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1. Parental methylation mediates how progeny respond to environments of parents and of progeny themselves

   https://doi.org/10.1093/aob/mcac125  

   Morgan, Britany L. ; Donohue, Kathleen ( October 2022 , Annals of Botany)

   Environments experienced by both parents and offspring influence progeny traits, but the epigenetic mechanisms that regulate the balance of parental vs. progeny control of progeny phenotypes are not known. We tested whether DNA methylation in parents and/or progeny mediates responses to environmental cues experienced in both generations.

   Using Arabidopsis thaliana, we manipulated parental and progeny DNA methylation both chemically, via 5-azacytidine, and genetically, via mutants of methyltransferase genes, then measured progeny germination responses to simulated canopy shade in parental and progeny generations.

   We first found that germination of offspring responded to parental but not seed demethylation. We further found that parental demethylation reversed the parental effect of canopy in seeds with low (Cvi-1) to intermediate (Col) dormancy, but it obliterated the parental effect in seeds with high dormancy (Cvi-0). Demethylation did so by either suppressing germination of seeds matured under white-light (Cvi-1) or under canopy (Cvi-0), or by increasing the germination of seeds matured under canopy (Col). Disruption of parental methylation also prevented seeds from responding to their own light environment in one genotype (Cvi-0, most dormant), but it enabled seeds to respond to their own environment in another genotype (Cvi-1, least dormant). Using mutant genotypes, we found that both CG and non-CG DNA methylation were involved in parental effects on seed germination.

   Parental methylation state influences seed germination more strongly than does the progeny’s own methylation state, and it influences how seeds respond to environments of parents and progeny in a genotype-specific manner.

    

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2. Precipitation timing and soil substrate drive phenology and fitness of Arabidopsis thaliana in a Mediterranean environment

   https://doi.org/10.1111/1365-2435.14391  

   Martínez‐Berdeja, Alejandra ; Okada, Miki ; Cooper, Martha D. ; Runcie, Daniel E. ; Burghardt, Liana T. ; Schmitt, Johanna ( July 2023 , Functional Ecology)

   In Mediterranean climates, the timing of seasonal rains determines germination, flowering phenology and fitness. As climate change alters seasonal precipitation patterns, it is important to ask how these changes will affect the phenology and fitness of plant populations. We addressed this question experimentally with the annual plant speciesArabidopsis thaliana.

   In a first experiment, we manipulated the date of rainfall onset and recorded germination phenology on sand and soil substrates. In a second experiment, we manipulated germination date, growing season length and mid‐season drought to measure their effects on flowering time and fitness. Within each experiment, we manipulated seed dormancy and flowering time using multilocus near‐isogenic lines segregating strong and weak alleles of the seed dormancy geneDOG1and the flowering time geneFRI. We synthesized germination phenology data from the first experiment with fitness functions from the second experiment to project population fitness under different seasonal rainfall scenarios.

   Germination phenology tracked rainfall onset but was slower and more variable on sand than on soil. Many seeds dispersed on sand in spring and summer delayed germination until the cooler temperatures of autumn. The high‐dormancyDOG1allele also prevented immediate germination in spring and summer. Germination timing strongly affected plant fitness. Fecundity was highest in the October germination cohort and declined in spring germinants. The late floweringFRIallele had lower fecundity, especially in early fall and spring cohorts. Projections of population fitness revealed that: (1) Later onset of autumn rains will negatively affect population fitness. (2) Slow, variable germination on sand buffers populations against fitness impacts of variable spring and summer rainfall. (3) Seasonal selection favours high dormancy and early flowering genotypes in a Mediterranean climate with hot dry summers. The high‐dormancyDOG1allele delayed germination of spring‐dispersed fresh seeds until more favourable early fall conditions, resulting in higher projected population fitness.

   These findings suggest that Mediterranean annual plant populations are vulnerable to changes in seasonal precipitation, especially in California where rainfall onset is already occurring later. The fitness advantage of highly dormant, early flowering genotypes helps explain the prevalence of this strategy in Mediterranean populations.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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3. A century of genetic variation inferred from a persistent soil‐stored seed bank

   https://doi.org/10.1111/eva.12675  

   Summers, Jennifer L. ; Bernik, Brittany ; Saunders, Colin J. ; McLachlan, Jason S. ; Blum, Michael J. ( July 2018 , Evolutionary Applications)

   Stratigraphic accretion of dormant propagules in soil can result in natural archives useful for studying ecological and evolutionary responses to environmental change. Few attempts have been made, however, to use soil‐stored seed banks as natural archives, in part because of concerns over nonrandom attrition and mixed stratification. Here, we examine the persistent seed bank ofSchoenoplectus americanus, a foundational brackish marsh sedge, to determine whether it can serve as a resource for reconstructing historical records of demographic and population genetic variation. After assembling profiles of the seed bank from radionuclide‐dated soil cores, we germinated seeds to “resurrect” cohorts spanning the 20th century. Using microsatellite markers, we assessed genetic diversity and differentiation among depth cohorts, drawing comparisons to extant plants at the study site and in nearby and more distant marshes. We found that seed density peaked at intermediate soil depths. We also detected genotypic differences among cohorts as well as between cohorts and extant plants. Genetic diversity did not decline with depth, indicating that the observed pattern of differentiation is not due to attrition. Patterns of differentiation within and among extant marshes also suggest that local populations persist as aggregates of small clones, likely reflecting repeated seedling recruitment and low immigration from admixed regional gene pools. These findings indicate that persistent and stratified soil‐stored seed banks merit further consideration as resources for reconstructing decadal‐ to century‐long records that can lend insight into the tempo and nature of ecological and evolutionary processes that shape populations over time.

    

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4. Seed Cryopreservation, Germination, and Micropropagation of Eastern Turkeybeard, Xerophyllum asphodeloides (L.) Nutt.: A Threatened Species from the Southeastern United States

   https://doi.org/10.3390/plants10071462  

   Issac, Michelle ; Kuriakose, Princy ; Leung, Stacie ; Costa, Alex B. ; Johnson, Shannon ; Bucalo, Kylie ; Stober, Jonathan M. ; Determann, Ron O. ; Rogers, Will L. ; Cruse-Sanders, Jenifer M. ; et al ( July 2021 , Plants)

   null (Ed.)

   Xerophyllum asphodeloides (Xerophyllaceae), known as eastern turkeybeard, is an herbaceous perennial found in eastern North America. Due to decline and destruction of its habitat, several states rank X. asphodeloides as “Imperiled” to “Critically Imperiled”. Protocols for seed cryopreservation, in vitro germination, sustainable shoot micropropagation, shoot establishment in soil, and seed germination are presented. Seeds from two tested sources were viable after 20 months of cryopreservation. Germination of isolated embryos in vitro was necessary to overcome strong seed dormancy. Shoot multiplication and elongation occurred on ½ MS medium without PGRs. Shoots rooted in vitro without PGRs or with 0.5 mg/L NAA or after NAA rooting powder treatment and placement in potting mix. When planted in wet, peaty soil mixes, shoots grew for two months and then declined. When planted in a drier planting mix containing aged bark, most plants continued growth. In the field, plant survival was 73% after three growing seasons. Safeguarding this species both ex situ and in situ is possible and offers a successful approach to conservation. Whole seeds germinated after double dormancy was overcome by incubation under warm moist conditions for 12 weeks followed by 12 weeks cold at 4 °C and then warm. 

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5. Closely related tree species support distinct communities of seed‐associated fungi in a lowland tropical forest

   https://doi.org/10.1111/1365-2745.13611  

   Zalamea, Paul‐Camilo ; Sarmiento, Carolina ; Arnold, A. Elizabeth ; Davis, Adam S. ; Ferrer, Astrid ; Dalling, James W. ; Mommer, ed., Liesje ( February 2021 , Journal of Ecology)

   Previous theoretical work has highlighted the potential for natural enemies to mediate the coexistence of species with similar life histories via density‐dependent effects on survivorship. For plant pathogens to play this role, they must differ in their ability to infect or induce disease in different host plant species. In tropical forests characterized by high diversity, these effects must extend to phylogenetically closely related species pairs. Mortality at the seed and seedling stage strongly influences the abundance and distribution of tropical tree species, but the host preferences and spatial distributions of fungi are rarely determined.

   We examined how host species identity, relatedness and seed viability influence the composition of fungal communities associated with seeds of four co‐occurring pioneer trees (Cecropia insignis,C. longipes,C. peltataandJacaranda copaia). Seeds were buried in mesh bags in five common gardens in the understorey of a lowland tropical forest in Panama and retrieved at intervals from 1 to 30 months. A subset of the seeds in each bag was used to determine germination success. One half of each remaining seed was tested for viability; and the other half was used to culture and identify seed‐infecting fungi.

   Seeds were infected by fungi after burial. Although fungal communities differed in viable versus dead seeds, and across burial locations, community composition primarily varied as a function of plant species identity (30.7% of variation in community composition vs. 4.5% for viability and location together), even for congenericCecropiaspecies. Phylogenetic reconstruction showed that relatedness of fungi mostly reflected differences betweenJacaranda(Bignoniaceae) andCecropia(Urticaceae).

   Although the proportion of germinable seeds decreased gradually over time for all species, intraspecific variation in survival was high at the same location (e.g. ranging from 0% to 100% forC. peltata) suggesting variable exposure or susceptibility to seed pathogens.

   Synthesis. Our study provides evidence under field conditions that congeneric tree species with similar life history traits differ markedly in seed‐associated fungal communities when exposed to the same soil‐borne fungi. This is a critical first step supporting pathogen‐mediated coexistence of closely related tree species.

    

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