Editors' Choice

Science  07 Jun 2019:
Vol. 364, Issue 6444, pp. 967
  1. Pollination

    Pollen trade wars

    1. Caroline Ash

    The toxic pollen of teasel flowers does not deter bumblebees from gathering nectar.


    For bees, pollen is an important source of protein and fats and is thus a strong motivation for visiting flowers. For plants, pollen is essential, and they do not want it lost to reproduction by greedy or inefficient pollinators. To circumvent this conflict, some plants have developed toxic pollen to deter consumption by pollinators. Wang et al. discovered that the flowers of teasel (Dipsacus spp.) contain a distasteful saponin in their pollen. After visiting a flower, bumblebees typically groom their hairy bodies to harvest adhering pollen grains—but not after visiting teasel flowers. The reason why some bumblebees still avidly visit this plant is because the nectar reward is generous and not tainted by the bitter saponin. Meanwhile, as bumblebees circulate among the plants to gather nectar, the ungroomed teasel pollen grains sticking to their hair ensures efficient pollination.

    Curr. Biol. 29, 1401 (2019).

  2. HIV Vaccines

    It's all about delivery

    1. Priscilla N. Kelly

    Human immunodeficiency virus (HIV) has proved to be a notoriously difficult virus to vaccinate against. Most immunization studies focus on altering components of the vaccine to improve immune responses. Cirelli et al. instead asked what would happen if they changed the delivery method rather than vaccine composition. Slow vaccine delivery—in small amounts over several days—was found to enhance HIV neutralizing antibodies when compared with standard methods where the vaccine is injected all at once. Rhesus monkeys developed more potent T follicular helper cell responses, and germinal center B cells showed improved engagement to viral envelope antigens. Slow-release vaccination strategies may open new avenues to tackle currently intractable pathogens.

    Cell 177, 1153 (2019).

  3. Diet Evolution

    A carnivore in herbivore's clothing

    1. Sacha Vignieri

    For pandas, bamboo can be as nutritious as meat.


    It is widely known that pandas eat bamboo. The conundrum is that these members of the order Carnivora show herbivore traits in their jaw and teeth but carnivore traits in their gut and digestive enzymes. Nie et al. used niche models, tracking, and nutrient analysis to better characterize the details of the bamboo diet and its absorption, and they find that pandas' motley traits may not be incongruous after all. Although their diet is vegetarian, pandas prefer to eat bamboo at stages in the plant's growth when it has the highest protein content. The macronutrient energy ratios that pandas obtain from bamboo by being picky are similar to those obtained by hypercarnivores that secure more than 70% of their diet from animal sources. Herbivory works well in bamboo forests with abundant resources.

    Curr. Biol. 29, 1677 (2019).

  4. Stem Cells

    Hormones control adrenal stem cells

    1. Beverly A. Purnell

    The adrenal cortex produces steroid hormones involved in stress responses. This part of the adrenal gland is sexually dimorphic. The cortex is larger in females, in whom it displays variable susceptibility to disease, including cancers. Grabek et al. examined the cellular basis of this sex bias. Females have much higher cell turnover, which means that the steroidogenic tissue is effectively replaced every 3 months. By contrast, male hormones suppress proliferation and stem cell recruitment. Females not only show increased proliferation but also recruitment of mesenchymal cells from the capsule. These responses depend on the hormonal environment rather than sex chromosomes. So, if androgens are removed, the stem cell compartment becomes activated, whereas adding androgens inhibits capsular stem cell activity. These sex-specific activities may be of relevance to disease susceptibility.

    Cell Stem Cell 10.1016/j.stem.2019.04.012 (2019).

  5. Targeted Degradation

    Pathogen-sourced enzyme redirected

    1. Michael A. Funk

    Confocal microscopy image of fluorescent protein targets expressed in HEK293T cells

    PHOTO: M. B. LUDWICKI ET AL., ACS CENT. SCI. 5, 852 (2019)

    Cells of all types have the means to degrade specific proteins. These pathways can be hijacked by some bacteria to diminish host immune responses. The enzymes involved can in turn be used in the lab to modulate the proteome of eukaryotic cells. Ludwicki et al. attached a bacterial ubiquitin ligase to a protein that binds green fluorescent protein (GFP), thus redirecting it to add ubiquitin to GFP and GFP fusion proteins, which causes their degradation. The authors used polyamines and mRNA-binding proteins to stabilize and deliver mRNAs encoding an engineered ubiquitin ligase to cells. The mRNA nanoplexes enabled proteome editing both in vitro and in mice.

    ACS Cent. Sci. 5, 852 (2019).

  6. Diversity

    No more excuses for all-male panels

    1. Melissa McCartney

    Biases, both implicit and explicit, impede the participation of women in STEM. Recent studies show that men are invited to speak on scientific panels at twice the rate that women are. McCullagh et al. describe the success of the “Request a Woman Scientist” database, part of the 500 Women Scientists organization, which works to build an inclusive scientific community. The database is composed of more than 7500 women from multiple disciplines and countries and provides anyone looking for scientific expertise with an extensive and multidisciplinary network of vetted women in science. To date, 11% of women scientists included in the database have been contacted to participate in media engagements, peer review, panel participation, educational outreach, and professional and research connections, further promoting the profile and participation of women in STEM.

    PLOS Biol. 17, e3000212 (2019).

  7. Organic Chemistry

    Outside help for a carbene catalyst

    1. Jake Yeston

    Metal catalysis is sometimes enhanced by secondary interactions with components that are not directly coordinated to the metal. Dhayalan et al. have explored this concept with metal-free organocatalysis. Specifically, they found that dynamically tethering a boronic acid to the periphery of an N-heterocyclic carbene catalyst raised enantioselectivity of a benzoin condensation. Furthermore, by applying a decision tree analysis correlating selectivity with parameters such as dipole moment and torsion angle, they efficiently optimized the boronic acid structure for gram-scale reactions.

    Nat. Chem. 11, 543 (2019).

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