phot1 inhibition of ABCB19 primes lateral auxin fluxes in the shoot apex required for phototropism

It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperm

Trophic stability and change across a sea ice cover gradient on the western Antarctic Peninsula

The western Antarctic Peninsula (AP) is experiencing significant changes to sea ice cover, altering the macroalgal cover and potentially affecting the foundation of benthic food webs. We used fatty acid signatures as dietary and physiological trophic biomarkers to test the hypothesis that a gradient of 36-88% mean annual ice cover would affect the trophic ecology of fleshy macroalgae and diverse benthic invertebrate consumers along the western AP. We used SCUBA to collect organisms from benthic rocky nearshore habitats, 5-35 m depth, at 15 study sites during April-May of 2019. There were no consistent ecosystem-scale differences in the nutritionally important polyunsaturated fatty acids or other univariate fatty acid summary categories in either the seaweeds or invertebrates across the ice gradient, but we did find site-level differences in the multivariate fatty acid signatures of all seaweeds and invertebrates. Ice cover was a significant driver of the fatty acid signatures of 5 invertebrates, including 3 sessile (an anemone, a sponge, and a tunicate) and 2 mobile consumers (a sea star and a sea urchin). The multivariate fatty acid signatures of 2 other sea stars and a limpet were not affected by the ice gradient. These results indicate that the trophic ecology and resource assimilation of sessile consumers that are more connected to the macroalgal-derived food web will be more sensitive than mobile consumers to impending changes to annual ice and macroalgal cover along the western AP.National Science Foundation.Abstract -- Key words -- 1. Introduction -- 2. Materials and methods -- 3. Results -- 4. Discussion -- 5. Conclusions -- Acknowledgements -- Literature CitedYe

Climate drives the geography of marine consumption by changing predator communities

Este artículo contiene 7 páginas, 3 figuras, 1 tabla.The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth’s ecosystems.We acknowledge funding from the Smithsonian Institution and the Tula Foundation.Peer reviewe

Structure of the OsSERK2 leucine-rich repeat extracellular domain

Somatic embryogenesis receptor kinases (SERKs) are leucine-rich repeat (LRR)-containing integral membrane receptors that are involved in the regulation of development and immune responses in plants. It has recently been shown that rice SERK2 (OsSERK2) is essential for XA21-mediated resistance to the pathogen Xanthomonas oryzae pv. oryzae. OsSERK2 is also required for the BRI1-mediated, FLS2-mediated and EFR-mediated responses to brassinosteroids, flagellin and elongation factor Tu (EF-Tu), respectively. Here, crystal structures of the LRR domains of OsSERK2 and a D128N OsSERK2 mutant, expressed as hagfish variable lymphocyte receptor (VLR) fusions, are reported. These structures suggest that the aspartate mutation does not generate any significant conformational change in the protein, but instead leads to an altered interaction with partner receptors

Characterization of a lily anther-specific gene encoding cytoskeleton-binding glycoproteins and overexpression of the gene causes severe inhibition of pollen tube growth

This work characterizes an anther/pollen-specific gene that encodes potential intermediate filament (IF)-binding glycoproteins in lily (Lilium longiflorum Thunb. cv. Snow Queen) anthers during the development and pollen germination. LLP13 is a single gene that encodes a polypeptide of 807 amino acids, and a calculated molecular mass of 91 kDa. The protein contains a predicted transmembrane domain at the N-terminus and a conserved domain of unknown function (DUF)593 at the C-terminal half of the polypeptide. Sequence analysis revealed that LLP13 shares significant identity (37-41 %) with two intermediate filament antigen-binding proteins, representing a unique subgroup of DUF593 domain proteins from known rice and Arabidopsis species. The expression of LLP13 gene is anther-specific, and the transcript accumulates only at the stage of pollen maturation. Both premature drying and abscisic acid (ABA) treatment of developing pollen indicated that LLP13 was not induced by desiccation and ABA, but by other developmental cues. Antiserum was raised against the overexpressed LLP13C fragment of the protein in Escherichia coli and affinity-purified antibodies were prepared. Immunoblot analyses revealed that the LLP13 protein was a heterogeneous, anther-specific glycoprotein that accumulated only at the stage of pollen maturation. The protein is not heat-soluble. The level of LLP13 protein remained for 24 h during germination in vitro. Overexpression of LLP13-GFP or GFP-LLP13 in lily pollen tubes caused severe inhibition of tube elongation. The LLP13 protein codistributed with mTalin in growing tubes, suggesting that it apparently decorates actin cytoskeleton and is likely a cytoskeleton-binding protein that binds with IFs that potentially exist in pollen tubes

Phototropism: Mechanism and Outcomes

Plants have evolved a wide variety of responses that allow them to adapt to the variable environmental conditions in which they find themselves growing. One such response is the phototropic response - the bending of a plant organ toward (stems and leaves) or away from (roots) a directional blue light source. Phototropism is one of several photoresponses of plants that afford mechanisms to alter their growth and development to changes in light intensity, quality and direction. Over recent decades much has been learned about the genetic, molecular and cell biological components involved in sensing and responding to phototropic stimuli. Many of these advances have been made through the utilization of Arabidopsis as a model for phototropic studies. Here we discuss such advances, as well as studies in other plant species where appropriate to the discussion of work in Arabidopsis