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1. All 17 S‐locus F‐box proteins of the S 2 ‐ and S 3 ‐haplotypes of Petunia inflata are assembled into similar SCF complexes with a specific function in self‐incompatibility

   https://doi.org/10.1111/tpj.13222  

   Li, Shu ; Williams, Justin S. ; Sun, Penglin ; Kao, Teh‐hui ( August 2016 , The Plant Journal)

   The collaborative non‐self‐recognition model for S‐RNase‐based self‐incompatibility predicts that multiple S‐locus F‐box proteins (SLFs) produced by pollen of a givenS‐haplotype collectively mediate ubiquitination and degradation of all non‐self S‐RNases, but not self S‐RNases, in the pollen tube, thereby resulting in cross‐compatible pollination but self‐incompatible pollination. We had previously used pollen extracts containingGFP‐fused S₂‐SLF1 (SLF1 with anS₂‐haplotype) ofPetunia inflatafor co‐immunoprecipitation (Co‐IP) and mass spectrometry (MS), and identified PiCUL1‐P (a pollen‐specific Cullin1), PiSSK1 (a pollen‐specific Skp1‐like protein) and PiRBX1 (a conventional Rbx1) as components of theSCF^S2–SLF1complex. Using pollen extracts containing PiSSK1:FLAG:GFPfor Co‐IP/MS, we identified two additionalSLFs (SLF4 andSLF13) that were assembled intoSCF^SLFcomplexes. As 17SLFgenes (SLF1toSLF17) have been identified inS₂andS₃pollen, here we examined whether all 17SLFs are assembled into similar complexes and, if so, whether these complexes are unique toSLFs. We modified the previous Co‐IP/MSprocedure, including the addition of style extracts from four differentS‐genotypes to pollen extracts containing PiSSK1:FLAG:GFP, to perform four separate experiments. The results taken together show that all 17SLFs and anSLF‐like protein,SLFLike1 (encoded by anS‐locus‐linked gene), co‐immunoprecipitated with PiSSK1:FLAG:GFP. Moreover, of the 179 other F‐box proteins predicted byS₂andS₃pollen transcriptomes, only a pair with 94.9% identity and another pair with 99.7% identity co‐immunoprecipitated with PiSSK1:FLAG:GFP. These results suggest thatSCF^SLFcomplexes have evolved specifically to function in self‐incompatibility.

    

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2. The Arabidopsis heterotrimeric G‐protein β subunit, AGB 1, is required for guard cell calcium sensing and calcium‐induced calcium release

   https://doi.org/10.1111/tpj.14318  

   Jeon, Byeong Wook ; Acharya, Biswa R. ; Assmann, Sarah M. ( April 2019 , The Plant Journal)

   Cytosolic calcium concentration ([Ca²⁺]_cyt) and heterotrimeric G‐proteins are universal eukaryotic signaling elements. In plant guard cells, extracellular calcium (Ca_o) is as strong a stimulus for stomatal closure as the phytohormone abscisic acid (ABA), but underlying mechanisms remain elusive. Here, we report that the sole Arabidopsis heterotrimeric Gβ subunit,AGB1, is required for four guard cell Ca_oresponses: induction of stomatal closure; inhibition of stomatal opening; [Ca²⁺]_cytoscillation; and inositol 1,4,5‐trisphosphate (InsP3) production. Stomata in wild‐type Arabidopsis (Col) and in mutants of the canonical Gα subunit,GPA1, showed inhibition of stomatal opening and promotion of stomatal closure by Ca_o. By contrast, stomatal movements ofagb1mutants andagb1/gpa1double‐mutants, as well as those of theagg1agg2 Gγ double‐mutant, were insensitive to Ca_o. These behaviors contrast withABA‐regulated stomatal movements, which involveGPA1 andAGB1/AGG3 dimers, illustrating differential partitioning of G‐protein subunits among stimuli with similar ultimate impacts, which may facilitate stimulus‐specific encoding.AGB1knockouts retained reactive oxygen species andNOproduction, but lostYC3.6‐detected [Ca²⁺]_cytoscillations in response to Ca_o, initiating only a single [Ca²⁺]_cytspike. Experimentally imposed [Ca²⁺]_cytoscillations restored stomatal closure inagb1. Yeast two‐hybrid and bimolecular complementation fluorescence experiments revealed thatAGB1 interacts with phospholipase Cs (PLCs), and Ca_oinduced InsP3 production in Col but not inagb1. In sum, G‐protein signaling viaAGB1/AGG1/AGG2 is essential for Ca_o‐regulation of stomatal apertures, and stomatal movements in response to Ca_oapparently require Ca²⁺‐induced Ca²⁺release that is likely dependent on Gβγ interaction withPLCs leading to InsP3 production.

    

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3. Ectomycorrhizal fungi and soil enzymes exhibit contrasting patterns along elevation gradients in southern Patagonia

   https://doi.org/10.1111/nph.15714  

   Truong, Camille ; Gabbarini, Luciano A. ; Corrales, Adriana ; Mujic, Alija B. ; Escobar, Julio M. ; Moretto, Alicia ; Smith, Matthew E. ( March 2019 , New Phytologist)

   The biological and functional diversity of ectomycorrhizal (ECM) associations remain largely unknown in South America. In Patagonia, theECMtreeNothofagus pumilioforms monospecific forests along mountain slopes without confounding effects of vegetation on plant–fungi interactions.

   To determine how fungal diversity and function are linked to elevation, we characterized fungal communities, edaphic variables, and eight extracellular enzyme activities along six elevation transects in Tierra del Fuego (Argentina and Chile). We also tested whether pairingITS1rDNAIllumina sequences generated taxonomic biases related to sequence length.

   Fungal community shifts across elevations were mediated primarily by soilpHwith the most species‐rich fungal families occurring mostly within a narrowpHrange. By contrast, enzyme activities were minimally influenced by elevation but correlated with soil factors, especially total soil carbon. The activity of leucine aminopeptidase was positively correlated withECMfungal richness and abundance, and acid phosphatase was correlated with nonECM fungal abundance. Several fungal lineages were undetected when using exclusively paired or unpaired forwardITS1 sequences, and these taxonomic biases need reconsideration for future studies.

   Our results suggest that soil fungi inN. pumilioforests are functionally similar across elevations and that these diverse communities help to maintain nutrient mobilization across the elevation gradient.

    

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4. Contribution and consequences of xylem‐transported CO 2 assimilation for C 3 plants

   https://doi.org/10.1111/nph.15907  

   Stutz, Samantha S. ; Hanson, David T. ( June 2019 , New Phytologist)

   Traditionally, leaves were thought to be supplied withCO₂for photosynthesis by the atmosphere and respiration. Recent studies, however, have shown that the xylem also transports a significant amount of inorganic carbon into leaves through the bulk flow of water. However, little is known about the dynamics and proportion of xylem‐transportedCO₂that is assimilated, vs simply lost to transpiration.

   Cut leaves ofPopulus deltoidesandBrassica napuswere placed in eitherKCl or one of three [NaH¹³CO₃] solutions dissolved in water to simultaneously measure the assimilation and the efflux of xylem‐transportedCO₂exiting the leaf across light andCO₂response curves in real‐time using a tunable diode laser absorption spectroscope.

   The rates of assimilation and efflux of xylem‐transportedCO₂increased with increasing xylem [¹³CO₂*] and transpiration. Under saturating irradiance, rates of assimilation using xylem‐transportedCO₂accounted forc.2.5% of the total assimilation in both species in the highest [¹³CO₂*].

   The majority of xylem‐transportedCO₂is assimilated, and efflux is small compared to respiration. Assimilation of xylem‐transportedCO₂comprises a small portion of total photosynthesis, but may be more important whenCO₂is limiting.

    

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5. Effects of external recirculation on a two‐stage mainstream anaerobic‐anammox treatment system

   https://doi.org/10.1002/wer.1019  

   Li, Xiaojin ; He, Zhen ( February 2019 , Water Environment Research)

   Nitritation‐anammox treatment can be a potentially energy‐ and resource‐efficient technology for treating mainstream wastewater. However, the issue of nitrate residue from anammox treatment remains to be addressed. Herein, external recirculation of the anammox effluent to a hybrid anaerobic reactor (HAR), which was also to provide a continuous flow with lowCOD/N for the nitritation‐anammox reactor, was employed to decrease the residue compounds. The recirculation ratio of 50% was observed to be the optimal to achieve the best overall performance with potential savings in energy demand. Specifically, in the operation scenario ofR = 50%, the highestCODremoval of ~90% by theHARwas achieved. Meanwhile, the lowestCOD/NH₄⁺‐N ratio of ~2.0 in theHAReffluent ensured the lowest observedNO₃⁻‐N/NH₄⁺‐N ratio of ~14% in the nitritation‐anammox reactor. These results have demonstrated the feasibility of applying external recirculation for nitrate residue removalviadenitrification in the anaerobic pretreatment stage.

   Nitritation‐anammox treatment is an attractive method for mainstream wastewater treatment.

   Nitrate residue from anammox processes contributes to total nitrogen in the final effluent.

   Recirculation of anammox effluent to an anaerobic reactor can decrease nitrate residue.

   A recirculation ratio of 50% results in a low COD/NH₄⁺ratio of 2 that benefits the subsequent anammox.

    

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