Zhenyu Yang, Jinghui Liu, Stefanie V. Tischer, Alexander Christmann, Wilhelm Windisch, Hans Schnyder, and Erwin Grill

Significance

Water is the major limiting factor for plant productivity in the field, and current water use in agriculture is not sustainable. Under water limitations, plants can ameliorate the carbon for water exchange leading to higher water use efficiencies. The plant hormone abscisic acid is activated in response to drought and regulates the water status and acclimation responses. Here we show in the model species Arabidopsis that abscisic acid receptors can be explored to constitutively increase the water use efficiency without impinging on growth potential. The finding may support future efforts to generate “more crop per drop” required for a more sustainable water use in agriculture.  

Abstract

Plant growth requires the influx of atmospheric CO₂ 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, ¹³C 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 CO₂ 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.

See http://www.pnas.org/content/113/24/6791.full

PNAS June 14 2016; vol.113; no.24: 6791–6796

Fig. 2.

Overexpression of ABA receptors affects growth and leaf temperatures. Arabidopsis Col-0 lines overexpressing the 14 different ABA receptors RCARs (R1–R14)/PYR1/PYLs (P1–P13) under the constitutive viral promoter 35S were homozygous for the transgene. Independent lines are denoted by subscript numbers. (A) Thermogram of the plants grown for 40 d under short day (8 h of light, photon density of 150 μmol⋅m⁻²⋅s⁻¹) and under well-watered conditions (Ψ ≥ −0.02 bar). Four plants were grown per line in separate pots at randomized positions and the thermal pictures were arranged in groups after imaging. (B) Leaf area as projected rosette size and leaf temperatures from data shown in A. The threshold value of Col-0 is indicated by a dotted line. n = 4 biological replicates per line, ± SEM, **P < 0.001 compared with wild type.