Plasticity of rosette size in response to nitrogen availability is controlled by an RCC1-family protein.

Nitrogen (N) is fundamental to plant growth, development and yield. Genes underlying N utilization and assimilation are well-characterized, but mechanisms underpinning plasticity of different phenotypes in response to N remain elusive. Here, using Arabidopsis thaliana accessions, we dissected the genetic architecture of plasticity in early and late rosette diameter, flowering time and yield, in response to three levels of N in the soil. Furthermore, we found that the plasticity in levels of primary metabolites were related with the plasticities of the studied traits. Genome-wide association analysis identified three significant associations for phenotypic plasticity, one for early rosette diameter and two for flowering time. We confirmed that the gene At1g19880, hereafter named as PLASTICITY OF ROSETTE TO NITROGEN 1 (PROTON1), encoding for a regulator of chromatin condensation 1 (RCC1) family protein, conferred plasticity of rosette diameter in response to N. Treatment of PROTON1 T-DNA line with salt implied that the reduced plasticity of early rosette diameter was not a general growth response to stress. We further showed that plasticities of growth and flowering-related traits differed between environmental cues, indicating decoupled genetic programs regulating these traits. Our findings provide a prospective to identify genes that stabilize performance under fluctuating environments.

Complexity of responses to ionizing radiation in plants, and the impact on interacting biotic factors.

In nature, plants are simultaneously exposed to different abiotic (e.g., heat, drought, and salinity) and biotic (e.g., bacteria, fungi, and insects) stresses. Climate change and anthropogenic pressure are expected to intensify the frequency of stress factors. Although plants are well equipped with unique and common defense systems protecting against stressors, they may compromise their growth and development for survival in such challenging environments. Ionizing radiation is a peculiar stress factor capable of causing clustered damage. Radionuclides are both naturally present on the planet and produced by human activities. Natural and artificial radioactivity affects plants on molecular, biochemical, cellular, physiological, populational, and transgenerational levels. Moreover, the fitness of pests, pathogens, and symbionts is concomitantly challenged in radiologically contaminated areas. Plant responses to artificial acute ionizing radiation exposure and laboratory-simulated or field chronic exposure are often discordant. Acute or chronic ionizing radiation exposure may occasionally prime the defense system of plants to better tolerate the biotic stress or could often exhaust their metabolic reserves, making plants more susceptible to pests and pathogens. Currently, these alternatives are only marginally explored. Our review summarizes the available literature on the responses of host plants, biotic factors, and their interaction to ionizing radiation exposure. Such systematic analysis contributes to improved risk assessment in radiologically contaminated areas.

Involvement of microRNA-related regulatory pathways in the glucose-mediated control of Arabidopsis early seedling development.

In plants, sugars such as glucose act as signalling molecules that promote changes in gene expression programmes that impact on growth and development. Recent evidence has revealed the potential importance of controlling mRNA decay in some aspects of glucose-mediated regulatory responses suggesting a role of microRNAs (miRNAs) in these responses. In order to get a better understanding of glucose-mediated development modulation involving miRNA-related regulatory pathways, early seedling development of mutants impaired in miRNA biogenesis (hyl1-2 and dcl1-11) and miRNA activity (ago1-25) was evaluated. All mutants exhibited a glucose hyposensitive phenotype from germination up to seedling establishment, indicating that miRNA regulatory pathways are involved in the glucose-mediated delay of early seedling development. The expression profile of 200 miRNA primary transcripts (pri-miRs) was evaluated by large-scale quantitative real-time PCR profiling, which revealed that 38 pri-miRs were regulated by glucose. For several of them, the corresponding mature miRNAs are known to participate directly or indirectly in plant development, and their accumulation was shown to be co-regulated with the pri-miR by glucose. Furthermore, the expression of several miRNA target genes was found to be deregulated in response to glucose in the miRNA machinery mutants ago1-25, dcl1-11, and hyl1-2. Also, in these mutants, glucose promoted misexpression of genes for the three abscisic acid signalling elements ABI3, ABI4, and ABI5. Thus, miRNA regulatory pathways play a role in the adjustments of growth and development triggered by glucose signalling.

Chronic Ionizing Radiation of Plants: An Evolutionary Factor from Direct Damage to Non-Target Effects.

In present times, the levels of ionizing radiation (IR) on the surface of Earth are relatively low, posing no high challenges for the survival of contemporary life forms. IR derives from natural sources and naturally occurring radioactive materials (NORM), the nuclear industry, medical applications, and as a result of radiation disasters or nuclear tests. In the current review, we discuss modern sources of radioactivity, its direct and indirect effects on different plant species, and the scope of the radiation protection of plants. We present an overview of the molecular mechanisms of radiation responses in plants, which leads to a tempting conjecture of the evolutionary role of IR as a limiting factor for land colonization and plant diversification rates. The hypothesis-driven analysis of available plant genomic data suggests an overall DNA repair gene families' depletion in land plants compared to ancestral groups, which overlaps with a decrease in levels of radiation exposure on the surface of Earth millions of years ago. The potential contribution of chronic IR as an evolutionary factor in combination with other environmental factors is discussed.

Are Arabidopsis thaliana plants able to recover from exposure to gamma radiation? A molecular perspective.

Most plant research focuses on the responses immediately after exposure to ionizing irradiation (IR). However, it is as important to investigate how plants recover after exposure since this has a profound effect on future plant growth and development and hence on the long-term consequences of exposure to stress. This study aimed to investigate the IR-induced responses after exposure and during recovery by exposing 1-week old A. thaliana seedlings to gamma dose rates ranging from 27 to 103.7 mGy/h for 2 weeks and allowing them to recover for 4 days. A high-throughput RNAsequencing analysis was carried out. An enrichment of GO terms related to the metabolism of hormones was observed both after irradiation and during recovery at all dose rates. While plants exposed to the lowest dose rate activate defence responses after irradiation, they recover from the IR by resuming normal growth during the recovery period. Plants exposed to the intermediate dose rate invest in signalling and defence after irradiation. During recovery, in the plants exposed to the highest dose rate, fundamental metabolic processes such as photosynthesis and RNA modification were still affected. This might lead to detrimental effects in the long-term or in the next generations of those irradiated plants.

Multi-Omics Analysis of Vicia cracca Responses to Chronic Radiation Exposure in the Chernobyl Exclusion Zone.

Our understanding of the long-term consequences of chronic ionising radiation for living organisms remains scarce. Modern molecular biology techniques are helpful tools for researching pollutant effects on biota. To reveal the molecular phenotype of plants growing under chronic radiation exposure, we sampled Vicia cracca L. plants in the Chernobyl exclusion zone and areas with normal radiation backgrounds. We performed a detailed analysis of soil and gene expression patterns and conducted coordinated multi-omics analyses of plant samples, including transcriptomics, proteomics, and metabolomics. Plants growing under chronic radiation exposure showed complex and multidirectional biological effects, including significant alterations in the metabolism and gene expression patterns of irradiated plants. We revealed profound changes in carbon metabolism, nitrogen reallocation, and photosynthesis. These plants showed signs of DNA damage, redox imbalance, and stress responses. The upregulation of histones, chaperones, peroxidases, and secondary metabolism was noted.

The Arabidopsis bZIP gene AtbZIP63 is a sensitive integrator of transient abscisic acid and glucose signals.

Glucose modulates plant metabolism, growth, and development. In Arabidopsis (Arabidopsis thaliana), Hexokinase1 (HXK1) is a glucose sensor that may trigger abscisic acid (ABA) synthesis and sensitivity to mediate glucose-induced inhibition of seedling development. Here, we show that the intensity of short-term responses to glucose can vary with ABA activity. We report that the transient (2 h/4 h) repression by 2% glucose of AtbZIP63, a gene encoding a basic-leucine zipper (bZIP) transcription factor partially involved in the Snf1-related kinase KIN10-induced responses to energy limitation, is independent of HXK1 and is not mediated by changes in ABA levels. However, high-concentration (6%) glucose-mediated repression appears to be modulated by ABA, since full repression of AtbZIP63 requires a functional ABA biosynthetic pathway. Furthermore, the combination of glucose and ABA was able to trigger a synergistic repression of AtbZIP63 and its homologue AtbZIP3, revealing a shared regulatory feature consisting of the modulation of glucose sensitivity by ABA. The synergistic regulation of AtbZIP63 was not reproduced by an AtbZIP63 promoter-5'-untranslated region::ß-glucuronidase fusion, thus suggesting possible posttranscriptional control. A transcriptional inhibition assay with cordycepin provided further evidence for the regulation of mRNA decay in response to glucose plus ABA. Overall, these results indicate that AtbZIP63 is an important node of the glucose-ABA interaction network. The mechanisms by which AtbZIP63 may participate in the fine-tuning of ABA-mediated abiotic stress responses according to sugar availability (i.e., energy status) are discussed.

Temperature-mediated flower size plasticity in Arabidopsis.

Organisms can rapidly mitigate the effects of environmental changes by changing their phenotypes, known as phenotypic plasticity. Yet, little is known about the temperature-mediated plasticity of traits that are directly linked to plant fitness such as flower size. We discovered substantial genetic variation in flower size plasticity to temperature both among selfing Arabidopsis thaliana and outcrossing A. arenosa individuals collected from a natural growth habitat. Genetic analysis using a panel of 290 A. thaliana accession and mutant lines revealed that MADS AFFECTING FLOWERING (MAF) 2-5 gene cluster, previously shown to regulate temperature-mediated flowering time, was associated to the flower size plasticity to temperature. Furthermore, our findings pointed that the control of plasticity differs from control of the trait itself. Altogether, our study advances the understanding of genetic and molecular factors underlying plasticity on fundamental fitness traits, such as flower size, in response to future climate scenarios.

The mitochondrial control region of blowflies (Diptera: Calliphoridae): a hot spot for mitochondrial genome rearrangements.

The family Calliphoridae consists of myiasis-causing flies, including species of economic, forensic, and medical importance. In this study, the complete control regions (CRs) of mitochondrial DNA from 15 calliphorid species were sequenced and structurally characterized. The CRs had a high content of adenines (A) and thymines (T) and varied in length from 854 to 2,018 bp, showing intraspecific variations in sequence and length. Two major domains were identified: the conserved domain containing conserved sequence blocks and cis-regulatory structures that may be related to the transcription and the origin of replication of mitochondrial DNA, and the variable domain, containing high sequence and length variation. Within the variable domain, duplication of the tRNA(Ile) gene, previously reported for three Chrysomya species, was identified in two more species of this genus and in two species of two other genera. The structural characterization shows the plasticity of the mitochondrial genome in dipterans. The organizational similarities of the duplicated region found in different species and the possible origin of the duplicated genes are discussed.