Abstract
In Arabidopsis thaliana, changes in metabolism and gene expression drive increased drought tolerance and initiate diverse drought avoidance and escape responses. To address regulatory processes that link these responses, we set out to identify genes that govern early responses to drought. To do this, a high-resolution time series transcriptomics data set was produced, coupled with detailed physiological and metabolic analyses of plants subjected to a slow transition from well-watered to drought conditions. A total of 1815 drought-responsive differentially expressed genes were identified. The early changes in gene expression coincided with a drop in carbon assimilation, and only in the late stages with an increase in foliar abscisic acid content. To identify gene regulatory networks (GRNs) mediating the transition between the early and late stages of drought, we used Bayesian network modeling of differentially expressed transcription factor (TF) genes. This approach identified AGAMOUS-LIKE22 (AGL22), as key hub gene in a TF GRN. It has previously been shown that AGL22 is involved in the transition from vegetative state to flowering but here we show that AGL22 expression influences steady state photosynthetic rates and lifetime water use. This suggests that AGL22 uniquely regulates a transcriptional network during drought stress, linking changes in primary metabolism and the initiation of stress responses.
Highlights
Water limitation in agriculture is poised to intensify in the coming decades due to urbanization, industrialization, depletion of aquifers, and increasingly erratic rainfall patterns exacerbated by climate346 The Plant CellPlants have adopted different strategies to respond to water limitation, such as drought escape through early flowering and reducing the size of plants to increase water use efficiency or drought avoidance through enhanced soil moisture capture or reduced transpiration (Ludlow, 1989; Blum, 2005; Aguirrezabal et al, 2006; Franks, 2011)
Time-series experiments were performed analyzing physiological, metabolic, and transcriptional changes in Arabidopsis thaliana to reveal the chronology of plant responses to drought stress
A progressive slow-drying experiment starting at 95% relative gravimetric soil water content and drying down to 17% rSWC was performed on 5-week-old Arabidopsis plants (Figure 1)
Summary
Water limitation in agriculture is poised to intensify in the coming decades due to urbanization, industrialization, depletion of aquifers, and increasingly erratic rainfall patterns exacerbated by climate. In many studies to identify genes important in the regulation of drought responses, the effects of water limitation at the transcriptional level have been analyzed by exposing plants to severe dehydration This involves treatments such as cutting and air drying leaves and/or roots or induction of osmotic shock through the application of highly concentrated osmotica such as polyethylene glycol or mannitol (Kreps et al, 2002; Seki et al, 2002; Kawaguchi et al, 2004; Kilian et al, 2007; Weston et al, 2008; Fujita et al, 2009; Abdeen et al, 2010; Deyholos, 2010; Mizoguchi et al, 2010). These results demonstrated the potential value of experimental strategies that combine time-series transcriptomics data with dynamic modeling as a means of identifying stress-responsive genes
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