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1. The long and short of the S ‐locus in Turnera (Passifloraceae)

   https://doi.org/10.1111/nph.15970  

   Shore, Joel S. ; Hamam, Hasan J. ; Chafe, Paul D. J. ; Labonne, Jonathan D. J. ; Henning, Paige M. ; McCubbin, Andrew G. ( July 2019 , New Phytologist)

   Distyly is an intriguing floral adaptation that increases pollen transfer precision and restricts inbreeding. It has been a model system in evolutionary biology since Darwin. Although theS‐locus determines the long‐ and short‐styled morphs, the genes were unknown inTurnera. We have now identified these genes.

   We used deletion mapping to identify, and then sequence,BACclones and genome scaffolds to constructS/shaplotypes. We investigated candidate gene expression, hemizygosity, and used mutants, to explore gene function.

   Thes‐haplotype possessed 21 genes collinear with a region of chromosome 7 of grape. TheS‐haplotype possessed three additional genes and two inversions.TsSPH1was expressed in filaments and anthers,TsYUC6in anthers andTsBAHDin pistils. Long‐homostyle mutants did not possessTsBAHDand a short‐homostyle mutant did not expressTsSPH1.

   Three hemizygous genes appear to determine S‐morph characteristics inT. subulata. Hemizygosity is common to all distylous species investigated, yet the genes differ. The pistil candidate gene,TsBAHD, differs from that ofPrimula, but both may inactivate brassinosteroids causing short styles.TsYUC6is involved in auxin synthesis and likely determines pollen characteristics.TsSPH1is likely involved in filament elongation. We propose an incompatibility mechanism involvingTsYUC6andTsBAHD.

    

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2. Higher fat stores contribute to persistence of little brown bat populations with white‐nose syndrome

   https://doi.org/10.1111/1365-2656.12954  

   Cheng, Tina L. ; Gerson, Alexander ; Moore, Marianne S. ; Reichard, Jonathan D. ; DeSimone, Joely ; Willis, Craig K. R. ; Frick, Winifred F. ; Kilpatrick, Auston Marm ; Tate, ed., Ann ( February 2019 , Journal of Animal Ecology)

   The persistence of populations declining from novel stressors depends, in part, on their ability to respond by trait change via evolution or plasticity. White‐nose syndrome (WNS) has caused rapid declines in several North America bat species by disrupting hibernation behaviour, leading to body fat depletion and starvation. However, some populations ofMyotis lucifugusnow persist withWNSby unknown mechanisms.

   We examined whether persistence ofM. lucifiguswithWNScould be explained by increased body fat in early winter, which would allow bats to tolerate the increased energetic costs associated withWNS. We also investigated whether bats were escaping infection or resistant to infection as an alternative mechanism explaining persistence.

   We measured body fat in early and late winter during initialWNSinvasion and 8 years later at six sites where bats are now persisting. We also measured infection prevalence and intensity in persisting populations.

   Infection prevalence was not significantly lower than observed in declining populations. However, at two sites, infection loads were lower than observed in declining populations. Body fat in early winter was significantly higher in four of the six persisting populations than duringWNSinvasion.

   Physiological models of energy use indicated that these higher fat stores could reduceWNSmortality by 58%–70%. These results suggest that differences in fat storage and infection dynamics have reduced the impacts ofWNSin many populations. Increases in body fat provide a potential mechanism for management intervention to help conserve bat populations.

    

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3. Increased adaxial stomatal density is associated with greater mesophyll surface area exposed to intercellular air spaces and mesophyll conductance in diverse C 4 grasses

   https://doi.org/10.1111/nph.16106  

   Pathare, Varsha S. ; Koteyeva, Nuria ; Cousins, Asaph B. ( September 2019 , New Phytologist)

   Mesophyll conductance (g_m) is the diffusion ofCO₂from intercellular air spaces (IAS) to the first site of carboxylation in the mesophyll cells. In C₃species,g_mis influenced by diverse leaf structural and anatomical traits; however, little is known about traits affectingg_min C₄species.

   To address this knowledge gap, we used online oxygen isotope discrimination measurements to estimateg_mand microscopy techniques to measure leaf structural and anatomical traits potentially related tog_min 18 C₄grasses.

   In this study,g_mscaled positively with photosynthesis and intrinsic water‐use efficiency (TE_i), but not with stomatal conductance. Also,g_mwas not determined by a single trait but was positively correlated with adaxial stomatal densities (SD_ada), stomatal ratio (SR), mesophyll surface area exposed toIAS(S_mes) and leaf thickness. However,g_mwas not related to abaxial stomatal densities (SD_aba) and mesophyll cell wall thickness (T_CW).

   Our study suggests that greaterSD_adaandSRincreasedg_mby increasingS_mesand creating additional parallel pathways forCO₂diffusion inside mesophyll cells. Thus,SD_ada,SRandS_mesare important determinants of C₄‐g_mand could be the target traits selected or modified for achieving greaterg_mandTE_iin C₄species.

    

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4. Nodule‐specific PLAT domain proteins are expanded in the Medicago lineage and required for nodulation

   https://doi.org/10.1111/nph.15697  

   Trujillo, Diana I. ; Silverstein, Kevin A. T. ; Young, Nevin D. ( February 2019 , New Phytologist)

   Symbiotic nitrogen fixation in legumes is mediated by an interplay of signaling processes between plant hosts and rhizobial symbionts. In legumes, several secreted protein families have undergone expansions and play key roles in nodulation. Thus, identifying lineage‐specific expansions (LSEs) of nodulation‐associated genes can be a strategy to discover candidate gene families.

   Using bioinformatic tools, we identified 13LSEs of nodulation‐related secreted protein families, each unique to eitherGlycine,ArachisorMedicagolineages. In theMedicagolineage, nodule‐specific Polycystin‐1, Lipoxygenase, Alpha Toxin (PLAT) domain proteins (NPDs) expanded to five members. We examinedNPDfunction usingCRISPR/Cas9 multiplex genome editing to createMedicago truncatulaNPDknockout lines, targeting one to fiveNPDgenes.

   Mutant lines with differing combinations ofNPDgene inactivations had progressively smaller nodules, earlier onset of nodule senescence, or ineffective nodules compared to the wild‐type control. Double‐ and triple‐knockout lines showed dissimilar nodulation phenotypes but coincided in upregulation of aDHHC‐type zinc finger and an aspartyl protease gene, possible candidates for the observed disturbance of proper nodule function.

   By postulating that gene family expansions can be used to detect candidate genes, we identified a family of nodule‐specificPLATdomain proteins and confirmed that they play a role in successful nodule formation.

    

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5. Nutrients associated with terrestrial dissolved organic matter drive changes in zooplankton:phytoplankton biomass ratios in an alpine lake

   https://doi.org/10.1111/fwb.12847  

   Kissman, Carrie E. H. ; Williamson, Craig E. ; Rose, Kevin C. ; Saros, Jasmine E. ( November 2016 , Freshwater Biology)

   Dissolved organic matter (DOM) is increasing in many lakes due to climate change and other environmental forcing. A 21‐day microcosm experiment that manipulated terrestrialDOMwas used to determine the effect ofDOMon zooplankton:phytoplankton biomass ratios (z:p). We predicted that ifDOMadditions increase the amount of fixed carbon available for higher trophic levels through stimulation of the microbial loop and hence zooplankton, the z:p will increase. However, ifDOMadditions increase other nutrients besides fixed carbon, we predict stable or decreasing z:p due to nutrient stimulation of phytoplankton that subsequently enhances zooplankton.

   The effects of experimental additions of terrestrially derivedDOMon zooplankton, phytoplankton, z:p and zooplankton net grazing were assessed in microcosms (sealed bags) incubated in the epilimnion (shallow; 1.5 m) and hypolimnion (deep; 8.0 m) strata of an alpine lake.

   DOMaddition treatments (DOM+) had a 6.0‐ to 7.5‐fold increase in phytoplankton biomass relative to controls, but only a 1.3‐ to 1.5‐fold increase in zooplankton biomass, on day 21 of the experiment. The z:p was, thus, lower in theDOM+ treatments (ratios: 2.3 deep and 4.4 shallow) than in the control treatments (ratios: 13.4 deep and 17.5 shallow), providing evidence thatDOMadditions provide nutrient subsidies besides fixed carbon that stimulate phytoplankton biomass accumulation.

   The increase in zooplankton biomass during the experiment was similar in magnitude to the total amount of dissolved organic carbon (DOC) in theDOMadded in the sealed bags at the beginning of the experiment, which suggests zooplankton biomass stimulation due to increased phytoplankton biomass, and not fromDOMthrough the microbial loop, which would have greater trophic transfer losses. The consumer net grazing effect in theDOM+ treatments was reduced by 2.8‐fold in the shallow stratum and by 2.9‐fold in the deep stratum relative to the control treatments, indicating that zooplankton were unable to exert strong top–down control on the primary producers.

   The role of nutrients needs to be considered when examining the response of pelagic ecosystems to inputs of terrestrialDOM, especially in lakes with lowerDOCconcentrations.

    

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