Global reprogramming of transcription and metabolism in Medicago truncatula during progressive drought and after rewatering

Abstract

Medicago truncatula is a model legume forage crop native to the arid and semi-arid environments of the Mediterranean. Given its drought-adapted nature, it is an ideal candidate to study the molecular and biochemical mechanisms conferring drought resistance in plants. Medicago plants were subjected to a progressive drought stress over 14 d of water withholding followed by rewatering under controlled environmental conditions. Based on physiological measurements of plant water status and changes in morphology, plants experienced mild, moderate and severe water stress before rehydration. Transcriptome analysis of roots and shoots from control, mildly, moderately and severely stressed, and rewatered plants, identified many thousands of genes that were altered in expression in response to drought. Many genes with expression tightly coupled to the plant water potential (i.e. drought intensity) were identified suggesting an involvement in Medicago drought adaptation responses. Metabolite profiling of drought-stressed plants revealed the presence of 135 polar and 165 non-polar compounds in roots and shoots. Combining Medicago metabolomic data with transcriptomic data yielded insight into the regulation of metabolic pathways operating under drought stress. Among the metabolites detected in drought-stressed Medicago plants, myo-inositol and proline had striking regulatory profiles indicating involvement in Medicago drought tolerance.Global transcriptional and metabolic responses to drought and rewatering were investigated in Medicago truncatula, a naturally drought-adapted model legume species. Integration of metabolomic and transcriptomic data yielded insights into the regulation of metabolic pathways underlying drought-stress adaptation. Many genes and metabolites with expression tightly coupled to drought intensity were identified, suggesting active involvement in Medicago drought resistance. These could prove useful targets for future translational approaches to improve closely related crop plants such as common bean, soybean and pea.

Time-Series Transcriptomics Reveals That AGAMOUS-LIKE22 Affects Primary Metabolism and Developmental Processes in Drought-Stressed Arabidopsis

“…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 experiments have substantially increased our knowledge of molecular responses under severe drought stress, but they do not always reflect physiological conditions experienced by drought-stressed soil-grown plants (Bechtold et al, 2010(Bechtold et al, , 2013Harb et al, 2010;Wilkins et al, 2010;Lawlor, 2013;Zhang et al, 2014). Physiological responses such as stomatal conductance, photosynthetic performance, and metabolic changes are usually not measured during the progression of the drought stress, and the varied nature of the stress induction treatments makes comparative analysis between experiments problematic.…”

Physiological adaptations to osmotic stress and characterization of a polyethylene glycol-responsive gene in Braya humilis

“…Generally, plants achieve a plateau in water status when they are exposed to drought within certain limits of stress severity or within a certain period of time. However, once the threshold is exceeded, plants begin to lose water rapidly [11,43]. In the present study, we inferred that B. humilis had a tolerance for PEG-6000 concentrations between 20% and 30%, thus providing a reference for future work on drought stress in B. humilis.…”

“…In addition, we hypothesized that the highest BhCIPK12 expression might occur when plants were treated with approximately 30% PEG. Since gene expression is regulated by a series of physiological and biochemical events, changes in expression levels are not necessarily synchronous with phenotypes or one physiological parameter [43]. Therefore, further studies are needed to confirm the exact PEG treatment concentration and time for the highest expression of BhCIPK12.…”

“…It is important to note that a recent study mostly focused on stimulus-induced and tissue-specific expression profiles [23], Furthermore, the differential expression of many genes is detected during different stress time courses and under various stress conditions [3,43]. However, very little data are available regarding the expression of CIPK homologs in response to various drought levels, especially for CIPK12.…”

Review on Arbuscular Mycorrhizal Fungi: An Approach to Overcome Drought Adversities in Plants

“…AM symbiosis increases plant growth and photosynthetic rate which in turn causes increased transport and building up of carbohydrates in cells which act as excellent osmoprotectants to lower osmotic potential (Khalvati et al, 2005). Studies have shown an increase in sugars levels in AM plants exposed to drought in Cyclobalanpsis glauca (Zhang et al, 2014) and in Poncirus trifoliata (Qiangsheng et al, 2006). High sugar content of Poncirus trifoliata confirms a high natural physiological metabolism of AM plants under water stress and well watered conditions leading to accumulation of carbohydrates resulting in decrease of osmotic potential of host cells.…”