From: Tobacco drought stress responses reveal new targets for Solanaceae crop improvement
 | Tissue | Observations | Comments |
---|---|---|---|
UP-REGULATED GENES | Â | Â | Â |
NtERF187 | Leaves and roots | 295-fold induced after 40Â minutes in root. 23-fold in leaf after one hour. | Similar to Arabidopsis drought-inducible AtERF53, that regulates drought-responsive gene expression by binding to the GCC box and/or dehydration-responsive element (DRE) in the promoter of downstream genes. Overexpression of AtERF53 driven by the CaMV35S promoter resulted in an unstable drought-tolerant phenotype. |
NtERF114 and NtERF202 | Leaves | Rapid and transient up-regulation in leaves with a maximum of 37-55-fold induction after one hour. | Similar to Arabidopsis AtDREB1a/AtCBF3 which is involved in response to low temperature, drought, and abscisic acid. |
NtERF228 | Leaves and roots | Rapid and transient up-regulation in roots with a maximum of 127-fold induction at the first time point. Similar rapid and transient up-regulation in leaves. | Similar to Arabidopsis AtDREB1a/AtCBF3 which is involved in response to low temperature, drought, and abscisic acid. |
NtMYB149 | Roots only | Rapid up-regulation reaching 131-fold after 40Â minutes. Not inducible in leaves. | Similar to AtMYB15. AtMYB15 is involved in ABA-, ethylene-, and JA-mediated signaling pathways, the response to salt stress, and the response to water deprivation |
NtERF218 | Leaves and roots | Rapid and transient up-regulation in both tissues. | Similar to Arabidopsis AtDREB1a/AtCBF3 which is involved in response to low temperature, drought, and abscisic acid. |
NtWRKY1 | Leaves and roots | Rapid and transient induction in leaves (28-fold). Low level induction in roots. | The apparent ortholog of AtWRKY33, which had been shown to play major roles in the response to stress including abiotic stress. |
NtERF75 | Leaves and roots | Strong (130-fold) late induction in leaves. Late and lower level induction in roots. | Similar to a member of the DREB subfamily A-6 in Arabidopsis. There are 8 members in this subfamily including RAP2.4. |
Ninja-family protein AFP3/ABI five-binding protein 3 | Leaves only | 25-fold induced in leaves. Not induced in roots. (CHO_OF648xm02r1) | The Arabidopsis ortholog acts as a negative regulator of abscisic acid (ABA) responses and stress responses. Also called ABI five-binding protein 3. |
Glutathione peroxidases | Â | 75-fold induced in leaves and 24-fold in roots. (CHO_OF6818xm12r1 and FG645026) | Control of H2O2 homeostasis, and linking ABA and H2O2 signaling in stomatal closure. |
Protein phosphatase 2C genes | Leaves and roots | Several genes up-regulated 20–70 fold in leaves and roots. (CHO_OF4760xf16r1 and EST EB442706) | Protein phosphatase PP2Cs acts as constitutive negative regulators of SnRK2 kinases whose autophosphorylation is required for kinase activity towards downstream targets in the ABA signaling network. |
NtUPLL1 and NtUPLL2 | Leaves and roots | NtUPLL1 is the most strongly up-regulated gene in leaves (291-fold) and both genes are strongly induced in both leaves and roots. (CHO_OF4952xo16r1 and CHO_OF569xh04r1) | Similar to the Arabidopsis U-Box E3 ubiquitin ligases AtPUB18 and AtPUB19 that negatively regulate ABA-mediated stomatal closure and drought stress responses. |
ABA 8'-hydroxylase CYP707A1 | Leaves and roots | Transiently up-regulated in the leaf (28-fold after 40Â minutes). 6-fold in roots. (EST TC18468) | Play a major regulatory role in controlling the level of ABA in plants. Catabolizes ABA. |
5-Epiaristolochene 1,3-Dihydroxylase | Leaves and roots | 33-fold transiently induced in leaves. Not induced in roots. (EST AM821089) | Capsidiol is produced by Solanaceae plants in response to stresses such as pathogen or elicitor challenge. |
Cytochrome P450 CYP94C1 | Leaves and roots | Transiently up-regulated with a peak of 115-fold after 40Â minutes in roots. Up-regulated later and less in leaves. (CHO_OF3036xp15r1, CHO_OF4654xf08r1 and CHO_OF3295xn18r1) | Arabidopsis cytochrome P450, CYP94C1 is involved in JA-Ile oxidation. The enzyme catalyzes catabolic turnover of JA-Ile. CYP94C1 and CYP94B3 catalyze successive oxidation steps in JA-Ile turnover. |
Cytochrome P450 CYP94B3 | Leaves and roots | Transiently up-regulated with a peak of 101-fold after 40Â minutes in roots. Up-regulated later and less in leaves. (EST TC39596 and CHO_OF646xl21r1) | Arabidopsis cytochrome P450, CYP94C1 is involved in JA-Ile oxidation. The enzyme catalyzes catabolic turnover of JA-Ile. CYP94C1 and CYP94B3 catalyze successive oxidation steps in JA-Ile turnover. |
Anthocyanidin synthase | Roots | 61-fold induced after one hour of drought. (CHO_OF559xd02r1) | Catalyzes the penultimate step in the biosynthesis of anthocyanins |
UDP-glycosyltransferase 74B1 | Roots | 54-fold induced after four hours of drought. (CHO_OF354xn10f1) | Involved in glucosinolate biosynthesis. |
Inositol polyphosphate 5-phosphatase | Roots | 35-fold after four hours of drought. (EST AM835516) | Predicted to modulate the phosphoinositide pathway, ABA levels and drought responses. |
NtWRKY69, NtWRKY3, NtWRKY10, and NtWRKY12 | Leaves (NtWRKY3 and 69) and roots (others) | All show early induction (20–40 minutes) | Apparent Solanaceae-specific induction of genes in Group IId. Tomato SlWRKY10 is also induced by drought in leaves. Potential genes for improvement of Solanaceae drought responses. |
DOWN-REGULATED GENES | Â | Â | Â |
Heat shock proteins HSF25 and HSP40/DnaJ | Roots | HSF25-like gene down-regulated 39-fold in roots only. HSP40/DnaJ-like gene 16-fold down-regulated in roots only. (CHO_OF623xn12f1 and EST AM780669) | Function in unfolded protein binding, heat shock protein binding. |
bZIP102 | Leaves | mRNA level goes down 11-fold in leaves | Closest Arabidopsis proteins are AtbZIP34 and AtbZIP61. Function unclear. |
METABOLITES | Â | Â | Â |
4-hydroxy-2-oxoglutaric acid (KHG) | Roots | Rapid early increase and 70-fold increase by 4Â hours. | Possible novel mechanism to restart respiration upon water availability after drought. Appears specific to tobacco/Solanaceae as there is no increase in level during drought in soybean. |
Mannitol and trehalose | Roots | Later time points were marked by a sharp increase in mannitol and trehalose. | Act as an osmoprotectants (compatible solute). |
Galactinol and Raffinose | Leaves | In the leaf, galactinol and raffinose were undetectable until the final 240Â min time point, suggesting an activation of the pathway due to the stress. | The raffinose pathway can provide osmolytes in situations of low water potential. |
Oxidized glutathione (GSSG) and dehydroascorbate | Roots and leaves | GSSG levels increase 12-fold in roots. Dehydroascorbate levels double in leaves. | The glutathione-ascorbate cycle detoxifies hydrogen peroxide which is a reactive oxygen species and the cycle is activated in tobacco as a response to drought. |
γ-aminobutyrate (GABA) | Roots | GABA levels increase 7.8-fold in roots. | The GABA shunt is a stress response pathway, the functions of which include controlling cytoplasmic pH, maintaining C/N balance by converting glutamate in the cytosol to succinate in the TCA cycle, and aiding in oxidative stress protection by generating NADH and succinate. |
Glycine and serine | Leaves | Dramatic reduction of glycine and serine levels in leaves to 2-4% of initial values. | Tobacco tissues down-regulate photorespiration during drought as a mechanism to reduce the accumulation of toxic ammonia. |
Inosine | Roots | Increases nearly 50-fold. | Probable nucleotide salvage pathway to recycle nucleosides. Inosine is formed by the deamination of adenosine. |
HORMONES | Â | Â | Â |
ABA (abscisate/abscisic acid) | Roots and leaves | The ABA concentration increased 8-fold after four hours in root tissue. ABA 8'-hydroxylase CYP707A1 genes are strongly and transiently up-regulated in the leaf. Many ABA responsive genes are up-regulated in both tissues. Components of ABA signaling such as protein phosphatase 2C genes are up-regulated. | ABA clearly plays a central role in regulating drought responses in tobacco. |
JA (Jasmonate) | Roots | All of the biosynthetic enzyme genes in the JA biosynthetic pathway are rapidly and coordinately up-regulated in roots. At the metabolite level, there was a biphasic increase in N-delta-acetylornithine, which rises in response to JA. Many JA signaling components such as JAZ repressors are differentially regulated. | JA clearly plays an important role in the response to drought in tobacco, especially in the roots. |
Ethylene (Ethene) | Roots and leaves | The biosynthetic enzyme genes in the ethylene biosynthetic pathway show up-regulation with strong tissue-specific up-regulation of ACC synthase genes and, to a lesser extent, ACC oxidase genes. | Ethylene plays a role in the regulation of drought responses. |
PROMOTERS | Â | Â | Â |
NtWRKY69 | Leaves | Inducible by drought. Expression progresses upwards from the root and is initially in the vascular tissue before expression in all of the leaf. Also inducible by cold and possibly wounding. | Drought inducible promoter for leaf-inducible expression. ABA independent. Expression initially follows the vascular tissue upwards from the roots before spreading into all leaf cells. Contains three potential bHLH binding sites (CANNTG), one W box (TTGACT), one MYB binding site (CGGTCA). |
One of the Group IId genes that our data suggest may be part of a Solanaceae-specific response to drought. | |||
NtWRKY3 | Leaves | Inducible by drought. Also inducible by cold and possibly wounding | Drought and cold inducible promoter. One of the Group IId genes that our data suggest may be part of a Solanaceae-specific response to drought. |
NtWRKY70 | Leaves | Inducible by drought. Also inducible by cold and wounding | Drought, wound, and cold inducible promoter. |
NtUPLL2 | Leaves | Inducible by drought. Also inducible by cold and possibly wounding | Drought and cold inducible promoter. |
NtGolS | Leaves | Inducible by drought. Also inducible by cold and wounding | Drought, wound, and cold inducible promoter. |