treatment for 3 weeks, compared with TG plants, the WT plants were smaller and more withered (Fig. 5A). After 3 weeks of exposure to 400 mM NaCl, most leaves of the TG tobacco remained green, while leaves of the WT turned yellow (Fig. 6A). The TG lines exhibited lower rates of leaf yellowing (Fig. 5B and 5C) and higher survival rates (Fig. 6B and 6C) than WT lines under drought and salt treatments. The rate of leaf yellowing, plant height and survival rate are the typical phenotypic and physiological parameters used to evaluate resistance in crop plants. Plants that are taller, with higher survival rates and fewer yellow leaves are more tolerant tostresses. The phenotypic characteriza- Figure 3. The genomic organization, protein localization and transcriptional activation activity of the TaWRKY10 gene. (A) Southern blot analysis of the TaWRKY10 gene. 10 mg genomic DNA of hexaploid wheat cv. Chinese Spring was digested completely with the restriction enzymes. The ORF of TaWRKY10 was used as the hybrid probe. The TaWRKY10 overexpressing vector was used as control. The 1 kb DNA Ladder (MBI Fermentas) are indicated on the left. (B) Subcellular localization of TaWRKY10in onion epidermal cells. Onion epidermal cells were transferred with vector carrying GFP or TaWRKY10-GFP using bombardment method. Free GFP and TaWRKY10-GFP fusion proteins were transiently expressed in onion epidermal cells and observed with an inverted fluorescence microscope. (C) Transactivation activity of the TaWRKY10 protein in Yeast. The schematic diagram demonstrating the TaWRKY10 cDNA fragments encoding different portions of TaWRKY10 that were fused to the yeast vector pGBKT7 (pBD). Transactivation activity analysis of TaWRKY10 was performed using yeast strain AH109. The transformants were streaked on the SD/ 2Trp or on SD/2His medium. The transformants were examined for growth in the presence of 3-AT and X-a-D-gal. Three biological experiments were carried out, which produced similar results.
and form complex gene regulatory networks [9,14,15]. Up to now, little is known about the abiotic stress tolerance of parsley. Cormack  isolated two WRKYtranscription factors from parsley using the yeast one-hybrid system. Weisshaar  cloned three bZIP genes from parsley and found that these genes are involved in the response to environmental changes and disease invasion. However, almost no AP2/ERF members have been identified in parsley. AP2/ERF was one of the largest transcriptionfactor families in higher plants and has received much attention in recent years. This family can be further classified into four subfamiles: ERF, DREB, AP2, RAV [18–20]. Numerous reports have demonstrated that the family members can regulate plant responses toabioticstresses [21,22]. JERF3, an ERF member in tomato, can be induced by abscisic acid, ethylene, jasmonic acid, and low temperature; ectopic overexpression of JERF3 intransgenictobacco enhances salt tolerance . A DREB-type gene LsDREB2A, was isolated from lettuce, can increased the tolerance of salt stress intransgenic plants .
The bHLH proteins are one of the largest families of transcription factors both in animals and plants and are well characterized in mammalian system . The bHLH domain contains approximately 60 amino acids, with two functionally distinctive regions, the basic region and the HLH region. The basic region consists of 15 amino acids and functions as a DNA binding domain and HLH region contains two amphipathic α- helices linked by a loop. This allows the formation of homodimers or heterodimers [9, 10]. bHLH proteins bind to sequences contain- ing a consensus core elements of the E-box (5’-CANNTG-3’), and the G box (5’-CACGTG-3’) cis elements. In Arabidopsis and rice, 162 and 167 bHLH encoding genes have been identified respectively [11, 12]. Many of these genes have been characterized for their role in developmen- tal processes such as flavonoid and anthocyanin biosynthesis [10, 13], trichome and tapetum development [14, 15], shoot branching , controlling grain length and width [17, 18]. Some of the genes are also involved in signaling processes [19, 20, 21]. A number of bHLH genes have been shown to be involved in stress tolerance. The microarray analysis of NaCl treated Arabidopsis roots showed a differential regulation of 29 bHLH genes . In soybean, out of 45 bHLH genes, 14 are responsive toabiotic/biotic stresses. Improved toleranceto diverse abioticstresses has been reported intransgenic plants overexpressing AtbHLH92 , AtICE1 , OsbHLH1 , MdCIbHLH1 . Both, AtICE1 in Arabidopsis and MdCIbHLH1 in apple enhanced the expression of C-repeat binding factor (CBF) regulons.
Abioticstresses are major environmental factors that affect agricultural productivity worldwide. NAC transcription factors play pivotal roles inabiotic stress signaling in plants. As a staple crop, wheat production is severely constrained by abioticstresses whereas only a few NAC transcription factors have been characterized functionally. To promote the application of NAC genes inwheat improvement by biotechnology, a novel NAC gene designated TaNAC67 was characterized in common wheat. To determine its role, transgenic Arabidopsis overexpressing TaNAC67-GFP controlled by the CaMV-35S promoter was generated and subjected to various abioticstresses for morphological and physiological assays. Gene expression showed that TaNAC67 was involved in response to drought, salt, cold and ABA treatments. Localization assays revealed that TaNAC67 localized in the nucleus. Morphological analysis indicated the transgenics had enhanced tolerances to drought, salt and freezing stresses, simultaneously supported by enhanced expression of multipleabiotic stress responsive genes and improved physiological traits, including strengthened cell membrane stability, retention of higher chlorophyll contents and Na + efflux rates, improved photosynthetic potential, and enhanced water retention capability. Overexpression of TaNAC67
WRKY family is defined by a DNA binding domain that contains the strictly conserved amino acid sequence WRKY. Members of WRKY family transcription factors have been implicated in the response to biotic and abioticstresses. Overexpression of the GhWRKY39-1 gene enhances the resis- tance to pathogen infection and toleranceto high salt and oxidative stress intransgenic Nicotiana benthamiana . The same results were obtained from the research of Tamarix hispida, overexpression of ThWRKY4 conferred toleranceto salt, oxida- tive and ABA treatment intransgenic plants . The overex- pression of a subgroup IIe WRKYtranscriptionfactor CaWRKY27 of Capsicum annuum also positively regulates the resistance of tobaccoto the pathogen Ralstonia solanacearum infection . In the present study of the two transcriptome libraries, three WRKY showed higher expression levels in SM as compared to SMT that may enhance the tolerance of SM to biotic and abiotic stress.
superfamily. Several GSTL features make them important targets for functional characterization. In particular, specific GSTLs are strongly upregulated in response to exposure to xenobiotic compounds, including herbicides, herbicide safeners and pharmaceuticals (Hershey and Stoner 1991, Dixon et al. 2002, Theodoulou et al. 2003). As with other GST classes, this correlation provides circumstantial evidence for a role in stress tolerance (Dixon et al. 2011). OsGSTL2 is a glutathione S-transferase, lambda class gene from rice, which showed response to chlorsulfuron. OsGSTL2 protein has a specific activity of GST (Hu et al. 2011). The purpose of this study was to over-express OsGSTL2 in rice and investigate the role of OsGSTL2 in protecting plants from the injury caused by herbicides.
to a final concentration of 2.5 pmol/µL. Labelling efficiency was tested by spotting serial dilutions on nylon membrane along with control labelled oligonucleotides provided with the kit. DIG labeled (50 fmol) and unlabeled (10 pmol) oligonucleotides were mixed with GST-OsMYB1 (1 µg) in binding buffer and incubated at room temperature for 30 min. The reaction products were fractionated through a pre-run 6% non-denaturing polyacrylamide gel for 90 min in 0.5X TBE buffer at 4°C, then electrophoretically transferred to a positively charged nylon membrane (Roche) by applying a constant current of 300 mA for 30 min. The DNA was cross-linked to the membrane using a UV stratalinker (Stratagene). The nylon membrane was blocked in 1X blocking reagent for 1 h at room temperature and then incubated with a 1:20,000 dilution of anti-DIG antibody coupled to alkaline phosphatase for 30 min. The membrane was washed twice in 0.1 M maleic acid (pH 7.5), 0.15 M NaCl, 0.3% (v/v) Tween 20 for 20 min each. Then after a 5 min equilibration in detection buffer (100 mM Tris-HCl pH 9.5, 100 mM NaCl), membrane was kept carefully on a plastic sheet and 1:100 dilution of the CSPD substrate was added on membrane dropwise around membrane edges and then covered the whole membrane by tilting it. Membrane was incubated at room temperature for 5 min and then placed in a plastic folder and incubated at 37°C for more 15 min. Then membrane was exposed to X-ray film for 3 h to capture the chemiluminescent signal.
green PCR Kit (Tianwei, China), and following the manu- facturer’s instructions, amplifications were performed with OsGSTL2-qf (5’-CGTTCAACAAAGCATCGTAC-3’), and OsGST-qr (5’-GCAAAAACTGTGGGTCCTGT-3’). Data were normalized to OsEF1α, which was amplified with prim- ers OsEF1α-f (5’-AGGGATGGGTCAAAAGGATGC-3’) and OsEF1α-r (5’-GAGACAACACCGCCTGAATAGC-3’). Standard curves were constructed using serial cDNA di- lutions. RT-PCR data were normalized with the relative efficiency of each primer pair. PCR amplification was performed using two-step cycling conditions of 98 °C for 3 min, followed by 40 cycles of 98 °C for 2 s, and 58 °C for 10 s. Amplification was followed by a melting curve analysis with continual fluorescence data acquisition from the 55-95 °C melt. Melt curve analysis of qPCR samples revealed that there was only one product for each gene primer reaction. Relative gene expression was determined using the Pfaffl method (Pfaffl 2001), and the non-transformed plant product was set as 1.0.
Although excess salt is toxic to physiological and biochemical processes in plants, some spe- cies can grow in environments containing high levels of salts because they have evolved the unique ability to resist salinity . One key mechanism in salinity tolerance is the ability to remove excessive Na + from the cytosol via tonoplast Na + /H + antiporters (NHXs) and the plasma membrane Na + /H + antiporter (SOS1). The proton motive force utilized by vacuolar Na + /H + antiporters is generated by H + -translocating enzymes in the tonoplast, such as V-ATPase and H + -inorganic PPase. Recent studies have demonstrated that the vacuolar Na + / H + antiporter can utilize the electrochemical H + gradient generated by tonoplast H + -pumps to sequester Na + into vacuoles via the simultaneous overexpression of the two tonoplast proteins in plants. The salt tolerance of rice co-expressing SsNHX1 and AtAVP1 was higher than that achieved by single-gene transformation , and rice plants engineered to overexpress native NHX and H + -PPase genes showed higher salt tolerance than plants expressing OsNHX1 or OsVP1 alone . In addition, Gouiaa et al. reported that tobacco plants transformed with both TNHXS1 and TVP1 grew better than the single gene-transformed lines under salinity . The plasma membrane Na + /H + antiporter can also transport excess Na + in the cytoplasm out of cells using the driving force of the H + gradient produced by plasma membrane H + -pumps. Arabidopsis plants transformed with the AtSOS1 gene showed higher salt tolerance than wild- type plants . Although plasma membrane H + -ATPase activity correlates with the adapta- tion of plants to salt stress , the overexpression of plasma membrane H + -ATPase has not been reported to confer strong salt tolerancetotransgenic plants. It is difficult to engineer organisms with vacuolar H + -ATPase because it comprises multiple protein subunits located in the tonoplast, and there is no experimental evidence for enhanced salt toleranceintransgenic organisms with a vacuolar H + -ATPase. In the present investigation, SpAHA1 produced an increased electrochemical gradient of protons to promote the Na + /H + exchange activity of SpSOS1, with more Na + ion being transported out of cells. Correspondingly, yeast cells co- expressing SpSOS1 and SpAHA1 grew better than cells transformed with SpSOS1 or SpAHA1
Sample characterisation - The sample in this study consisted of 118 women infected with HIV-1 and 99 HIV- 1-uninfected individuals (49 males and 50 females). The ages of the HIV-1-infected women ranged from 20-73 years (median age = 33 ± 17.6 years). Clinical factors, such as the duration of antiretroviral treatment, the appearance of HIV-1 constitutional symptoms, VL and CD4 T cell counts, among the individuals infected with HIV-1 showed high heterogeneity in the group. The median HIV-1 VL was 386 ± 17.93 copies/mL and the median CD4 T cell count was 382.5 ± 2.03 cells/µL. In total, 88 (75.9%) pa- tients were receiving antiretroviral therapy, whereas 23 (24.1%) were therapy-naïve. The main route of HIV-1 in- fection among women was sexual transmission (66.2%). One patient reported infection via a blood transfusion (1.5%) and one was infected during intravenous drug use (2.2%). Seven patients did not have data available in their medical records. The median age of the HIV-1-uninfected individuals was 29 ± 15.2 years. All of the blood samples from the HIV-1-uninfected group had negative serology for HIV-1/2 and human T-lymphotropic virus-1/2.
The binding sequence for any transcriptionfactor can be found millions of times within a ge- nome, yet only a small fraction of these sequences encode functional transcriptionfactor binding sites. One of the reasons for this dichotomy is that many other factors, such as nu- cleosomes, compete for binding. To study how the competition between nucleosomes and transcription factors helps determine a functional transcriptionfactor site from a predicted transcriptionfactor site, we compared experimentally-generated in vitro nucleosome occu- pancy with in vivo nucleosome occupancy and transcriptionfactor binding in murine embry- onic stem cells. Using a solution hybridization enrichment technique, we generated a high- resolution nucleosome map from targeted regions of the genome containing predicted sites and functional sites of Oct4/Sox2 regulation. We found that at Pax6 and Nes, which are bivalently poised in stem cells, functional Oct4 and Sox2 sites show high amounts of in vivo nucleosome displacement compared toin vitro. Oct4 and Sox2, which are active, show no significant displacement of in vivo nucleosomes at functional sites, similar to nonfunctional Oct4/Sox2 binding. This study highlights a complex interplay between Oct4 and Sox2 tran- scription factors and nucleosomes among different target genes, which may result in distinct patterns of stem cell gene regulation.
It has been reported previously that cauliflower mosaic virus 35S promoter was not active during embryogenesis prior to the torpedo stage and that it did not show any activity in the syncytial endosperm . We performed a MINI3 ChIP analysis in 35S::MINI3:GFP transgenic plants. Although we observed slightly higher MINI3:GFP expression compared with the background fluorescence of non-transgenic Ws plants, we are not convinced and do not present these images. Instead, we present data from six independent transgenic lines that each shows a consistently increase in seed mass compared with non-transgenic Ws plants (Figure 3C). MINI3 is normally expressed in the endosperm and the embryo, and its expression in the endosperm is required to maintain IKU2 expression for endosperm proliferation and seed cavity enlargement. The observed seed phenotype may be due to the low expression of MINI3:GFP driven by the CaMV 35S promoter in the endosperm. In addition, in our experiments, we harvested siliques at approximately 4 DAP or at the early heart stage, and the embryo constitutes only a small volume of the seed at this stage. The weak expression of MINI3:GFP in embryo only does not account for our positive ChIP results. Therefore, the 35S::MINI:GFP transgenic plants may produce sufficient levels of tagged MINI3 for the ChIP analysis.
Commercial and non-commercial plants face a variety of environmental stressors that often cannot be controlled. In this study, transgenic hybrid poplar (Populus 6 euramericana ‘Guariento’) harboring five effector genes (vgb, SacB, JERF36, BtCry3A and OC-I) were subjected to drought, salinity, waterlogging and insect stressors in greenhouse or laboratory conditions. Field trials were also conducted to investigate long-term effects of transgenic trees on insects and salt tolerancein the transformants. In greenhouse studies, two transgenic lines D5-20 and D5-21 showed improved growth, as evidenced by greater height and basal diameter increments and total biomass relative to the control plants after drought or salt stress treatments. The improved toleranceto drought and salt was primarily attributed to greater instantaneous water use efficiency (WUEi) in the transgenic trees. The chlorophyll concentrations tended to be higher in the transgenic lines under drought or saline conditions. Transformed trees in drought conditions accumulated more fructan and proline and had increased Fv/Fm ratios (maximum quantum yield of photosystem II) under waterlogging stress. Insect-feeding assays in the laboratory revealed a higher total mortality rate and lower exuviation index of leaf beetle [Plagiodera versicolora (Laicharting)] larvae fed with D5-21 leaves, suggesting enhanced insect resistance in the transgenic poplar. In field trials, the dominance of targeted insects on 2-year-old D5-21 transgenic trees was substantially lower than that of the controls, indicating enhanced resistance to Coleoptera. The average height and DBH (diameter at breast height) of 2.5-year-old transgenic trees growing in naturally saline soil were 3.80% and 4.12% greater than those of the control trees, but these increases were not significant. These results suggested that multiple stress-resistance properties in important crop tree species could be simultaneously improved, although additional research is needed to fully understand the relationships between the altered phenotypes and the function of each transgene in multigene transformants.
It has been suggested that miR393 is one of the key miRNAs during stress responses because of its altered ex- pression in A. thaliana, Oryza sativa, Medicago truncatula, Phaseolus vulgaris and other plants under drought, salinity, low temperature, and aluminium stress conditions (Sunkar and Zhu, 2004; Zhao et al., 2007; Liu et al., 2008; Arenas- Huertero et al., 2009; Trindade et al., 2010). However, the molecular evidence that miR393 regulates its targets in sev- eral environmental conditions remains to be considered. Recently, Arabidopsis plants overexpressing osaMIR393 became more tolerant to salt excess, suggesting a regula- tory role in salinity tolerance (Gao et al., 2011). It is known that miRNAs from the miR169 family respond differently to drought, salinity, low temperatures and aluminium in plants (Zhao et al., 2007; Liu et al., 2008; Zhou et al., 2008; Zhao et al., 2009). In response to salinity and drought stress in rice, the expression of the nuclear transcriptionfactor YA (NF-YA) genes is modulated by members of the miR169 family (Zhao et al., 2009). In A. thaliana, nf-ya plants and plants overexpressing miR169 are more sensi- tive to drought (Li et al., 2008). On the contrary in tomato, plants overexpressing miR169c, which targets a gene in- volved in the opening and closing of stomata, are more tol- erant to drought (Zhang et al., 2011a). A reduction in the expression of miR530a, miR1445, miR1446a-e and miR1447 in Populus trichocarpa was detected in plants un- der drought and salinity, which is different from the miR1450 pattern of expression, downregulation under drought conditions and upregulation under high salinity (Lu et al., 2008). In Triticum dicoccoides, the ancestor of cultivated wheat, the upregulation of miR1450 revealed an inverse response when compared with Populus trichocarpa under drought conditions (Kantar et al., 2011). Although the gene MIR1450 is present in both monocot and dicots, the expression patterns suggest regulatory differences un- der drought (Lu et al., 2008; Kantar et al., 2011). The for- mation of the superoxide anion O 2- in response tostresses is converted into less toxic molecules by superoxide dismu- tases SOD1 and SOD2 proteins, whose mRNAs are tar- geted by miR398 (Sunkar et al., 2006; Jagadeeswaran et
The intensity and quality of light (e.g. the amount of UV-B available) signiﬁcantly affect grape quality as they modulate the production of phenolic compounds (mostly ﬂavonoids) and cuticular waxes (Tilbrook et al. 2013). In a commercial vineyard of ‘Sauvignon Blanc’ in South Africa, plants were shaded with UV-excluding acrylic panels applied to the bunch zone in order to monitor the differences on core metabolic processes in grapes due to the amount of UV-B (Joubert et al. 2016). Metabolite proﬁles during berry developmental revealed speciﬁc adjustments to typical UV-acclimation processes, such as the content of carotenoids and asso- ciated xanthophyll cycle metabolites in photosyntheti- cally active green berries (Joubert et al. 2016). In ripe berries, on the other hand, UV-B favored the produc- tion of volatile and polyphenolic compounds with direct antioxidant and/or ‘sunscreening’ abilities (Joubert et al. 2016), directly inﬂuencing grape composition. In ‘Mal- bec’ berries, UV-B screening was shown to delay berry development and maturation, whereas UV-B combined with ABA hastened berry sugar and phenol accumu- lation, anticipating ripening up to 20 days (Berli et al. 2011). Therefore, it is possible to notice that the increase of UV-B radiation inherent to the forthcoming climate changes may in fact work in favor of viticulture by antic- ipating ripening and thus helping to decrease exposure to summer heat waves and also by countering the predicted decreases in grape quality.
C-repeat-binding factors (CBFs) are a type of important regulon in stress-related signal transduction pathways that control plant tolerance of abiotic stress. Ammopiptanthus mongolicus is the only evergreen broadleaf shrub in the northwest desert of China. The species shows strong resistance to environmental stress, especially to cold stress. An A. mongolicus CBF1 gene (AmCBF1) was cloned and transformed into tobacco. Expression of AmCBF1 could be detected in A. mongolicus shortly after exposure to low temperature of 4°C. Analysis on ratio of electrolytic leakage, soluble sugar content, free proline content, malondialdehyde (MDA) content and peroxidase (POD) activity before and after cold treatment (4°C) for 24 h indicated AmCBF1 conferred higher cold toleranceto AmCBF1 transgenictobacco compared with the wild type and empty vector transformed tobacco.
presence of the allele. A sample was considered negati- ve for a particular allele when the amplicon was absent. Furthermore, as the DNA starting material for each allele-specifi c genotyping reaction came from the same DNA sample, one control the other in detecting either a false negative reaction secondary to extraction failure or the presence of an inhibitor. The accuracy of the genotype discrimination was demonstrated by direct sequencing of the PCR product amplifi ed from 63 se- lected samples using primers rs7903146 seq and rs7903146 R, which span the polymorphic region. PCR products were sequenced in both the sense and antisense orientations, with the use of an automated sequencer (ABI-377, Perkin-Elmer).
In contrast to the wealth of supportive data obtained by Notch gain-of-function analysis, several genetic studies using loss-of- function approaches have not identified an essential role for Notch signaling in adult HSCs. Conditional deletion of either Jag1, Notch1, Notch1 and Notch2 together, or Rbpj in adult HSCs show no effect on HSC maintenance or proliferation (Radtke et al., 1999; Mancini et al., 2005; Maillard et al., 2008). Similarly, combinatorial deletion of Jag1 in BM stromal cells and inactivation of Notch1 in HSCs revealed no effect on HSC maintenance, therefore excluding an essential contribution of Jag1-mediated Notch1 signaling for adult HSC self-renewal (Mancini et al., 2005). However, these studies did not address the redundancy that could result from expression of other Notch receptors or ligands in hematopoietic tissues. This issue was subsequently addressed using genetic approaches inhibiting all canonical Notch signals in adult HSCs by conditional ablation of Rbpj, and in parallel experiments where a dominant-negative (dn) MAML1 retroviral construct (Maillard et al., 2008) was expressed in HSCs. Neither RBPJ- deficient nor dnMAML1-expressing HSCs showed any HSC defects in stringent SC assays (Maillard et al., 2008). Although Notch1, Notch2 and Hes1 are expressed in HSCs, albeit at low transcript levels (Maillard et al., 2008), a physiological role for the transcriptional Notch target Hes1 has not been established in HSCs (Wendorff et al., 2010). Consequently, these results provide conclusive evidence that Notch signaling does not play an obligate physiological role in adult HSC homeostasis under steady-state conditions or in competitive and stress situations. Nevertheless, although Notch signaling is dispensable in adult HSCs, the studies showing that HSCs can be successfully expanded by Notch activation in vitro may still prove useful, particularly for clinical purposes (Fig. 6).
Previous studies of abiotic stress response in the grapevine variety Aragonez assigned metabolism and its sub-bin protein folding as the mostly upregulated bin in HS and WS (Rocheta et al., 2014). In our study, this bin (protein metabolism and modification) was well distributed between downregulated and upregulated DEGs but the overall tendency observed in most of the varieties studied here, both in Dois Portos and in Pegões, was indeed for a strong upregulation of DEGs belonging to this bin (even those previously identified as downregulated). In grapevine subjected to drought and salinity the most representative functional categories were also protein fate and metabolism (Cramer et al., 2007) as was the case of rice under drought (Gorantla et al., 2007). In Quercus suber subjected to drought, the most representative bins were metabolism, response to stimulus, and cellular processes (Magalhães et al., 2016), which falls in line with the behavior of all the grapevine varieties studied here, with the exception of AV in Pegões and TB in Dois Portos. In a recent study of several varieties subjected do defoliation, common markers of response to that treatment were found (Zenoni et al., 2017), an indication that, despite a high degree of varietal specificity there is some room for finding universal indicators to use as a screening method. Even varieties with different levels of toleranceto a specific stress, such as ‘Cabernet Sauvignon,’ ‘Riparia Gloire,’ and ‘Ramsey’ in relation to drought, the response of ABA and ethylene signaling hubs was found to be highly similar (Hopper et al., 2016). Nevertheless, if the differences intolerance are related to a physiologically specific mechanism such as whether the variety in question is isohydric or anisohydric, the type of response is specific to each condition, with isohydric varieties showing faster transcriptome response, swifter ABA- related gene modulation, higher HSP expression levels and faster return to basal levels once the stress subsides (Dal Santo et al., 2016). Anisohydric varieties, on the other hand, show stronger activation of ROS-scavenging enzymes, molecular chaperones and abiotic stress-related genes (Dal Santo et al., 2016).
obtained from studies with tobacco (Nicotiana tabacum L.) plants infected with Tobacco mosaic virus (TMV) genus Tobamovirus (van Kooten et al., 1990; Balachandran & Osmond, 1994; Seo et al., 2000). Various results indicate increase in non-photochemical quenching of fluorescence and reduction in the fraction of open reaction centres, leading to an increased reduction state of the primary electron transport acceptor quinone A (Q A ). This suggests pronounced photo inhibitory processes following viral infection and symptom development. In addition to the influence on the photosynthetic processes, other studies with transgenic plants expressing the movement protein of TMV have shown its effects on carbon metabolism, altering carbohydrate partitioning and plasmodesmal function between mesophyll cells (Balachandran et al., 1995; Lucas et al., 1996; Olesinski et al., 1996). Similar results arose from studies with transgenictobacco plants expressing the movement protein of Potato leafroll virus (PLRV), family Luteoviridae, genus Potyvirus (Herbers et al., 1997). The source leaves of the transgenic plants showed accumulation of carbohydrates leading to a decrease in photosynthetic capacity, probably due to decreased expression of photosynthetic proteins. An inhibitory feedback mechanism was postulated to be responsible for decreasing photosynthetic gene expression, since the reduction in photosynthesis was restricted to leaves with high carbohydrate content. In plants expressing the luteoviral movement protein (MP17), plasmodesmal alterations took place in the phloem tissue, while plasmodesmata in the mesophyll were indistinguishable from the wild-type (Herbers et al., 1997). In addition, Hofius et al. (2001) demonstrated that the plasmodesmal targeting and gating capacity of MP17 is not influenced by protein amount, whereas changes in carbohydrate status and viral resistance follow a protein level-dependent mechanism. Corroborating these findings, Herbers et al. (2000) described apoplastic sucrose accumulation intobacco plants infected with Potato virus Y (PVY) family Potyviridae, genus Potyvirus. These authors proposed a role for cell wall invertase in up-regulating the accumulation of soluble sugars and down-regulating photosynthesis, thus strengthening defence responses against viral attack.