[show abstract][hide abstract] ABSTRACT: Carotenoid cleavage, catalyzed by the 9-cis-epoxycarotenoid dioxygenase (NCED) constitutes a key step in the regulation of ABA biosynthesis. In Arabidopsis, this enzyme is encoded by five genes. NCED3 has been shown to play a major role in the regulation of ABA synthesis in response to water deficit, whereas NCED6 and NCED9 have been shown to be essential for the ABA production in the embryo and endosperm that imposes dormancy. Reporter gene analysis was carried out to determine the spatiotemporal pattern of NCED5 and NCED9 gene expression. GUS activity from the NCED5 promoter was detected in both the embryo and endosperm of developing seeds with maximal staining after mid-development. NCED9 expression was found at early stages in the testa outer integument layer 1, and after mid-development in epidermal cells of the embryo, but not in the endosperm. In accordance with its temporal- and tissue-specific expression, the phenotypic analysis of nced5 nced6 nced9 triple mutant showed the involvement of the NCED5 gene, together with NCED6 and NCED9, in the induction of seed dormancy. In contrast to nced6 and nced9, however, nced5 mutation did not affect the gibberellin required for germination. In vegetative tissues, combining nced5 and nced3 mutations reduced vegetative growth, increased water loss upon dehydration, and decreased ABA levels under both normal and stressed conditions, as compared with nced3. NCED5 thus contributes, together with NCED3, to ABA production affecting plant growth and water stress tolerance.
The Plant Journal 12/2011; 70(3):501-12. · 6.58 Impact Factor
[show abstract][hide abstract] ABSTRACT: Water economy in agricultural practices is an issue that is being addressed through studies aimed at understanding both plant water-use efficiency (WUE), i.e. biomass produced per water consumed, and responses to water shortage. In the model species Arabidopsis thaliana, the ESKIMO1 (ESK1) gene has been described as involved in freezing, cold and salt tolerance as well as in water economy: esk1 mutants have very low evapo-transpiration rates and high water-use efficiency. In order to establish ESK1 function, detailed characterization of esk1 mutants has been carried out. The stress hormone ABA (abscisic acid) was present at high levels in esk1 compared to wild type, nevertheless, the weak water loss of esk1 was independent of stomata closure through ABA biosynthesis, as combining mutant in this pathway with esk1 led to additive phenotypes. Measurement of root hydraulic conductivity suggests that the esk1 vegetative apparatus suffers water deficit due to a defect in water transport. ESK1 promoter-driven reporter gene expression was observed in xylem and fibers, the vascular tissue responsible for the transport of water and mineral nutrients from the soil to the shoots, via the roots. Moreover, in cross sections of hypocotyls, roots and stems, esk1 xylem vessels were collapsed. Finally, using Fourier-Transform Infrared (FTIR) spectroscopy, severe chemical modifications of xylem cell wall composition were highlighted in the esk1 mutants. Taken together our findings show that ESK1 is necessary for the production of functional xylem vessels, through its implication in the laying down of secondary cell wall components.
PLoS ONE 01/2011; 6(2):e16645. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The cleavage of 9-cis-epoxycarotenoids to xanthoxin, catalyzed by 9-cis-epoxycarotenoid dioxygenases, is considered to be the key regulatory step of abscisic acid (ABA) biosynthesis. In Arabidopsis, genes for these enzymes form a multigene family with nine members, only five of which are thought to be involved in ABA production. In contrast to the prominent function of AtNCED3 in stress responses, the physiological and developmental role of the other 9-cis-epoxycarotenoid dioxygenases (NCEDs) remain unknown. Our functional and expression analyses have revealed that AtNCED6 and AtNCED9 are required for ABA biosynthesis during seed development. Reverse genetic analysis showed that ABA levels were reduced in Atnced6 and Atnced9 mutant seeds. In addition, transgenic plants overexpressing the AtNCED6 gene overproduced ABA. In accordance with mutant phenotypes, both AtNCED6 and AtNCED9 exhibited seed-specific expression. Detailed cytological studies were carried out, either by using transcriptional fusions of the promoter with GUS and GFP reporter genes, or by in situ hybridization. Expression of AtNCED6 was observed exclusively in the endosperm during seed development, that of AtNCED9 in both embryo and endosperm at mid-development. In addition to reduced ABA levels, Atnced6 and Atnced9 mutant seeds were also resistant to paclobutrazol, a gibberellin biosynthesis inhibitor. Although seeds of single mutants were still dormant, reduced dormancy was observed in the Atnced6 Atnced9 double-mutant seeds. These demonstrate that ABA synthesized in both the endosperm and the embryo participates in the hormonal balance that controls seed dormancy and germination.
The Plant Journal 03/2006; 45(3):309-19. · 6.58 Impact Factor
[show abstract][hide abstract] ABSTRACT: In response to drought, plants synthesise the hormone abscisic acid (ABA), which triggers closure of the stomatal pores. This process is vital for plants to conserve water by reducing transpirational water loss. Moreover, recent studies have demonstrated the advantages of the Arabidopsis stomatal guard cell for combining genetic, molecular and biophysical approaches to characterise ABA action. However, genetic dissection of stomatal regulation has been limited by the difficulty of identifying a reliable phenotype for mutant screening. Leaf temperature can be used as an indicator to detect mutants with altered stomatal control, since transpiration causes leaf cooling. In this study, we optimised experimental conditions under which individual Arabidopsis plants with altered stomatal responses to drought can be identified by infrared thermography. These conditions were then used to perform a pilot screen for mutants that displayed a reduced ability to close their stomata and hence appeared colder than the wild type. Some of the mutants recovered were deficient in ABA accumulation, and corresponded to alleles of the ABA biosynthesis loci ABA1, ABA2 and ABA3. Interestingly, two of these novel aba2 alleles were able to intragenically complement the aba2-1 mutation. The remaining mutants showed reduced ABA responsiveness in guard cells. In addition to the previously known abi1-1 mutation, we isolated mutations at two novel loci designated as OST1 (OPEN STOMATA 1) and OST2. Remarkably, ost1 and ost2 represent, to our knowledge, the first Arabidopsis mutations altering ABA responsiveness in stomata and not in seeds.
The Plant Journal 07/2002; 30(5):601-9. · 6.58 Impact Factor