Water Stress Responses of Tomato Mutants Impaired in Hormone Biosynthesis Reveal Abscisic Acid, Jasmonic Acid and Salicylic Acid Interactions

To investigate the putative crosstalk between JA and ABA in Solanum lycopersicum plants in response to drought, suppressor of prosystemin-mediated responses2 (spr2, JA-deficient) and flacca (flc, ABA-deficient) mutants together with the naphthalene/salicylate hydroxylase (NahG) transgenic (SA-deficient) line were used. Hormone profiling and gene expression of key enzymes in ABA, JA and SA biosynthesis were analyzed during early stages of drought. ABA accumulation was comparable in spr2 and wild type (WT) plants whereas expression of 9-cis-epoxycarotenoid dioxygenase 1 (NCED1) and NCED2 was different, implying a compensation mechanism between NCED genes and an organ-specific regulation of NCED1 expression. JA levels and 12-oxo-phytodienoic acid reductase 3 (OPR3) expression in flc plants suggest that ABA regulates the induction of the OPR3 gene in roots. By contrast, ABA treatment to flc plants leads to a reduction of JA and SA contents. Furthermore, different pattern of SA accumulation (and expression of isochorismate synthase and phenylalanine ammonia lyase 1) was observed between WT seedlings and mutants, suggesting that SA plays an important role on the early response of tomato plants to drought and also that JA and ABA modulate its biosynthesis. Finally, hormone profiling in spr2 and NahG plants indicate a crosstalk between JA and SA that could enhance tolerance of tomato to water stress

Expression of LHC genes and their relation to photooxidative stress tolerance in Solanum lycopersicum L. and Solanum chilense (Dunal) Reiche

Simultaneous exposition to low temperature and high light radiation cause photoinhibition of photosynthetic apparatus, affecting the productivity and geographical distribution of agricultural crops. In several Solanaceous species, tolerance to low temperature stress in combination with high light has been associated with some stimulation in non-photochemical quenching (NPQ), which involved reorganization in light-harvesting complex (LHC) proteins. To study photosynthetic performance in Solanum lycopersicum L. and S. chilense (Dunal) Reiche, and to investigate transcriptional regulation of genes encoding LHC proteins and their involvement in the NPQ, plants of both species were exposed to low temperature (4 °C) and high light radiation (1300 μmol m-2 s-1). Lipid peroxidation, photochemical efficiency, and changes in xanthophyll cycle pigments were measured. The results presented here indicate that S. chilense showed higher tolerance to photoinhibition than S. lycopersicum under low-temperature and high light conditions, increasing light-energy consumption in photochemical processes by increasing photosynthetic capacity as indicated by photochemical quenching (qP) and relative electron transport rate (ETR) parameters. The contribution of light-harvesting chlorophyll a/b binding (LHC) protein was not related to dissipate excess excitation energy as heat (NPQ), but rather with the antioxidant function attributable to zeaxanthin as indicated by the amount of peroxidized lipids in S. chilense. We suggest that the differential expression of Lhca1 transcripts, with zeaxanthin binding sites could contribute to the greater tolerance of S. chilense to photoxidative stress

Modulation of organic acids and sugar content in tomato fruits by an abscisic acid-regulated transcription factor

Growing evidence suggests that the phytohormone abscisic acid (ABA) plays a role in fruit development. ABA signaling components of developmental programs and responses to stress conditions include the group of basic leucine zipper transcriptional activators known as ABA-response element binding factors (AREBs/ABFs). AREB transcription factors mediate ABA-regulated gene expression involved in desiccation tolerance and are expressed mainly in seeds and in vegetative tissues under stress; however, they are also expressed in some fruits such as tomato. In order to get an insight into the role of ABA signaling in fruit development, the expression of two AREB-like factors were investigated during different developmental stages. In addition, tomato transgenic lines that overexpress and downregulate one AREB-like transcription factor, SlAREB1, were used to determine its effect on the levels of some metabolites determining fruit quality. Higher levels of citric acid, malic acid, glutamic acid, glucose and fructose were observed in SlAREB1-overexpressing lines compared with those in antisense suppression lines in red mature fruit pericarp. The higher hexose concentration correlated with increased expression of genes encoding a vacuolar invertase (EC 3.2.1.26) and a sucrose synthase (EC 2.4.1.13). No significant changes were found in ethylene content which agrees with the normal ripening phenotype observed in transgenic fruits. These results suggest that an AREB-mediated ABA signal affects the metabolism of these compounds during the fruit developmental program

The transcription factor AREB1 regulates primary metabolic pathways in tomato fruits

Tomato fruit development is regulated both by the action of plant hormones and by tight genetic control. Recent studies suggest that abscisic acid (ABA) signalling may affect different aspects of fruit maturation. Previously, it was shown that SlAREB1, an ABA-regulated transcription factor involved in stress-induced responses, is expressed in seeds and in fruit tissues in tomato. Here, the role of SlAREB1 in regulating the expression of genes relevant for primary metabolic pathways and affecting the metabolic profile of the fruit was investigated using transgenic tomato lines. Metabolite profiling using gas chromatography–time of flight mass spectrometry (GC-TOF-MS) and non-targeted liquid chromatography–mass spectrometry (LC-MS) was performed on pericarp tissue from fruits harvested at three stages of fruit development. Principal component analysis of the data could distinguish the metabolite profiles of non-transgenic fruits from those that overexpress and down-regulate SlAREB1. Overexpression of SlAREB1 resulted in increased content of organic acids, hexoses, hexose-phosphates, and amino acids in immature green, mature green, and red ripe fruits, and these modifications correlated with the up-regulation of enzyme-encoding genes involved in primary carbohydrate and amino acid metabolism. A non-targeted LC-MS analysis indicated that the composition of secondary metabolites is also affected in transgenic lines. In addition, gene expression data revealed that some genes associated with fruit ripening are also up-regulated in SlAREB1-overexpressing lines compared with wild-type and antisense lines. Taken together, the results suggest that SlAREB1 participates in the regulation of the metabolic programming that takes place during fruit ripening and that may explain part of the role of ABA in fruit development in tomato

Engineered drought-induced biosynthesis of α-tocopherol alleviates stress-induced leaf damage in tobacco

Tocopherols are members of the vitamin E complex and essential antioxidant compounds synthesized in chloroplasts that protect photosynthetic membranes against oxidative damage triggered by most environmental stresses. Tocopherol deficiency has been shown to affect germination, retard growth and change responses to abiotic stress, suggesting that tocopherols may be involved in a number of diverse physiological processes in plants. Instead of seeking constitutive synthesis of tocopherols to improve stress tolerance, we followed an inducible approach of enhancing α-tocopherol accumulation under dehydration conditions in tobacco. Two uncharacterized stress inducible promoters isolated from Arabidopsis and the VTE2.1 gene from Solanum chilense were used in this work. VTE2.1 encodes the enzyme homogentisate phytyltransferase (HPT), which catalyzes the prenylation step in tocopherol biosynthesis. Transgenic tobacco plants expressing ScVTE2.1 under the control of stress-inducible promoters showed increased levels of α-tocopherol when exposed to drought conditions. The accumulation of α-tocopherol correlated with higher water content and increased photosynthetic performance and less oxidative stress damage as evidenced by reduced lipid peroxidation and delayed leaf senescence. Our results indicate that stress-induced expression of VTE2.1 can be used to increase the vitamin E content and to diminish detrimental effects of environmental stress in plants. The stress-inducible promoters introduced in this work may prove valuable to future biotechnological approaches in improving abiotic stress resistance in plants.We thank Mónica Yañez (Universidad de Talca) and Sara Izquierdo (Universitat Jaume I) for their technical assistance. This work was supported by Fondo de Fomento al Desarrollo Científico y Tecnológico (Chile; grant No. D081-1118). A.E. was supported by fellowships from Mecesup (Chile), Comisión Nacional de Investigación Científica y Tecnológica (Chile) and the Federation of European Biochemical Societies

Characterization of a putative grapevine Zn transporter, VvZIP3, suggests its involvement in early reproductive development in Vitis vinifera L

Abstract Background Zinc (Zn) deficiency is one of the most widespread mineral nutritional problems that affect normal development in plants. Because Zn cannot passively diffuse across cell membranes, it must be transported into intracellular compartments for all biological processes where Zn is required. Several members of the Zinc-regulated transporters, Iron-regulated transporter-like Protein (ZIP) gene family have been characterized in plants, and have shown to be involved in metal uptake and transport. This study describes the first putative Zn transporter in grapevine. Unravelling its function may explain an important symptom of Zn deficiency in grapevines, which is the production of clusters with fewer and usually smaller berries than normal. Results We identified and characterized a putative Zn transporter from berries of Vitis vinifera L., named VvZIP3. Compared to other members of the ZIP family identified in the Vitis vinifera L. genome, VvZIP3 is mainly expressed in reproductive tissue - specifically in developing flowers - which correlates with the high Zn accumulation in these organs. Contrary to this, the low expression of VvZIP3 in parthenocarpic berries shows a relationship with the lower Zn accumulation in this tissue than in normal seeded berries where its expression is induced by Zn. The predicted protein sequence indicates strong similarity with several members of the ZIP family from Arabidopsis thaliana and other species. Moreover, VvZIP3 complemented the growth defect of a yeast Zn-uptake mutant, ZHY3, and is localized in the plasma membrane of plant cells, suggesting that VvZIP3 has the function of a Zn uptake transporter. Conclusions Our results suggest that VvZIP3 encodes a putative plasma membrane Zn transporter protein member of the ZIP gene family that might play a role in Zn uptake and distribution during the early reproductive development in Vitis vinifera L., indicating that the availability of this micronutrient may be relevant for reproductive development.</p