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1. Breakdown of species boundaries in Mandevilla : floral morphological intermediacy, novel fragrances and asymmetric pollen flow

   https://doi.org/10.1111/plb.12924  

   Rubini_Pisano, A. ; Moré, M. ; Cisternas, M_A ; Raguso, R_A ; Benitez‐Vieyra, S. ; Ren, ed., Z‐X ( November 2018 , Plant Biology)

   Phenotypic intermediacy is an indicator of putative hybrid origin and has provided the main clues to discovering hybrid plants in nature.Mandevilla pentlandianaandM. laxa(Apocynaceae) are sister species with clear differences in floral phenotype and associated pollinator guilds: diurnal Hymenoptera and nocturnal hawkmoths, respectively. The presence of individuals with intermediate phenotypes in a wild population raises questions about the roles of visual and olfactory signals (i.e. corolla morphology and floral fragrances) as barriers to interbreeding, and how the breakdown of floral isolation occurs.

   We examined phenotypic variation in a mixedMandevillapopulation, analysing the chemical composition of floral fragrances, characterising floral shape through geometric morphometrics and assessing individual grouping through taxonomically relevant traits and an unsupervised learning algorithm. We quantified the visitation frequencies of floral visitors and tracked their foraging movements using pollen analogues.

   The presence of morphologically intermediate individuals and pollen analogue movement suggested extensive hybridisation betweenM. laxaandM. pentlandiana, along with asymmetrical rates of backcrossing between these putative hybrids andM. laxa. Floral volatiles from putative hybrid individuals showed a transgressive phenotype, with additional compounds not emitted by either parental species.

   Our results suggest the presence of a hybrid swarm between sympatricM. pentlandianaandM. laxaand indicate that initial hybridisation events between these parental species are rare, but once they occur, visits between putative hybrids andM. laxaare common and facilitate continued introgression.

    

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2. Replaying the evolutionary tape to investigate subgenome dominance in allopolyploid Brassica napus

   https://doi.org/10.1111/nph.17137  

   Bird, Kevin A. ; Niederhuth, Chad E. ; Ou, Shujun ; Gehan, Malia ; Pires, J. Chris ; Xiong, Zhiyong ; VanBuren, Robert ; Edger, Patrick P. ( January 2021 , New Phytologist)

   Allopolyploidisation merges evolutionarily distinct parental genomes (subgenomes) into a single nucleus. A frequent observation is that one subgenome is ‘dominant’ over the other subgenome, often being more highly expressed.

   Here, we ‘replayed the evolutionary tape’ with six isogenic resynthesisedBrassica napusallopolyploid lines and investigated subgenome dominance patterns over the first 10 generations postpolyploidisation.

   We found that the same subgenome was consistently more dominantly expressed in all lines and generations and that >70% of biased gene pairs showed the same dominance patterns across all lines and anin silicohybrid of the parents. Gene network analyses indicated an enrichment for network interactions and several biological functions for theBrassica oleraceasubgenome biased pairs, but no enrichment was identified forBrassica rapasubgenome biased pairs. Furthermore, DNA methylation differences between subgenomes mirrored the observed gene expression bias towards the dominant subgenome in all lines and generations. Many of these differences in gene expression and methylation were also found when comparing the progenitor genomes, suggesting that subgenome dominance is partly related to parental genome differences rather than just a byproduct of allopolyploidisation.

   These findings demonstrate that ‘replaying the evolutionary tape’ in an allopolyploid results in largely repeatable and predictable subgenome expression dominance patterns.

    

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3. No local adaptation in leaf or stem xylem vulnerability to embolism, but consistent vulnerability segmentation in a North American oak

   https://doi.org/10.1111/nph.15886  

   Skelton, Robert P. ; Anderegg, Leander D. L. ; Papper, Prahlad ; Reich, Emma ; Dawson, Todd E. ; Kling, Matthew ; Thompson, Sally E. ; Diaz, Jessica ; Ackerly, David D. ( June 2019 , New Phytologist)

   Vulnerability to embolism varies between con‐generic species distributed along aridity gradients, yet little is known about intraspecific variation and its drivers. Even less is known about intraspecific variation in tissues other than stems, despite results suggesting that roots, stems and leaves can differ in vulnerability. We hypothesized that intraspecific variation in vulnerability in leaves and stems is adaptive and driven by aridity.

   We quantified leaf and stem vulnerability ofQuercus douglasiiusing the optical technique. To assess contributions of genetic variation and phenotypic plasticity to within‐species variation, we quantified the vulnerability of individuals growing in a common garden, but originating from populations along an aridity gradient, as well as individuals from the same wild populations.

   Intraspecific variation in water potential at which 50% of total embolism in a tissue is observed (P₅₀) was explained mostly by differences between individuals (>66% of total variance) and tissues (16%). There was little between‐population variation in leaf/stem P₅₀in the garden, which was not related to site of origin aridity. Unexpectedly, we observed a positive relationship between wild individual stem P₅₀and aridity.

   Although there is no local adaptation and only minor phenotypic plasticity in leaf/stem vulnerability inQ. douglasii, high levels of potentially heritable variation within populations or strong environmental selection could contribute to adaptive responses under future climate change.

    

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4. Mutations in the predicted DNA polymerase subunit POLD3 result in more rapid flowering of Brachypodium distachyon

   https://doi.org/10.1111/nph.16546  

   Woods, Daniel P. ; Dong, Yinxin ; Bouché, Frédéric ; Mayer, Kevin ; Varner, Leah ; Ream, Thomas S. ; Thrower, Nicholas ; Wilkerson, Curtis ; Cartwright, Amy ; Sibout, Richard ; et al ( April 2020 , New Phytologist)

   The timing of reproduction is a critical developmental decision in the life cycle of many plant species.

   Fine mapping of a rapid‐flowering mutant was done using whole‐genome sequence data from bulked DNA from a segregating F2 mapping populations. The causative mutation maps to a gene orthologous with the third subunit of DNA polymerase δ (POLD3), a previously uncharacterized gene in plants. Expression analyses of POLD3 were conducted via real time qPCR to determine when and in what tissues the gene is expressed.

   To better understand the molecular basis of the rapid‐flowering phenotype, transcriptomic analyses were conducted in the mutant vs wild‐type. Consistent with the rapid‐flowering mutant phenotype, a range of genes involved in floral induction and flower development are upregulated in the mutant.

   Our results provide the first characterization of the developmental and gene expression phenotypes that result from a lesion inPOLD3in plants.

    

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5. Genetic and functional variation across regional and local scales is associated with climate in a foundational prairie grass

   https://doi.org/10.1111/nph.16547  

   Hoffman, Ava M. ; Bushey, Julie A. ; Ocheltree, Troy W. ; Smith, Melinda D. ( April 2020 , New Phytologist)

   Global change forecasts in ecosystems require knowledge of within‐species diversity, particularly of dominant species within communities. We assessed site‐level diversity and capacity for adaptation inBouteloua gracilis, the dominant species in the Central US shortgrass steppe biome.

   We quantified genetic diversity from 17 sites across regional scales, north to south from New Mexico to South Dakota, and local scales in northern Colorado. We also quantified phenotype and plasticity within and among sites and determined the extent to which phenotypic diversity inB. graciliswas correlated with climate.

   Genome sequencing indicated pronounced population structure at the regional scale, and local differences indicated that gene flow and/or dispersal may also be limited. Within a common environment, we found evidence of genetic divergence in biomass‐related phenotypes, plasticity, and phenotypic variance, indicating functional divergence and different adaptive potential. Phenotypes were differentiated according to climate, chiefly median Palmer Hydrological Drought Index and other aridity metrics.

   Our results indicate conclusive differences in genetic variation, phenotype, and plasticity in this species and suggest a mechanism explaining variation in shortgrass steppe community responses to global change. This analysis ofB. gracilisintraspecific diversity across spatial scales will improve conservation and management of the shortgrass steppe ecosystem in the future.

    

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