Abiotic stresses influence the transcript abundance of PIP and TIP aquaporins in Festuca species

Influences of blue and red light irradiations on Cd phytoexcretion using Festuca arundinacea

Although phytoremediation is more economical when compared with traditional physical and chemical soil remediation methods, it remains very expensive when considering the substantial area of the contaminated field. If the quantity of harvested residues can be reduced after each phytoremediation cycle, the practicability and commercial implementation of this environment friendly method can be improved. In this study, cadmium excretion on the leaf surface of Festuca arundinacea was evaluated under various blue and red light conditions. The results indicated that the percentage of decaying and deceased leaves increased by 8.5%, 31.1%, 59.7%, and 35.9% at a blue light ratio of 10%, 50%, 75%, and 100%, respectively, when compared with the control. The highest cadmium concentration was found in decaying and deceased leaves under 75% blue light treatment. Light treatments also altered the excreted cadmium amount on different leaf types. Under all treatments including the control, significantly more cadmium can be washed off from emerging and mature leaves than from decaying and deceased leaves, owing to the detoxification mechanism of the plant (p < 0.05). The differences in cadmium excretion on senescent and dead leaves under all treatments were not statistically significant, but the mass of cadmium excretion on young leaves under 75% and 100% blue light irradiation were significantly higher than that under other treatments (p < 0.05). Herein, a novel phytoremediation method involving the harvesting decaying and deceased leaves and washing emerging and mature leaves was proposed to decrease the costs of plant residue disposal.

Analysis of aquaporins in northern grasses reveal functional importance of Puccinellia nuttalliana PIP2;2 in salt tolerance

To better understand the roles of aquaporins in salt tolerance, we cloned PIP2;1, PIP2;2, PIP2;3, PIP1;1, PIP1;3, and TIP1;1 aquaporins from three northern grasses varying is salt tolerance including the halophytic grass Puccinellia nuttalliana, moderately salt tolerant Poa juncifolia, and relatively salt sensitive Poa pratensis. We analysed aquaporin expression in roots by exposing the plants to 0 and 150 mM for 6 days in hydroponic culture. NaCl treatment upregulated several PIP transcripts in P. nuttalliana while decreasing PnuTIP1;1. The PnuPIP2;2 transcripts increased by about six-fold in P. nuttalliana, two-fold in Poa juncifolia, and did not change in Poa pratensis. The NaCl treatment enhanced the rate of water transport in yeast expressing PnuPIP2;2 by 56% compared with control. PnuPIP2,2 expression also resulted in a higher Na⁺ uptake in yeast cells compared with an empty vector suggesting that PnuPIP2;2 may have both water and ion transporting functions. Structural analysis revealed that the transport properties of PnuPIP2;2 could be affected by its unique pore characteristics, which include a combination of hourglass, cylindrical, and increasing diameter conical entrance shape with pore hydropathy of -0.22.

Reversible changes in structure and function of photosynthetic apparatus of pea (Pisum sativum) leaves under drought stress

The effects of drought on photosynthesis have been extensively studied, whereas those on thylakoid organization are limited. We observed a significant decline in gas exchange parameters of pea (Pisum sativum) leaves under progressive drought stress. Chl a fluorescence kinetics revealed the reduction of photochemical efficiency of photosystem (PS)II and PSI. The non-photochemical quenching (NPQ) and the levels of PSII subunit PSBS increased. Furthermore, the light-harvesting complexes (LHCs) and some of the PSI and PSII core proteins were disassembled in drought conditions, whereas these complexes were reassociated during recovery. By contrast, the abundance of supercomplexes of PSII-LHCII and PSII dimer were reduced, whereas LHCII monomers increased following the change in the macro-organization of thylakoids. The stacks of thylakoids were loosely arranged in drought-affected plants, which could be attributed to changes in the supercomplexes of thylakoids. Severe drought stress caused a reduction of both LHCI and LHCII and a few reaction center proteins of PSI and PSII, indicating significant disorganization of the photosynthetic machinery. After 7 days of rewatering, plants recovered well, with restored chloroplast thylakoid structure and photosynthetic efficiency. The correlation of structural changes with leaf reactive oxygen species levels indicated that these changes were associated with the production of reactive oxygen species.

Genome-Wide Characterization of the Aquaporin Gene Family in Radish and Functional Analysis of RsPIP2-6 Involved in Salt Stress

Aquaporins (AQPs) constitute a highly diverse family of channel proteins that transport water and neutral solutes. AQPs play crucial roles in plant development and stress responses. However, the characterization and biological functions of RsAQPs in radish (Raphanus sativus L.) remain elusive. In this study, 61 non-redundant members of AQP-encoding genes were identified from the radish genome database and located on nine chromosomes. Radish AQPs (RsAQPs) were divided into four subfamilies, including 21 plasma membrane intrinsic proteins (PIPs), 19 tonoplast intrinsic proteins (TIPs), 16 NOD-like intrinsic proteins (NIPs), and 5 small basic intrinsic proteins (SIPs), through phylogenetic analysis. All RsAQPs contained highly conserved motifs (motifs 1 and 4) and transmembrane regions, indicating the potential transmembrane transport function of RsAQPs. Tissue- and stage-specific expression patterns of AQP gene analysis based on RNA-seq data revealed that the expression levels of PIPs were generally higher than TIPs, NIPs, and SIPs in radish. In addition, quantitative real-time polymerase chain reaction (qRT-PCR) revealed that seven selected RsPIPs, according to our previous transcriptome data (e.g., RsPIP1-3, 1-6, 2-1, 2-6, 2-10, 2-13, and 2-14), exhibited significant upregulation in roots of salt-tolerant radish genotype. In particular, the transcriptional levels of RsPIP2-6 dramatically increased after 6 h of 150 mM NaCl treatment during the taproot thickening stage. Additionally, overexpression of RsPIP2-6 could enhance salt tolerance by Agrobacterium rhizogenes-mediated transgenic radish hairy roots, which exhibited the mitigatory effects of plant growth reduction, leaf relative water content (RWC) reduction and alleviation of O2- in cells, as shown by nitro blue tetrazolium (NBT) staining, under salt stress. These findings are helpful for deeply dissecting the biological function of RsAQPs on the salt stress response, facilitating practical application and genetic improvement of abiotic stress resistance in radish.

Genome-Wide Dissection of the Genetic Basis for Drought Tolerance in Gossypium hirsutum L. Races

Drought seriously threats the growth and development of Gossypium hirsutum L. To dissect the genetic basis for drought tolerance in the G. hirsutum L. germplasm, a population, consisting of 188 accessions of G. hirsutum races and a cultivar (TM-1), was genotyped using the Cotton80KSNP biochip, and 51,268 high-quality single-nucleotide polymorphisms (SNPs) were obtained. Based on the phenotypic data of eight drought relative traits from four environments, we carried out association mapping with five models using GAPIT software. In total, thirty-six SNPs were detected significantly associated at least in two environments or two models. Among these SNPs, 8 and 28 (including 24 SNPs in 5 peak regions) were distributed in the A and D subgenome, respectively; eight SNPs were found to be distributed within separate genes. An SNP, TM73079, located on chromosome D10, was simultaneously associated with leaf fresh weight, leaf wilted weight, and leaf dry weight. Another nine SNPs, TM47696, TM33865, TM40383, TM10267, TM59672, TM59675, TM59677, TM72359, and TM72361, on chromosomes A13, A10, A12, A5, D6, and D9, were localized within or near previously reported quantitative trait loci for drought tolerance. Moreover, 520 genes located 200 kb up- and down-stream of 36 SNPs were obtained and analyzed based on gene annotation and transcriptome sequencing. The results showed that three candidate genes, Gh_D08G2462, Gh_A03G0043, and Gh_A12G0369, may play important roles in drought tolerance. The current GWAS represents the first investigation into mapping QTL for drought tolerance in G. hirsutum races and provides important information for improving cotton cultivars.

Identification of Aquaporin Gene Family in Response to Natural Cold Stress in Ligustrum × vicaryi Rehd

Plants are susceptible to a variety of abiotic stresses during the growing period, among which low temperature is one of the more frequent stress factors. Maintaining water balance under cold stress is a difficult and critical challenge for plants. Studies have shown that aquaporins located on the cytomembrane play an important role in controlling water homeostasis under cold stress, and are involved in the tolerance mechanism of plant cells to cold stress. In addition, the aquaporin gene family is closely related to the cold resistance of plants. As a major greening tree species in urban landscaping, Ligustrum× vicaryi Rehd. is more likely to be harmed by low temperature after a harsh winter and a spring with fluctuating temperatures. Screening the target aquaporin genes of Ligustrum × vicaryi responding to cold resistance under natural cold stress will provide a scientific theoretical basis for cold resistance breeding of Ligustrum × vicaryi. In this study, the genome-wide identification of the aquaporin gene family was performed at four different overwintering periods in September, November, January and April, and finally, 58 candidate Ligustrum × vicaryi aquaporin (LvAQP) genes were identified. The phylogenetic analysis revealed four subfamilies of the LvAQP gene family: 32 PIPs, 11 TIPs, 11 NIPs and 4 SIPs. The number of genes in PIPs subfamily was more than that in other plants. Through the analysis of aquaporin genes related to cold stress in other plants and LvAQP gene expression patterns identified 20 LvAQP genes in response to cold stress, and most of them belonged to the PIPs subfamily. The significantly upregulated LvAQP gene was Cluster-9981.114831, and the significantly downregulated LvAQP genes were Cluster-9981.112839, Cluster-9981.107281, and Cluster-9981.112777. These genes might play a key role in responding to cold tolerance in the natural low-temperature growth stage of Ligustrum × vicaryi.

Overexpression of a Cotton Aquaporin Gene GhTIP1;1-like Confers Cold Tolerance in Transgenic Arabidopsis

Cold stress can significantly affect the development, yield, and quality of crops and restrict the geographical distribution and growing seasons of plants. Aquaporins are the main channels for water transport in plant cells. Abiotic stresses such as cold and drought dehydrate cells by changing the water potential. In this study, we cloned a gene GhTIP1;1-like encodes tonoplast aquaporin from the transcriptome database of cotton seedlings after cold stress. Expression analysis showed that GhTIP1;1-like not only responds to cold stress but was also induced by heat, drought and salt stress. Subcellular localization showed that the protein was anchored to the vacuole membrane. Promoter deletion analysis revealed that a MYC motif within the promoter region of GhTIP1;1-like were the core cis-elements in response to low temperature. Virus-induced gene silencing (VIGS) and histochemical staining indicate that GhTIP1;1-like plays a positive role in plant cold tolerance. Overexpression of GhTIP1;1-like in Arabidopsis delayed the senescence process and enhanced the cold tolerance of transgenic plants. Compared with the wild type, the soluble protein concentration and peroxidase activity of the transgenic lines under cold stress were higher, while the malondialdehyde content was lower. In addition, the expression levels of cold-responsive genes were significantly increased in transgenic plants under cold stress. Our results indicate that GhTIP1;1-like could respond to different abiotic stresses and be positively involved in regulating the cold tolerance of cotton.

Increasing yield on dry fields: molecular pathways with growing potential

Drought stress constitutes one of the major constraints to agriculture all over the world, and its devastating effect is only expected to increase in the following years due to climate change. Concurrently, the increasing food demand in a steadily growing population requires a proportional increase in yield and crop production. In the past, research aimed to increase plant resilience to severe drought stress. However, this often resulted in stunted growth and reduced yield under favorable conditions or moderate drought. Nowadays, drought tolerance research aims to maintain plant growth and yield under drought conditions. Overall, recently deployed strategies to engineer drought tolerance in the lab can be classified into a 'growth-centered' strategy, which focuses on keeping growth unaffected by the drought stress, and a 'drought resilience without growth penalty' strategy, in which the main aim is still to boost drought resilience, while limiting the side effects on plant growth. In this review, we put the scope on these two strategies and some molecular players that were successfully engineered to generate drought-tolerant plants: abscisic acid, brassinosteroids, cytokinins, ethylene, ROS scavenging genes, strigolactones, and aquaporins. We discuss how these pathways participate in growth and stress response regulation under drought. Finally, we present an overview of the current insights and future perspectives in the development of new strategies to improve drought tolerance in the field.

Screening and identification of salt-tolerance genes in Sophora alopecuroides and functional verification of SaAQP

Overexpression of SaAQP can improve the salt tolerance of transgenic soybean hairy roots and A. thaliana. Salt stress severely affects crop yield and food security. There is a need to improve the salt tolerance of crops, but the discovery and utilization of salt-tolerance genes remains limited. Owing to its strong stress tolerance, Sophora alopecuroides is ideal for the identification of salt-tolerance genes. Therefore, we aimed to screen and identify the salt-tolerance genes in S. alopecuroides. With a yeast expression library of seedlings, salt-tolerant genes were screened using a salt-containing medium to simulate salt stress. By combining salt-treatment screening and transcriptome sequencing, 11 candidate genes related to salt tolerance were identified, including genes for peroxidase, inositol methyltransferase, aquaporin, cysteine synthase, pectinesterase, and WRKY. The expression dynamics of candidate genes were analyzed after salt treatment of S. alopecuroides, and salt tolerance was verified in yeast BY4743. The candidate genes participated in the salt-stress response in S. alopecuroides, and their overexpression significantly improved the salt tolerance of yeast. Salt tolerance mediated by SaAQP was further verified in soybean hairy roots and Arabidopsis thaliana, and it was found that SaAQP might enhance the salt tolerance of A. thaliana by participating in a reactive oxygen species scavenging mechanism. This result provides new genetic resources in plant breeding for salt resistance.

Mycorrhizal response strategies of trifoliate orange under well-watered, salt stress, and waterlogging stress by regulating leaf aquaporin expression

Aquaporins (AQPs) involved in water and small molecule transport respond to environmental stress, while it is not clear how arbuscular mycorrhizal fungi (AMF) regulate AQP expression. Here, we investigated the change in leaf water potential and expression level of four tonoplast intrinsic proteins (TIPs), six plasma membrane intrinsic proteins (PIPs), and four nodin-26 like intrinsic proteins (NIPs) genes in trifoliate orange (Poncirus trifoliata) inoculated with Funneliformis mosseae under well-watered (WW), salt stress (SS), and waterlogging stress (WS). Root AMF colonization and soil hyphal length collectively were reduced by SS and WS. Under WW, inoculation with AMF gave diverse responses of AQPs: six AQPs up-regulated, three AQPs down-regulated, and five AQPs did not change. Such up-regulation of more AQPs under mycorrhization and WW partly accelerated water absorption, thereby, maintaining higher leaf water potential. However, under SS, all the fourteen AQPs were dramatically induced by AMF inoculation, which improved water permeability of membranes and stimulated water transport of the host. Under WS, AMF colonization almost did not induce or even down-regulated these AQPs expressions with three exceptions (PtTIP2;2, PtPIP1;1, and PtNIP1;2), thus, no change in leaf water potential. As a result, mycorrhizal plants under flooding may have an escape mechanism to reduce water absorption. It is concluded that AMF had different strategies in response to environmental stresses (e.g. SS and WS) by regulating leaf AQP expression in the host (e.g. trifoliate orange).

Controversial Regulation of Gene Expression and Protein Transduction of Aquaporins under Drought and Salinity Stress

Enhancement of the passage of water through membranes is one of the main mechanisms via which cells can maintain their homeostasis under stress conditions, and aquaporins are the main participants in this process. However, in the last few years, a number of studies have reported discrepancies between aquaporin messenger RNA (mRNA) expression and the number of aquaporin proteins synthesised in response to abiotic stress. These observations suggest the existence of post-transcriptional mechanisms which regulate plasma membrane intrinsic protein (PIP) trafficking to the plasma membrane. This indicates that the mRNA synthesis of some aquaporins could be modulated by the accumulation of the corresponding encoded protein, in relation to the turnover of the membranes. This aspect is discussed in terms of the results obtained: on the one hand, with isolated vesicles, in which the level of proteins present provides the membranes with important characteristics such as resistance and stability and, on the other, with isolated proteins reconstituted in artificial liposomes as an in vitro method to address the in vivo physiology of the entire plant.

Stomatal closure response to soil drying at different vapor pressure deficit conditions in maize

A plant transpiration rate under progressive soil drying remains constant until a threshold fraction of transpirable soil water (FTSW) is reached, and subsequently decreases linearly. The sensitivity of this function and the involvement of abscisic acid (ABA) and aquaporins in such responses have not been compared at various levels of atmospheric evaporative demand conditions. This study was conducted in controlled environment chambers with a drought-tolerant maize hybrid imposing progressive drought stress under three levels of vapor pressure deficit (VPD- 1.2, 2.3, and 3.5 kPa). A shift in threshold-FTSW from 1.2 kPa (FTSW-0.42) VPD to 3.5 kPa(FTSW-0.51) VPD was observed, showing an effect of VPD on stomatal closure response under soil drought conditions. Foliar ABA showed a substantial rise approximately at the same time as of stomatal closure initiated (FTSW-threshold), indicating ABA involvement. As the drought progressed, an increase in plasma membrane intrinsic protein and a decrease in tonoplast intrinsic protein expression levels were observed. Overall, this study suggests the influence of evaporative demand on the initiation of stomatal closure of drought-tolerant maize subjected to soil drying. The sensitivity of stomatal closure was associated with foliar ABA under drought stress but not under high evaporative demand conditions, indicating alternative water conservative mechanisms.

Two Festuca Species-F. arundinacea and F. glaucescens-Differ in the Molecular Response to Drought, While Their Physiological Response Is Similar

Impact of photosynthetic and antioxidant capacities on drought tolerance of two closely related forage grasses, Festuca arundinacea and Festuca glaucescens, was deciphered. Within each species, two genotypes distinct in drought tolerance were subjected to a short-term drought, followed by a subsequent re-watering. The studies were focused on: (i) analysis of plant physiological performance, including: water uptake, abscisic acid (ABA) content, membrane integrity, gas exchange, and relative water content in leaf tissue; (ii) analysis of plant photosynthetic capacity (chlorophyll fluorescence; gene expression, protein accumulation, and activity of selected enzymes of the Calvin cycle); and (iii) analysis of plant antioxidant capacity (reactive oxygen species (ROS) generation; gene expression, protein accumulation and activity of selected enzymes). Though, F. arundinacea and F. glaucescens revealed different strategies in water uptake, and partially also in ABA signaling, their physiological reactions to drought and further re-watering, were similar. On the other hand, performance of the Calvin cycle and antioxidant system differed between the analyzed species under drought and re-watering periods. A stable efficiency of the Calvin cycle in F. arundinacea was crucial to maintain a balanced network of ROS/redox signaling, and consequently drought tolerance. The antioxidant capacity influenced mostly tolerance to stress in F. glaucescens.

Versatile roles of aquaporin in physiological processes and stress tolerance in plants

Aquaporins are pore-forming transmembrane proteins that facilitate the movement of water and many other small neutral solutes across the cells and intracellular compartments. Plants exhibits high diversity in aquaporin isoforms and broadly classified into five different subfamilies on the basis of phylogenetic distribution and subcellular occurrence: plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), nodulin 26-like proteins (NIPs), small basic intrinsic proteins (SIPs) and uncharacterized intrinsic proteins (XIPs). The gating mechanism of aquaporin channels is tightly regulated by post-translational modifications such as phosphorylation, methylation, acetylation, glycosylation, and deamination. Aquaporin expression and transport functions are also modulated by the various phytohormones-mediated signalling in plants. Combined physiology and transcriptome analysis revealed the role of aquaporins in regulating hydraulic conductance in roots and leaves. The present review mainly focused on aquaporin functional activity during solute transport, plant development, abiotic stress response, and plant-microbe symbiosis. Genetically modified plants overexpressing aquaporin-encoding genes display improved agronomic and abiotic stress tolerance.

Drought stress and re-watering affect the abundance of TIP aquaporin transcripts in barley

Tonoplast Intrinsic Proteins (TIP) are plant aquaporins that are primarily localized in the tonoplast and play a role in the bidirectional flux of water and other substrates across a membrane. In barley, eleven members of the HvTIP gene subfamily have been identified. Here, we describe the transcription profile of the HvTIP genes in the leaves of barley seedlings being grown under optimal moisture conditions, drought stress and a re-watering phase. The applied drought stress caused a 55% decrease in the relative water content (RWC) in seedlings, while re-watering increased the RWC to 90% of the control. Our analysis showed that all HvTIP genes, except HvTIP3;2, HvTIP4;3 and HvTIP5.1, were expressed in leaves of ten-day-old barley seedlings under optimal water conditions with the transcripts of HvTIP2;3, HvTIP1;2 and HvTIP1;1 being the most abundant. We showed, for the first time in barley, a significant variation in the transcriptional activity between the analysed genes under drought stress. After drought treatment, five HvTIP genes, which are engaged in water transport, were down-regulated to varying degrees, while two, HvTIP3;1 and HvTIP4;1, were up-regulated. The HvTIP3;1 isoform, which is postulated as transporting hydrogen peroxide, expressed the highest increase of activity (ca. 5000x) under drought stress, thus indicating its importance in the response to this stress. Re-hydration caused the return of the expression of many genes to the level that was observed under optimal moisture conditions or, at least, a change in this direction Additionally, we examined the promotor regions of HvTIP and detected the presence of the cis-regulatory elements that are connected with the hormone and stress responses in all of the genes. Overall, our results suggest that 7 of 11 studied HvTIP (HvTIP1;1, HvTIP1;2, HvTIP2;1, HvTIP2;2, HvTIP2;3, HvTIP3;1, HvTIP4;1) have an important function during the adaptation of barley to drought stress conditions. We discuss the identified drought-responsive HvTIP in terms of their function in the adaptation of barley to this stress.

Molecular cloning and functional analysis of lotus salt-induced NnDREB2C, NnPIP1-2 and NnPIP2-1 in Arabidopsis thaliana

Dehydration-responsive element bindings transcription factor (DREBs) and plasma membrane intrinsic proteins (PIPs) have been characterized multi-functions in plant growth and metabolism, as well as in the adaptation to various stresses. In this study, we cloned the full-length cDNA of NnDREB2C from a salt-tolerated lotus species with RT-PCR methods. Analysis of qRT-PCR demonstrated that NnDREB2C mRNA in the leaf dramatically increased after the treatments of NaCl, abscisic acid, low temperature and mannitol. Next, NnDREB2C was cloned into constitutive expression vector pSN1301, which in turn transformed into Arabidopsis thaliana to investigate its function in plants. NnDREB2C overexpression significantly elevated Arabidopsis tolerance against salt and drought stresses, showing higher survival rates, lower conductivity and more chlorophyll content than those of wild-type plants. Moreover, higher germination rates were observed in the NnDREB2C overproducing plants when subjected into the stresses of NaCl and mannitol. Furthermore, we investigate the potential down-stream genes regulated by NnDREB2C and observed a significant increase in expressions of several genes belonging to PIPs family, including PIP1-1, PIP1-2, PIP1-3, PIP1-4 and PIP1-5. Consistently, overexpressed NnPIP1-2 and NnPIP2-1 conferred Arabidopsis the tolerance to stresses. Taken together, we concluded that overexpression of NnDREB2C enhanced the tolerance of salt and drought stresses in plants, which might probably be derived from the increased expression of the genes belonging to PIPs family.

Identification of Sugarcane Host Factors Interacting with the 6K2 Protein of the Sugarcane Mosaic Virus

The 6K2 protein of potyviruses plays a key role in the viral infection in plants. In the present study, the coding sequence of 6K2 was cloned from Sugarcane mosaic virus (SCMV) strain FZ1 into pBT3-STE to generate the plasmid pBT3-STE-6K2, which was used as bait to screen a cDNA library prepared from sugarcane plants infected with SCMV based on the DUALmembrane system. One hundred and fifty-seven positive colonies were screened and sequenced, and the corresponding full-length genes were cloned from sugarcane cultivar ROC22. Then, 24 genes with annotations were obtained, and the deduced proteins were classified into three groups, in which eight proteins were involved in the stress response, 12 proteins were involved in transport, and four proteins were involved in photosynthesis based on their biological functions. Of the 24 proteins, 20 proteins were verified to interact with SCMV-6K2 by yeast two-hybrid assays. The possible roles of these proteins in SCMV infection on sugarcane are analyzed and discussed. This is the first report on the interaction of SCMV-6K2 with host factors from sugarcane, and will improve knowledge on the mechanism of SCMV infection in sugarcane.

Variation in Aquaporin and Physiological Responses Among Pinus contorta Families Under Different Moisture Conditions

A population of eight open pollinated families of Pinus contorta was selected from sites varying in precipitation regimes and elevation to examine the possible role of aquaporins in adaptation to different moisture conditions. Five Pinus contorta aquaporins encoding PiconPIP2;1, PiconPIP2;2, PiconPIP2;3, PiconPIP1;2, and PiconTIP1;1 were cloned and detailed structural analyses were conducted to provide essential information that can explain their biological and molecular function. All five PiconAQPs contained hydrophilic aromatic/arginine selective filters to facilitate the transport of water. Transcript abundance patterns of PiconAQPs varied significantly across the P. contorta families under varying soil moisture conditions. The transcript abundance of five PiconPIPs remained unchanged under control and water-stress conditions in two families that originated from the sites with lower precipitation levels. These two families also displayed a different adaptive strategy of photosynthesis to cope with drought stress, which was manifested by reduced sensitivity in photosynthesis (maintaining the same rate) while exhibiting a reduction in stomatal conductance. In general, root:shoot ratios were not affected by drought stress, but some variation was observed between families. The results showed variability in drought coping mechanisms, including the expression of aquaporin genes and plant biomass allocation among eight families of Pinus contorta.

Aquaporins as a link between water relations and photosynthetic pathway in abiotic stress tolerance in plants

Plant aquaporins constitute a large family of proteins involved in facilitating the transport of water and small neutral molecules across biological membranes. In higher plants they are divided into several sub-families, depending on membrane-type localization and permeability to specific solutes. They are abundantly expressed in the majority of plant organs and tissues, and play a function in primary biological processes. Many studies revealed the significant role of aquaporins in acquiring abiotic stresses' tolerance. This review focuses on aquaporins belonging to PIPs sub-family that are permeable to water and/or carbon dioxide. Isoforms transporting water are involved in hydraulic conductance regulation in the leaves and roots, whereas those transporting carbon dioxide control stomatal and mesophyll conductance in the leaves. Changes in PIP aquaporins abundance/activity in stress conditions allow to maintain the water balance and photosynthesis adjustment. Broad analyses showed that tight control between water and carbon dioxide supplementation mediated by aquaporins influences plant productivity, especially in stress conditions. Involvement of aquaporins in adaptation strategies to dehydrative stresses in different plant species are discussed in this review.

Remodeling of chloroplast proteome under salinity affects salt tolerance of Festuca arundinacea

Acclimation of photosynthetic apparatus to variable environmental conditions is an important component of tolerance to dehydration stresses, including salinity. The present study deals with the research on alterations in chloroplast proteome of the forage grasses. Based on chlorophyll fluorescence parameters, two genotypes of a model grass species-Festuca arundinacea with distinct levels of salinity tolerance: low salt tolerant (LST) and high salt tolerant (HST), were selected. Next, two-dimensional electrophoresis and mass spectrometry were applied under both control and salt stress conditions to identify proteins accumulated differentially between these two genotypes. The physiological analysis revealed that under NaCl treatment the studied plants differed in photosystem II activity, water content, and ion accumulation. The differentially accumulated proteins included ATPase B, ATP synthase, ribulose-1,5-bisphosphate carboxylase large and small subunits, cytochrome b6-f complex iron-sulfur subunit, oxygen-evolving enhancer proteins (OEE), OEE1 and OEE2, plastidic fructose-bisphosphate aldolase (pFBA), and lipocalin. A higher level of lipocalin, potentially involved in prevention of lipid peroxidation under stress, was also observed in the HST genotype. Our physiological and proteomic results performed for the first time on the species of forage grasses clearly showed that chloroplast metabolism adjustment could be a crucial factor in developing salinity tolerance.

Insight into cellular proteome of Lolium multiflorum/Festuca arundinacea introgression forms to decipher crucial mechanisms of cold acclimation in forage grasses

Frost tolerance is the main component of winter-hardiness. To express this trait, plants sense low temperature, and respond by activating the process of cold acclimation. The molecular mechanisms of this acclimation have not been fully understood in the agronomically important group of forage grasses, including Lolium-Festuca species. Herein, the introgression forms of L. multiflorum/F. arundinacea distinct with respect to their frost tolerance, were used as models for the comprehensive, proteomic and physiological, research to recognize the crucial components of cold acclimation in forage grasses. The obtained results stressed the importance of photosynthetic performance under acclimation to low temperature. The stable level of photochemical processes after three weeks of cold acclimation in the introgression form with a higher level of frost tolerance, combined simultaneously with only slightly (but not significantly) decreased level of CO₂ assimilation after that period, despite significantly lower stomatal conductance, indicated the capacity for that form to acclimate its photosynthesis to low temperature. This phenomenon was driven by the Calvin cycle efficiency, associated with revealed here accumulation profiles and activities of chloroplastic aldolase. The capacity to acclimate the photosynthetic machinery to cold could be one of the most crucial components of forage grass metabolism to improve frost tolerance.

Dissection of resistance to Microdochium nivale in Lolium multiflorum/Festuca arundinacea introgression forms

The potential of resistance to Microdochium nivale is still not recognized for numerous plant species. The forage grasses of Lolium-Festuca complex are important for grass-biomass production in the temperate regions. Lolium multiflorum is a grass with a high forage quality and productivity but also a relatively low resistance to M. nivale. On the contrary, F. arundinacea has a higher potential of resistance but simultaneously a significantly lower forage quality. These two species cross with each other and the intergeneric hybrids possess complementary characters of both genera. Herein, for the first time, we perform the research on L. multiflorum/F. arundinacea introgression forms to decipher mechanisms of resistance to M. nivale in that group of plants. Two forms with distinct levels of resistance were used as models in cytogenetic and biochemical studies. The resistant plant was shown to be a tetraploid with 28 L. multiflorum chromosomes, including one with three F. arundinacea introgressions. The susceptible introgression form revealed the unbalanced genomic structure and only 25 chromosomes. Twenty four chromosomes were shown to be L. multiflorum chromosomes, including one chromosome with F. arundinacea segment. One Festuca chromosome with additional two interstitial F. arundinacea segments, was also revealed in the susceptible form. The selected introgression forms differed in the accumulation profiles of total soluble carbohydrates, phytohormones, and phenolics in the leaf and crown tissue under the control and infection conditions. The higher amount of carbohydrates and salicylic acid in the leaves and crowns as well as a lower amount of abscisic acid in both studied organs and jasmonic acid in the crowns, were shown to be crucial for the expression of resistance to M. nivale in the analyzed hybrids.