Search

Rain-mediated reproduction, or hydrophily, is present in only 0.1% higher plant taxa. Pinus spp. is included on this list so here we present a synthesis illustrating three roles for rain in pine reproductive biology: pollen transport, pollen delivery and pollination. Pine pollen has been shown to survive long-range transport beneath and inside rain clouds after which germination still occurs. Pine pollen is captured inside raindrops so rain delivers pine pollen back to the earth's surface and this pollen can also germinate. Rain is the primary pollination mode for Pinus taeda. The pollination drop only appears later if rain does not fall. Pine pollen does not appear to burst into subpollen pieces (SPP) upon water contact. For these reasons, wind and rain are vectors of pollen transport, deposition and pollination. Accordingly, research gaps abound and we formulated these as three testable hypotheses: (1) wetted pollen has aerodynamic properties which deter transport, (2) rain delivers its own load of pollen and (3) rain contributes to long-distance gene flow among populations within a species. Rain acts as a fluid medium contributing to Pinus spp. reproduction. [ABSTRACT FROM AUTHOR]

Pollen release by Northern Hemisphere pine forests is well-documented yet little is known about its atmospheric layering. At what altitudes are these atmospheric layers and how do they influence pollen dispersal? To answer this, pollen concentrations were analysed using radiosonde soundings and LiDAR imagery over the Pamlico Sound, a large marine body at 35.4062° N, 76.3259° W between coastal of North Carolina, USA and its barrier islands. Pollen sampled over the sound ranged from 11 to 861 pollen m−3. During daylight, the planetary boundary layer (PBL) height was 1932 m and it was capped by a warm, dry inversion from 2015 to 3072 m. Similarly, PBL height was estimated at 2000 m using a CALIPSO LiDAR image. Mixed-phase clouds could form above the PBL starting at 5650 m where temperatures were less than −13.5 °C and wind speeds exceeded 29.8 m s−1. During cooler night hours, the PBL height dropped to 724 m and its inversion cap also dropped to 1027–1904 m. Strong westerly winds with a low vertical shear drove pollen across water on a cloudless sunny day. Wind speeds below the PBL stayed strong at night while rising relative humidity influenced pollen deposition. Structuring atmospheric layers during pollen dispersal provided more understanding of how long-distance pollen is dispersed at a land–atmosphere interface. [ABSTRACT FROM AUTHOR]

* Premise of the Study: Pine pollen (Pinus spp.), along with other atmospheric particles, is dispersed by the water cycle, but this mode of dispersal requires cloud--pollen interactions that depend on taxon-specific biological properties. In the simplest form of this dispersal, pine pollen ascends vertically to altitudes of 2 to 6 km, where a fraction is captured by mixed-phase cloud formation. Captured pollen accretes into frozen droplets, which ultimately descend as rain, snow, or hail. Whether Pinus pollen can still germinate after its exposure to high-altitude freezing is pertinent to (1) how forests adapt to climate change and (2) potential gene flow between genetically modified plantation species and their conspecific relatives. * Methods: To address this question, pollen from four Old World and two New World Pinus species were subjected to immersion freezing, a common cloud formation mode, under laboratory conditions. * Key Results: Some pollen grains immersed at -20°C for 15, 60, or 120 min in either a dehydrated or a water-saturated state were still capable of germination. After exposure, dehydrated pine pollen had higher germination (43.3%) than water-saturated pollen (7.6%). * Conclusions: Pine pollen exposed to freezing during cloud formation can still germinate, raising the question of whether rain-delivered live pollen might be linked to rain-facilitated pollination. Dispersal of live pine pollen via cloud formation and the water cycle itself deserves closer study. [ABSTRACT FROM AUTHOR]

Long-distance dispersal (LDD) theory requires a method for marking live LDD pollen. Such a method must complement more intensive sampling methods inclusive of molecular cytogenetics, proteomics and genomics. We developed a new method for marking live Pinus taeda pollen using two dyes, rhodamine 123 and aniline blue, dissolved in a sucrose solution. Marked and unmarked pollen were compared with respect to in vitro germination, storage, terminal velocity, and in vivo pollen tube penetration of ovules. We found that: (1) both types of marked pollen retained their capacity for germination, (2) both types of marked pollen had similar aerodynamic properties when compared to unmarked pollen controls, (3) marked pollen retained its germination capacity for 48 h, and (4) of the marked pollen, only the aniline-marked pollen penetrated ovules during pollination. Germination declined rapidly for both types of marked pollen after 48 h and before 37 days at −20°C storage, while unmarked pollen lots retained 93% germination at all stages. This method for marking live P. taeda pollen is feasible for tracing LDD pollen only if released and deposited within 48 h of dye treatment. [ABSTRACT FROM AUTHOR]

Study of long-distance dispersal (LDD) theory requires a method for marking live LDD pollen. Such a method must complement the more intensive sampling methods involving molecular cytogenetics, proteomics, and genomics. We have developed a new method for marking live Pinus taeda pollen using two dyes, rhodamine 123 and aniline blue, dissolved in a sucrose solution. Marked and unmarked pollen were compared with respect to in vitro germination, storage, terminal velocity and in vivo pollen-tube penetration of ovules. We found that: (1) both types of marked pollen retained their capacity for germination, (2) both types of marked pollen had similar aerodynamic properties as unmarked pollen controls, (3) marked pollen retained its germination capacity for 48 h, and (4) of the marked pollen, only the aniline-marked pollen penetrated ovules during pollination. Germination declined rapidly for both types of marked pollen after 48 h and before 37 days at −20°C storage, while the unmarked pollen lots retained 93% germination at all stages. Our method for marking live P. taeda pollen is feasible for tracing LDD pollen if released and deposited within 48 h of dye treatment. [ABSTRACT FROM AUTHOR]

Better knowledge of aerobiological properties of pollen clouds is needed for pines and other woody perennials because these properties shape the predictive accuracy of spatially explicit pollen dispersal models. Four properties were experimentally measured in this study using processed Pinus taeda L. (loblolly pine) pollen as well as pollen concentration and viability data collected from an 18-year-old P. taeda plantation. Results showed that P. taeda pollen had a settling or terminal velocity value of 2.1 cm·s–1; that daytime pollen count from a plantation was sparse, reaching a maximum of 1480 grains·m–3 at peak pollen shed; and that pollen concentration showed no vertical gradient above or below the plantation’s canopy. Pollen sampled above and within the canopy had comparable germination rates. Surprisingly, a low concentration of viable Pinus spp. pollen was present during nighttime. Study results added further to the idea that P. taeda pollen has a higher nuisance value than either Zea mays L. (maize) or Agrostis stolonifera L. (creeping bentgrass) pollen because of its low terminal velocity value, persistent viability, and perennial production. [ABSTRACT FROM AUTHOR]

Comparative mapping in conifers has not yet been used to test for small-scale genomic disruptions such as inversions, duplications, and deletions occurring between closely related taxa. Using comparative mapping to probe this smaller scale of inquiry may provide clues about speciation in a phylogenetically problematic taxon, the diploxylon pine subsection Australes (genus Pinus, family Pinaceae). Genetic maps were constructed for two allopatric species of Australes, P. elliottii var. elliottii and P. caribaea var. hondurensis, using microsatellites and an F1 hybrid. A third map was generated directly from the meiotic products of an adult F1 hybrid, eliminating the need for an F2 generation. Numerous small-scale disruptions were detected in addition to synteny and collinearity, and these included (1) map shrinkage, (2) a paracentric inversion, (3) transmission ratio distortion, and (4) mild selection against a parental haplotype. Such cryptic signatures of genomic divergence between closely related interfertile species are useful in elucidating this problematic evolutionary history. [ABSTRACT FROM AUTHOR]

• Selective elimination of selfed embryos, or inbreeding depression, is shared among many members of the Pinaceae but it has not been fully characterized at the phenotypic level. • Here, two death pattern model hypotheses are tested using 10 621 Pinus taeda embryos sampled in two cohorts. Cones from a single pedigree based on selfed, outbred, parent–offspring and offspring–parent matings were destructively sampled weekly before, during and after fertilization. • Selfed embryo deaths adhered to two patterns over the course of development: death was linear with respect to days from fertilization; and a stage-specific death peak occurred during the early embryogeny stage. This death peak occurred from 23 to 36 d after fertilization in the 2004 cohort and from 27 to 34 d after fertilization in the 2006 cohort. Of those selfed embryos that died, 64–83% died at stages where a single dominant embryo was elongating inside the female gametophyte. • Additional genetic models are needed to account for the stage-specific death component of selfed P. taeda embryos. [ABSTRACT FROM AUTHOR]

Validation of a quantitative trait locus (QTL) for outcrossing perennial plants is rarely reported due to complexity of plausible genetic models and reliance on field designs already available. Here, a particular marker-QTL haplotype exerted a large, positive effect on height for Pinus taeda and its origin could be traced to a founder, GP3, in a three-generation QTL pedigree. To validate this QTL effect, we used an extended GP3-based pedigree. In the validation cross, each of the 46 offspring was clonally propagated from developing seeds using somatic embryogenesis technology. Subsequent analyses were conducted separately for seedlings and for other somatic emblings. For seedlings, the original QTL effect could not be fully validated. For somatic emblings, a strong negative QTL effect was detected in the validation cross; some evidence from another cross-supported the original positive QTL effect. From this part of the analysis, three distinct marker-QTL haplotypes at a single locus could be inferred. Validating QTL haplotypes in readily available field tests was feasible despite the genetic model complexity inherent to outcrossing long-lived perennials. [ABSTRACT FROM AUTHOR]

Outcrossing, wind-pollinated members of the Pinaceae have high self-pollination rates yet produce few selfed seedlings. How are selfs selectively eliminated? Barriers to selfing have long been considered to be (i) avoidance of self-pollen capture, (ii) competition via simple polyembryony, and (iii) lower viability of selfed embryos. Here, reviews — and some revisions — are offered in addition to future research needs. First, avoiding self-pollen capture is largely ineffectual. Second, simple polyembrony is also a weak or nonexistent barrier against selfed embryos. Third, selfed embryos die at all stages, but a stage-specific death peak occurs during early embryogeny in some taxa and this death peak, if prevalent across a wider range of taxa, deserves a closer look. The death peak does not preclude the prevailing genetic model for embryo viability loci, but could indicate that other genetic mechanisms are operative. Molecular dissection shows that zygotic lethals are distributed across different chromosomal segments. To date, these are mostly semi-lethal rather than lethal, and they range from partially dominant to overdominant. A literature survey suggests that only 5 of the 10 genera within the Pinaceae (Abies, Larix, Picea, Pinus, and Pseudotsuga) have been well characterized with respect to selfing. Extreme inbreeding depression during embryo development may not be a shared feature among conifers as a group. A critical research question is whether dual death patterns are present in other genera, and if they are, alternative genetic models to account for the death peak. Addressing these questions has broad relevance to conservation, domestication, and management of closed populations, not just conifers or gymnosperms. [ABSTRACT FROM AUTHOR]

The question of how to estimate a founder’s proportion of a single descendant’s genome has renewed relevance for outbred pedigrees, given the abundant DNA sequence data for model and nonmodel eukaryotes alike. Here we show that a donor-recurrent shortcut method can provide a robust estimation of founder proportions. In addition, we define the theoretical variance and estimate confidence intervals using a nonparameteric bootstrap method. Using actual marker data from a highly heterozygous outbred Pinus taeda pedigree, it was found that each founder’s genomic proportion varied widely for each descendant, ranging from 8.8% to 38.7%. In 1 case, skewed transmission of a founder’s genome could be statistically detected. Its founder proportions ranged from 1.54% to 48.46%, and its mean value was 17.59%, well below the expected value of 25%. Two-thirds of its 91 descendants had 1 or the other founder haplotype, despite 2 successive meioses. The donor-recurrent method was robust; variation for estimated founder’s proportions was also wide for simulated high-density datasets whether markers were dispersed or clustered. Estimating founder contributions using this computational shortcut has broad application for highly heterozygous outbred pedigrees characterized by large sibships, low population differentiation, and shallow physical mapping resources. The relevance of this computational shortcut for outbred populations used for conservation, domestication, and evolutionary biology research is discussed. [ABSTRACT FROM AUTHOR]

The opportunity to trace the evolution of a triplet repeat is rare, especially for seed-plant lineages with a well-defined fossil record. Microsatellite PtTX2133 sequences from 18 species in 2 conifer genera were used to calibrate the birth of a CAGn repeat, from its protomicrosatellite origins to its repeat expansion. Birth occurred in the hard-pine genome ~ 136 million years ago, or 14 million generations ago, then expanded as a polymorphic triplet repeat 136-100 million years before a major North American vicariance event. Calibration of the triplet-repeat birth and expansion is supported by the shared allelic lineages among Old and New World hard pines and the shared alleles solely among North American diploxylon or hard pines. Five CAGn repeat units appeared to be the expansion threshold for Old and New World diploxylon pines. Haploxylon pine species worldwide did not undergo birth and repeat expansion, remaining monomorphic, with a single imperfect 198-bp allele. A sister genus, Picea, had only a region of cryptic simplicity, preceding a proto-microsatellite region. The polymorphic triplet repeat in hard pines is older than some long-lived microsatellites reported for reptiles, yet younger than those reported for insects. Some cautionary points are raised about phylogenetic applications for this long-lived microsatellite.Key words: gymnosperms, microsatellite evolution, cladogenesis, phylogenetic analysis. [ABSTRACT FROM AUTHOR]

A DNA extraction protocol for submerged pine logs was developed with the following properties: (i) high molecular weight DNA, (ii) PCR amplification of chloroplast and nuclear sequences, and (iii) high sequence homology to voucher pine specimens. The DNA extraction protocol was modified from a cetyltrimehtylammonium bromide (CTAB) protocol by adding stringent electrophoretic purification, proteinase K, RNAse, polyvinyl pyrrolidone (PVP), and Gene Releaser®. Chloroplast rbcL (ribulose-1,5-bisphosphate carboxylase) could be amplified. Nuclear ribosomal sequences had >95% homology to Pinus taeda and Pinus palustris. Microsatellite polymorphism for PtTX2082 matched 2 of 14 known P. taeda alleles. Our results show DNA analysis for submerged conifer wood is feasible. [ABSTRACT FROM AUTHOR]

The retreating edge hypothesis for species responding to climate change predicts severe bottlenecks and eventual extinction. The disjunct Lost Pines population at the westernmost edge of the widespread Pinus taeda range is well suited for testing this prediction. The occurrence of one or more genetic bottlenecks in the Lost Pines population was tested using 34 nuclear microsatellite markers and a control sample from the larger, more continuous east Texas P. taeda forests. The Lost Pines population has undergone drastic contractions in effective population size between 3000 and 30 000 years bp. These results were supported by: (i) detection of transient heterozygosity excess, (ii) a mode-shift indicator of allele frequencies, and (iii) a ratio of allele number to allele size range. No bottleneck was detected for the east Texas control using any of the three methods. The distribution of allele frequencies was skewed for the Lost Pines population compared to the control, indicating a loss of rare alleles. However, allelic diversity was similar between the Lost Pines population and its east Texas control; the mean allele number per locus was 5.29 and 5.38, respectively. It is proposed that the Lost Pines population was the western refugium for P. taeda during Pleistocene glaciation and that East Texas P. taeda forests descended from the bottlenecked Lost Pines population. [ABSTRACT FROM AUTHOR]

Clustering has been reported for conifer genetic maps based on hypomethylated or low-copy molecular markers, resulting in uneven marker distribution. To test this, a framework genetic map was constructed from three types of microsatellites: low-copy, undermethylated, and genomic. These Pinus taeda L. microsatellites were mapped using a three-generation pedigree with 118 progeny. The microsatellites were highly informative; of the 32 markers in intercross configuration, 29 were segregating for three or four alleles in the progeny. The sex-averaged map placed 51 of the 95 markers in 15 linkage groups at LOD > 4.0. No clustering or uneven distribution across the genome was observed. The three types of P. taeda microsatellites were randomly dispersed within each linkage group. The 51 microsatellites covered a map distance of 795 cM, an average distance of 21.8 cM between markers, roughly half of the estimated total map length. The minimum and maximum distances between any two bins was 4.4 and 45.3 cM, respectively. These microsatellites provided anchor points for framework mapping for polymorphism in P. taeda and other closely related hard pines. [ABSTRACT FROM AUTHOR]

Investigates the genetic mechanism promoting outcrossing in conifers. Link of a semilethal factor to a polymorphic expressed sequence tag; Application of the genotypic frequencies for the linkage group; Presence of a balancing selection system.

Deducing the origin of early 20th century introductions of Pinus taeda into Zimbabwe is possible given microsatellite markers and clear population differentiation in ancestral U.S. populations. This study was designed to determine whether P. taeda introductions into Zimbabwe came from one U.S. region or whether the present-day population is an admixture of introductions from east and west of the Mississippi River Valley. Principal components analysis, Cavalli-Sforza and Edwards’ chord distances and presence of diagnostic alleles each indicate that the Zimbabwe population is an admixture. There were five novel alleles in the Zimbabwe population not represented in the indigenous U.S. populations, possibly because of de novo mutation, introgression with other introduced North American pines or sampling error. [ABSTRACT FROM AUTHOR]

Describes results of comparative mapping of recombination distances for 16 widely diverse populations representing maize and teosinte. Causes of variability in recombination distance; Relationship among distorted segregation ratios, recombination shrinkage and map distances wide crosses and interspecific hybrids; Construction of a composite genetic map.

Presents letters to the editor commenting on issues related to biotechnology. Highlights on the rapid advances being made in forest molecular domestication; Disagreement with the assertion that most of the global funding for forest biotech is being funneled to universities; Discussion on important issues surrounding the state of forest biotechnology.

A letter to the editor is presented in response to several articles on genetically modified plants, plant made pharmaceuticals and plant made industrial proteins that were published in the past issues.

A correction to the article "Marking live conifer pollen for long-distance dispersal experiments," that was published in the 2011 issue is presented.

This hypothesis is based on an observed correlation between DNA content and thermal regime for fish, zooplankton, salamanders, and some flowering plants. The Asian pine results provided no support for the latitudinal hypothesis; Asian tropical pine species did not have smaller genomes than their temperate or boreal relatives. DNA content of haploid megagametophyte tissue varied from 21.85 pg/C for hard pine Pinus densiflora Sieb. & Zucc. to 29.59 pg/C for soft pine Pinus bungeana Zucc. Pinus merkusii Jung. & De Vriese (29.63 pg/C) was the exceptional hard pine, with a genome size larger than many soft pines. The mean DNA content of Asian soft pines exceeded Asian hard pines (Δ 3.22 pg/C), a parallel to the previously reported trends for New World pines. No continental effect was detected. Based on 46 pines species sampled in centers of species diversity in Asian and the New World, soft pines had mean DNA content which exceeded hard pines by 4.97 pg/C.Key words: gymnosperms, conifers, laser flow cytometry, megagametophytes, C values, phylogeny.Afin de vérifier l'hypothèse de la latitude ou du régime thermique, les auteurs ont utilisé les valeurs des teneurs en ADN nucléique chez 13 espèces de pin asiatiques/eurasiatiques et 5 espèces additionnelles du Nouveau Monde. Cette hypothèse est basée sur une corrélation observée entre la teneur en ADN et le régime thermique chez les poissons, le zooplancton, et certaines plantes angiospermes. Les résultats provenant de pins asiatiques ne donnent aucun support à l'hypothèse latitudinale; les espèces de pin tropicales ne possèdent pas des génomes plus petits que les espèces apparentées des régions tempérées ou boréales. Les teneurs en ADN du tissu du mégagamétophyte haploïde varient de 21,85 pg/C chez le pin dur Pinus densiflora Sieb. & Zucc. à 29,59 pg/C chez le pin tendre Pinus bungeana Zucc. Exceptionnellement pour les pins durs, le Pinus merkusii Jung. & De Vriese (29,63 pg/C) possède un génome plus grand que plusieurs pins tendres. La teneur moyenne en ADN des pins tendres asiatiques dépasse celle des pins durs asiatiques (Δ 3,22 pg/C), tendance qui a déjà été rapportée chez les pins du Nouveau Monde. Aucun effet continental n'a pu être décelé. Sur la base de 46 espèces de pin échantillonnées dans des centres de diversité spécifique en Asie et au Nouveau Monde, les pins tendres ont une teneur moyenne en ADN supérieure à celle des pins durs de 4,97 pg/C.Mots clés : gymnospermes, conifères, cytométrie par flux au laser, mégagamétophyte, valeurs C, phylogénie.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]