Abscisic Acid Metabolism in Leaves and Roots of Four Vitis Species in Response to Water Deficit

Background: Abscisic acid is a phytohormone involved in water deficit response. Abscisic acid metabolism is regulated by biosynthesis, conjugation, and catabolism. NCED3 is the rate limiting step of abscisic acid biosynthesis and is a key contributor to plant water deficit responses. In this study NCED3 transcript accumulation and abscisic acid metabolism were further characterized as key water deficit responses in four Vitis species (Vitis vinifera (Cabernet Sauvignon), Vitis champinii (Ramsey), Vitis riparia (Riparia Gloire), and Vitis vinifera x Vitis girdiana (SC2)) under three levels of water deficit in leaves and roots. Results: The concentrations of abscisic acid and derivative metabolites increased with water deficit and was dependent upon the species. RNA-Seq and RT-qPCR data were consistent with the changes in abscisic acid metabolite concentrations; the corresponding transcript abundances substantiate NCED3 as a key gene in the water deficit response; however, NCED3 protein concentrations assayed in Western Blots were not affected. Major differences in abscisic acid metabolism at the gene, protein, and metabolite levels were detected between leaves and roots in these four species. NCED3 transcript abundance and abscisic acid concentration in drought-tolerant Ramsey increased earlier and more significantly than the other species during long-term, moderate to severe water deficits but were not stimulated as much by short-term, rapid dehydration. In drought-sensitive Riparia, NCED3 transcript abundance and abscisic acid metabolite concentrations increased to a lower extent than in Ramsey during moderate to severe water deficits, but short-term rapid dehydration induced a significantly higher abscisic acid concentration in Riparia than Ramsey. Conclusions: Grapevine species have distinct abscisic acid metabolism that depends highly on the severity and duration of stress and organ (leaves or roots). This study confirms that abscisic acid metabolism and NCED3 are part of a core water deficit response in Vitis species. Relative quantities of transcripts, proteins, abscisic acid and derivative metabolites were determined, but many aspects of abscisic acid metabolism and water deficit responses warrant additional investigation. This study provides a better understanding of how Vitis is adapted to dry environments, which may be exploited for future breeding programs.

ACCUMULATION, DISTRIBUTION AND FUNCTIONAL ROLE OF ABSCISIC ACID UNDER SHORT-TERM SALT STRESS IN WHEAT PLANTS

Local effects on plant roots or shoots are accompanied by a change of plant hormones concentration providing signal transduction in plants and their adaptation to changing environmental conditions. It is known that plants respond to drought stress by increasing the concentration of abscisic acid (ABA) in xylem sap which leads to decrease in stomatal conductance to prevent plant water loss from transpirational pathways. Earlier, we found a rapid leaf ABA accumulation in barley and wheat plants under influence of the shortterm salinity. However, the mechanism of the salt stress induced rapid accumulation of abscisic acid in plant leaves remained unclear. The aim of this study was to investigate whether the salt-induced rapid accumulation of abscisic acid in the leaves was the result of its inflow from the roots (as a root signal). In our experiments the short-term salinity did not increase but decreased the concentration of abscisic acid in xylem sap of wheat plants. Thus, detected accumulation of ABA in the leaves did not result from an increase in its inflow from the roots. Apparently leaf ABA accumulation already detected in 15 min after the onset of salinity stress could be a local reaction due to its metabolism in the shoot itself. The decrease in the leaf water potential could induce the change of abscisic acid metabolism pathways in the shoot that led to the accumulation of this hormone. A small short-term accumulation of ABA in the roots did not lead to an increase in their hydraulic conductivity.

Contrasting dynamics in abscisic acid metabolism in different Fragaria spp. during fruit ripening and identification of involved enzymes

Abscisic acid (ABA) is a key hormone in non-climacteric Fragaria spp, regulating multiple physiological processes throughout fruit ripening. Its level increases during ripening, and it promotes fruit (receptacle) development. However, its metabolism in the fruit is largely unknown. We analyzed the levels of ABA and its catabolites at different developmental stages of strawberry ripening in diploid and octoploid genotypes and identified two functional ABA-glucosyltransferases (FvUGT71A49 and FvUGT73AC3) and two regiospecific ABA-8’-hydroxylases (FaCYP707A4a and FaCYP707A1/3). ABA-glucose-ester content increased during ripening in diploid F. vesca varieties but decreased in octoploid F. xananassa. Dihydrophaseic acid content increased throughout ripening in all analyzed receptacles, while 7’-hydroxy-ABA and neo-phaseic acid did not show significant changes during ripening. In the studied F. vesca varieties, the receptacle seems to be the main tissue for ABA metabolism, as the content of ABA and its metabolites in the receptacle was generally 100 times higher than in achenes, respectively. The accumulation patterns of ABA catabolites and transcriptomic data from the literature show that all strawberry fruits produce and metabolize considerable amounts of the plant hormone ABA during ripening, which is therefore a conserved process, but also illustrate the diversity of this metabolic pathway which is species, variety and tissue dependent.

Transcript and metabolite changes during the early phase of abscisic acid-mediated induction of crassulacean acid metabolism in Talinum triangulare

Crassulacean acid metabolism (CAM) has evolved as a water-saving strategy, and its engineering into crops offers an opportunity to improve their water use efficiency. This requires a comprehensive understanding of the regulation of the CAM pathway. Here, we use the facultative CAM species Talinum triangulare as a model in which CAM can be induced rapidly by exogenous abscisic acid. RNA sequencing and metabolite measurements were employed to analyse the changes underlying CAM induction and identify potential CAM regulators. Non-negative matrix factorization followed by k-means clustering identified an early CAM-specific cluster and a late one, which was specific for the early light phase. Enrichment analysis revealed abscisic acid metabolism, WRKY-regulated transcription, sugar and nutrient transport, and protein degradation in these clusters. Activation of the CAM pathway was supported by up-regulation of phosphoenolpyruvate carboxylase, cytosolic and chloroplastic malic enzymes, and several transport proteins, as well as by increased end-of-night titratable acidity and malate accumulation. The transcription factors HSFA2, NF-YA9, and JMJ27 were identified as candidate regulators of CAM induction. With this study we promote the model species T. triangulare, in which CAM can be induced in a controlled way, enabling further deciphering of CAM regulation.