Sampling of Recent Articles

Sept 2004 - Pollutant causes delayed flowering in plants

Prof. Zhen-Ming Pei and coworkers report in Science (Vol 305, Issue 5692, 1968-1971 , 24 September 2004) that the naturally-occurring plant growth hormone nitric oxide—which controls flowering—can be detrimental when it occurs in high, external concentrations as a pollutant. Because massive amounts of nitric oxide are annually emitted as air pollutants from burning fossil fuels, this has serious implications in terms of its potential to delay flowering in plants. See article in Duke News Release

April 2004 - Faced with Flowers, Ferns Flourished

The rise of flowering plants was an important evolutionary force that apparently nearly drove some lineages to extinction (e.g., Ginkgo), yet spurred diversification in many others (e.g., beetles and bees). For this reason, angiosperms may be credited for most of terrestrial biodiversity as we know it. In an article in Nature [428: 553-557], Prof. Kathleen Pryer and her colleagues demonstrate that an increase in polypod fern diversity followed the rise in angiosperm diversity, challenging the general belief that ferns are mostly evolutionary relicts from the Late Paleozoic/Early Mesozoic, and suggesting that the enhanced speciation of polypod ferns was enabled by the rise of flowering plants. This result is especially interesting because ferns are only loosely associated with angiosperms as ecological opportunists - merely inhabiting niches provided in angiosperm-dominated ecosystems. Other lineages for which angiosperms-triggered radiations have been proposed, such as the plant-feeding insect groups, have more specialized or intimate coevolutionary associations with angiosperms. The integration of fossils with molecular phylogenetic data is an extremely powerful tool for identifying historical trends and events across the Tree of Life. This approach, which was applied in this study, permits the most comprehensive understanding of the past by combining information from the incomplete fossil record with information provided by the genetic blueprints of living organisms.
http://www.biomedcentral.com/news/20040401/02
http://www.nsf.gov/od/lpa/newsroom/pr.cfm?ni=65
http://sciencenow.sciencemag.org/cgi/content/full/2004/331/3?
http://www.dukenews.duke.edu/news/pryer_0304.html

December 2003 - Fungal endophytes limit pathogen damage in a tropical tree

Dr. Elizabeth Arnold, a postdoctoral fellow in the Department of Biology, and collagues at the Smithsonian Tropical Research Institute in Panama report a new, intricate relationship between cacao trees and the fungi that inhabit them (Proceedings of the National Academy of Sciences, December 23, 2003 | vol. 100 | no. 26 | 15649-15654). Abstract: Every plant species examined to date harbors endophytic fungi within its asymptomatic aerial tissues, such that endophytes represent a ubiquitous, yet cryptic, component of terrestrial plant communities. Fungal endophytes associated with leaves of woody angiosperms are especially diverse; yet, fundamental aspects of their interactions with hosts are unknown. In contrast to the relatively species-poor endophytes that are vertically transmitted and act as defensive mutualists of some temperate grasses, the diverse, horizontally transmitted endophytes of woody angiosperms are thought to contribute little to host defense. Here, we document high diversity, spatial structure, and host affinity among foliar endophytes associated with a tropical tree (Theobroma cacao, Malvaceae) across lowland Panama. We then show that inoculation of endophyte-free leaves with endophytes isolated frequently from naturally infected, asymptomatic hosts significantly decreases both leaf necrosis and leaf mortality when T. cacao seedlings are challenged with a major pathogen (Phytophthorasp.). In contrast to reports of fungal inoculation inducing systemic defense, we found that protection was primarily localized to endophyte-infected tissues. Further, endophyte-mediated protection was greater in mature leaves, which bear less intrinsic defense against fungal pathogens than do young leaves. In vitro studies suggest that host affinity is mediated by leaf chemistry, and that protection may be mediated by direct interactions of endophytes with foliar pathogens. Together, these data demonstrate the capacity of diverse, horizontally transmitted endophytes of woody angiosperms to play an important but previously unappreciated role in host defense. Article in Duke Dialogue

December 2003 - Gene Expression Map of the Arabidopsis Root

Prof. Philip Benfey and colleagues present a global map of gene expression within an organ that can identify genes with coordinated expression in localized domains, thereby relating gene activity to cell fate and tissue specialization. In this Science paper (Dec 12 2003: 1956-1960) they present localization of expression of more than 22,000 genes in the Arabidopsis root. Gene expression was mapped to 15 different zones of the root that correspond to cell types and tissues at progressive developmental stages. Patterns of gene expression traverse traditional anatomical boundaries and show cassettes of hormonal response. Chromosomal clustering defined some coregulated genes. This expression map correlates groups of genes to specific cell fates and should serve to guide reverse genetics. Article in Duke Dialogue

September 2003 - CAS may be a primary transducer of Ca 2+o in plants

Prof. Zhen-Ming Pei, graduate students Shengcheng Han and Lisa Anderson, and postdoc Ruhang Tang used a functional screening assay in mammalian cells to isolate an Arabidopsis complementary DNA clone encoding a Ca 2+ - sensing receptor, CAS. In this article (Nature, Vol 425 , 196 - 200), they conclude that CAS may be a primary transducer of Ca 2+ o in plants.

September 2003 - Baboon fathers rush to protect their kids in fights

Postdoc Jason Buchan and Prof. Susan Alberts, using DNA, report in Nature (Vol. 425 , 179 - 181) that adult males of many cercopithecine primate species provide care for infants and juveniles, including grooming, carrying, support in agonistic interactions, and protection against infanticide. This care might be a form of parental effort if males are able to direct care selectively to their own offspring. Alternatively, male care might represent a form of mating effort that is offered to the mother as an incentive to mate with the caring male. In the absence of comprehensive genetic analyses of paternity and male behavior, it has been impossible to differentiate between these hypotheses. Alberts and Buchan show that wild male savannah baboons differentiate their offspring from unrelated juveniles and selectively care for their own offspring. These data demonstrate that male care represents true paternal care in this population. Media links

June 2003 - Ancient Pollen Yields Insight Into Forest Biodiversity

Prof. Jim Clark and graduate student Jason McLachlan analyzed data on tree pollen extracted from ancient lake sediments in an effort to sharpen the understanding of how forests can maintain a diversity of species. Their findings, published in Nature (Vol 423, 635 - 638), indicate that stabilizing processes have been more important than previously thought, and that the human-caused loss of species could upset that stability in ways that remain poorly understood.

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June 2003 - Identification of asteroid genera with species capable of larval cloning

In this article in The Biological Bulletin (Vol. 204(3):246-55) Prof. Greg Wray and colleagues compare DNA sequences of mitochondrial tRNA genes (Ala, Leu, Asn, Pro, and Gln) from larvae in the process of cloning collected in the field with sequences from adults of known species in order to identify asteroid taxa capable of cloning. This study is the first to identify field-collected cloning asteroid larvae, and provides evidence that larval cloning is phylogenetically widespread within the Asteroidea. Additionally, they note that cloning occurs regularly and in multiple ways within species that are capable of cloning, emphasizing the need for further investigation of the role of larval cloning in the ecology and evolution of asteroids.

June 2003 - Missing link between accumulation of SA and activation of NPR1 in the SAR signaling pathway

Prof. Xinnian Dong and graduate students Zhonglin Mou and Weihua Fan report in Cell (Vol 113, 935-944, 27 June 2003). NPR1 is an essential regulator of plant systemic acquired resistance (SAR), which confers immunity to a broad-spectrum of pathogens. SAR induction results in accumulation of the signal molecule salicylic acid (SA), which induces defense gene expression via activation of NPR1. We found that in an uninduced state, NPR1 is present as an oligomer formed through intermolecular disulfide bonds. Upon SAR induction, a biphasic change in cellular reduction potential occurs, resulting in reduction of NPR1 to a monomeric form. Monomeric NPR1 accumulates in the nucleus and activates gene expression. Inhibition of NPR1 reduction prevents defense gene expression, whereas mutation of Cys82 or Cys216 in NPR1 leads to constitutive monomerization, nuclear localization of the mutant proteins, and defense gene expression. These data provide a missing link between accumulation of SA and activation of NPR1 in the SAR signaling pathway.

May 2003 - Butterflies Are Flashers To Attract Mates

Graduate student Alison Sweeney and Prof. Sonke Johnsen have discovered that some iridescent butterflies use the polarization of light refracted from their intricate prismatic scales as a mating signal. This finding, reported in Nature (Vol. 423, 31 - 32), is the first time that light polarization has been identified as a mating signal for any terrestrial animal species.

March 2003 - Global Change Affects Squirrels

Profs. John Mercer and Louise Roth present evidence that shifting continents and global climate changes helped create the diversity of the 273 species in the squirrel family. By modifying habitats and creating bridges and barriers between landmasses, climate change and tectonic events are believed to have important consequences for diversification of terrestrial organisms. Such consequences should be most evident in phylogenetic histories of groups that are ancient, widespread, and diverse. The squirrel family (Sciuridae) is one of very few mammalian families endemic to Eurasia, Africa, and North and South America and is ideal for examining these issues. Employing phylogenetic and molecular-clock analyses, Mercer and Roth inferred that arrival and diversication of squirrels in Africa, on Sunda Shelf islands, across Beringea, and across the Panamanian isthmus coincide in timing and location with multiple well-documented sea-level, tectonic, and paleontological events. These precise correspondences point to an important role for global change in the diversification of a major group of mammals. For full report, see Science (Vol. 299, 1568-1572, "The Effects of Cenozoic Global Change on Squirrel Phylogeny."

January 2003 - Cell adhesion: Keeping it together

Prof. Rick Fehon reports in Nature (Vol. 421, 83ñ87, 2003) that moesin promotes cortical actin assembly and apical-basal polarity - not by virtue of it linking the plasma membrane and the actin cytoskeleton, but by its ability to antagonize the activity of the small GTPase Rho.