Abscisic Acid Flux Alterations Result in Differential Abscisic Acid Signaling Responses and Impact Assimilation Efficiency in Barley under Terminal Drought Stress

Abstract

Abscisic acid (ABA) is a central player in plant responses to drought stress. How variable levels of ABA under short-term versus long-term drought stress impact assimilation and growth in crops is unclear. We addressed this through comparative analysis, using two elite breeding lines of barley (Hordeum vulgare) that show senescence or stay-green phenotype under terminal drought stress and by making use of transgenic barley lines that express Arabidopsis (Arabidopsis thaliana) 9-cis-epoxycarotenoid dioxygenase (AtNCED6) coding sequence or an RNA interference (RNAi) sequence of ABA 89-hydroxylase under the control of a droughtinducible barley promoter. The high levels of ABA and its catabolites in the senescing breeding line under long-term stress were detrimental for assimilate productivity, whereas these levels were not perturbed in the stay-green type that performed better. In transgenic barley, drought-inducible AtNCED expression afforded temporal control in ABA levels such that the ABA levels rose sooner than in wild-type plants but also subsided, unlike as in the wild type , to near-basal levels upon prolonged stress treatment due to down-regulation of endogenous HvNCED genes. Suppressing of ABA catabolism with the RNA interference approach of ABA 89-hydroxylase caused ABA flux during the entire period of stress. These transgenic plants performed better than the wild type under stress to maintain a favorable instantaneous water use efficiency and better assimilation. Gene expression analysis, protein structural modeling, and protein-protein interaction analyses of the members of the PYRABACTIN RESISTANCE1/PYRABACTIN RESISTANCE1-LIKE/REGULATORY COMPONENT OF ABA RECEPTORS, TYPE 2C PROTEIN PHOSPHATASE Sucrose nonfermenting1-related protein kinase2, and ABA-INSENSITIVE5/ABA-responsive element binding factor family identified specific members that could potentially impact ABA metabolism and stress adaptation in barley.Drought compromises grain yield in cereals, especially when the stress occurs during postanthesis (Boyer and Westgate, 2004;Sreenivasulu et al., 2007).In some crops, selection for and use of stay-green types has been promoted as a means for combating drought stress susceptibility (Thomas and Howarth, 2000). However, the molecular basis of stay-green phenotype in barley (Hordeum vulgare) has not been explored in detail. As the flag leaf is the principal source organ, sustaining its photosynthetic activity under postanthesis drought stress is considered a strategy to mitigate the yield penalty. Water use efficiency (WUE) is the amount of biomass (carbon) accumulated per unit of water, hence an important trait under water-limited conditions (Condon and Richards, 1992;Rebetzke et al., 2002;Richards et al., 2002). Breeding for WUE is considered important for developing drought-tolerant crops (Blum, 1996;Richards, 1996;Richards et al., 2002). Genetic loci that control transpiration efficiency have been identified (Teulat et al., 2002;Hall et al., 2005;Juenger et al., 2005). In Arabidopsis (Arabidopsis tha...

Involvement of homocastasterone, salicylic and abscisic acids in the regulation of drought and freezing tolerance in doubled haploid lines of winter barley

“…The level of ABA measured in optimally watered plants at generative phase of development ranged from 228 to 475 pmol g −1 FW and showed no significant variation among tested DH lines. Quite similar results were published also by Seiler et al (2014), who investigated breeding and transgenic barley lines.…”

Mesophyll Abscisic Acid Restrains Early Growth and Flowering But Does Not Directly Suppress Photosynthesis

“…Morover, under severe or prolonged stress, ABA is involved in the regulation of leaf senescence. Examples of this can be found in wheat (Triticum aestivum), in which rising ABA concentrations lead to the movement of carbohydrates from stems to seeds (Yang et al, 2003); in barley (Hordeum vulgare), in which lines exhibiting delayed stress-induced senescence had lower ABA levels (Seiler et al, 2014); and in tomato, in which ABA concentration-dependent promotion of senescense was also seen (Tung et al, 2008). In Arabidopsis, some of the mechanisms underlying ABAregulated leaf senescence have recently been revealed.…”

Early Metabolic and Photosynthetic Responses to Drought Stress in Common and Tepary Bean

“…However, drought tolerance is not simply a matter of accumulating ABA, as no relation exists between ABA concentration under drought stress and a plant's degree of drought tolerance (Chaves and Oliveira, 2004). Although ABA has been studied in Arabidopsis and cereal crops (Kanno et al, 2010;Ji et al, 2011;Seiler et al, 2014;Dalal and Inupakutika, 2014), information on ABA's role in beans is limited, despite the crucial step in ABA biosynthesis first being discovered in common bean (Qin and Zeevaart, 1999). Although ABA has been studied in Arabidopsis and cereal crops (Kanno et al, 2010;Ji et al, 2011;Seiler et al, 2014;Dalal and Inupakutika, 2014), information on ABA's role in beans is limited, despite the crucial step in ABA biosynthesis first being discovered in common bean (Qin and Zeevaart, 1999).…”

“…Rather, a plant's survival and productivity under drought stress depends on the maintenance of ABA homeostasis (Sreenivasulu et al, 2007). Although ABA has been studied in Arabidopsis and cereal crops (Kanno et al, 2010;Ji et al, 2011;Seiler et al, 2014;Dalal and Inupakutika, 2014), information on ABA's role in beans is limited, despite the crucial step in ABA biosynthesis first being discovered in common bean (Qin and Zeevaart, 1999).…”