Dispatch R649 by the counteracting phosphatases kinase–phosphatase pair with interactions to reshape MAP kinase pathway signaling dynamics. Science 319, (Figure 1B). While phosphatase overlapping docking specificity, 1539–1543. docking is much less studied, recent mutation only needs to generate a 8. Peter, M., and Herskowitz, I. (1994). Direct work suggests it may be prevalent and, single docking site, rather than two. inhibition of the yeast cyclin-dependent kinase Cdc28-Cln by Far1. Science 265, intriguingly, overlap with kinase Thus, overlapping docking specificity 1228–1231. docking. The protein phosphatase 1 may explain why the same network 9. Gartner, A., Jovanovic, A., Jeoung, D.I., Bourlat, S., Cross, F.R., and Ammerer, G. docking site on the retinoblastoma functions are regulated by the same (1998). Pheromone-dependent G1 cell cycle protein overlaps with the known kinases and phosphatases across arrest requires Far1 phosphorylation, but docking site for S phase cyclin–Cdk diverse eukaryotes. may not involve inhibition of Cdc28-Cln2 kinase, in vivo. Mol. Cell Biol. 18, 3681–3691. [12]. A new study examining 10. Doncic, A., Falleur-Fettig, M., and Ca2+/calmodulin-regulated References Skotheim, J.M. (2011). Distinct interactions 1. Coudreuse, D., and Nurse, P. (2010). Driving the select and maintain a specific cell fate. Mol. phosphatase (CN) showed that its cell cycle with a minimal CDK control network. Cell. 43, 528–539. docking specificity overlaps with that Nature 468, 1074–1079. 11. Doncic, A., and Skotheim, J.M. (2013). of the pheromone-activated MAPK 2. Murray, A.W., and Kirschner, M.W. (1989). Feedforward regulation ensures stability and Cyclin synthesis drives the early embryonic cell rapid reversibility of a cellular state. Mol. Cell. Fus3 [13]. This presents two examples cycle. Nature 339, 275–280. 50, 856–868. where competing kinase–phosphatase 3. Bloom, J., and Cross, F.R. (2007). Multiple 12. Hirschi, A., Cecchini, M., Steinhardt, R.C., pairs recognize the same docking site, levels of cyclin specificity in cell-cycle control. Schamber, M.R., Dick, F.A., and Rubin, S.M. Nat. Rev. Mol. Cell Biol. 8, 149–160. (2010). An overlapping kinase and phosphatase which might enhance switch-like 4. Wilmes, G.M., Archambault, V., Austin, R.J., docking site regulates activity of the transitions of the phospho-state of Jacobson, M.D., Bell, S.P., and Cross, F.R. retinoblastoma protein. Nat. Struct. Mol. Biol. (2004). Interaction of the S-phase cyclin Clb5 17, 1051–1057. individual targets. In addition, we with an ‘‘RXL’’ docking sequence in the initiator 13. Goldman, A., Roy, J., Bodenmiller, B., are immediately provided with a protein Orc6 provides an origin-localized Wanka, S., Landry, C.R., Aebersold, R., and mechanism through which competition replication control switch. Genes Dev. 18, Cyert, M.S. (2014). The calcineurin signaling 981–991. networks evolves via conserved between kinase–phosphatase pairs 5. Ko˜ ivoma¨ gi, M., Valk, E., Venta, R., Iofik, A., kinase-phosphatase modules that transcend can be conserved. Goldman et al. [13] Lepiku, M., Morgan, D.O., and Loog, M. (2011). substrate identity. Mol. Cell. http://dx.doi.org/ Dynamics of Cdk1 substrate specificity 10.1016/j.molcel.2014.05.012. compared kinase and CN targets during the cell cycle. Mol. Cell 42, in mammals and yeast to find that 610–623. while nearly no specific substrates 6. Pope, P.A., Bhaduri, S., and Pryciak, P.M. Department of Biology, Stanford University, (2014). Regulation of cyclin-substrate Stanford, CA 94305, USA. were conserved, the same kinases docking by a G1 arrest signaling pathway and *E-mail: [email protected] opposed CN on both sets of the Cdk inhibiitor Far1. Curr. Biol. 24, 1390–1396. substrates. To evolve co-regulation of a 7. Bashor, C.J., Helman, N.C., Yan, S., and substrate by a specific Lim, W.A. (2008). Using engineered scaffold http://dx.doi.org/10.1016/j.cub.2014.05.060

Coevolution: Puff Pollination in designed bellows pollination system, where the bite of the bird’s beak Tropical Flowers releases a puff of pollen that is either carried by wind or by pollen-dusted birds depositing pollen on the A new study shows that birds plucking anthers of the Melastome, Axinaea, exerted stigmas of the next flowers demonstrate a novel bird pollination mechanism. Each stamen of Axinaea they visit. offers a nutrient-rich, berry-like food body that, when bitten, releases a puff The authors document this system of pollen allowing transfer to stigmas by wind or the pollen-dusted bird. with detailed analyses of stamen morphology. Using X-ray computed Joan Edwards the novel bird pollination system tomography, SEM and thin sectioning, reported for the neotropical they present stunning 3-D images and Flowers and their pollinators offer a Melastomataceae, Axinaea, by longitudinal cross-sections illustrating palette of diversity to study Dellinger et al. in this issue of Current the anatomy of the anthers. Each of the coevolution and provide data for Biology [5], adding a new twist to our ten anthers in the flower is modified to unraveling Darwin’s ‘‘abominable thinking about how birds can effect be a miniature turkey baster where the mystery’’, the sudden appearance pollination and how pollination ‘bulb’ is the nutritious food body made and extraordinarily rapid diversification syndromes can develop. up of large air-filled cells that connects of the angiosperms [1]. Yet with over For Axinaea flowers, the bird to the ‘shaft’ made of pollen-filled 350,000 species of flowering plants [2], pollinators are not hummingbirds, but anther sacs with a pore-sized opening we are still discovering new methods of a diverse group of tropical fruit-eating at the end. The whole operation points pollination. For New World bird tanagers. Flowers vary in color from downward to the center of the flower, pollination syndromes we typically white to pale lavender to red and so that when the bird plucks the food think of tubular red flowers, copious offer no nectar reward, but instead body, it forces air from the food body amounts of dilute nectar, and the provide berry-like food bodies rich in into the anther sacs and releases a whirr of hummingbirds hovering as they citric acid, fructose and glucose pollen puff that is directed towards the collect nectar through specially (Figure 1A). In return for the food top of the flower and the bird’s head engineered tongues [3,4]. Not so for bodies, the birds power a uniquely and beak (Figure 1B). Current Biology Vol 24 No 14 R650

Figure 1. Co-evolution of a flower and its pollinator. (A) Flower of Axinaea costaricensis, showing five mature anthers with large white food body appendages. The tubular magenta anther sacs extend from the base of each food body. (B) A schematic showing how birds pluck and squeeze the food body causing a puff of pollen to exit the anthers from the apical pore. The pollen can then be transferred to stigmas by wind or by birds when visiting other flowers. (C) Chlorospingus pileatus (sooty-capped bush tanager) holding a food body and anther sac from A. costaricensis. The food bodies primarily provide sugars and vitamin C. Credits: (A) Photo cropped from image by Juan Franscisco Morales (http://melas-centroamerica.com/ axinaea-costaricensis/); (B) drawing by Ann Kremers; (C) photo by Florian Etl.

The biomechanics of this puff mass spectrometry) show the food feed on the berry-like anthers. All pollination system depend completely bodies are high in the hexoses, are nine-primaried oscines, a on the power of the beak. Spores, sucrose and glucose, and also high large diverse group that radiated including pollen, are perfect for in vitamin C. recently in the neotropics [14,15]. dispersal in puffs, but the dilemma The stamen structure in the However, within this large clade the plants and fungi face is how to power Melastomataceae may have birds observed on Axinaea the puffs. The small size of spores predisposed them to develop into surprisingly are not all closely means they have a low terminal velocity the miniature bellows we see in related. Three species visiting and thus require substantial force to Axinaea. Most members of the A. confusa are closely related montane move any distance. Puffball fungi Melastomataceae are buzz pollinated tanagers, but the orange-bellied harness the energy of falling raindrops [11] where the pollen is released Euphonia (Euphonia xanthogaster) [6]. Sphagnum moss builds pressure in from anthers in response to the observed on A. confusa, the bush capsules that eventually blow their tops vibrational buzz of bees. Typical tanager (Chlorospingus pileatus) propelling spores in vortex rings [7]. buzz-pollinated flowers have poricidal (Figure 1C) observed on In angiosperms, both bunchberry anthers and dry, smooth-walled pollen A. costaricensis, and the masked dogwood [8] and white mulberry [9] for easy release when buzzed [12]. flower piercer (Diglossa cyanea) use stored mechanical energy in their These general buzz-pollination observed on A. sclerophylla are all in catapult-like stamens to power pollen features are also effective for the puffs separate distantly related puffs. Here, the flowers co-opt the produced by the bellows. But in groups [14,15]. force of the bird’s beak to power addition, Melastome anthers often The ecological flexibility of the the puff. have stamen appendages, which are an system where different birds can The fruit-like traits of the food bodies extension of the connective tissue. In effect pollination may contribute to may have predisposed fruit-eating other species these may serve to the persistence of some Axinaea birds to be attracted to the stamens enhance floral displays or to facilitate species. Axinaea is a neotropical of Axinaea flowers, thus initiating the buzz pollination, but in Axinaea they genus, with 39 species of small trees bellows pollination system. The food have been modified to be sugary food and shrubs that are primarily restricted bodies themselves are modified anther bodies with air-filled cells. to the Andes between 1200 and 3800 m connective tissue. They are clearly The phylogenetic diversity of the with A. costaricensis occurring further berry-like with high food value and bird visitors and the differences in north in Costa Rica and Panama bright colors that markedly contrast visitors among sites suggests that [16,17]. Within this genus some with bowl shaped flower corollas the association between Axinaea species, including A. sclerophylla in (Figure 1). Although each food body is and birds may have evolved this study, are considered rare due to tiny, on a per weight basis, the measure independently in different locations. small population sizes or distributions of caloric gain from the food bodies In situ observations including over limited to one locale in unprotected averages 3.61 kcal/g, just slightly less 200 hours of video show that for the areas [17,18]. The observation of than the calories in sugar (3.81 kcal/g) three species of Axinaea observed, different birds at different sites and slightly more than the calories in birds are the only pollinators. All six suggests a generalist system where raisins (3 kcal/g) [10]. This is not bird species observed visiting the flowers in each locality can draw surprising since the metabolomic Axinaea are known fruit and insect on the local birds for pollination analyses (gas chromatography and eaters [13], predisposing them to services. Dispatch R651

Biologists have long been fascinated 3. Proctor, M., Yeo, P., and Lack, A. (1996). The 13. Isler, M.L., and Isler, P.R. (1987). The Tanagers: Natural History of Pollination (Portland, Oregon: Natural History, Distribution and Identification by pollination syndromes, easily Timber Press). (Washington, DC: Smithsonian Institution characterizing flowers by floral 4. Rico-Guevara, A., and Rubega, M.A. (2011). Press). features that are adaptive for attracting The hummingbird tongue is a fluid trap, not a 14. Barker, F.K., Burns, K.J., Klicka, J., capillary tube. Proc. Natl. Acad. Sci. USA 108, Lanyon, S.M., and Lovette, I.J. (2013). Going to specific pollinators, thus allowing 9356–9360. extremes: contrasting rates of diversification in targeted gene flow among the 350,000 5. Dellinger, A.S., Penneys, D.S., Staedler, Y.M., a recent radiation of new world passerine birds. Fragner, L., Weckwerth, W., and Syst. Biol. 62, 298–320. plus angiosperms, 94% of which use Schonenberger, J. (2014). A specialized bird 15. Burns, K.J., Shultz, A.J., Title, P.O., biotic vectors for pollination [19]. pollination system involving a bellows Mason, N.A., Barker, F.K., Klicka, J., Indeed, the directed gene flow itself is mechanism for pollen transfer and stamina Lanyon, S.M., and Lovette, I.J. (2014). food body rewards. Curr. Biol. 24, 1615– Phylogenetics and diversification of tanagers an explanation for Darwin’s 1619. (Passeriformes: Thraupidae), the largest abominable mystery. But increasingly 6. Gregory, P.H. (1949). The operation of the radiation of Neotropical songbirds. Mol. puff-ball mechanism of Lycoperdon perlatum Phylogent. Evol. 75, 41–77. as we explore plant–pollinator by raindrops shown by ultra-high-speed 16. Cotton, E., Bussmann, R.W., and Lozano, P. systems with a more careful eye, the Schlieren cinematography. T. Brit. Mycol. Soc. (2004). Three new Ecuadorian species of simplicity of pollination syndromes 32, 11–15. Axinaea (Melastomataceae). Nord. J. Bot. 23, 7. Whitaker, D., and Edwards, J. (2010). 49–55. seems much less applicable. The Sphagnum moss disperses spores with vortex 17. Bussmann, R.W., Gruhn, J., and Glenn, A. Axinaea–bird system is a case in rings. Science 329, 406. (2010). Axinaea fernando-cabiesii and 8. Edwards, J., Whitaker, D., Klionsky, S., and A. reginae spp. nov. (Melastomataceae) from point as it deviates from the Laskowski, M. (2005). Botany: A record- upper Amazonia of Peru, with notes on the hummingbird pollination system, breaking pollen catapult. Nature 435, 164. conservation status of A. flava. Nord. J. Bot. 28, provides insight into how syndromes or 9. Taylor, P.E., Card, G., House, J., 518–522. Dickinson, M.H., and Flagan, R.C. (2006). 18. Cotton, E. and Pitman, N. 2004. Axinaea clusters of traits can evolve in High-speed pollen release in the white mulberry sclerophylla. In: IUCN (2013). IUCN Red List of pollination systems, and presents a tree, Morus alba L. Sex. Plant Reprod. 19, Threatened Species. Version 2013.2. www. 19–24. iucnredlist.org. Downloaded on 09 June case for ecological flexibility, which 10. Vinson, J.A., Zubik, L., Bose, P., Sammam, N., 2014. may contribute to the persistence of and Proch, J. (2005). Dried fruits: excellent 19. Ollerton, J.R., Winfree, R., and Tarrant, S. angiosperm species in complex in vitro and in vivo antioxidants. J. Am. Coll. (2011). How many flowering plants are Nutr. 24, 44–50. pollinated by animals? Oikos 120, communities. 11. Renner, S.S. (2004). Melastomataceae (Black 321–326. Mouth Family). In Flowering Plants of the Neotropics, N. Smith, S.A. Mori, A. Henderson, References D.Wm. Stevenson, and S.V. Heald, eds. Biology Department, Thompson Biology Lab, 1. Friedman, W.E. (2009). The meaning of (Princeton, NJ: Princeton University Press), Williams College, Williamstown, MA, USA. Darwin’s ‘‘abominable mystery’’. Am. J. Bot. pp. 240–243. E-mail: [email protected] 96, 5–21. 12. DeLuca, P.A., and Vallejo-Marin, M. (2013). 2. The Plant List (2013). Version 1.1. Published on What’s the ‘buzz’ about? The ecology and the Internet: http://www.theplantlist.org/ evolutionary significance of buzz-pollination. (accessed 30 May 2014). Curr. Opin. Plant Biol. 16, 429–435. http://dx.doi.org/10.1016/j.cub.2014.06.020

Centrosome Duplication: Suspending [6–9]. Together, these findings have revealed that centrosome a License by Phosphorylating a duplication is ‘licensed’ once per cell cycle. The concept of licensing was Template originally introduced through studies of DNA replication where the key licensing step is the loading of The phosphorylation status of Sfi1, a structural component of the yeast pre-replicative complexes prior to the centrosome, governs the centrosome duplication cycle, raising the possibility unwinding of double-strand DNA [10]. that licensing of centrosome duplication occurs by modulating Sfi1, which In the context of centrosomes, potentially acts as a template for a new centrosome. licensing involves the process of centriole ‘disengagement’, an event Kayoko Tanaka associated with malignant tumor cells where two orthogonally placed [3,4]. In a recent issue of Current centrioles becomes detached in late The centrosome is a fascinating Biology, Schiebel and coworkers mitosis [11]. A protease called single copy organelle present in reveal that cell-cycle regulatory separase, which becomes active in almost all higher eukaryotic cells. It kinases and a phosphatase tightly anaphase, is required for acts as the major microtubule regulate the centrosome duplication disengagement, and the loosened organizing centre (MTOC) as well as a cycle by targeting Sfi1, a structural centrioles are expected to expose the platform for various cell proliferation component of the yeast site of duplication for the next round and differentiation regulators [1,2]. centrosome [5]. of duplication [9]. Apart from the centrosome’s divergent The direct link between the cell cycle More direct involvement of fundamental roles, its mode of and the centrosome cycle has spurred structural component(s) of the duplication has intrigued us for studies examining whether key cell centrosome in the licensing process decades — it occurs strictly once per cycle regulators, including was proposed by Kilmartin and cell cycle in a semi-conservative cyclin-dependent kinases (CDKs), colleagues based on elegant studies manner. Failure to keep precise control Polo-like kinases and separase, also of spindle pole bodies (SPBs), the over centrosome number is often play roles in the centrosome cycle centrosome equivalent in budding