Rizhsky et al., 2002 Rizhsky et al., 2004 Suzuki et al., 2005) and physiological (e.g. Instead, wild and crop plants respond to the combination of diverse stressors such as drought, heat, and salinity, simultaneously and at both molecular (e.g.

For example, single abiotic stresses rarely occur in isolation in the field ( Mittler, 2006). Natural soil moisture variation, which has shaped adaptive responses to drought in wild populations, is not necessarily recapitulated by controlled (often, “shock”) laboratory experiments. A common finding among such studies is that physiological and gene expression responses to drought vary considerably depending on the severity and temporal dynamics of drying soil ( Chaves et al., 2003 Barker et al., 2005 Malmberg et al., 2005 Mittler, 2006 Mishra et al., 2012). To understand plant stress responses, it is critical to determine the physiological and genetic underpinnings of drought adaptation in both field and laboratory conditions ( Travers et al., 2007 Gaudin et al., 2013). Plants that exhibit dehydration avoidance strategies compensate for soil water deficit through phenotypic plasticity of gene expression ( Verslues et al., 2006 DesMarais and Juenger, 2010 DesMarais et al., 2013 Lovell et al., 2015) and downstream physiological phenotypes ( Levitt, 1980), among others. Plants therefore seek to maintain homeostasis of leaf water potential, with the highest (least negative) values supporting the most efficient functioning of photosynthesis and other metabolic processes in most species ( Lawlor and Fock, 1978 Turner and Begg, 1981 Kramer and Boyer, 1995 Cornic and Massacci, 1996 Jones, 2007). Under drought, decreasing water availability results in reduced leaf water potentials and a sequence of physiological responses including reduced photosynthesis, growth rate, and ultimately, fitness ( Taiz and Zeiger, 2014). Leaf water potential is a bellwether of the physiological impact of water deficit ( Jones, 2007).

Specifically, phenotypic plasticity of stomatal conductance, water foraging, and growth traits (among many others) may effectively maintain homeostasis of leaf water potential despite soil water deficits. Dehydration avoidance and other drought adaptive strategies permit plants to survive or maintain growth during periodic droughts ( Blum, 1996 Chaves et al., 2003 Chaves and Oliveira, 2004). The impact of drought and soil water deficit in agriculture is estimated to be the largest abiotic determinant of yield ( Boyer, 1982 Araus et al., 2002), while drought is also considered a primary cause of speciation and adaptation in nature ( Stebbins, 1952). The strong across-experiment correlations between physiological plasticity-but not differential gene expression-highlight the complex and diverse genetic mechanisms that can produce phenotypically similar responses to various soil water deficits.Ĭrop productivity and wild plant distributions are governed by the availability of soil moisture ( Axelrod, 1972 Boyer, 1982 Ciais et al., 2005). This list was strongly enriched in photosynthesis, water status, and reactive oxygen species responsive genes.

However, we were able to define a suite of several hundred genes that were differentially expressed across all experiments. Critically, a drought experiment utilizing small pots in the greenhouse elicited nearly identical physiological changes as an experiment conducted in the field, but an order of magnitude more differentially expressed genes. Relatively similar physiological responses and expression coefficients of variation across experiments masked highly dissimilar gene expression responses to drought. We analyzed physiological and gene expression variation across four locations, two sampling times, and three years. To test the comparability of drought responses across field and greenhouse environments, we undertook three independent experiments using the switchgrass reference genotype Alamo AP13. However, many discoveries were initially made in the controlled conditions of greenhouses or laboratories, not in the field. Identifying the physiological and genetic basis of stress tolerance in plants has proven to be critical to understanding adaptation in both agricultural and natural systems.

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