44 research outputs found
Seed Dormancy: The Complex Process Regulated by Abscisic Acid, Gibberellins, and Other Phytohormones that Makes Seed Germination Work
Seed dormancy is one of the most important adaptive mechanisms in plants, which protects seeds from precocious germination in the presence of the inappropriate conditions for growth continuation. Numerous environmental and molecular signals regulate seed dormancy. Maintenance or release of seed dormancy is dependent on light, temperature, and water availability. Precise response of seeds to environmental factors is mediated by different phytohormonal pathways. ABA is considered as a main phytohormone regulating seed dormancy induction and maintenance. ABA‐ and GA‐responsive components, ensure crosstalk between the GA and ABA pathways and enable seed response adequate to the environment. Phytohormonal regulation mechanism of seed dormancy is similar in dicot and monocot plants. Recently, it is suggested that other phytohormones, such as auxin, jasmonates, brassinosteroids, and ethylene, also take part in seed dormancy regulation. Auxin regulators, enhance ABA action and positively influence seed dormancy. However, jasmonates, brassinosteroids, and ethylene reduce seed dormancy level. Here, we describe recent advances in understanding the complex process of seed dormancy regulated by many phytohormonal pathways and their components. Seed dormancy studies can help obtain crop varieties producing seeds with the most desirable timing of germination
The role and regulation of ABI5 (ABA-Insensitive 5) in plant development, abiotic stress responses and phytohormone crosstalk
ABA Insensitive 5 (ABI5) is a basic leucine zipper transcription factor that plays a key role in the regulation of seed germination and early seedling growth in the presence of ABA and abiotic stresses. ABI5 functions in the core ABA signaling, which is composed of PYR/PYL/RCAR receptors, PP2C phosphatases and SnRK2 kinases, through the regulation of the expression of genes that contain the ABSCISIC ACID RESPONSE ELEMENT (ABRE) motif within their promoter region. The regulated targets include stress adaptation genes, e.g., LEA proteins. However, the expression and activation of ABI5 is not only dependent on the core ABA signaling. Many transcription factors such as ABI3, ABI4, MYB7 and WRKYs play either a positive or a negative role in the regulation of ABI5 expression. Additionally, the stability and activity of ABI5 are also regulated by other proteins through post-translational modifications such as phosphorylation, ubiquitination, sumoylation and S-nitrosylation. Moreover, ABI5 also acts as an ABA and other phytohormone signaling integrator. Components of auxin, cytokinin, gibberellic acid, jasmonate and brassinosteroid signaling and metabolism pathways were shown to take part in ABI5 regulation and/or to be regulated by ABI5. Monocot orthologs of AtABI5 have been identified. Although their roles in the molecular and physiological adaptations during abiotic stress have been elucidated, knowledge about their detailed action still remains elusive. Here, we describe the recent advances in understanding the action of ABI5 in early developmental processes and the adaptation of plants to unfavorable environmental conditions. We also focus on ABI5 relation to other phytohormones in the abiotic stress response of plants
Updates on the Role of ABSCISIC ACID INSENSITIVE 5 (ABI5) and ABSCISIC ACID-RESPONSIVE ELEMENT BINDING FACTORs (ABFs) in ABA Signaling in Different Developmental Stages in Plants
The core abscisic acid (ABA) signaling pathway consists of receptors, phosphatases, kinases
and transcription factors, among them ABA INSENSITIVE 5 (ABI5) and ABRE BINDING
FACTORs/ABRE-BINDING PROTEINs (ABFs/AREBs), which belong to the BASIC LEUCINE ZIPPER
(bZIP) family and control expression of stress-responsive genes. ABI5 is mostly active in seeds
and prevents germination and post-germinative growth under unfavorable conditions. The activity
of ABI5 is controlled at transcriptional and protein levels, depending on numerous regulators, including
components of other phytohormonal pathways. ABFs/AREBs act redundantly in regulating
genes that control physiological processes in response to stress during vegetative growth. In this
review, we focus on recent reports regarding ABI5 and ABFs/AREBs functions during abiotic stress
responses, which seem to be partially overlapping and not restricted to one developmental stage in
Arabidopsis and other species. Moreover, we point out that ABI5 and ABFs/AREBs play a crucial
role in the core ABA pathway’s feedback regulation. In this review, we also discuss increased stress
tolerance of transgenic plants overexpressing genes encoding ABA-dependent bZIPs. Taken together,
we show that ABI5 and ABFs/AREBs are crucial ABA-dependent transcription factors regulating
processes essential for plant adaptation to stress at different developmental stages
Barley ABI5 (Abscisic Acid INSENSITIVE 5) Is Involved in Abscisic Acid-Dependent Drought Response
ABA INSENSITIVE 5 (ABI5) is a basic leucine zipper (bZIP) transcription factor which acts
in the abscisic acid (ABA) network and is activated in response to abiotic stresses.
However, the precise role of barley (Hordeum vulgare) ABI5 in ABA signaling and its
function under stress remains elusive. Here, we show that HvABI5 is involved in ABAdependent
regulation of barley response to drought stress. We identified barley TILLING
mutants carrying different alleles in the HvABI5 gene and we studied in detail the
physiological and molecular response to drought and ABA for one of them. The
hvabi5.d mutant, carrying G1751A transition, was insensitive to ABA during seed
germination, yet it showed the ability to store more water than its parent cv.
“Sebastian” (WT) in response to drought stress. The drought-tolerant phenotype of
hvabi5.d was associated with better membrane protection, higher flavonoid content,
and faster stomatal closure in the mutant under stress compared to the WT. The
microarray transcriptome analysis revealed up-regulation of genes associated with cell
protection mechanisms in the mutant. Furthermore, HvABI5 target genes: HVA1 and
HVA22 showed higher activity after drought, which may imply better adaptation of
hvabi5.d to stress. On the other hand, chlorophyll content in hvabi5.d was lower than
in WT, which was associated with decreased photosynthesis efficiency observed in the
mutant after drought treatment. To verify that HvABI5 acts in the ABA-dependent manner
we analyzed expression of selected genes related to ABA pathway in hvabi5.d and its WT
parent after drought and ABA treatments. The expression of key genes involved in ABA
metabolism and signaling differed in the mutant and the WT under stress. Droughtinduced
increase of expression of HvNCED1, HvBG8, HvSnRK2.1, and HvPP2C4 genes
was 2–20 times higher in hvabi5.d compared to “Sebastian”. We also observed a faster
stomatal closure in hvabi5.d and much higher induction of HvNCED1 and HvSnRK2.1
genes after ABA treatment. Together, these findings demonstrate that HvABI5 plays a role
in regulation of drought response in barley and suggest that HvABI5 might be engaged in
the fine tuning of ABA signaling by a feedback regulation between biosynthetic and
signaling events. In addition, they point to different mechanisms of HvABI5 action in
regulating drought response and seed germination in barley
Methyl Jasmonate Affects Photosynthesis Efficiency, Expression of HvTIP Genes and Nitrogen Homeostasis in Barley
Jasmonates modulate many growth and developmental processes and act as stress hormones
that play an important role in plant tolerance to biotic and abiotic stresses. Therefore, there is a
need to identify the genes that are regulated through the jasmonate signalling pathway. Aquaporins,
and among them the Tonoplast Intrinsic Proteins (TIPs), form the channels in cell membranes that
are responsible for the precise regulation of the movement of water and other substrates between
cell compartments. We identified the cis-regulatory motifs for the methyl jasmonate (MeJA)-induced
genes in the promoter regions of all the HvTIP genes, which are active in barley seedlings, and thus we
hypothesised that the HvTIP expression could be a response to jasmonate signalling. In the presented
study, we determined the e ect of methyl jasmonate on the growth parameters and photosynthesis
e ciency of barley seedlings that had been exposed to di erent doses of MeJA (15–1000 M 120 h)
in a hydroponic solution. All of the applied MeJA concentrations caused a significant reduction of
barley seedling growth, which was most evident in the length of the first leaf sheath and dry leaf
weight. The observed decrease of the PSII parameters after the exposure to high doses of MeJA
(500 M or higher) was associated with the downregulation of HvPsbR gene encoding one of the
extrinsic proteins of the Oxygen Evolving Complex. The reduced expression of HvPsbR might lead
to the impairment of the OEC action, manifested by the occurrence of the K-band in an analysis of
fluorescence kinetics after MeJA treatment as well as reduced photosynthesis e ciency. Furthermore,
methyl jasmonate treatment caused a decrease in the nitrogen content in barley leaves, which was
associated with an increased expression the four tonoplast aquaporin genes (HvTIP1;2, HvTIP2;2,
HvTIP4;1 and HvTIP4;2) predicted to transport the nitrogen compounds from the vacuole to the
cytosol. The upregulation of the nitrogen-transporting HvTIPs might suggest their involvement in
the vacuolar unloading of ammonia and urea, which both could be remobilised when the nitrogen
content in the leaves decreases. Our research provides tips on physiological role of the individual TIP
subfamily members of aquaporins under methyl jasmonate action
Transcriptome analysis reveals the role of the root hairs as environmental sensors to maintain plant functions under water-deficiency conditions
An important part of the root system is the root hairs, which play a role in mineral and water uptake. Here, we present an analysis of the transcriptomic response to water deficiency of the wild-Type (WT) barley cultivar 'Karat' and its root-hairless mutant rhl1.a. A comparison of the transcriptional changes induced by water stress resulted in the identification of genes whose expression was specifically affected in each genotype. At the onset of water stress, more genes were modulated by water shortage in the roots of the WT plants than in the roots of rhl1.a. The roots of the WT plants, but not of rhl1.a, specifically responded with the induction of genes that are related to the abscisic acid biosynthesis, stomatal closure, and cell wall biogenesis, thus indicating the specific activation of processes that are related to water-stress signalling and protection. On the other hand, the processes involved in the further response to abiotic stimuli, including hydrogen peroxide, heat, and high light intensity, were specifically up-regulated in the leaves of rhl1.a. An extended period of severe stress caused more drastic transcriptome changes in the roots and leaves of the rhl1.a mutant than in those of the WT. These results are in agreement with the much stronger damage to photosystem II in the rhl1.a mutant than in its parent cultivar after 10 d of water stress. Taking into account the putative stress sensing and signalling features of the root hair transcriptome, we discuss the role of root hairs as sensors of environmental conditions
Arabidopsis suppressor mutant of abh1 shows a new face of the already known players : ABH1 (CBP80) and ABI4-in response to ABA and abiotic stresses during seed germination
Although the importance of abscisic acid (ABA) in plant development and response to abiotic and biotic stresses is well recognized, the molecular basis of the signaling pathway has not been fully elucidated. Mutants in genes related to ABA are widely used as a tool for gaining insight into the mechanisms of ABA signal transduction and ABA-dependent stress response. We used a genetic approach of a suppressor screening in order to decipher the interaction between ABH1 (CBP80) and other components of ABA signaling. ABH1 (CBP80) encodes a large subunit of CBC (CAP BINDING COMPLEX) and the abh1 mutant is drought-tolerant and hypersensitive to ABA during seed germination. The suppressor mutants of abh1 were generated after chemical mutagenesis. The mutant named soa1 (suppressor of abh1 hypersensitivity to ABA 1) displayed an ABA-insensitive phenotype during seed germination. The genetic analysis showed that the soa1 phenotype is dominant in relation to abh1 and segregates as a single locus. Based on soa1's response to a wide spectrum of physiological assays during different stages of development, we used the candidate-genes approach in order to identify a suppressor gene. The molecular analysis revealed that mutation causing the phenotype of soa1 occurred in the ABI4 (ABA insensitive 4) gene. Analysis of pre-miR159 expression, whose processing depends on CBC, as well as targets of miR159: MYB33 and MYB101, which are positive regulators of ABA signaling, revealed a possible link between CBP80 (ABH1) and ABI4 presented here
Identification of the Genetic Basis of Response to de-Acclimation in Winter Barley
Mechanisms involved in the de-acclimation of herbaceous plants caused by warm periods
during winter are poorly understood. This study identifies the genes associated with this mechanism
in winter barley. Seedlings of eight accessions (four tolerant and four susceptible to de-acclimation
cultivars and advanced breeding lines) were cold acclimated for three weeks and de-acclimated
at 12 C/5 C (day/night) for one week. We performed differential expression analysis using
RNA sequencing. In addition, reverse-transcription quantitative real-time PCR and enzyme activity
analyses were used to investigate changes in the expression of selected genes. The number of
transcripts with accumulation level changed in opposite directions during acclimation and deacclimation
was much lower than the number of transcripts with level changed exclusively during
one of these processes. The de-acclimation-susceptible accessions showed changes in the expression
of a higher number of functionally diverse genes during de-acclimation. Transcripts associated
with stress response, especially oxidoreductases, were the most abundant in this group. The results
provide novel evidence for the distinct molecular regulation of cold acclimation and de-acclimation.
Upregulation of genes controlling developmental changes, typical for spring de-acclimation, was
not observed during mid-winter de-acclimation. Mid-winter de-acclimation seems to be perceived
as an opportunity to regenerate after stress. Unfortunately, it is competitive to remain in the coldacclimated
state. This study shows that the response to mid-winter de-acclimation is far more
expansive in de-acclimation-susceptible cultivars, suggesting that a reduced response to the rising
temperature is crucial for de-acclimation tolerance