Content Snapshots; Annals of Botany Volume 112 Number 3 2013


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Content Snapshots; Annals of Botany Volume 112 Number 3 2013

  1. 1. Improving crop models in the face of climate change (Viewpoint) doi:10.1093/aob/mct016 and 10.1093/aob/ mct130 Crop models need improving for an accurate assessment of the impacts of climate change on crop productivity. Yin (pp. 465–475) considers that most existing models are unable to accommodate photosynthetic acclimation to CO2 concentrations, and therefore tend to overpredict crop responses to elevated CO2. Strong evidence is provided for the need to quantify carbon–nitrogen interactions in order to simulate this acclimation mechanism. This would provide a basis for a mechanistic framework that models critical physiological processes and traits in response to other climatic factors and extreme weather events. In an accompanying article, Kimball (pp. 477–478) comments on a methodological error in a previously published report of a free-air CO2 enrichment (FACE) study that is cited by Yin. Plant biodiversity conservation in montane ecosystems (Invited Review) doi:10.1093/aob/mct125 Mountain ecosystems are hot spots for plant conservation efforts because they have high plant diversity as communities replace each other along altitudinal and climatic gradients, and they have a high proportion of endemic species. Khan et al. (pp. 479–501) review the need to integrate different conservation criteria and methodologies and suggest new means of assessing anthropogenic pressure on plant biodiversity at both species and community levels. They consider plant diversity in mountain ecosystems with special reference to the western Himalayas, ethnobotanical and ecosystem service values of mountain vegetation within the context of anthropogenic impacts, and local and regional plant conservation strategies and priorities. Pectin and AGP mapping in germinating olive pollen doi:10.1093/aob/mct118 Cell wall pectins and arabinogalactan proteins (AGPs) are important for pollen tube growth. Castro et al. (pp. 503–513) study AGPs in olive (Olea europaea) pollen and find that they are newly synthesized during germination, with production and secretion being spatially and temporally regulated. They suggest that galactans may provide mechanical stability to the pollen tube, reinforcing those regions that are sensitive to tension stress and mechanical damage, and arabinans and AGPs may be important in recognition and adhesion properties of the pollen tube and the stylar transmitting cells, as well as the egg and sperm cells. Species coherence in a cytogenetically diverse sedge doi:10.1093/aob/mct119 The sedge genus Carex, the most diversified angiosperm genus of the northern temperate zone, is known for its holocentric chromosomes and karyotype variability. Escudero et al. (pp. 515–526) provide the first comprehensive study of population-level patterns of molecular and cytogenetic differentiation in the genus. They demonstrate dispersal and genetic connectivity among populations of the North American Carex scopariathat differ in chromosome numbers, demonstrating that cytogenetically variable sedge species can still cohere genetically. This finding is important to our understanding of what constitutes a species in one of the world’s largest angiosperm genera. Highly conserved B chromosomes in rye doi:10.1093/aob/mct121 Supernumerary B chromosomes (Bs) represent a specific type of ‘selfish’ genetic element. As they are dispensable for normal growth, they generally show polymorphisms among populations. Marques et al. (pp. 527–534) analyse the distribution and activity of B-located repeats in cultivated rye, Secale cereale subsp. cereale, and weedy relatives from seven countries ranging from Turkey to Japan and find that Bs maintain a similar molecular structure at the subspecies level. The high degree of conservation of the non-disjunction control region underlines its functional importance for the maintenance of B chromosomes. The conserved structure suggests that although rye Bs experienced rapidevolutionincludingmultiplerearrangementsat the early evolutionary stages, this process has slowed significantly and may have even ceased during its recent evolution. Gymnosperm B-sister genes and ovule/seed development doi:10.1093/aob/mct124 Seeds are producedbygymnosperms andangiosperms butonly the latter have an ovary to be transformed into a fruit. Lovsisetto et al. (pp. 535–544) study B-sister genes from two gymnosperms, Ginkgo biloba and Taxus baccata, and find that in Ginkgo the gene is involved in the growth of ovular-derived fleshy fruit. They functionally characterize the gene by ectopically expressing it in tobacco. In contrast, the fleshy structure in Taxus derives from an outgrowth of the ovule peduncle, and the B-sister gene is not involved in its growth. They suggest that B-sister genes have a primary function in ovule/seed development and a subsidiary role in the formation of fleshy fruit-like structures when the latter have an ovular origin, as observed in Ginkgo. i ContentSnapshots Annals of Botany Volume112 Number 3 2013 byguestonAugust14,2013
  2. 2. Repetitive component of the peanut A genome doi:10.1093/aob/mct128 Peanut (Arachis hypogaea) is an allotetraploid (AABB-type genome) of recent origin. Bertioli et al. (pp. 545–559) study the evolution of the A genome, focusing on its highly repetitive component. They find that a substantial proportion of the repetitive content appears to be accounted for by relatively few long terminal repeat (LTR) retrotransposons and their truncated copies or solo LTRs, mostly non-autonomous. The retrotransposons described are all transcribed, although levels are low. They conclude that the activity of these retrotransposons has been a very significant driver of genome evolution since the divergence of the peanut A and B genomes. Individual mating patterns in mixed oak stands doi:10.1093/aob/mct131 Individual variation in mating patterns may have significant implications for persistence and adaptation of plant populations, but field data generally focus on population averages. Using a Bayesian approach, Chybicki and Burczyk (pp. 561–574) examine the extent of individual variation of several components of mating patterns in a mixed stand of Quercus robur and Q. petraea. They find that there is a great variation in intra- and inter-specific individual mating preferences, individual pollen immigration rates and heterogeneity of immigrating pollen. They show that trees can mate assortatively, with little respect to spatial proximity. Such selective mating may be a result of variable compatibility among trees due to genetic and/or environmental factors. Carbohydrate storage and allometric partitioning in juvenile trees doi:10.1093/aob/mct132 Biomass partitioning for resource conservation might affect plant allometry, accounting for a substantial amount of unexplained variation in existing plant allometry models. Tomlinson et al. (pp. 575–587) compare root carbohydrate storage and organ biomass allometries for juveniles of 20 savannatree species of different leaf habit – nine evergreen and 11 deciduous – and find that deciduous species have greater root non-structural carbohydrate than evergreens, and lower scaling exponents for leaf-to-root and stem-to-root partitioning. The data provide strong support for the hypothesis that deciduous and evergreen trees differ in juvenile biomass allometries because of differences in allocation to root storage. Substantial unexplained variation in biomass allometry of woody species may be related to selection for resource conservation against environmental stresses, such as resource seasonality. Molecular analyses help resolve the evolution of Platanus doi:10.1093/aob/mct134 Recent research on the history of Platanus has shown that complex hybridization phenomena occurred in the central American species, and its evolutionary history remains unresolved. De Castro et al. (pp. 589–602) employ sequencing of a uniparental cpDNA marker ( psbA-trnH(GUG) intergenic spacer) and qualitative and quantitative SNP genotyping of biparental nrDNA markers (LFY-i2 and ITS2) to confirm that hybridization and introgression events between lineages ancestral to modern central and eastern North American Platanus species occurred. Chloroplast haplotypes and qualitative and quantitative SNP genotyping provide information critical for understanding the complex history of Mexican Platanus. Compared with the usual molecular techniques of sub-cloning, sequencing and genotyping, the real-time PCR assay employed provides a quick and sensitive technique for analysing complex evolutionary patterns. HvAACT1 increases Al31 -tolerance in wheat and barley doi:10.1093/aob/mct135 Al3+ -activated release of citrate from the root apices of aluminium-tolerant genotypes of barley is controlled by a MATE gene named HvAACT1 that encodes a citrate transporter. Zhou et al. (pp. 603–612) over-express HvAACT1 in wheat (Triticum aestivum) and barley (Hordeum vulgare) using the maize ubiquitin promoter, and find that increased expression in both species is associated with increased citrate efflux from root apices, and that this enhances Al3+ tolerance in both hydroponic solution and in acid soil. Genetically modifying barley and wheat to express the barley gene HvAACT1 gene therefore has potential in helping to alleviate the effects of aluminium toxicity in acid soils. Maternal sex effects and inbreeding depression in Fragaria doi:10.1093/aob/mct120 Gynodioecy (coexistence of females and hermaphrodites) is a sexual system that occurs in numerous flowering plant lineages. In order to understand the maintenance of gynodioecy, Dalton et al. (pp. 613–621) examine the effect of maternal sex type and inbreeding depression (IBD) on plant performance across several resource conditions and life stages in woodland strawberry, Fragariavesca subsp. bracteata. They find that maternal genotype and resources influence the magnitude of both maternal sex effects and IBD, with progeny of females being more likely to germinate under benign conditions and survive under stress. Cumulative IBD is low but increases with life stage. Assuming the results are representative for this long-lived perennial, then neither female maternal advantage nor IBD are strong enough to maintain gynodioecy under nuclear models of sex inheritance. ii byguestonAugust14,2013
  3. 3. Carbon budgets in deciduous and evergreen treeline species doi:10.1093/aob/mct127 The growth limitation hypothesis proposes that treelines form becausecarbonsinksaremorerestrictedbylowtemperaturesthanby carbonsources,butmostsupportingevidencecomesfromevergreen species. Fajardo et al. (pp. 623–631) examine tree growth and concentrations of non-structural carbohydrates (NSCs) at four elevations in six deciduous–evergreen mixed-species forests in the southern Andes and the Swiss Alps, and find that both foliar types are sink-limited when faced with decreasing temperatures. Despitethe deciduoustreespecies havingsignificantlyhigher NSCs than evergreens, no indication is found of carbon limitation in deciduous species in the alpine treeline ecotone. miRNAs responsive to low nitrate doi:10.1093/aob/mct133 MicroRNAs (miRNAs) play an important role in adaptation of plants to many stresses including low nitrogen availability. Zhao et al. (pp. 633–642) identify miRNAs and their targets in maize (Zea mays) subjected to low-nitrogen stress by combined analysis of deep sequencing of small RNA and degradome libraries. Of 85 potentially new miRNAs, 25 show a more than two-fold relative change in response to low-nitrogen compared to optimal conditions, and two novel putative miR169 species are identified. The results will help increase understanding of the physiological basis for low-nitrogen tolerance and adaptation in maize. Plant Cuttings Annals of Botany 112: iii–v, 2013 Available online at News in Botany: Nigel Chaffey presents a round-up of plant-based items from the world’s media Plant Cuttings has changed . . . We’re experimenting with a new format for the Plant Cuttings this month. Whilst applauding the eclectic mix of content each issue, some readers of this column have expressed concern that inclusion of thefullcitationswithinthetextspoils their enjoyment of the news items because this hinders the narrative flow. So, balancing the need to provideevidence-basedsciencecommunicationandreadability, for this issue, in-text references are replaced with numbers, and fullercitation(s)appearbelowthenewsitem.Whatdoyouthink? Is this better? Do let me know – either on Twitter: @NChaffey, or via e-mail: Thank you. Image: Wikimedia Commons. Brachypodium is NOT Arabidopsis(!) Yes, arabidopsis is a model organism[1–3] , but for what exactly? Many would like us to believe that it is a model for all things botanical, i.e. plants. However, with those organisms newly defined as ‘photosynthetic eukaryotic organisms, including algae and possibly cyanobacteria’[4] , that is a truly tall order for such a slight specimen! And arguably an extreme point of view (although entirely understandable if one’s past, present and future employment is tied to research grants using this beast). And, at the other end of the spectrum, there are those who espouse the view that arabidopsis is truly only a model for other arabidopses. Well, adding to the debate, David Pacheco-Villalobos et al. reveal that interactions between the plant hormones[5,6] ethylene and auxin in roots of the monocot Brachypodium distachyon (‘another’ model plant[7,8] ) differ to those in roots of the dicot Arabidopsis[9] . Wheras lowered levels of auxin in Arabidopsis, which can be caused by increases in another hormone – ethylene – result in shorter roots, in Brachypodium increases in ethylene lead to elevated levels of auxin and longer roots(!). The latter’s ‘inverted regulatory relation between the two hormones’ points to ‘a complex homeostatic crosstalk between auxin and ethylene in Brachypodium roots, which is fundamentally different from Arabidopsis and might be conserved in other monocotyledons’. So, and as those scientists sagely state, ‘Observationsgainedfrommodelorganismsareessential,yetit remains unclear to which degree they are applicable to distant relatives’. And, further complicating the ethylene story – if suchwasneededatthisstage – ‘Scientistsidentifythousandsof plant genes activated by ethylene gas’[10] . Examining transcriptional response to ethylene, Katherine Chang et al. have shown that this gaseous plant hormone is involved in an extensive network of cross-regulation with many other plant hormones centred around EIN3, a transcription factor that acts as the ‘master regulator’ of the ethylene signalling pathway[11] . Although this work was performed in arabidopsis, EIN3 orthologs[12,13] exist in many other plants, so this study is anticipated to have broader relevance to . . . poplar, soybean, rice, maize, moss and multicellular algae. Image: Neil Harris, University of Alberta/Wikimedia Commons. [1]; [2]; [3]; [4]; [5]; [6]; [7] John Draper et al., Plant Physiology 127: 1539–1555, 2001; [8]; [9] Pacheco-Villalobos et al., PloS Genetics 9: e1003564, 2013; [10]; [11] Chang et al., eLIFE, 2: e00675, 2013; [12]; [13] iii byguestonAugust14,2013