Long-Term Alleviation of the Functional Phenotype in Chlorophyll-Deficient Wheat and Impact on Productivity: A Semi-Field Phenotyping Experiment

Coding and non-coding transcripts modulated by transparent and blue PET micro-nanoplastics in Arabidopsis thaliana

To get further insights on the micro-nanoplastic (MNP) effects on plants, the aim of this study was to evaluate the response of hydroponically cultivated Arabidopsis thaliana to the presence of differentially colored polyethylene terephthalate (PET) particles. MNP impacts on the root organ were studied at a molecular level, with a special focus on the role of long non-coding RNAs (lncRNAS) in the regulation of gene expression after PET exposure. MNPs of transparent (Tr-PET) and blue (Bl-PET) material at environmentally realistic concentration caused a significant reduction in root length, while only Bl-PET significantly reduced rosette area. MNPs induced oxidative stress markers. Tr-PET upregulated genes involved in signaling of xenobiotics, whereas Bl-PET scarcely affected root transcriptomic profile, activating few gene categories for abiotic stresses. Regarding hormones, genes involved in ABA response were repressed, while brassinosteroid-related genes were differentially regulated by Tr-PET. Both MNPs, but especially Tr-PET, upregulated major latex protein-related genes. Plant molecular response to MNPs was linked to differential abundance of lncRNAs on both comparisons. Tr-PET affected the expression of much more lncRNAs than bl-PET (80 and 11 respectively). These lncRNAs were predicted to interact with several repressed protein-coding genes (i.e. glucosyltransferase UGT2, oxidative stress genes etc.), with possible effects on their regulation. A lncRNA (AT1G09297) interacted with CYP81D8, a key gene of cytochrome P450 gene family involved in xenobiotics detoxification. Two lncRNAs interacted with two members of repressed HSP (HSP90 and HSP17.4) family. Finally, genes involved in redox detoxification and stress responses were inhibited by the interaction with two microplastics-regulated lncRNAs. These data highlighted the need of investigating non-coding RNAs in the future in addition to the mostly studied protein coding transcriptome.

Thylakoid ultrastructural variations in chlorophyll-deficient wheat: aberrations or structural acclimation?

MAIN CONCLUSION

A structural re-modeling of the thylakoid system, including granum size and regularity, occurs in chlorophyll-deficient wheat mutants affected by photosynthetic membrane over-reduction. In the chloroplast of land plants, the thylakoid system is defined by appressed grana stacks and unstacked stroma lamellae. This study focuses on the variations of the grana organization occurring in outdoor-grown wheat mutants characterized by low chlorophyll content and a tendency for photosynthetic membrane over-reduction. Triticum aestivum ANK-32A and Triticum durum ANDW-7B were compared to their corresponding WT lines, NS67 and LD222, respectively. Electron micrographs of chloroplasts were used to calculate grana ultrastructural parameters. Photosynthetic parameters were obtained by modulated chlorophyll fluorescence and applying Light Curves (LC) and Rapid Light Curves (RLC) protocols. For each photosynthetic parameter, the difference Δ(RLC-LC) was calculated to evaluate the flexible response to light in the examined lines. In the mutants, fewer and smaller disks formed grana stacks characterized by a marked increase in lateral and cross-sectional irregularity, both negatively correlated with the number of layers per granum. A relationship was found between membrane over-reduction and granum structural irregularity. The possible acclimative significance of a greater proportion of stroma-exposed grana domains in relieving the excess electron pressure on PSI is discussed.

Growth, physiological parameters and DNA methylation in Spirodela polyrhiza (L.) Schleid exposed to PET micro-nanoplastic contaminated waters

The effects of polyethylene terephthalate micro-nanoplastics (PET-MNPs) were tested on the model freshwater species Spirodela polyrhiza (L.) Schleid., with focus on possible particle-induced epigenetic effects (i.e. alteration of DNA methylation status). MNPs (size ∼ 200-300 nm) were produced as water dispersions from PET bottles through repeated cycles of homogenization and used to prepare N-medium at two environmentally relevant concentrations (∼0.05 g L-1 and ∼0.1 g L-1 of MNPs). After 10 days of exposure, a reduction in fresh and dry weight was observed in treated plants, even if the average specific growth rate for both frond number and area was not altered. Impaired growth was coupled with a MNP-induced decrease of chlorophyll fluorescence parameters (i.e. ΨETo and Piabs, indicators of photochemical efficiency) and starch concentration, as well as with alterations in plant ionomic profile and oxidative status. The methylation-sensitive amplification polymorphism (MSAP) technique was used to assess possible changes in DNA methylation levels induced by plastic particles. The analysis showed unusual hypermethylation in 5'-CCGG sites that could be implicated in DNA protection from dangerous agents (i.e. reactive oxygen species) or in the formation of new epialleles. This work represents the first evidence of MNP-induced epigenetic modifications in the plant world.

Photosynthesis under Environmental Fluctuations: A Challenge for Plants, a Challenge for Researchers

The ability of plants to cope successfully with environmental fluctuations is a result of their evolution in subaerial environments, where fluctuations in parameters such as temperature, light, and water availability, are the norm and stable states are the exception [...].