Summary
Flowering time is a relevant agronomic trait because is crucial for the optimal formation of seeds and fruits. The genetic pathways controlling this developmental phase transition have been ...studied extensively in Arabidopsis thaliana. These pathways converge in a small number of genes including FT, the so‐called florigen, which integrates environmental cues like ambient temperature. Nevertheless, detailed and functional studies about flowering time in Brassica crops are scarce. Here we study the role of the FT Brassica rapa homologues and the effect of high ambient temperature on flowering time in this crop. Phenotypic characterization and gene‐expression analyses suggest that BraA.FT.a (BraA02g016700.3C) is decisive for initiating floral transition; consequently, braA.ft.a loss‐of‐function and hypomorphic mutations result in late flowering phenotypes. We also show that high ambient temperature delays B. rapa floral transition by reducing BraA.FT.a expression. Strikingly, these expression changes are associated with increased histone H2A.Z levels and less accessible chromatin configuration of the BraA.FT.a locus at high ambient temperature. Interestingly, increased H2A.Z levels at high ambient temperature were also observed for other B. rapa temperature‐responsive genes. Previous reports delimited that Arabidopsis flowers earlier at high ambient temperature due to reduced H2A.Z incorporation in the FT locus. Our data reveal a conserved chromatin‐mediated mechanism in B. rapa and Arabidopsis in which the incorporation of H2A.Z at FT chromatin in response to warm ambient temperature results in different flowering time responses. This work will help to develop improved Brassica crop varieties with flowering time requirements to cope with global warming.
Open Research Badges
This article has earned an Open Materials Badge for making publicly available the components of the research methodology needed to reproduce the reported procedure and analysis. Methods are available at protocols.iodx.doi.org/10.17504/protocols.io.zmff43n.
Significance Statement
Flowering time is a key agronomic trait that responds to moderate changes in ambient temperature. We found that high ambient temperature modulates Brassica rapa flowering time, altering the chromatin composition of BraA.FT.a locus differently from its orthologue Arabidopsis thaliana FT locus. Although in both species a role for H2A.Z is conserved in response to warmth, we uncovered unexpected H2A.Z‐nucloseome differences in behaviour between these model and crop Brassica species.
Knowledge concerning the integration of genetic pathways mediating the responses to environmental cues controlling flowering initiation in crops is scarce. Here, we reveal the diversity in oilseed ...rape (OSR) flowering response to high ambient temperature. Using a set of different spring OSR varieties, we found a consistent flowering delay at elevated temperatures. Remarkably, one of the varieties assayed exhibited the opposite behaviour. Several FT‐like paralogs are plausible candidates to be part of the florigen in OSR. We revealed that BnaFTA2 plays a major role in temperature‐dependent flowering initiation. Analysis of the H2A.Z histone variant occupancy at this locus in different Brassica napus varieties produced contrasting results, suggesting the involvement of additional molecular mechanisms in BnaFTA2 repression at high ambient temperature. Moreover, BnARP6 RNAi plants showed little accumulation of H2A.Z at high temperature while maintaining temperature sensitivity and delayed flowering. Furthermore, we found that H3K4me3 present in BnaFTA2 under inductive flowering conditions is reduced at high temperature, suggesting a role for this hallmark of transcriptionally active chromatin in the OSR flowering response to warming. Our work emphasises the plasticity of flowering responses in B. napus and offers venues to optimise this process in crop species grown under suboptimal environmental conditions.
Summary statement
Ambient temperature is critical to set the timing for flowering and farming practices. We have uncovered variability in flowering time in spring varieties of oilseed rape (OSR) under high ambient temperature and determined their transcriptomic profiles. We concluded that warm temperature delays flowering in these varieties by decreasing the expression of FT homologues, being BnaFTA2 a key candidate in temperature‐dependent flowering control. Both H2A.Z‐dependent and independent mechanisms control OSR flowering time under high ambient temperatures.
Root knot nematodes (RKNs) penetrate into the root vascular cylinder, triggering morphogenetic changes to induce galls, de novo formed ‘pseudo-organs’ containing several giant cells (GCs). ...Distinctive gene repression events observed in early gall/GCs development are thought to be mediated by post-transcriptional silencing via microRNAs (miRNAs), a process that is far from being fully characterized.
Arabidopsis thaliana backgrounds with altered activities based on target 35S:: MIMICRY172 (MIM172), 35S::TARGET OF EARLY ACTIVATION TAGGED 1 (TOE1)-miR172-resistant (35S::TOE1
R) and mutant (flowering locus T-10 (ft-10)) lines were used for functional analysis of nematode infective and reproductive parameters. The GUS-reporter lines, MIR172A–E::GUS, treated with auxin (IAA) and an auxin-inhibitor (a-(phenyl ethyl-2-one)-indole-3-acetic acid (PEO-IAA)), together with the MIR172C AuxRE::GUS line with two
mutated auxin responsive elements (AuxREs), were assayed for nematode-dependent gene expression.
Arabidopsis thaliana backgrounds with altered expression of miRNA172, TOE1 or FT showed lower susceptibility to the RKNs and smaller galls and GCs. MIR172C–D::GUS showed restricted promoter activity in galls/GCs that was regulated by auxins through auxin-responsive factors. IAA induced their activity in galls while PEO-IAA treatment and mutations in AuxRe motifs abolished it.
The results showed that the regulatory module miRNA172/TOE1/FT plays an important role in correct GCs and gall development, where miRNA172 is modulated by auxins.
Arabidopsis ESD7 locus encodes the catalytic subunit of the DNA Pol ϵ involved in the synthesis of the DNA leading strand and is essential for embryo viability. The hypomorphic allele esd7-1 is ...viable but displays a number of pleiotropic phenotypic alterations including an acceleration of flowering time. Furthermore, Pol ϵ is involved in the epigenetic silencing of the floral integrator genes FT and SOC1, but the molecular nature of the transcriptional gene silencing mechanisms involved remains elusive. Here we reveal that ESD7 interacts with components of the PRC2 such as CLF, EMF2 and MSI1, and that mutations in ESD7 cause a decrease in the levels of the H3K27me3 mark present in the chromatin of FT and SOC1 We also demonstrate that a domain of the C-terminal region of ESD7 mediates the binding to the different PRC2 components and this interaction is necessary for the proper recruitment of PRC2 to FT and SOC1 chromatin. We unveil the existence of interplay between the DNA replication machinery and the PcG complexes in epigenetic transcriptional silencing. These observations provide an insight into the mechanisms ensuring that the epigenetic code at pivotal loci in developmental control is faithfully transmitted to the progeny of eukaryotic cells.
A combination of cost effective sublethal
Daphnia magna feeding tests, yeast- and cell culture-based bioassays and Toxicity Identification Evaluation (TIE) procedures was used to characterize toxic ...compounds within sediments collected in a river area under the influence of the effluents from a chlor-alkali industry (Ebro River, NE Spain). Tests were designed to measure and identify toxic compounds in the particulate and filtered water fractions of sediment elutriates. The combined use of bioassays responding to elutriates and dioxin-like compounds evidenced the existence of three major groups of hazardous contaminants in the most contaminated site: (A) metals such as cadmium and mercury bound to sediment fine particles that could be easily resuspended and moved downstream, (B) soluble compounds (presumably, lye) able to alkalinize water to toxic levels, and (C) organochlorine compounds with high dioxin-like activity. These results provided evidence that elutriate
D. magna feeding responses can be used as surrogate assays for more tedious chronic whole sediment tests, and that the incorporation of such tests in sediment TIE procedures may improve the ability to identify the toxicity of particle-bound and water-soluble contaminants in sediments.
Summary
Pollen development is a crucial step in higher plants, which not only makes possible plant fertilization and seed formation, but also determines fruit quality and yield in crop species. Here, ...we reported a tomato T‐DNA mutant, pollen deficient1 (pod1), characterized by an abnormal anther development and the lack of viable pollen formation, which led to the production of parthenocarpic fruits. Genomic analyses and the characterization of silencing lines proved that pod1 mutant phenotype relies on the tomato SlMED18 gene encoding the subunit 18 of Mediator multi‐protein complex involved in RNA polymerase II transcription machinery. The loss of SlMED18 function delayed tapetum degeneration, which resulted in deficient microspore development and scarce production of viable pollen. A detailed histological characterization of anther development proved that changes during microgametogenesis and a significant delay in tapetum degeneration are associated with a high proportion of degenerated cells and, hence, should be responsible for the low production of functional pollen grains. Expression of pollen marker genes indicated that SlMED18 is essential for the proper transcription of a subset of genes specifically required to pollen formation and fruit development, revealing a key role of SlMED18 in male gametogenesis of tomato. Additionally, SlMED18 is able to rescue developmental abnormalities of the Arabidopsis med18 mutant, indicating that most biological functions have been conserved in both species.
Significance Statement
Pollination is a key development process in the life cycle of flowering plants. Genetic and molecular characterization of a tomato mutant have led to the identification of POD1 gene encoding the Mediator complex subunit MED18 whose function is required for tapetum tissue degeneration, a crucial step for pollen development. Furthermore, we show that MED18 fulfils an essential role in tomato, ensuring proper gene regulation during pollen ontogeny.
One of the greatest threats to wild strawberries (
Fragaria vesca
Mara des Bois) after harvest is the highly perishability at ambient temperature. Breeders have successfully met the quality demands ...of consumers, but the prevention of waste after harvest in fleshy fruits is still pending. Most of the waste is due to the accelerated progress of senescence-like process after harvest linked to a rapid loss of water and firmness at ambient temperature. The storage life of strawberries increases at low temperature, but their quality is limited by the loss of cell structure. The application of high CO
2
concentrations increased firmness during cold storage. However, the key genes related to resistance to softening and cell wall disassembly following transference from cold storage at 20°C remain unclear. Therefore, we performed RNA-seq analysis, constructing a weighted gene co-expression network analysis (WGCNA) to identify which molecular determinants play a role in cell wall integrity, using strawberries with contrasting storage conditions, CO
2
-cold stored (CCS), air-cold stored (ACS), non-cold stored (NCS) kept at ambient temperature, and intact fruit at harvest (AH). The hub genes associated with the cell wall structural architecture of firmer CO
2
-treated strawberries revealed xyloglucans stabilization attributed mainly to a down-regulation of
Csl E1
,
XTH 15
,
Exp-like B1
and the maintenance of expression levels of nucleotide sugars transferases such as
GMP
and
FUT
as well as improved lamella integrity linked to a down-regulation of
RG-lyase
,
PL-like
and
PME
. The preservation of cell wall elasticity together with the up-regulation of
LEA
,
EXPA4
, and
MATE
, required to maintain cell turgor, is the mechanisms controlled by high CO
2
. In stressed air-cold stored strawberries, in addition to an acute softening, there is a preferential transcript accumulation of genes involved in lignin and raffinose pathways. Non-cold stored strawberries kept at 20°C after harvest are characterized by an enrichment in genes mainly involved in oxidative stress and up-expression of genes involved in jasmonate biosynthesis. The present results on transcriptomic analysis of CO
2
-treated strawberries with enhanced resistance to softening and oxidative stress at consumption will help to improve breeding strategies of both wild and cultivated strawberries.
Aquatic organisms are often exposed to mixtures of low levels of pollutants whose presence and effects can pass easily unnoticed if only traditional monitoring strategies are employed. The main aim ...of this work was to assess the presence and effects of trace levels of pollutants in a scarcely affected area through the combination of chemical and biological approaches. Sediments were collected along a river with little anthropogenic pressure and assayed for cytochrome P450 (Cyp1a)-dependent ethoxyresorufin-
O
-deethylase (EROD) activity with the rainbow trout gonadal cell line RTG-2. Chemical analyses were performed in these sediments using two-dimensional gas chromatography-time-of-flight mass spectrometry. Sediment samples induced EROD activity, and chemical analyses evidenced the presence of a wide variety of contaminants in the range of nanograms per gram of dry weight. Correlation analysis between EROD induction and chemical analyses data showed an
r
value of 0.840 (
p
<
0.05). In addition, fish from a fish farm located downstream of the sampling points exhibited high hepatic EROD levels as well as an induced expression of
cyp1a
and
cyp3a
. In conclusion, only an appropriate combination of biological and chemical techniques allowed the detection of the presence of trace levels of contaminants in a theoretically nonaffected river.
Pathogen infections require the production of effectors that enable host colonization. Effectors have diverse functions and are only expressed at certain stages of the infection cycle. Thus, effector ...genes are tightly regulated by several mechanisms, including chromatin remodeling. Here, we investigate the role of histone acetylation in effector gene activation in the fungal wheat pathogen
. We demonstrate that lysine acetyltransferases (KATs) are essential for the spatiotemporal regulation of effector genes. We show that the KAT Sas3 is involved in leaf symptom development and pycnidia formation. Importantly, our results indicate that Sas3 controls histone acetylation of effector loci and is a regulator of effector gene activation during stomatal penetration. Overall, our work demonstrates the key role of histone acetylation in regulating gene expression associated with plant infection.
Summary
Pollen development is a crucial step in higher plants, which not only makes possible plant fertilization and seed formation, but also determines fruit quality and yield in crop species. Here, ...we reported a tomato T‐
DNA
mutant,
pollen deficient1
(
pod1
), characterized by an abnormal anther development and the lack of viable pollen formation, which led to the production of parthenocarpic fruits. Genomic analyses and the characterization of silencing lines proved that
pod1
mutant phenotype relies on the tomato
Sl
MED
18
gene encoding the subunit 18 of Mediator multi‐protein complex involved in
RNA
polymerase
II
transcription machinery. The loss of
Sl
MED
18
function delayed tapetum degeneration, which resulted in deficient microspore development and scarce production of viable pollen. A detailed histological characterization of anther development proved that changes during microgametogenesis and a significant delay in tapetum degeneration are associated with a high proportion of degenerated cells and, hence, should be responsible for the low production of functional pollen grains. Expression of pollen marker genes indicated that
Sl
MED
18
is essential for the proper transcription of a subset of genes specifically required to pollen formation and fruit development, revealing a key role of
Sl
MED
18
in male gametogenesis of tomato. Additionally,
Sl
MED
18
is able to rescue developmental abnormalities of the Arabidopsis
med18
mutant, indicating that most biological functions have been conserved in both species.
Significance Statement
Pollination is a key development process in the life cycle of flowering plants. Genetic and molecular characterization of a tomato mutant have led to the identification of
POD
1
gene encoding the Mediator complex subunit
MED
18 whose function is required for tapetum tissue degeneration, a crucial step for pollen development. Furthermore, we show that
MED
18 fulfils an essential role in tomato, ensuring proper gene regulation during pollen ontogeny.
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