Overexpression of a 9-cis-Epoxycarotenoid Dioxygenase Gene in Nicotiana plumbaginifolia Increases Abscisic Acid and Phaseic Acid Levels and Enhances Drought Tolerance

Abstract

The plant hormone abscisic acid (ABA) plays important roles in seed maturation and dormancy and in adaptation to a variety of environmental stresses. An effort to engineer plants with elevated ABA levels and subsequent stress tolerance is focused on the genetic manipulation of the cleavage reaction. It has been shown in bean (Phaseolus vulgaris) that the gene encoding the cleavage enzyme (PvNCED1) is up-regulated by water stress, preceding accumulation of ABA. Transgenic wild tobacco (Nicotiana plumbaginifolia Viv.) plants were produced that overexpress the PvNCED1 gene either constitutively or in an inducible manner. The constitutive expression of PvNCED1 resulted in an increase in ABA and its catabolite, phaseic acid (PA). When the PvNCED1 gene was driven by the dexamethasone (DEX)-inducible promoter, a transient induction of PvNCED1 message and accumulation of ABA and PA were observed in different lines after application of DEX. Accumulation of ABA started to level off after 6 h, whereas the PA level continued to increase. In the presence of DEX, seeds from homozygous transgenic line TN1 showed a 4-d delay in germination. After spraying with DEX, the detached leaves from line TN1 had a drastic decrease in their water loss relative to control leaves. These plants also showed a marked increase in their tolerance to drought stress. These results indicate that it is possible to manipulate ABA levels in plants by overexpressing the key regulatory gene in ABA biosynthesis and that stress tolerance can be improved by increasing ABA levels.Abscisic acid (ABA) is necessary for seed maturation and dormancy and adaptation to a variety of environmental stresses. The role of ABA in these processes is mediated by changes in gene expression and stomatal closure. Mutants impaired in ABA biosynthesis display precocious germination and have a wilty phenotype (Zeevaart, 1999). Application of ABA results in delayed germination and increased tolerance to a variety of stresses.It is now well established that ABA in higher plants is derived from C 40 -carotenoids (Cutler and Krochko, 1999;Liotenberg et al., 1999;Taylor et al., 2000). Epoxidation of the C 40 -carotenoid, zeaxanthin, gives rise to all-trans-violaxanthin, one of the xanthophylls in higher plants. This reaction is catalyzed by zeaxanthin epoxidase (ZEP). The ZEP gene was isolated from the aba2 mutant of wild tobacco (Nicotiana plumbaginifolia) and the aba1 mutant of Arabidopsis (Marin et al., 1996). The xanthophylls also include three other isomers, 9-cis-violaxanthin, all-transneoxanthin, and 9-cis-neoxanthin. Genes encoding neoxanthin synthase have been cloned from potato (Solanum tuberosum; Al-Babili et al., 2000) and tomato (Lycopersicon esculentum; Bouvier et al., 2000).The first C 15 precursor of ABA is xanthoxin, which is a cleavage product of C 40 -epoxy-carotenoids. Current evidence indicates that the key regulatory step in ABA biosynthesis is the oxidative cleavage reaction . The gene encoding the cleavage enzyme was first cloned from the ABA-deficient muta...

Phytohormones and Effects on Growth and Metabolites of Microalgae: A Review

“…The concentration fluctuation of endogenous ABA is considered a signal for the gene expression of proteins such as dehydrins, which is sensitive to cold, drought, and salinity stress [62]. It has also been stated that overexpressing the key regulatory gene involved in ABA biosynthesis can increase ABA concentration in plants and the higher ABA level boosts stress tolerance [63]. Similarly, it has been shown that ABA improves resistance to temperature and salinity stresses by controlling the uptake of water and ions in higher plants [64].…”

Expression and Localization of Arachis Hypogaea 9-Cis Epoxycarotenoid Dioxygenase 1 (AhNCED1) of Peanut Under Water Stress

“…the promoter activity was enhanced by water stress. thompson et al (22) indicated that in leaves of tomato 9-cis-epoxycarotenoids is present in abundance, and the enzyme activities involved in the reaction from xanthoxin to ABA are constitutive (14). therefore, these results provide evidence that leaves and roots may be responsive to water stress resulting in increased ABA accumulation.…”

An Update on the Role of NCED and CYP707A ABA Metabolism Genes in Seed Dormancy Induction and the Response to After-Ripening and Nitrate

“…Thus, induction of AtNCED6 during A. thaliana (Col-0) imbibition increases the ABA level more than 20-fold and this is sufficient to prevent germination; whereas induction of AtNCED6 during seed development increased seed dormancy and reduced or eliminated viviparism. Inducing expression of a bean NCED gene in tobacco (N. tabacum) seeds also using the dexamethasone-inducible system resulted in incomplete suppression of germination (Qin and Zeevaart 2002). On the other hand, the overexpression of AtNCED6 in non-dormant mutants of Arabidopsis tt3 and tt4 (tt refers to a transparent testa; Debeaujon andothers 2000, 2003 ) restores the dormant status (Martínez-Andújar and others 2011).…”

“…2). The 9-cis-xanthoxin formation is now considered to be the rate-limiting step and the NCED genes play a pivotal role in ABA biosynthesis (Qin and Zeevaart 2002;Toh and others 2008;Nambara and others 2010). Specifically, the cleavage of xanthophylls (C40) by NCED that generates cis-xanthoxin is a highly regulated point in higher plants (North and others 2007;Jia and others 2011) and although both 9-cis-neoxanthin and 9-cisviolaxanthin are substrates of NCED in vivo, 9-cis-neoxanthin seems to be the major substrate.…”

“…On the other hand, HvNCED1 and HvN-CED2 expression was studied in relation to induction of primary and secondary dormancy and the authors conclude that both genes seem to be linked to secondary dormancy (Leymarie and others 2008). Overexpression of bean PvNCED1 in tobacco, and of AtNCED3 in Arabidopsis provokes increased ABA levels in seeds and extended seed dormancy (Iuchi and others 2001;Qin and Zeevaart 2002).…”