Abstract
Survival and productivity of perennial plants in temperate zones are dependent on robust responses to prolonged and seasonal cycles of unfavorable conditions. Here we report whole-genome microarray, expression, physiological, and transgenic evidence in hybrid poplar (Populus tremula × Populus alba) showing that gibberellin (GA) catabolism and repressive signaling mediates shoot growth inhibition and physiological adaptation in response to drought and short-day (SD) induced bud dormancy. Both water deprivation and SDs elicited activation of a suite of poplar GA2ox and DELLA encoding genes. Poplar transgenics with up-regulated GA 2-oxidase (GA2ox) and DELLA domain proteins showed hypersensitive growth inhibition in response to both drought and SDs. In addition, the transgenic plants displayed greater drought resistance as evidenced by increased pigment concentrations (chlorophyll and carotenoid) and reductions in electrolyte leakage (EL). Comparative transcriptome analysis using whole-genome microarray showed that the GA-deficiency and GA-insensitivity, SD-induced dormancy, and drought response in poplar share a common regulon of 684 differentially-expressed genes, which suggest GA metabolism and signaling plays a role in plant physiological adaptations in response to alterations in environmental factors. Our results demonstrate that GA catabolism and repressive signaling represents a major route for control of growth and physiological adaptation in response to immediate or imminent adverse conditions.
Highlights
Phenotypic plasticity in response to adverse conditions determines plant productivity and survival
We studied expression of four poplar DELLA protein (PtaGAI1, PtaGAI2, PtaRGL1-1, and PtaRGL1-2) and seven PtaGA2ox (PtaGA2ox1 to 7) encoding genes (Table 1) in leaves in response to drought and SD photoperiods (Figures 1 and 2)
Because our studies suggest that GA-insensitive and GAdeficient plants have faster and more robust responses to dormancy-inducing conditions and drought, we speculated that alterations in GA metabolism and signaling in transgenics may result in transcriptome level changes that are shared with plants that are responding to stress (i.e., SD photoperiod and drought)
Summary
Phenotypic plasticity in response to adverse conditions determines plant productivity and survival. Improving abiotic stress resistance is considered to be a main route for sustainable yield growth and will likely become progressively more important as arable land is becoming increasingly limited [3] due to (1) the deterioration of previously productive lands [4], (2) the predicted expansion of areas affected by droughts [5] and high salinity [6], and (3) the predicted increase in the occurrences of climatic extremes [7]. Woody perennials (trees and shrubs) from temperate latitudes stop shoot growth in response to short-day (SD) photoperiods that signal the approaching winter and impending months of dehydration and freezing conditions. The cessation of shoot growth precedes a more permanent growth inhibition known as winter dormancy that can last months, requires development of a specialized organ (e.g., bud), and entails physiological resetting to allow resumption of growth [10]
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