Early Flowering Plants Research Articles

Некоторые виды раннецветущих травянистых растений, произрастающих на территории Северного Казахстана, их состав и использование

Некоторые виды раннецветущих травянистых растений, произрастающих на территории Северного Казахстана, их состав и использование

Flower closure enhances pollen viability in Crocus discolor G. Reuss

Repetitive flower closure (nyctinasty) is influenced by various regulatory mechanisms, but its ultimate function remains unclear. It is hypothesized that closed corolla may protect a plant's reproductive organs against various unfavourable environmental conditions. We investigated if repetitive flower closure enhances pollen viability and prevents pollen loss in an early spring flowering species, Crocus discolor, occurring in open grasslands of submontane to subalpine zones of the Western Carpathian Mountains. Artificially interrupted temporal petal closure resulted in lower pollen viability, but it had no effect on the pollen availability in flowers. The latter result suggests that wind did not cause pollen loss from open flowers, but whether closed corolla may protect reproductive organs from being damaged by hail or rain remains to be tested. Closing corolla may serve as a pollen protection mechanism, particularly in early flowering plants facing harsh environmental conditions.

Evidence for the Extensive Conservation of Mechanisms of Ovule Integument Development Since the Most Recent Common Ancestor of Living Angiosperms.

The ovules and seeds of most angiosperm groups are enclosed by two integuments, whose evolutionary origins are considerably separated in time, as the inner integument arose over 300 million years ago (MYA) in an ancestor of all living seed plants, while the outer integument arose, perhaps as recently as 164 MYA, in an ancestor of all living angiosperms. Studies of the model angiosperm Arabidopsis thaliana indicate that the mechanisms of development of the inner and outer integuments depend on largely different sets of molecular players. However, it was not known, in most cases, whether these differences were already present in early flowering plants, or arose later in the Arabidopsis lineage. Here, we analyze the expression patterns of integument regulators in Amborella trichopoda, the likely sister to all other living angiosperms. The data obtained indicate that regulators of the YABBY, KANADI, and homeodomain-leucine zipper class III transcription factor families have largely conserved their integument-specific expression profiles in the Amborella and Arabidopsis lineages since the most recent common ancestor (MRCA) of living angiosperms. We identified only one case, involving the paralogous genes ETTIN and AUXIN RESPONSE FACTOR4, in which integument-specific expression patterns had clearly diverged between Amborella and Arabidopsis. We use the data obtained to partially reconstruct molecular mechanisms of integument development in the MRCA of living angiosperms and discuss our findings in the context of alternative hypotheses for the origin of the angiosperm outer integument.

Genome-Wide Association Study in Pseudo-F2 Populations of Switchgrass Identifies Genetic Loci Affecting Heading and Anthesis Dates.

Switchgrass (Panicum virgatum) is a native prairie grass and valuable bio-energy crop. The physiological change from juvenile to reproductive adult can draw important resources away from growth into producing reproductive structures, thereby limiting the growth potential of early flowering plants. Delaying the flowering of switchgrass is one approach by which to increase total biomass. The objective of this research was to identify genetic variants and candidate genes for controlling heading and anthesis in segregating switchgrass populations. Four pseudo-F2 populations (two pairs of reciprocal crosses) were developed from lowland (late flowering) and upland (early flowering) ecotypes, and heading and anthesis dates of these populations were collected in Lafayette, IN and DeKalb, IL in 2015 and 2016. Across 2 years, there was a 34- and 73-day difference in heading and a 52- and 75-day difference in anthesis at the Lafayette and DeKalb locations, respectively. A total of 37,901 single nucleotide polymorphisms obtained by exome capture sequencing of the populations were used in a genome-wide association study (GWAS) that identified five significant signals at three loci for heading and two loci for anthesis. Among them, a homolog of FLOWERING LOCUS T on chromosome 5b associated with heading date was identified at the Lafayette location across 2 years. A homolog of ARABIDOPSIS PSEUDO-RESPONSE REGULATOR 5, a light modulator in the circadian clock associated with heading date was detected on chromosome 8a across locations and years. These results demonstrate that genetic variants related to floral development could lend themselves to a long-term goal of developing late flowering varieties of switchgrass with high biomass yield.

Comparing the flowering phenology between the only natural and a translocated population of Dianthus morisianus

ABSTRACTThe reproductive success of a plant species depends to some extent on its flowering phenology. Thus, it is important to understand the flowering period, the flowering intensity and the synchrony of flowering to determine their respective influence on the reproductive success of the plant species. This study was conducted on the only natural population of Dianthus morisianus and on the first attempted translocation of the species. The aim of this study was to analyse the flowering phenology of the two populations to understand each and compare them. To analyse the flowering phenology, the initiation date, the intensity, the maximum flowering moment, the synchrony and the duration of flowering were tested. The studied plants had different flowering durations between years and the intensity and number of stems were significantly lower in the offspring of translocated plants than the natural plants. The early flowering plants had a longer flowering period and produced more flowers than those that flowered later. The offspring of the translocated population were able to flower, fruit and reproduce. They presented high flowering synchrony and flowered at the same time as the natural plants. This can increase the attractiveness for pollinators and facilitate exchange pollen with the natural plants. After five years, the success of the translocation can, thus, be asserted. This new path increases the genetic diversity of the species and its distribution.

The complete mitochondrial genome of the early flowering plant Nymphaea colorata is highly repetitive with low recombination

BackgroundMitochondrial genomes of flowering plants (angiosperms) are highly dynamic in genome structure. The mitogenome of the earliest angiosperm Amborella is remarkable in carrying rampant foreign DNAs, in contrast to Liriodendron, the other only known early angiosperm mitogenome that is described as ‘fossilized’. The distinctive features observed in the two early flowering plant mitogenomes add to the current confusions of what early flowering plants look like. Expanded sampling would provide more details in understanding the mitogenomic evolution of early angiosperms. Here we report the complete mitochondrial genome of water lily Nymphaea colorata from Nymphaeales, one of the three orders of the earliest angiosperms.ResultsAssembly of data from Pac-Bio long-read sequencing yielded a circular mitochondria chromosome of 617,195 bp with an average depth of 601×. The genome encoded 41 protein coding genes, 20 tRNA and three rRNA genes with 25 group II introns disrupting 10 protein coding genes. Nearly half of the genome is composed of repeated sequences, which contributed substantially to the intron size expansion, making the gross intron length of the Nymphaea mitochondrial genome one of the longest among angiosperms, including an 11.4-Kb intron in cox2, which is the longest organellar intron reported to date in plants. Nevertheless, repeat mediated homologous recombination is unexpectedly low in Nymphaea evidenced by 74 recombined reads detected from ten recombinationally active repeat pairs among 886,982 repeat pairs examined. Extensive gene order changes were detected in the three early angiosperm mitogenomes, i.e. 38 or 44 events of inversions and translocations are needed to reconcile the mitogenome of Nymphaea with Amborella or Liriodendron, respectively. In contrast to Amborella with six genome equivalents of foreign mitochondrial DNA, not a single horizontal gene transfer event was observed in the Nymphaea mitogenome.ConclusionsThe Nymphaea mitogenome resembles the other available early angiosperm mitogenomes by a similarly rich 64-coding gene set, and many conserved gene clusters, whereas stands out by its highly repetitive nature and resultant remarkable intron expansions. The low recombination level in Nymphaea provides evidence for the predominant master conformation in vivo with a highly substoichiometric set of rearranged molecules.

Pollinator‐mediated mechanisms for increased reproductive success in early flowering plants

Mating activities change within a season in many animal and plant populations. In plants, selection towards early flowering is commonly observed. Pollinator‐mediated selection is hypothesized to be a pervasive evolutionary force acting directionally on flowering time. However, pollinator‐mediated mechanisms have rarely been tested in realistic field conditions, especially in perennial plants visited by a diversity of generalist insect pollinators. We examined pollinator visitation in eight Echinacea angustifolia populations in western Minnesota, USA, to gauge the potential for pollinator‐mediated selection. Echinacea is a common prairie perennial that persists in isolated remnant populations. Echinacea is self‐incompatible and is pollinated by a diversity of generalist solitary bees. A previous study found that early flowering Echinacea plants have higher seed set and their reproduction is less pollen‐limited than late flowering plants. Twelve times throughout a flowering season, we quantified pollinator visitation rates and pollinator community composition. In three sites, we also estimated the quality of pollinator visits by examining the composition of pollinators’ pollen loads brought to Echinacea plants. We found that three aspects of pollination dramatically decreased over the course of the flowering season. 1) Pollinators visited early flowering plants more frequently than late flowering plants. 2) The pollinator community was also less diverse late in the flowering season and became dominated by a single species of small bee, Augochlorella aurata. 3) Pollinators visiting Echinacea late in the season carried proportionally less conspecific pollen compared to pollinators visiting Echinacea early in the flowering season. Understanding within‐season dynamics of pollination helps predict the prevalence of inbreeding, phenological assortative mating, and reproductive failure, especially in fragmented plant populations.

Differential Effects of Climate Warming on the Nectar Secretion of Early- and Late-Flowering Mediterranean Plants.

Floral nectar is a vital resource for pollinators, thus having a very important role in ecosystem functioning. Ongoing climate warming could have a negative effect on nectar secretion, particularly in the Mediterranean, where a strong temperature rise is expected. In turn, decreased nectar secretion, together with shifts in flowering phenology can disrupt plant–pollinator interactions and consequently affect the entire ecosystem. Under fully controlled conditions, we tested how temperature influenced nectar secretion (through nectar volume, sugar concentration, sugar content, and number of flowers produced) in six Mediterranean plant species flowering from winter to summer (viz. Asphodelus ramosus, Ballota acetabulosa, Echium plantagineum, Lavandula stoechas, Rosmarinus officinalis, and Teucrium divaricatum). We compared the changes in nectar secretion under temperatures expected by the end of the century and estimated the effect of climate warming on nectar secretion of plants flowering in different seasons. We found a significant effect of temperature on nectar secretion, with a negative effect of very high temperatures in all species. Optimal temperatures for nectar secretion were similar to the mean temperatures in the recent past (1958–2001) during the respective flowering time of each species. Increasing temperatures, however, will affect differently the early-flowering (blooming in winter and early spring) and late-flowering species (blooming in late spring and early summer). Temperature rise expected by the end of the century will shift the average temperature beyond the optimal range for flower production and the sugar produced per plant in late-flowering species. Therefore, we expect a future decrease in nectar secretion of late-flowering species, which could reduce the amount of nectar resources available for their pollinators. Early-flowering plants will be less affected (optimal temperatures were not significantly different from the future projected temperatures), and may in some cases even benefit from rising temperatures. However, as many earlier studies have found that early-flowering species are more prone to shifts in phenology, the plant–pollinator interactions could instead become affected in a different manner. Consequently, climate warming will likely have a distinctive effect on both plant and pollinator populations and their interactions across different seasons.

Inflorescence photosynthetic contribution to fitness releases Arabidopsis thaliana plants from trade-off constraints on early flowering.

Leaves are thought to be the primary carbon source for reproduction in plants, so a positive relationship between vegetative size and reproductive output is expected, establishing a trade-off between time to reproduction and reproductive output. A common response to higher temperatures due to climate changes is the induction of earlier transition into reproduction. Thus, in annual plants, earlier transition into flowering can potentially constrain plant size and reduce seed production. However, trade-offs between early reproduction and fitness are not always observed, suggesting mechanisms to escape the constraints of early flowering do exist. Here, we test whether inflorescence photosynthesis contribution to the reproductive output of Arabidopsis thaliana can offset the cost of early reproduction. We followed the development, growth rate and fitness of 15 accessions, and removed all rosette leaves at flowering (prior to the completion of inflorescence development or any fruit production) in half of the plants to determine the ability of inflorescences to maintain fitness in the absence of leaves. Although leaf removal significantly reduced fruit number, seed weight and plant height, even the most severely impacted accessions maintained 35% of their fitness with the inflorescence as the sole photosynthetic organ; and some accessions experienced no reduction in fitness. Differences between accessions in their ability to maintain fitness after leaf removal is best explained by earlier flowering time and the ability to maintain as many or more branches after leaf removal as in the control treatment. Although earlier flowering does constrain plant vegetative size, we found that inflorescence photosynthesis can significantly contribute to seed production, explaining why early flowering plants can maintain high fitness despite a reduction in vegetative size. Thus, plants can be released from the usually assumed trade-offs associated with earlier reproduction, and selection on inflorescence traits can mediate the impact of climate change on phenology.

The transcriptional repressor complex FRS7-FRS12 regulates flowering time and growth in Arabidopsis

Most living organisms developed systems to efficiently time environmental changes. The plant-clock acts in coordination with external signals to generate output responses determining seasonal growth and flowering time. Here, we show that two Arabidopsis thaliana transcription factors, FAR1 RELATED SEQUENCE 7 (FRS7) and FRS12, act as negative regulators of these processes. These proteins accumulate particularly in short-day conditions and interact to form a complex. Loss-of-function of FRS7 and FRS12 results in early flowering plants with overly elongated hypocotyls mainly in short days. We demonstrate by molecular analysis that FRS7 and FRS12 affect these developmental processes in part by binding to the promoters and repressing the expression of GIGANTEA and PHYTOCHROME INTERACTING FACTOR 4 as well as several of their downstream signalling targets. Our data reveal a molecular machinery that controls the photoperiodic regulation of flowering and growth and offer insight into how plants adapt to seasonal changes.

Improvement of genetic variability in seedlings of Spathoglottis plicata orchids through X-ray irradiation

Abstract. Aloysius S, Purwantoro A, Dewi K, Semiarti E. 2017. Improvement of genetic variability in seedlings of Spathoglottis plicata orchids through X-ray irradiation. Biodiversitas 18: 20-27. Developing genetic variability of orchids via mutation is promising for orchid breeding. The objective of this research was to improve genetic variation of Spathoglottis plicata orchids through X-ray-irradiation of the orchid seeds. The method involved X-ray irradiation of one month old mature orchid seeds at doses of 0, 6, 12, 18, and 24 rad. The X-ray irradiated seeds were sown on a half strength of MS medium and grown into protocorms (developing orchid embryo). Eight weeks-old protocorms were subcultured onto NP-SIM medium. Five months-old seedlings were then subcultured again into a new flask and morphological observations were recorded. Genetic variability detection was conducted using PCR RAPD based on nine primers, i.e. OPA1, OPA2, OPA11, OPA12, OPA14, OPB1, OPB4, OPD12, OPD14. The data was analyzed using GenAlex 6.1 software to obtain the genetic distance. Moreover, NTSys ver.2 was used to analyze the data for clustering and constructing a dendrogram based on Neighbour Joining model. The result showed that X-ray irradiation with doses of 12-18 rad was able to stimulate morphological variation of seedlings, especially characters of leaf, root and shoot. Interestingly, we found 2 in vitro early flowering plants among one years old X-ray irradiated plants, indicated that somehow X-ray mutation affect flowering time in orchid. Based on the dendrogram of genetic distance that the group of mutants was farther than the WT group and the percentage of polymorphism was bigger than that of wild type group, it is concluded that 12-18 rad doses of X-ray irradiation can be used for induction of genetic variability in Spathoglottis orchid.Keywords: Genetic variability, seed, seedling phenotype, Spathoglottis plicata, X-rayAbbreviations: BAP = benzylaminopurine; NAA = naphthaleneacetic acid; 2iP = 2 = isopentenyl adenine; NP = new phalaenopsis; SIM = shoot induction medium

Do sown flower strips boost wild pollinator abundance and pollination services in a spring-flowering crop? A case study from UK cider apple orchards

Flower strips are widely recommended as a tool to boost insect pollinators and yield in pollinator-dependent crops. Using UK cider apple orchards (Malus domestica Borkhausen) as a model system, we assessed whether flower strips increased pollination services in orchards. Pollinator communities (visual observation) and pollination services (fruit set) were assessed at increasing distance from surrounding semi-natural habitats (0–200m) in eight orchards. In four orchards, perennial flower strips had been established and bloomed in the year before the main experiment. In a separate experiment, insect visits to apple flowers were observed to investigate possible functional mechanisms underpinning pollinator efficacy.The visit rate of wild insects to apple flowers (non-Apis bees and flies), but not that of honeybees (Apis mellifera L.), increased by 40% in flower strip orchards compared to control orchards, particularly in areas close to semi-natural habitat (<100m). Wild insect visitation was also positively related to dandelion (Taraxacum species) abundance in orchards. Fruit set in orchards was positively related to wild insect richness, and andrenid bee (Andrena species) visitation, but neither richness nor andrenid bee visit rate responded positively to flower strips. Wild bees (andrenid bees and bumblebees (Bombus species)) contacted apple stigma (95 and 100% of visits) more often than honeybees (81%), but only bumblebees moved frequently between different tree rows, an important trait for transfer of compatible pollen in apples.Our results demonstrate that flower strips enhanced overall wild insect abundance but not pollination services in cider orchards. Positive effects of ground flora on wild insect abundance in orchards suggest that flower mixtures or orchard management could be optimised for andrenid bees, the single most important pollinator taxa, by increasing the availability of early-flowering plants in orchards. Equally, wild insect richness was highest in areas close to semi-natural habitats. Therefore, whilst flower strips can boost abundance of the existing species pool, only large scale preservation of (semi-) natural habitat will maintain pollinator diversity in apple orchards.

Flowering Syndrome-Hybrid Performance Relationship in Maize 1-Agromonic Traits

To determine the relationship between flowering syndrome and hybrid performance in some maize (Zea mays L.) crosses, selection on early and late flowering plants was undertaken. Selection was applied on plants of four inbreds; Zm19, Zm32, Zm51, and Zm61. Selected plants were propagated in the next season, grown in the third season and crossed to two testers (Zm21 late, and Zm60 early). The F1 seeds were planted in the fourth season in a randomized complete block design of three replicates in 83’000 plants/ha. This was done in the farm of the College of Agric., Univ. of Baghdad. The results showed that selection for divergent flowering of inbred gave significant difference in days to silking among all crosses. The days ranged between 62 d for early selects, to 66 d for late selects. This was reflected on time of seed filling that increased grain yield. The best crosses gave plant growth rate of 18.3 – 21.6 g.m-2.d-1, seed growth rate of 3.2 – 3.5 g.plant-1.d-1, and seed filling of 35 – 38 d. The cross that gave highest response of selection (61 x 21) gave 1.79 kg.m-2 dry matter for early select, and 2.20 kg.m-2 for late flowering select cross. It was recommended to select on maize inbreds to create new variations for better traits provided using large inbred populations.

Cultivated Sub-Populations of Soil Microbiomes Retain Early Flowering Plant Trait

The collection of microorganisms found in the root zone of soil, termed the rhizosphere microbiome, has been shown to impact plant growth and development. Here, we tease apart the function of the cultivable portion of the microbiome from the whole microbiome in retaining plant traits modified through artificial selection on flowering time. Specifically, the whole microbiome associated with earlier flowering time of Arabidopsis thaliana was cultivated on four types of solid media to create cultivated fractions of the microbiome. These cultivated microbiomes were subsequently preserved in glycerol, frozen, and revived to yield a portion of the cultivable fraction to compare (1) whole microbiome, (2) cultivable microbiome, and (3) revived, cultivable microbiome controls on early flowering time. Plants grown in soils inoculated with bacteria grown on 25 % Luria broth and 10 % tryptic soy agar retained the early flowering trait. An increase in leaf biomass with two of the cultivated microbiomes (49.4 and 38.5 %) contrasted the lowered biomass effect of the whole microbiome. Inoculation with the cultivated microbiomes that were cryopreserved in glycerol showed no effect on flowering time or leaf biomass. The results indicate that the cultivable portion of a plant’s microbiome retains the early flowering effect in A. thaliana, but cryopreservation of the cultivated microbiomes disrupts the microbial effects on flowering time. Furthermore, the contrasting effects on leaf biomass (an indirect response from selection on early flowering time), seen with the whole microbiome versus the cultivable portion, suggests versatility in using cultivation methods to modify multiple traits of plants.

Increased variance in temperature and lag effects alter phenological responses to rapid warming in a subarctic plant community.

Summer temperature on the Cape Churchill Peninsula (Manitoba, Canada) has increased rapidly over the past 75years, and flowering phenology of the plant community is advanced in years with warmer temperatures (higher cumulative growing degree days). Despite this, there has been no overall shift in flowering phenology over this period. However, climate change has also resulted in increased interannual variation in temperature; if relationships between phenology and temperature are not linear, an increase in temperature variance may interact with an increase in the mean to alter how community phenology changes over time. In our system, the relationship between phenology and temperature was log-linear, resulting in a steeper slope at the cold end of the temperature spectrum than at the warm end. Because below-average temperatures had a greater impact on phenology than above-average temperatures, the long-term advance in phenology was reduced. In addition, flowering phenology in a given year was delayed if summer temperatures were high the previous year or 2 years earlier (lag effects), further reducing the expected advance over time. Phenology of early-flowering plants was negatively affected only by temperatures in the previous year, and that of late-flowering plants primarily by temperatures 2 years earlier. Subarctic plants develop leaf primordia one or more years prior to flowering (preformation); these results suggest that temperature affects the development of flower primordia during this preformation period. Together, increased variance in temperature and lag effects interacted with a changing mean to reduce the expected phenological advance by 94%, a magnitude large enough to account for our inability to detect a significant advance over time. We conclude that changes in temperature variability and lag effects can alter trends in plant responses to a warming climate and that predictions for changes in plant phenology under future warming scenarios should incorporate such effects.

Characterization and Selection of Phosphorus Deficiency Tolerant Rice Genotypes in Sri Lanka

Phosphorus (P) deficiency in soil is a major constrain for rice production. An important set of rice genotypes (landraces, old improved and new improved varieties) were screened for P deficiency tolerance in two major cropping seasons of Sri Lanka, in 2012. The Ultisol soil, which was collected from a plot cultivated with rice without fertilizer application for past 40 years (P0) at the Rice Research and Development Institute (RRDI), Bathalagoda, Sri Lanka, was used as the potting medium for greenhouse trials. Two field trials were conducted in the same plots at RRDI. Both P0 and P30 (30mg/kg P2O5) conditions were used in the two greenhouse trials. At the early vegetative (three weeks after transplanting), late vegetative (six weeks after transplanting) and flowering stages, plant height and number of tillers per plant were recorded. At the flowering stage, shoots were harvested and shoot dry weight, shoot P concentration, shoot P uptake and P utilization efficiency were measured. All data were statistically analyzed using analysis of variance, regression and cluster procedures. The measured parameters were significantly different between P0 and P30 conditions (P < 0.05). Higher shoot dry weight was reported by the rice genotypes H4 and Marss under P0 conditions. The regression analysis between shoot dry weight and P utilization efficiency revealed that the studied rice genotypes could be categorized to three P deficiency tolerance classes. A total of 13 genotypes could be considered as highly tolerant and 4 genotypes as sensitive for P deficiency. These results could be used to select parental genotypes for breeding and genetic studies and also to select interesting varieties or landraces for organic rice production.

Apple latent spherical virus vector-induced flowering for shortening the juvenile phase in Japanese gentian and lisianthus plants.

Infection by apple latent spherical virus (ALSV) vectors that promote the expression of Arabidopsis thaliana FLOWERING LOCUS T ( AtFT ) or Gentiana triflora GtFT s accelerates flowering in gentian and lisianthus plants. Apple latent spherical virus (ALSV) has isometric virus particles (25nm in diameter) that contain two ssRNA species (RNA1 and RNA2) and three capsid proteins (Vp25, Vp20, and Vp24). ALSV vectors are used for foreign gene expression and virus-induced gene silencing in a broad range of plant species. Here, we report the infection by ALSV vectors that express FLOWERING LOCUS T (AtFT) from Arabidopsis thaliana or its homolog GtFT1 from Gentiana triflora in three gentian cultivars ('Iwate Yume Aoi' [early flowering], 'Iwate' [medium flowering], and 'Alta' [late flowering]), and two lisianthus cultivars ('Newlination Pink ver. 2' and 'Torukogikyou daburu mikkusu') promotes flowering within 90days post-inoculation using particle bombardment. Additionally, seedlings from the progeny of the early-flowering plants were tested by tissue blot hybridization, and the results showed that ALSV was not transmitted to the next generation. The promotion of flowering in the family Gentianaceae by ALSV vectors shortened the juvenile phase from 1-3years to 3-5months, and thus, it could be considered as a new plant breeding technique in ornamental gentian and lisianthus plants.

Phenological change in a spring ephemeral: implications for pollination and plant reproduction.

Climate change has had numerous ecological effects, including species range shifts and altered phenology. Altering flowering phenology often affects plant reproduction, but the mechanisms behind these changes are not well-understood. To investigate why altering flowering phenology affects plant reproduction, we manipulated flowering phenology of the spring herb Claytonia lanceolata (Portulacaceae) using two methods: in 2011-2013 by altering snow pack (snow-removal vs. control treatments), and in 2013 by inducing flowering in a greenhouse before placing plants in experimental outdoor arrays (early, control, and late treatments). We measured flowering phenology, pollinator visitation, plant reproduction (fruit and seed set), and pollen limitation. Flowering occurred approx. 10 days earlier in snow-removal than control plots during all years of snow manipulation. Pollinator visitation patterns and strength of pollen limitation varied with snow treatments, and among years. Plants in the snow removal treatment were more likely to experience frost damage, and frost-damaged plants suffered low reproduction despite lack of pollen limitation. Plants in the snow removal treatment that escaped frost damage had higher pollinator visitation rates and reproduction than controls. The results of the array experiment supported the results of the snow manipulations. Plants in the early and late treatments suffered very low reproduction due either to severe frost damage (early treatment) or low pollinator visitation (late treatment) relative to control plants. Thus, plants face tradeoffs with advanced flowering time. While early-flowering plants can reap the benefits of enhanced pollination services, they do so at the cost of increased susceptibility to frost damage that can overwhelm any benefit of flowering early. In contrast, delayed flowering results in dramatic reductions in plant reproduction through reduced pollination. Our results suggest that climate change may constrain the success of early-flowering plants not through plant-pollinator mismatch but through the direct impacts of extreme environmental conditions.

Variation in the flowering time orthologsBrFLCandBrSOC1in a natural population ofBrassica rapa

Understanding the genetic basis of natural phenotypic variation is of great importance, particularly since selection can act on this variation to cause evolution. We examined expression and allelic variation in candidate flowering time loci in Brassica rapa plants derived from a natural population and showing a broad range in the timing of first flowering. The loci of interest were orthologs of the Arabidopsis genes FLC and SOC1 (BrFLC and BrSOC1, respectively), which in Arabidopsis play a central role in the flowering time regulatory network, with FLC repressing and SOC1 promoting flowering. In B. rapa, there are four copies of FLC and three of SOC1. Plants were grown in controlled conditions in the lab. Comparisons were made between plants that flowered the earliest and latest, with the difference in average flowering time between these groups ∼30 days. As expected, we found that total expression of BrSOC1 paralogs was significantly greater in early than in late flowering plants. Paralog-specific primers showed that expression was greater in early flowering plants in the BrSOC1 paralogs Br004928, Br00393 and Br009324, although the difference was not significant in Br009324. Thus expression of at least 2 of the 3 BrSOC1 orthologs is consistent with their predicted role in flowering time in this natural population. Sequences of the promoter regions of the BrSOC1 orthologs were variable, but there was no association between allelic variation at these loci and flowering time variation. For the BrFLC orthologs, expression varied over time, but did not differ between the early and late flowering plants. The coding regions, promoter regions and introns of these genes were generally invariant. Thus the BrFLC orthologs do not appear to influence flowering time in this population. Overall, the results suggest that even for a trait like flowering time that is controlled by a very well described genetic regulatory network, understanding the underlying genetic basis of natural variation in such a quantitative trait is challenging.

Genetic structure of a montane perennial plant: the influence of landscape and flowering phenology

The way that genetic variation is distributed geographically has important conservation and evolutionary implications. Here, we examined the distribution of genetic variation within and among populations of the montane perennial Ipomopsis aggregata. We sampled plants in western Colorado and examined (1) population genetic structure over a geographic area that spanned 130 km, including genetic variation within disturbed and undisturbed sites; (2) the relationship between genetic differentiation and geographic distance; and (3) the relationship between flowering time and genetic differentiation among plants within and among geographic areas. F IS was significantly higher (t test, P = 0.006), expected heterozygosity was significantly lower (t test, P = 0.04), and allelic richness was marginally significantly lower (t test, P = 0.078) among anthropogenically-disturbed sites compared to undisturbed sites. We found moderate genetic differentiation over the area sampled (average pairwise F ST = 0.04; average pairwise $$F^{\prime}_{ST} = 0.19$$ ), but no association of genetic and geographic distance (Mantel test P values 0.44 for F ST and 0.36 for $$F^{\prime}_{ST}$$ ). We found a strong association of flowering time and genetic differentiation over small and large spatial scales. Genetic differentiation between early and late flowering plants within a focal site was statistically significant (genic test for population differentiation combined P value <0.001; F ST = 0.05). There was a significant correlation between genetic distance ( $$F^{\prime}_{ST}$$ ) and distance in flowering time, when controlling for geographic distance, over the whole geographic area (Partial Mantel test R xy = 0.32, P = 0.013). A multiple regression with randomization further supported the inference that flowering time, but not geographic distance or elevation, predicted $$F^{\prime}_{ST}$$ (geographic distance: β = −0.03, P = 0.89; elevation: β = 0.01, P = 0.96; phenological distance: β = 0.30, P = 0.05), but not F st (geographic distance: β = −0.02, P = 0.92; elevation: β = 0.14, P = 0.38; phenological distance: β = 0.25, P = 0.11), unless elevation was left out of the model (geographic distance: β = −0.03, P = 0.9; phenological distance: β = 0.29, P = 0.03). The association of flowering time and genetic distance despite the lack of isolation by distance provides further evidence for the usefulness of incorporating this variable into plant landscape genetic studies when possible.