Leveraging abscisic acid receptors for efficient water use in Arabidopsis

Abstract

Plant growth requires the influx of atmospheric CO 2 through stomatal pores, and this carbon uptake for photosynthesis is inherently associated with a large efflux of water vapor. Under water deficit, plants reduce transpiration and are able to improve carbon for water exchange leading to higher water use efficiency (WUE). Whether increased WUE can be achieved without trade-offs in plant growth is debated. The signals mediating the WUE response under water deficit are not fully elucidated but involve the phytohormone abscisic acid (ABA). ABA is perceived by a family of related receptors known to mediate acclimation responses and to reduce transpiration. We now show that enhanced stimulation of ABA signaling via distinct ABA receptors can result in plants constitutively growing at high WUE in the model species Arabidopsis. WUE was assessed by three independent approaches involving gravimetric analyses, 13 C discrimination studies of shoots and derived cellulose fractions, and by gas exchange measurements of whole plants and individual leaves. Plants expressing the ABA receptors RCAR6/PYL12 combined up to 40% increased WUE with high growth rates, i.e., are water productive. Water productivity was associated with maintenance of net carbon assimilation by compensatory increases of leaf CO 2 gradients, thereby sustaining biomass acquisition. Leaf surface temperatures and growth potentials of plants growing under well-watered conditions were found to be reliable indicators for water productivity. The study shows that ABA receptors can be explored to generate more plant biomass per water transpired, which is a prime goal for a more sustainable water use in agriculture.carbon assimilation | drought resistance | water deficit | water productivity | water use efficiency P lants are ferocious consumers of water, and plant transpiration is the dominant vector for water mobilization from terrestrial surfaces to the atmosphere (1). Plant transpiration is sustained by efficient water uptake through the root systems, which can comprise 500 m 2 of root surface and 500 km in combined length even in a single barley plant. Water is the major factor limiting crop productivity in the field (2). Thus, more than two-thirds of the fresh water resources used globally are channeled into agriculture, thereby contributing to potential social conflicts over water (3).Whereas the gas exchange of CO 2 and water vapor at the stomatal pore is a physical process controlled by both the ratio in partial pressure gradients and gas diffusivities (4, 5), terrestrial plants are able to capture carbon more efficiently under water deficit. Both short-term leaf gas exchange measurements and 13 C isotope discrimination analyses revealed increases of the instantaneous water use efficiency (insWUE) and intrinsic WUE (iWUE), respectively, by a factor of 1.5-2.5 in wheat and other species (6, 7). The underlying mechanisms, however, are not fully elucidated. Gains in WUE have been found to be associated with trade-offs in growth potential (8-10). WUE is control...

Drought resistance is mediated by divergent strategies in closely related Brassicaceae

“…It is possible that a smaller stomata aperture affects the water use efficiency (WUE) of the resistant Aly and Esa . Importantly, a recent overexpression screen found that higher levels of the Aly ‐ and Esa ‐elevated ABA receptors increase Ath WUE (Yang et al ., ; Tischer et al ., ), suggesting a causal contribution to Aly and Esa drought resistance. While the functional orthology of the Aly and Esa proteins remains to be shown, this possibly convergent evolution of higher ABA receptor levels in Aly and Esa is consistent with their resistant phenotype.…”

Over‐accumulation of abscisic acid in transgenic tomato plants increases the risk of hydraulic failure

“…Overexpression of the rate-limiting enzyme in ABA biosynthesis, 9-cis-epoxycarotenoid dioxygenase (NCED), led to increased ABA accumulation (Thompson et al, 2000), lower stomatal conductance, and up to 79% higher gravimetric transpiration efficiency (another term for WUE) with only small effects on photosynthetic carbon assimilation or growth (Thompson, Andrews, et al, 2007). Similarly, in Arabidopsis and wheat, activation of ABA signalling through manipulation of ABA receptors led to an increase in WUE of up to 40% without impacting growth significantly (Mega et al, 2019;Papacek, Christmann, & Grill, 2019;Yang et al, 2016). The use of candidate genes therefore holds huge promise for the production of crops with enhanced WUE.…”

Combinatorial interaction network of abscisic acid receptors and coreceptors from Arabidopsis thaliana

“…The moderate effects of subfamily II members on the ABA response at basal ABA levels make these RCARs prime candidates to reduce transpiration under nonstress conditions without curbing photosynthesis. Recent analysis of all Arabidopsis RCARs showed that overexpression of two subfamily II members, RCAR6/PYL12 and RCAR10/PYL4, increased water-use efficiency and resulted in water-productive plants, which are characterized by reduced transpiration with little or no trade-offs in CO 2 uptake and biomass accumulation (49). Important for the trait is the altered ABA response at resting ABA levels.…”