Salinity is one of the major abiotic stresses which impose constraints to plant growth and production. Rice (Oryza sativa L.) is one of the most important staple food crops and a model monocot plant. ...Its production is expanding into regions that are affected by soil salinity, requiring cultivars more tolerant to saline conditions. Understanding the molecular mechanisms of such tolerance could lay a foundation for varietal improvement of salt tolerance in rice. In spite of extensive studies exploring the mechanism of salt tolerance, there has been limited progress in breeding for increased salinity tolerance. In this review, we summarize the information about the major molecular mechanisms underlying salinity tolerance in rice and further discuss the limitations in breeding for salinity tolerance. We show that numerous gene families and interaction networks are involved in the regulation of rice responses to salinity, prompting a need for a comprehensive functional analysis. We also show that most studies are based on whole-plant level analyses with only a few reports focused on tissue- and/or cell-specific gene expression. More details of salt-responsive channel and transporter activities at tissue- and cell-specific level still need to be documented before these traits can be incorporated into elite rice germplasm. Thus, future studies should focus on diversity of available genetic resources and, particular, wild rice relatives, to re-incorporate salinity tolerance traits lost during domestication.
Waterlogging is a serious environmental problem that limits agricultural production in low-lying rainfed areas around the world. The major constraint that plants face in a waterlogging situation is ...the reduced oxygen availability. Accordingly, all previous efforts of plant breeders focused on traits providing adequate supply of oxygen to roots under waterlogging conditions, such as enhanced aerenchyma formation or reduced radial oxygen loss. However, reduced oxygen concentration in waterlogged soils also leads to oxygen deficiency in plant tissues, resulting in an excessive accumulation of reactive oxygen species (ROS) in plants. To the best of our knowledge, this trait has never been targeted in breeding programs and thus represents an untapped resource for improving plant performance in waterlogged soils. To identify the quantitative trait loci (QTL) for ROS tolerance in barley, 187 double haploid (DH) lines from a cross between TX9425 and Naso Nijo were screened for superoxide anion (O₂
) and hydrogen peroxide (H₂O₂)-two major ROS species accumulated under hypoxia stress. We show that quantifying ROS content after 48 h hypoxia could be a fast and reliable approach for the selection of waterlogging tolerant barley genotypes. The same QTL on chromosome 2H was identified for both O₂
(QSO.TxNn.2H) and H₂O₂ (QHP.TxNn.2H) contents. This QTL was located at the same position as the QTL for the overall waterlogging and salt tolerance reported in previous studies, explaining 23% and 24% of the phenotypic variation for O₂
and H₂O
contents, respectively. The analysis showed a causal association between ROS production and both waterlogging and salt stress tolerance. Waterlogging and salinity are two major abiotic factors affecting crop production around the globe and frequently occur together. The markers associated with this QTL could potentially be used in future breeding programs to improve waterlogging and salinity tolerance.
Autophagy-related proteins Atg5 and Atg7 are rate-limiting components of autophagic flux in Arabidopsis. Overexpression of ATG5 or ATG7 genes stimulates Atg8 lipidation, autophagosome formation, and ...autophagic flux, leading to improved plant fitness.
Abstract
Autophagy is a major catabolic process whereby autophagosomes deliver cytoplasmic content to the lytic compartment for recycling. Autophagosome formation requires two ubiquitin-like systems conjugating Atg12 with Atg5, and Atg8 with lipid phosphatidylethanolamine (PE), respectively. Genetic suppression of these systems causes autophagy-deficient phenotypes with reduced fitness and longevity. We show that Atg5 and the E1-like enzyme, Atg7, are rate-limiting components of Atg8-PE conjugation in Arabidopsis. Overexpression of ATG5 or ATG7 stimulates Atg8 lipidation, autophagosome formation, and autophagic flux. It also induces transcriptional changes opposite to those observed in atg5 and atg7 mutants, favoring stress resistance and growth. As a result, ATG5- or ATG7-overexpressing plants exhibit increased resistance to necrotrophic pathogens and oxidative stress, delayed aging and enhanced growth, seed set, and seed oil content. This work provides an experimental paradigm and mechanistic insight into genetic stimulation of autophagy in planta and shows its efficiency for improving plant productivity.
Reactive oxygen species (ROS) production is a common denominator in a variety of biotic and abiotic stresses, including salinity. In recent years, haem oxygenase (HO; EC 1.14.99.3) has been described ...as an important component of the antioxidant defence system in both mammalian and plant systems. Moreover, a recent report on Arabidopsis demonstrated that HO overexpression resulted in an enhanced salinity tolerance in this species. However, physiological mechanisms and downstream targets responsible for the observed salinity tolerance in these HO mutants remain elusive. To address this gap, ion transport characteristics (K+ and H+ fluxes and membrane potentials) and gene expression profiles in the roots of Arabidopsis thaliana HO-overexpressing (35S:HY1-1/2/3/4) and loss-of-function (hy-100, ho2, ho3, and ho4) mutants were compared during salinity stress. Upon acute salt stress, HO-overexpressing mutants retained more K+ (less efflux), and exhibited better membrane potential regulation (maintained more negative potential) and higher H+ efflux activity in root epidermis, compared with loss-of-function mutants. Pharmacological experiments suggested that high activity of the plasma membrane H+-ATPase in HO overexpressor mutants provided the proton-motive force required for membrane potential maintenance and, hence, better K+ retention. The gene expression analysis after 12h and 24h of salt stress revealed high expression levels of H+-ATPases (AHA1/2/3) and Na+/H+ antiporter salt overly sensitive1 (SOS1) transcripts in the plasma membrane of HO overexpressors. It is concluded that HO modifies salinity tolerance in Arabidopsis by controlling K+ retention via regulation of the plasma membrane H+-ATPase and by altering SOS1 transcript levels in roots.
Abstract
Medicinal plants represent a valuable commodity due to beneficial effects of their natural products on human health, prompting a need for finding a way to optimize/increase their production. ...In this study, a novel growing media with various perlite particle size and its mixture with peat moss was tested for hydroponic-based production of
Echinacea purpurea
medicinal plant under greenhouse conditions. The plant growth parameters such as plant height, total fresh leave weight, fresh root weight, total biomass, total chlorophyll, leaf area, and essential oil compositions were assessed. Perlite particle size in the growing media was varied from very coarse (more than 2 mm) to very fine (less than 0.5 mm), and the ratio between perlite and peat moss varied from 50:50 v/v to 30:70 v/v. In addition, two nitrate (NO
3
−
) to ammonium (NH
4
+
) ratios (90:10 and 70:30) were tested for each growing media. The medium containing very fine-grade perlite and 50:50 v/v perlite to peat moss ratio was found to be most optimal and beneficial for
E. purpurea
performance, resulting in maximal plant height, fresh and dry weight, leaf surface area, and chlorophyll content. It was also found that an increase in NO
3
−
/NH
4
+
ratio caused a significant increase in plant growth parameters and increase the plant essential oil content. The major terpene hydrocarbons found in extract of
E. purpurea
with the best growth parameters were germacrene D (51%), myrcene (15%), α-pinene (12%), β-caryophyllene (11%), and 1-Pentadecene (4.4%), respectively. The percentages of these terpene hydrocarbons were increased by increasing of NO
3
−
/NH
4
+
ratio. It can be concluded that decreasing the perlite particle size and increasing the NO
3
−
/NH
4
+
ratio increased the plant growth parameters and essential oil compositions in
E. purpurea
.
The processes of plant nutrition, stress tolerance, plant growth, and development are strongly dependent on transport of mineral nutrients across cellular membranes. Plant membrane transporters are ...key components of these processes. Among various membrane transport proteins, the monovalent cation proton antiporter (CPA) superfamily mediates a broad range of physiological and developmental processes such as ion and pH homeostasis, development of reproductive organs, chloroplast operation, and plant adaptation to drought and salt stresses. CPA family includes plasma membrane-bound Na
/H
exchanger (NhaP) and intracellular Na
/H
exchanger NHE (NHX), K
efflux antiporter (KEA), and cation/H
exchanger (CHX) family proteins. In this review, we have completed the phylogenetic inventory of CPA transporters and undertaken a comprehensive evolutionary analysis of their development. Compared with previous studies, we have significantly extended the range of plant species, including green and red algae and Acrogymnospermae into phylogenetic analysis. Our data suggest that the multiplication and complexation of CPA isoforms during evolution is related to land colonisation by higher plants and associated with an increase of different tissue types and development of reproductive organs. The new data extended the number of clades for all groups of CPAs, including those for NhaP/SOS, NHE/NHX, KEA, and CHX. We also critically evaluate the latest findings on the biological role, physiological functions and regulation of CPA transporters in relation to their structure and phylogenetic position. In addition, the role of CPA members in plant tolerance to various abiotic stresses is summarized, and the future priority directions for CPA studies in plants are discussed.
SUMMARY
Polyamines, such as putrescine, spermidine and spermine (Spm), are low‐molecular‐weight polycationic molecules present in all living organisms. Despite their implication in plant cellular ...processes, little is known about their molecular mode of action. Here, we demonstrate that polyamines trigger a rapid increase in the regulatory membrane lipid phosphatidylinositol 4,5‐bisphosphate (PIP2), and that this increase is required for polyamine effects on K+ efflux in Arabidopsis roots. Using in vivo 32Pi‐labelling of Arabidopsis seedlings, low physiological (μm) concentrations of Spm were found to promote a rapid PIP2 increase in roots that was time‐ and dose‐dependent. Confocal imaging of a genetically encoded PIP2 biosensor revealed that this increase was triggered at the plasma membrane. Differential 32Pi‐labelling suggested that the increase in PIP2 was generated through activation of phosphatidylinositol 4‐phosphate 5‐kinase (PIP5K) activity rather than inhibition of a phospholipase C or PIP2 5‐phosphatase activity. Systematic analysis of transfer DNA insertion mutants identified PIP5K7 and PIP5K9 as the main candidates involved in the Spm‐induced PIP2 response. Using non‐invasive microelectrode ion flux estimation, we discovered that the Spm‐triggered K+ efflux response was strongly reduced in pip5k7 pip5k9 seedlings. Together, our results provide biochemical and genetic evidence for a physiological role of PIP2 in polyamine‐mediated signalling controlling K+ flux in plants.
Significance Statement
Polyamines, such as putrescine, spermidine and spermine, are low‐molecular‐weight polycations present in all living organisms. Despite their involvement in various plant cellular processes, little is known about their molecular mode of action. Here, we demonstrate that polyamines trigger a rapid increase in the signalling lipid PIP2 at the plasma membrane of Arabidopsis roots by activating two lipid kinases, PIP5K7 and PIP5K9, and that this lipid response is required for the K+ efflux that is triggered downstream.
Brassinosteroids (BR) are key hormonal regulators of plant development. However, whereas the individual components of BR perception and signaling are well characterized experimentally, the question ...of how they can act and whether they are sufficient to carry out the critical function of cellular elongation remains open. Here, we combined computational modeling with quantitative cell physiology to understand the dynamics of the plasma membrane (PM)-localized BR response pathway during the initiation of cellular responses in the epidermis of the
Arabidopsis
root tip that are be linked to cell elongation. The model, consisting of ordinary differential equations, comprises the BR-induced hyperpolarization of the PM, the acidification of the apoplast and subsequent cell wall swelling. We demonstrate that the competence of the root epidermal cells for the BR response predominantly depends on the amount and activity of H
+
-ATPases in the PM. The model further predicts that an influx of cations is required to compensate for the shift of positive charges caused by the apoplastic acidification. A potassium channel was subsequently identified and experimentally characterized, fulfilling this function. Thus, we established the landscape of components and parameters for physiological processes potentially linked to cell elongation, a central process in plant development.
► The beneficial effect of salt acclimation is reported for Pisum sativum. ► Acclimation to salinity is related to ion-specific rather than osmotic component of stress. ► Physiological process in ...roots are involved in plant acclimation. ► Regulation of xylem ion loading is essential for acclimation.
Pea (Pisum sativum L.) seedlings were grown in half strength Hoagland solution and exposed to 0, 10, 25mM NaCl and 2.5% PEG 6000 for 1 week (pre-treatment). Thereafter plants were exposed to 0 and 80mM NaCl for 2 weeks (main treatment). The control plants were maintained in half strength Hoagland solution without NaCl. Various physiological parameters were recorded from control, pretreated and non-pretreated plants. There was no negative effect of the pre-treatments on growth (total fresh and dry matter production), and plants pre-treated with 10mM NaCl had biomass accumulation equal to control plants. The beneficial effect of salt acclimation was also evident in the prevention of K+ leakage and Na+ accumulation, primary in roots, suggesting that here the physiological processes play the major role. 2.5% PEG 6000 was not as efficient as salt in enhancing salt tolerance and acclimation appears to be more related to ion-specific rather than osmotic component of stress. We also recorded an increase of the xylem K/Na in the salt acclimated plants. Therefore, the present study reveals that short-term exposure of the glycophyte P. sativum species activates a set of physiological adjustments enabling the plants to withstand severe saline conditions, and while acclimation takes place primary in the root tissues, control of xylem ion loading and efficient Na+ sequestration in mesophyll cells are also important components of this process.
Chenopodium quinoa is a halophytic pseudocereal crop that is being cultivated in an ever-growing number of countries. Because quinoa is highly resistant to multiple abiotic stresses and its seed has ...a better nutritional value than any other major cereals, it is regarded as a future crop to ensure global food security. We generated a high-qual- ity genome draft using an inbred line of the quinoa cultivar Real. The quinoa genome experienced one recent genome duplication about 4.3 million years ago, likely reflecting the genome fusion of two Chenopodium parents, in addition to the y paleohexaploidization reported for most eudicots. The genome is highly repetitive （64.5% repeat content） and contains 54 438 protein-coding genes and 192 microRNA genes, with more than 99.3% having orthologons genes from glycophylic species. Stress tolerance in quinoa is associated with the expansion of genes involved in ion and nu- trient transport, ABA homeostasis and signaling, and enhanced basal-level ABA responses. Epidermal salt bladder ceils exhibit similar characteristics as trichomes, with a significantly higher expression of genes related to energy import and ABA biosynthesis compared with the leaf lamina. The quinoa genome sequence provides insights into its exceptional nutritional value and the evolution of halophytes, enabling the identification of genes involved in salinity tolerance, and providing the basis for molecular breeding in quinoa.
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