Effects of primary seed dormancy on lifetime fitness of Arabidopsis thaliana in the field

Accelerated Phenology Fails to Buffer Fitness Loss from Delayed Rain Onset in a Clade of Wildflowers

AbstractThe timing of early life cycle events has cascading effects on phenology and fitness. These effects may be critical for climate resilience of plant populations, especially in Mediterranean environments, where delayed rainfall onset causes delayed germination. To examine impacts of germination timing on 10 species of the Streptanthus/Caulanthus clade, we induced germination across a range of dates in ambient seasonal conditions and recorded phenological and fitness traits. Later-germinating cohorts accelerated flowering, partially stabilizing flowering date, but the degree of this compensatory plasticity differed across species. Fitness declined with later germination; the magnitude of this decline depended on the balance between direct negative effects of later germination and compensatory positive effects of accelerated flowering. The resulting species' differences in fitness responses suggest differential vulnerability to climate change. Species from wetter, cooler, less variable habitats exhibited greater phenological plasticity, accelerating flowering more and declining less in seed set with later germination than desert species. However, other fitness responses to germination timing, such as first-year fitness, were evolutionarily labile across the clade and unrelated to climate. Although compensatory phenological plasticity may buffer the impacts of delayed germination, it cannot prevent long-term declines in population fitness as fall rains come later with climate change.

Warm temperature perceived at the vegetative stage affects progeny seed germination in natural accessions of Arabidopsis thaliana

Temperatures perceived early in the life cycle of mother plants can affect the germination of the offspring seeds. In Arabidopsis thaliana, vernalisation-insensitive mutants showed altered germination response to elevated maternal temperature, hence revealing a strong genetic determinism. However, the genetic control of this maternal effect and its prevalence across natural populations remain unclear. Here, we exposed a collection of European accessions of A. thaliana to increased temperature during the vegetative phase and assessed germination in their progeny to identify the genetic basis of transgenerational germination response. We found that genotypes with rapidly germinating progeny after early maternal exposure to elevated temperature originated from regions with low-light radiation. Combining genome-wide association, expression analysis and functional assays across multiple genetic backgrounds, we show a central role for PHYB in mediating the response to maternally perceived temperature at the vegetative stage. Differential gene expression analysis in leaves identified a similar genetic network as previously found in seed endosperm under elevated temperature, supporting the pleiotropic involvement of PHYB signalling across different tissues and stages. This provides evidence that complex environmental responses modulated by the maternal genotype can rely on a consistent set of genes yet produce different effects at the different stages of exposure.

Can plants build their niche through modulation of soil microbial activities linked with nitrogen cycling? A test with Arabidopsis thaliana

In natural systems, different plant species have been shown to modulate specific nitrogen (N) cycling processes so as to meet their N demand, thereby potentially influencing their own niche. This phenomenon might go beyond plant interactions with symbiotic microorganisms and affect the much less explored plant interactions with free-living microorganisms involved in soil N cycling, such as nitrifiers and denitrifiers. Here, we investigated variability in the modulation of soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), and their ratio (NEA : DEA), across 193 Arabidopsis thaliana accessions. We studied the genetic and environmental determinants of such plant-soil interactions, and effects on plant biomass production in the next generation. We found that NEA, DEA, and NEA : DEA varied c. 30-, 15- and 60-fold, respectively, among A. thaliana genotypes and were related to genes linked with stress response, flowering, and nitrate nutrition, as well as to soil parameters at the geographic origin of the analysed genotypes. Moreover, plant-mediated N cycling activities correlated with the aboveground biomass of next-generation plants in home vs away nonautoclaved soil, suggesting a transgenerational impact of soil biotic conditioning on plant performance. Altogether, these findings suggest that nutrient-based plant niche construction may be much more widespread than previously thought.

Non-stressful temperature changes affect transgenerational phenotypic plasticity across the life cycle of Arabidopsis thaliana plants

BACKGROUND AND AIMS

Plants respond in a plastic manner to seasonal changes, often resulting in adaptation to environmental variation. Although much is known about how seasonality regulates developmental transitions within generations, transgenerational effects of non-stressful environmental changes are only beginning to be unveiled. This study aimed to evaluate the effects of ambient temperature changes on the expression of transgenerational plasticity in key developmental traits of Arabidopsis thaliana plants.

METHODS

We grew Columbia-0 plants in two contrasting temperature environments (18 and 24 °C) during their whole life cycles, or the combination of those temperatures before and after bolting (18-24 and 24-18 °C) across two generations. We recorded seed germination, flowering time and reproductive biomass production for the second generation, and seed size of the third generation.

KEY RESULTS

The environment during the whole life cycle of the first generation of plants, even that experienced before flowering, influenced the germination response and flowering time of the second generation. These effects showed opposing directions in a pattern dependent on the life stage experiencing the cue in the first generation. In contrast, the production of reproductive biomass depended on the immediate environment of the progeny generation. Finally, the seed area of the third generation was influenced positively by correlated environments across generations.

CONCLUSIONS

Our results suggest that non-stressful environmental changes affect the expression of key developmental traits across generations, although those changes can have contrasting effects depending on the parental and grandparental life stage that perceives the cue. Thus, transgenerational effects in response to non-stressful cues might influence the expression of life-history traits and potential adaptation of future generations.

Is winter coming? Impact of the changing climate on plant responses to cold temperature

Climate change is causing alterations in annual temperature regimes worldwide. Important aspects of this include the reduction of winter chilling temperatures as well as the occurrence of unpredicted frosts, both significantly affecting plant growth and yields. Recent studies advanced the knowledge of the mechanisms underlying cold responses and tolerance in the model plant Arabidopsis thaliana. However, how these cold-responsive pathways will readjust to ongoing seasonal temperature variation caused by global warming remains an open question. In this review, we highlight the plant developmental programmes that depend on cold temperature. We focus on the molecular mechanisms that plants have evolved to adjust their development and stress responses upon exposure to cold. Covering both genetic and epigenetic aspects, we present the latest insights into how alternative splicing, noncoding RNAs and the formation of biomolecular condensates play key roles in the regulation of cold responses. We conclude by commenting on attractive targets to accelerate the breeding of increased cold tolerance, bringing up biotechnological tools that might assist in overcoming current limitations. Our aim is to guide the reflection on the current agricultural challenges imposed by a changing climate and to provide useful information for improving plant resilience to unpredictable cold regimes.

Non-viviparous pre-dispersal seed germination in Amaranthaceae in the cold deserts of Central Asia

In the broad context of understanding the relationship between timing of seed germination and adaptation of a plant species to its habitat, the purpose of this study was to purse an observation of pre-dispersal seed germination of Salsola brachiata (Amaranthaceae) in late winter 2021 in the Amaranthaceae species-rich cold deserts in northwest China (Central Asia). We searched for pre-dispersal germination in species of Amaranthaceae growing in sand dunes (S), salt deserts (SD) and gravel deserts (GD). We examined 69 species in 155 populations in autumn 2021 and 52 species in 12 populations in early spring 2022. No seeds of any of the 69 species germinated on the mother plants in autumn 2021, while 30 of 52 species (57.7%) did so during snowmelt in early spring 2022. The rank order of species with few to many seeds germinated on the mother plants was annuals (66.7%) > small shrubs (23.3%) > small trees (6.7%) > shrubs (3.3%). The number of species in S, SD, and GD with pre-dispersal germinated seeds was 16 of 27 (59.3%), 15 of 31 (48.4%), and 15 of 30 (50.0%), respectively. The high species occurrence of pre-dispersal germination in early spring suggested that it might be adaptive in the unpredictable-rainfall growing-season environment of the cold deserts of Central Asia, a center of diversity of Amaranthaceae. However, preliminary studies on seedling/juvenile survival of S. brachiata showed that those from post-dispersal soil-germinated seeds had the best survival, suggesting that pre-dispersal seed germination may be maladaptive.

Seed dormancy varies widely among Arabidopsis thaliana populations both between and within Fennoscandia and Italy

The timing of germination is a key life‐history trait in plants, which is strongly affected by the strength of seed dormancy. Continental‐wide genetic variation in seed dormancy has been related to differences in climate and the timing of conditions suitable for seedling establishment. However, for predictions of adaptive potential and consequences of climatic change, information is needed regarding the extent to which seed dormancy varies within climatic regions and the factors driving such variation.

We quantified dormancy of seeds produced by 17 Italian and 28 Fennoscandian populations of Arabidopsis thaliana when grown in the greenhouse and at two field sites in Italy and Sweden. To identify possible drivers of among‐population variation in seed dormancy, we examined the relationship between seed dormancy and climate at the site of population origin, and between seed dormancy and flowering time.

Seed dormancy was on average stronger in the Italian compared to the Fennoscandian populations, but also varied widely within both regions. Estimates of seed dormancy in the three maternal environments were positively correlated. Among Fennoscandian populations, seed dormancy tended to increase with increasing summer temperature and decreasing precipitation at the site of population origin. In the smaller sample of Italian populations, no significant association was detected between mean seed dormancy and climate at the site of origin. The correlation between population mean seed dormancy and flowering time was weak and not statistically significant within regions.

The correlation between seed dormancy and climatic factors in Fennoscandia suggests that at least some of the among‐population variation is adaptive and that climate change will affect selection on this trait. The weak correlation between population mean seed dormancy and flowering time indicates that the two traits can evolve independently.