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1. Leaf margins in a deciduous lineage from the Greater Cape Floristic Region track climate in unexpected directions

   https://doi.org/10.1002/ajb2.1472  

   Frye, Henry A. ; Mocko, Kerri ; Moore, Timothy E. ; Schlichting, Carl D. ; Jones, Cynthia S. ( May 2020 , American Journal of Botany)

   The functional significance of leaf margins has long been debated. In this study, we explore influences of climate, leaf lobing, woodiness, and shared evolutionary history on two leaf margin traits within the genusPelargonium.

   Leaves from 454 populations ofPelargonium(161 species) were collected in the Greater Cape Floristic Region and scored for tooth presence/absence and degree of lobing. Tooth density (number of teeth per interior perimeter distance) was calculated for a subset of these. We compared five hypotheses to explain tooth presence and density using mixed effect models.

   Tooth presence/absence was best predicted by the interaction of leaf lobing and mean annual temperature (MAT), but often in patterns opposite those previously reported: species were more likely to be toothed with warmer temperatures, particularly for unlobed and highly lobed leaves. In contrast, tooth density was best predicted by the interaction ofMATand the season of most rain; density declines with temperature as consistent with expectations, but only in winter‐rain dominated areas. Woody and nonwoody species withinPelargoniumhave similar associations between tooth presence/absence andMAT, contrary to the expectation that patterns within nonwoody species would be insignificant.

   We concludePelargoniumleaf margins show predictable responses to climate, but these responses are complex and can contradict those found for global patterns across plant communities.

    

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2. Tooth and consequences: Heterodonty and dental replacement in piranhas and pacus (Serrasalmidae)

   https://doi.org/10.1111/ede.12306  

   Kolmann, Matthew A. ; Cohen, Karly E. ; Bemis, Katherine E. ; Summers, Adam P. ; Irish, Frances J. ; Hernandez, L. Patricia ( August 2019 , Evolution & Development)

   Tooth replacement in piranhas is unusual: all teeth on one side of the head are lost as a unit, then replaced simultaneously. We used histology and microCT to examine tooth‐replacement modes across carnivorous piranhas and their herbivorous pacu cousins (Serrasalmidae) and then mapped replacement patterns onto a molecular phylogeny. Pacu teeth develop and are replaced in a manner like piranhas. For serrasalmids, unilateral tooth replacement is not an “all or nothing” phenomenon; we demonstrate that both sides of the jaws have developing tooth rows within them, albeit with one side more mineralized than the other. All serrasalmids (except one) share unilateral tooth replacement, so this is not an adaptation for carnivory. All serrasalmids have interlocking teeth; piranhas interdigitate lateral tooth cusps with adjacent teeth, forming a singular saw‐like blade, whereas lateral cusps in pacus clasp together. For serrasalmids to have an interlocking dentition, their teeth need to develop and erupt at the same time. We propose that interlocking mechanisms prevent tooth loss and ensure continued functionality of the feeding apparatus. Serrasalmid dentitions are ubiquitously heterodont, having incisiform and molariform dentitions reminiscent of mammals. Finally, we propose that simultaneous tooth replacement be considered as a synapomorphy for the family.

    

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3. Control of leaf blade outgrowth and floral organ development by LEUNIG , ANGUSTIFOLIA 3 and WOX transcriptional regulators

   https://doi.org/10.1111/nph.15921  

   Zhang, Fei ; Wang, Hui ; Kalve, Shweta ; Wolabu, Tezera W. ; Nakashima, Jin ; Golz, John F. ; Tadege, Million ( July 2019 , New Phytologist)

   Plant lateral organ development is a complex process involving both transcriptional activation and repression mechanisms. TheWOXtranscriptional repressorWOX1/STF, theLEUNIG(LUG) transcriptional corepressor and theANGUSTIFOLIA3 (AN3) transcriptional coactivator play important roles in leaf blade outgrowth and flower development, but how these factors coordinate their activities remains unclear. Here we report physical and genetic interactions among these key regulators of leaf and flower development.

   We developed a novelin plantatranscriptional activation/repression assay and suggest thatLUGcould function as a transcriptional coactivator during leaf blade development.

   MtLUGphysically interacts with MtAN3, and this interaction appears to be required for leaf and flower development. A single amino acid substitution at position 61 in theSNHdomain of MtAN3 protein abolishes its interaction with MtLUG, and its transactivation activity and biological function. Mutations inlugandan3enhanced each other's mutant phenotypes. Both thelugand thean3mutations enhanced thewox1 prsleaf and flower phenotypes inArabidopsis.

   Our findings together suggest that transcriptional repression and activation mediated by theWOX,LUGandAN3 regulators function in concert to promote leaf and flower development, providing novel mechanistic insights into the complex regulation of plant lateral organ development.

    

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4. Late Quaternary changes in sediment composition on the NE Greenland margin (~73° N) with a focus on the fjords and shelf

   https://doi.org/10.1111/bor.12169  

   Andrews, John T. ; Stein, Rüdiger ; Moros, Matthias ; Perner, Kerstin ( February 2016 , Boreas)

   In order to document changes in Holocene glacier extent and activity inNEGreenland (~73° N) we study marine sediment records that extend from the fjords (PS2631 andPS2640), across the shelf (PS2623 andPS2641), to the Greenland Sea (JM07‐174GC). The primary bedrock geology of the source areas is the Caledonian sediment outcrop, including Devonian red beds, plus early Neoproterozoic gneisses and early Tertiary volcanics. We examine the variations in colour (CIE*), grain size, and bulk mineralogy (from X‐ray diffraction of the <2 mm sediment fraction). Fjord corePS2640 in Sofia Sund, with a marked red hue, is distinct in grain size, colour and mineralogy from the other fjord and shelf cores. Five distinct grain‐size modes are distinguished of which only one is associated with a coarse ice‐rafting signal – this mode is rare in the mid‐ and late Holocene. A sediment unmixing program (SedUnMixMC) is used to characterize down‐core changes in sediment composition based on the upper late Holocene sediments from coresPS2640 (Sofia Sund),PS2631 (Kaiser Franz Joseph Fjord) andPS2623 (south of Shannon Is), and surface samples from the Kara Sea (as an indicator of transport from the Russian Arctic shelves). Major changes in mineral composition are noted in all cores with possible coeval shifts centredc. 2.5, 4.5 and 7.5 cal. kaBP(±0.5 ka) but are rarely linked with changes in the grain‐size spectra. CoarseIRD(>2 mm) andIRD‐grain‐size spectra are rare in the last 9–10 cal. kaBPand, in contrast with areas farther south (~68° N), there is no distinctIRDsignal at the onset of neoglaciation. Our paper demonstrates the importance of the quantitative analysis of sediment properties in clarifying source to sink changes in glacial marine environments.

    

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5. Membrane topology and identification of key residues of Ea DAcT, a plant MBOAT with unusual substrate specificity

   https://doi.org/10.1111/tpj.13636  

   Tran, Tam N. T. ; Shelton, Jennifer ; Brown, Susan ; Durrett, Timothy P. ( August 2017 , The Plant Journal)

   Euonymus alatusdiacylglycerol acetyltransferase (EaDAcT) catalyzes the transfer of an acetyl group from acetyl‐CoA to thesn‐3 position of diacylglycerol to form 3‐acetyl‐1,2‐diacyl‐sn‐glycerol (acetyl‐TAG).EaDAcT belongs to a small, plant‐specific subfamily of the membrane bound O‐acyltransferases (MBOAT) that acylate different lipid substrates. Sucrose gradient density centrifugation revealed thatEaDAcT colocalizes to the same fractions as an endoplasmic reticulum (ER)‐specific marker. By mapping the membrane topology ofEaDAcT, we obtained an experimentally determined topology model for a plantMBOAT. TheEaDAcT model contains four transmembrane domains (TMDs), with both the N‐ and C‐termini orientated toward the lumen of theER. In addition, there is a large cytoplasmic loop between the first and secondTMDs, with theMBOATsignature region of the protein embedded in the thirdTMDclose to the interface between the membrane and the cytoplasm. During topology mapping, we discovered two cysteine residues (C187 and C293) located on opposite sides of the membrane that are important for enzyme activity. In order to identify additional amino acid residues important for acetyltransferase activity, we isolated and characterized acetyltransferases from other acetyl‐TAG‐producing plants. Among them, the acetyltransferase fromEuonymus fortuneipossessed the highest activityin vivoandin vitro. Mutagenesis of conserved amino acids revealed that S253, H257, D258 and V263 are essential forEaDAcT activity. Alteration of residues unique to the acetyltransferases did not alter the unique acyl donor specificity ofEaDAcT, suggesting that multiple amino acids are important for substrate recognition.

    

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