What is going on with the hormonal control of flowering in plants?

Molecular genetic studies using Arabidopsis thaliana as a model system have overwhelmingly revealed many important molecular mechanisms underlying the control of various biological events, including floral induction in plants. The major genetic pathways of flowering have been characterized in-depth, and include the photoperiod, vernalization, autonomous and gibberellin pathways. In recent years, novel flowering pathways are increasingly being identified. These include age, thermosensory, sugar, stress and hormonal signals to control floral transition. Among them, hormonal control of flowering except the gibberellin pathway is not formally considered a major flowering pathway per se, due to relatively weak and often pleiotropic genetic effects, complex phenotypic variations, including some controversial ones. However, a number of recent studies have suggested that various stress signals may be mediated by hormonal regulation of flowering. In view of molecular diversity in plant kingdoms, this review begins with an assessment of photoperiodic flowering, not in A. thaliana, but in rice (Oryza sativa); rice is a staple crop for human consumption worldwide, and is a model system of short-day plants, cereals and breeding crops. The rice flowering pathway is then compared with that of A. thaliana. This review then aims to update our knowledge on hormonal control of flowering, and integrate it into the entire flowering gene network.     

Strawberry Genes and Genomics

Despite its value as a crop and potential utility as an experimental system, relatively little is known about the molecular-genetic aspects of inheritance or physiology in the cultivated strawberry (Fragaria xananassa). This lack of information exists at a time when biotechnology may offer important remedies to address traditional and contemporary challenges that growers face. An improved understanding of genome structure will hasten the development of molecular markers and unveil clues to the composition of this unique, octoploid genome. Definition of gene function will guide the generation of transgenic resources for research use and possibly toward cultivar development. This review seeks to compile and present the current knowledge state of the molecular-genetic basis of cultivated strawberry genomic form and function. Ongoing studies promise to expand the use of genomic tools and appropriate model systems to rapidly discern the structural and functional basis for traits of interest to agriculture, such as those associated with disease, ripening, and volatile production. Together these studies bring new molecular tools to dissect complex traits, implement marker-assisted selection and address important physiological questions in the cultivated strawberry, the Fragaria genus, and the Rosaceae family.     

An examination of targeted gene neighborhoods in strawberry

Background  

Strawberry (Fragaria spp.) is the familiar name of a group of economically important crop plants and wild relatives that also represent an emerging system for the study of gene and genome evolution. Its small stature, rapid seed-to-seed cycle, transformability and miniscule basic genome make strawberry an attractive system to study processes related to plant physiology, development and crop production; yet it lacks substantial genomics-level resources. This report addresses this deficiency by characterizing 0.71 Mbp of gene space from a diploid species (F. vesca). The twenty large genomic tracks (30-52 kb) captured as fosmid inserts comprise gene regions with roles in flowering, disease resistance, and metabolism.     

Small wild bee abundance declines with distance into strawberry crops regardless of field margin habitat

The preservation of pollinator habitat on croplands in the form of hedgerows, wildflower strips, and natural and semi-natural areas can help maintain and enhance wild bee populations in agricultural landscapes. However, there have been few comparisons of the effectiveness of different types of field-margin pollinator habitat in maintaining bee diversity and pollination of the focal crops. We compared wild bee abundance, species richness and community composition between strawberry crops bordered by hedgerows, and those bordered by larger expanses of natural land (forests). Strawberry is an ideal crop in which to investigate pollinator export from field margins as the rows are covered with straw, which reduces habitat for ground-nesting bees within the crop; thus, most wild pollinators need to enter the crop from the margins. We sampled bees in six strawberry fields with hedgerow margins and six strawberry fields with forested margins of at least 200 m in length, using a paired design. We examined strawberry pollen deposition at regular intervals into the fields, and the magnitude of pollinator export from the field margins towards the centre of the crops. We found that bees as a group were no more species-rich or abundant in crops bordered by forests than in crops bordered by hedgerows, although large-bodied bees were more abundant in the former than the latter. Regardless of field-margin type, we found that small wild bee abundance declined significantly from the edge to the centre of the crop, but honey bee (Apis mellifera L.) and large-bodied bee abundance did not. Strawberry pollen deposition also did not decline with distance into the crop. Although previous work indicates that small wild bees are more effective (yield-increasing) pollinators of strawberry on a per-visit basis, their limited foraging ranges suggest they may only pollinate areas near the crop margins, given typical field sizes in our area.     

Identification of flowering genes in strawberry, a perennial SD plant

Background  

We are studying the regulation of flowering in perennial plants by using diploid wild strawberry (Fragaria vesca L.) as a model. Wild strawberry is a facultative short-day plant with an obligatory short-day requirement at temperatures above 15°C. At lower temperatures, however, flowering induction occurs irrespective of photoperiod. In addition to short-day genotypes, everbearing forms of wild strawberry are known. In 'Baron Solemacher' recessive alleles of an unknown repressor, SEASONAL FLOWERING LOCUS (SFL), are responsible for continuous flowering habit. Although flower induction has a central effect on the cropping potential, the molecular control of flowering in strawberries has not been studied and the genetic flowering pathways are still poorly understood. The comparison of everbearing and short-day genotypes of wild strawberry could facilitate our understanding of fundamental molecular mechanisms regulating perennial growth cycle in plants.     

Resting sites,edge effects and dispersion of a polyphagous Bactrocera fruit fly within crops of different architecture

The spot or strip application of poisoned protein bait is a lure‐and‐kill technique used for the management of fruit flies. Knowledge of where flies occur in the crop environment is an important part of maximizing the efficacy of this tool. Bactrocera tryoni is a polyphagous pest of horticulture for which very little is known about its distribution within crops. With particular reference to edge effects, we monitored the abundance of B. tryoni in two crops of different architecture; strawberry and apple. In strawberries, we found more flies on the crop edge early in the fruiting season, which lessened gradually and eventually disappeared as the season progressed. In apple orchards, no such edge effect was observed and flies were found equally throughout the orchard. We postulated these differences may be due to differences in crop height (high vs. short) and/or crop canopy architecture (opened and branched in apple, dense and closed in strawberry). In a field cage trial, we tested these predictions using artificial plants of different height and canopy condition. Height and canopy structure type had no significant effects on fly oviposition and protein feeding, but the ‘apple’ type canopy significantly influenced resting. We thus postulate that there was an edge effect in strawberry because the crop was not providing resting sites and flies were doing so in vegetation around the field margins. The finding that B. tryoni shows different resting site preferences based on plant architecture offers the potential for strategic manipulation of the fly through specific border or inter‐row plantings.     

Setaria genome sequencing: an overview

The genus Setaria includes two important C₄ Panicoid grass species, namely S. italica (cultivated) and S. viridis (weed; wild ancestor), which together represent an appropriate model system for architectural, physiological, evolutionary, and genomic studies in related grasses. It is a diploid, inbreeder, self-fertile annual cereal grass having short life cycle and minimal growth requirements. There close relatedness to biofuel crops like switch grass and napier grass further signifies their importance. Further, foxtail millet is an important food and fodder grain crop grown in arid and semi-arid regions in many parts of the world. Therefore, an increasing interest in these species has led to a gradual accumulation and development of genomic data and genetic resources. Setaria genome sequencing is an outcome of such endeavors. These sequencing efforts uncovered several distinctive attributes of Setaria genome that may help in understanding its physiology, evolution and adaptation. This will not only aid in comparative genomics studies of Setaria and related crops including bioenergy grasses but also help in rapid advancements of genomics information for developing varieties with superior traits either through marker-assisted selection (MAS) or using transgenic approaches in these crops.     

Reduced abundance and earlier collection of bumble bee workers under intensive cultivation of a mass‐flowering prairie crop

One of the most commonly seeded crops in Canada is canola, a cultivar of oilseed rape (Brassica napus). As a mass‐flowering crop grown intensively throughout the Canadian Prairies, canola has the potential to influence pollinator success across tens of thousands of square kilometers of cropland. Bumble bees (Bombus sp.) are efficient pollinators of many types of native and crop plants. We measured the influence of this mass‐flowering crop on the abundance and phenology of bumble bees, and on another species of social bee (a sweat bee; Halictus rubicundus), by continuously deploying traps at different levels of canola cultivation intensity, spanning the start and end of canola bloom. Queen bumble bees were more abundant in areas with more canola cover, indicating that this crop is attractive to queens. However, bumble bee workers were significantly fewer in these locations later in the season, suggesting reduced colony success. The median collection dates of workers of three bumble bee species were earlier near canola fields, suggesting a dynamic response of colonies to the increased floral resources. Different species experienced this shift to different extents. The sweat bee was not affected by canola cultivation intensity. Our findings suggest that mass‐flowering crops such as canola are attractive to bumble bee queens and therefore may lead to higher rates of colony establishment, but also that colonies established near this crop may be less successful. We propose that the effect on bumble bees can be mitigated by spacing the crop more evenly with respect to alternate floral resources.     

Can a late bloomer become an early bird? Tools for flowering time adjustment

The transition from the vegetative to reproductive stage followed by inflorescence is a critical step in plant life; therefore, studies of the genes that influence flowering time have always been of great interest to scientists. Flowering is a process controlled by many genes interacting mutually in a genetic network, and several hypothesis and models of flowering have been suggested so far. Plants in temperate climatic conditions must respond mainly to changes in the day length (photoperiod) and unfavourable winter temperatures. To avoid flowering before winter, some plants exploit a specific mechanism called vernalization. This review summarises current achievements in the study of genes controlling flowering in the dicot model species thale cress (Arabidopsis thaliana), as well as in monocot model species rice (Oryza sativa) and temperate cereals such as barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.). The control of flowering in crops is an attractive target for modern plant breeding efforts aiming to prepare locally well-adapted cultivars. The recent progress in genomics revealed the importance of minor-effect genes (QTLs) and natural allelic variation of genes for fine-tuning flowering and better cultivar adaptation. We briefly describe the up-to-date technologies and approaches that scientists may employ and we also indicate how these modern biotechnological tools and “-omics” can expand our knowledge of flowering in agronomically important crops.     

Environmentally Modified Organisms – Expanding Genetic Potential with Light

Light is a potent regulator of plant growth and development, impacting gene expression to global physiology and metabolism. Plants sense a broad range of wavelengths, from UV to far-red, through separate photoreceptors. These light sensors direct adaptive responses under changing environmental conditions and specifically activate precise downstream signaling pathways. Research studies in photobiology, mostly in Arabidopsis thaliana, have characterized light effects on many plant behaviors, along with the genetic mechanisms that control them. Transferring this knowledge to crops has opened a new field in plant science where variation in light quantity, quality, duration or combinations can be used to change plant growth, development or metabolism to influence a desired final product. With the potential of easily being introduced into production chains, and given its safety and relative low cost, this approach can be combined with, or used as an alternative to, breeding or genetic engineering. We review how light has been used in 22 different crop species to manipulate growth characteristics, nutritional value, and yield. We also discuss future opportunities in using light to control produce quality or timing of plant product production.     

Decision-making tools for Frankliniella occidentalis management in strawberry: consideration of target markets

The western flower thrips (WFT), Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), a cosmopolitan pest of many crops, is considered a major pest of low tunnel and greenhouse strawberries. The extent of damage to strawberry is unclear because different studies have produced contradictory results. Also, economic thresholds published for WFT in strawberry vary greatly, and most fail to incorporate economic factors. This study was aimed at developing a decision‐making tool for WFT management in strawberries in Israel. Toward this end, economic injury levels (EIL) and economic thresholds were calculated, based on target markets (export vs. domestic). Results indicate that serious infestation of ripe berries may cause a dull, rough appearance, and the fruit may be soft and have a reduced shelf life, rendering it unsuitable for export. Most fruit damage occurred at green and turning‐red stages of development. Two decision‐making tools were developed, one for winter, when WFT populations increase slowly but crop value is high (export market); and the second for spring, when the pest increases rapidly but crop value is low (local markets). Economic thresholds of 10 and 24 WFT/flower were calculated for winter and spring strawberries, respectively, based on direct thrips damage to fruit. This calculation does not take into account the recorded WFT damage to flowers, or its role in facilitating Botrytis cinerea fruit infection. Western flower thrips has proved only an occasional economic pest in Israeli strawberries, and no routine control measures are warranted. Furthermore, augmentative releases of Orius laevigatus or Neoseilus cucumeris against WFT are not justified in this system, because Orius colonizes strawberry fields spontaneously in high numbers when no broad spectrum insecticides are used.     

植物miRNA参与调控作物农艺性状的研究进展

植物microRNA (miRNA)是一类长度约为20～24 nt的内源非编码小RNA,它们通过在转录后水平调控靶基因的表达,在植物的生长发育、逆境响应和环境适应等过程中起着关键作用. miRNA对水稻、玉米、大豆等重要经济作物的农艺性状也起着重要的调控作用,在改良农作物性状上具有重大的应用潜能.本文重点介绍了参与作物农艺性状(如株型、花期、种子发育及抗逆等)调控的关键miRNA及其调控途径,同时总结了miRNA参与作物性状改良的主要研究方法和手段,并讨论了miRNA在作物性状改良应用中的前景.     

Mycotrophy of crops in rotation and soil amendment with peat influence the abundance and effectiveness of indigenous arbuscular mycorrhizal fungi in field soil

Mycotrophy of previous crops has been shown to have an impact on arbuscular mycorrhizal fungi (AMF), and the growth and productivity of succeeding crops. We studied the impact of 3 years of cultivation of eight crops with different degrees of mycotrophy, including mycorrhizal (strawberry, rye, timothy, onion, caraway) and non-mycorrhizal (turnip rape, buckwheat, fiddleneck) hosts, as well as the impact of peat amendment, on the effectiveness, amount and diversity of indigenous AMF. A field experiment having a split-plot design with peat amendment as the main plot, crop cultivation as a sub-plot and three replications, was carried out on silt clay mineral soil in 1999–2001. A well-humified dark peat was applied immediately before establishment of the field experiment. Each year, the relative mycorrhizal effectiveness of soil collected in September, in terms of shoot dry weight (RME_DW), was determined in a bioassay. In the 3rd year of the experiment, AMF spores were also extracted and identified from the field soil. Expressed as the mean of 3 years of cropping in unamended soil, the mycorrhizal crops strawberry and caraway maintained RME_DW most effectively, while the values were lower in the non-host crops buckwheat, turnip rape and fiddleneck. In addition, the numbers of AM spores detected in soil were considerably greater during 3 years of strawberry cultivation. In soil under caraway, there were high numbers of AM spores compared to the other crops. In soil amended with peat, the situation was in some cases opposite of that of unamended soil; RME_DW was highest in rye and onion and lowest in strawberry and caraway. The reasons behind the negative impact of peat on mycorrhizal effectiveness in strawberry soil may be due to the microbiological properties of peat. The importance of including mycotrophic species in crop rotations for maintaining high soil quality and for increasing yields of subsequent crops is discussed.     

Companion planting to attract pollinators increases the yield and quality of strawberry fruit in gardens and allotments

1. Global pollinator declines have led to concern that crop yields might fall as a result of a pollination deficit. Companion planting is a traditional practice thought to increase yield of insect pollinated crops by planting a co-flowering species next to the crop. 2. Using a combination of conventional researcher-led experiments and observational citizen scientist data, we tested the effectiveness of bee-friendly borage (Borago officinalis) as a companion plant to strawberry (Fragaria x ananassa). Insect visitors to the ‘Test’ (strawberry + borage) versus ‘Control’ (strawberry only) plants were observed, and strawberry fruit collected. Strawberries collected during the researcher-led experiment were also subject to fruit measurements and assessments of market quality. 3. Companion plants were found to significantly increase both yield and market quality of strawberries, suggesting an increase in insect pollination per plant. Test strawberries companion planted with borage produced an average of 35% more fruits, and 32% increased yield by weight. Test strawberry plants produced significantly more fruit of higher aesthetic quality when assessed by Marketing Standards for Strawberries. 4. Although there was no significant difference in the overall insect visits, when broken down by broad insect group there were significantly more flies visiting the test strawberries than controls. 5. These results could have implications for both gardeners and commercial growers. As consumers prefer a cosmetically perfect fruit, the production of fruit with increased aesthetics aids food waste reduction.     

Evidence of genetic influence on the flowering pattern of Ficus microcarpa

Flowering patterns result from the interactions between genetic and environmental factors. While the genetic basis for flowering time variation in commercial plants is often well understood, few studies have been conducted to investigate these patterns in plants without economic importance. Ficus microcarpa is a commonly introduced horticultural fig tree. Asynchrony in syconium development and the initiation, frequency, and size of crops may affect its fitness as well as the success of mutualism with its pollinating wasps. In order to identify genetically determined patterns in the flowering traits in F. microcarpa, a 14-month census was taken on the flowering characteristics of 28 trees growing in close proximity along an urban street in Taipei, Taiwan. Weekly surveys were taken on 7 characteristics: crop number, syconia per branch, crop asynchrony, as well as flowering onset and seed development duration for both the spring and summer crops. Post-census genotyping at microsatellite loci distinguished 16 genetic groups (5 clonal groups and 11 non-clone trees). All crop characteristics presented higher variation across different genotype groups than within groups except for seed development duration. We found no evidence of adjacency effects or spatial auto-correlation of flowering traits. The study offers the first evidence of genetic variations in the flowering patterns in a species of Ficus. These findings lend insight into the adaptive characteristics that potentially facilitate the local establishment of F. microcarpa in new locations.     

Genetic architecture of the circadian clock and flowering time in <Emphasis Type="Italic">Brassica rapa</Emphasis>

The circadian clock serves to coordinate physiology and behavior with the diurnal cycles derived from the daily rotation of the earth. In plants, circadian rhythms contribute to growth and yield and, hence, to both agricultural productivity and evolutionary fitness. Arabidopsis thaliana has served as a tractable model species in which to dissect clock mechanism and function, but it now becomes important to define the extent to which the Arabidopsis model can be extrapolated to other species, including crops. Accordingly, we have extended our studies to the close Arabidopsis relative and crop species, Brassica rapa. We have investigated natural variation in circadian function and flowering time among multiple B. rapa collections. There is wide variation in clock function, based on a robust rhythm in cotyledon movement, within a collection of B. rapa accessions, wild populations and recombinant inbred lines (RILs) derived from a cross between parents from two distinct subspecies, a rapid cycling Chinese cabbage (ssp. pekinensis) and a Yellow Sarson oilseed (ssp. trilocularis). We further analyzed the RILs to identify the quantitative trait loci (QTL) responsible for this natural variation in clock period and temperature compensation, as well as for flowering time under different temperature and day length settings. Most clock and flowering-time QTL mapped to overlapping chromosomal loci. We have exploited micro-synteny between the Arabidopsis and B. rapa genomes to identify candidate genes for these QTL.     

Experimental evidence that wildflower strips increase pollinator visits to crops

Wild bees provide a free and potentially diverse ecosystem service to farmers growing pollination‐dependent crops. While many crops benefit from insect pollination, soft fruit crops, including strawberries are highly dependent on this ecosystem service to produce viable fruit. However, as a result of intensive farming practices and declining pollinator populations, farmers are increasingly turning to commercially reared bees to ensure that crops are adequately pollinated throughout the season. Wildflower strips are a commonly used measure aimed at the conservation of wild pollinators. It has been suggested that commercial crops may also benefit from the presence of noncrop flowers; however, the efficacy and economic benefits of sowing flower strips for crops remain relatively unstudied. In a study system that utilizes both wild and commercial pollinators, we test whether wildflower strips increase the number of visits to adjacent commercial strawberry crops by pollinating insects. We quantified this by experimentally sowing wildflower strips approximately 20 meters away from the crop and recording the number of pollinator visits to crops with, and without, flower strips. Between June and August 2013, we walked 292 crop transects at six farms in Scotland, recording a total of 2826 pollinators. On average, the frequency of pollinator visits was 25% higher for crops with adjacent flower strips compared to those without, with a combination of wild and commercial bumblebees (Bombus spp.) accounting for 67% of all pollinators observed. This effect was independent of other confounding effects, such as the number of flowers on the crop, date, and temperature. Synthesis and applications. This study provides evidence that soft fruit farmers can increase the number of pollinators that visit their crops by sowing inexpensive flower seed mixes nearby. By investing in this management option, farmers have the potential to increase and sustain pollinator populations over time.     

Identification and characterization of QTL underlying whole-plant physiology in Arabidopsis thaliana: δ13C, stomatal conductance and transpiration efficiency

Water limitation is one of the most important factors limiting crop productivity world-wide and has likely been an important selective regime influencing the evolution of plant physiology. Understanding the genetic and physiological basis of drought adaptation is therefore important for improving crops as well as for understanding the evolution of wild species. Here, results are presented from quantitative trait loci (QTL) mapping of flowering time (a drought escape mechanism) and carbon stable isotope ratio (δ¹³C) (a drought-avoidance mechanism) in Arabidopsis thaliana. Whole-genome scans were performed using multiple-QTL models for both additive and epistatic QTL effects. We mapped five QTL affecting flowering time and five QTL affecting δ¹³C, but two genomic regions contained QTL with effects on both traits, suggesting a potential pleiotropic relationship. In addition, we observed QTL–QTL interaction for both traits. Two δ¹³C QTL were captured in near-isogenic lines to further characterize their physiological basis. These experiments revealed allelic effects on δ¹³C through the upstream trait of stomatal conductance with subsequent consequences for whole plant transpiration efficiency and water loss. Our findings document considerable natural genetic variation in whole-plant, drought resistance physiology of Arabidopsis and highlight the value of quantitative genetic approaches for exploring functional relationships regulating physiology.     

Sugarcane biotechnology: The challenges and opportunities

Summary Commercial sugarcane, belonging to the genus Saccharum (Poaceae), is an important industrial crop accounting for nearly 70% of sugar produced worldwide. Compared to other major crops, efforts to improve sugarcane are limited and relatively recent, with the first introduction of interspecific hybrids about 80 yr ago. Progress in traditional breeding of sugareane, a highly polyploid and frequently aneuploid plant, is impeded by its narrow gene pool, complex genome, poor fertility, and the long breeding/selection cycle. These constraints, however, make sugarcane a good candidate for molecular breeding. In the past decade considerable progress has been made in understanding and manipulating the sugarcane genome using various biotechnological and cell biological approaches. Notable among them are the creation of transgenic plants with improved agronomic or other important traits, advances in genomics and molecular markers, and progress in understanding the molecular aspects of sucrose transport and accumulation. More recently, substantial effort has been directed towards developing sugarcane as a biofactory for high-value products. While these achievements are commendable, a greater understanding of the sugarcane genome, and cell and whole plant physiology, will accelerate the implementation of commercially significant biotechnology outcomes. We anticipate that the rapid advancements in molecular biology and emerging biotechnology innovations would play a significant role in the future sugarcane crop improvement programs and offer many new opportunities to develop it as a new-generation industrial crop.