or apomixis. H. perforatum has successfully invaded North America since the first record of introduction in Lancaster, Pennsylvania in 1793. Its high genotypic plasticity in conjunction with variable levels of facultative apomixis are hypothesized to have contributed to its rapid spread throughout the continent. For example, in an analysis of multiple phenotypic traits, Maron et al. (2004) demonstrated that the introduction of H. perforatum into North America was accompanied by rapid climatic adaptation.

Using an analysis of a collection of European native and North American invasive accessions, a recent paper in Molins Annals of Botany examines biogeographic differentiation in both natural and introduced populations, and test whether variation in apomixis traits is correlated with the propensity for H. perforatum to invade novel environments.

 

Molins, M.P., Corral, J.M., Aliyu, O.M., Koch, M.A., Betzin, A., Maron, J.L., & Sharbel, T.F. (2014) Biogeographic variation in genetic variability, apomixis expression and ploidy of St. John’s wort (Hypericum perforatum) across its native and introduced range. Annals of Botany, 113 (3): 417-427 doi: 10.1093/aob/mct268.
St. John’s wort (Hypericum perforatum) is becoming an important model plant system for investigations into ecology, reproductive biology and pharmacology. This study investigates biogeographic variation for population genetic structure and reproduction in its ancestral (European) and introduced (North America) ranges. Over 2000 individuals from 43 localities were analysed for ploidy, microsatellite variation (19 loci) and reproduction (flow cytometric seed screen). Most individuals were tetraploid (93 %), while lower frequencies of hexaploid (6 %), diploid (<1 %) and triploid (<1 %) individuals were also identified. The presence of pure and mixed populations representing all three genetic clusters in North America demonstrates that H. perforatum was introduced multiple times onto the continent, followed by gene flow between the different gene pools. Taken together, the data presented here suggest that plasticity in reproduction has no influence on the invasive potential of H. perforatum.