Ectopic expression of Arabidopsis Target of Rapamycin (AtTOR) improves water-use efficiency and yield potential in rice

Abstract

The target of Rapamycin (TOR) present in all eukaryotes is a multifunctional protein, regulating growth, development, protein translation, ribosome biogenesis, nutrient, and energy signaling. In the present study, ectopic expression of TOR gene of Arabidopsis thaliana in a widely cultivated indica rice resulted in enhanced plant growth under water-limiting conditions conferring agronomically important wateruse efficiency (WUE) trait. The AtTOR high expression lines of rice exhibited profuse tillering, increased panicle length, increased plant height, high photosynthetic efficiency, chlorophyll content and low ∆ 13 C. Δ 13 C, which is inversely related to high WUE, was as low as 17‰ in two AtTOR high expression lines. These lines were also insensitive to the ABA-mediated inhibition of seed germination. The significant upregulation of 15 stress-specific genes in high expression lines indicates their contribution to abiotic stress tolerance. The constitutive expression of AtTOR is also associated with significant transcriptional upregulation of putative TOR complex-1 components, OsRaptor and OsLST8. Glucosemediated transcriptional activation of AtTOR gene enhanced lateral root formation. Taken together, our findings indicate that TOR, in addition to its multiple cellular functions, also plays an important role in response to abiotic stress and potentially enhances WUE and yield related attributes.Rice is a staple cereal food consumed by more than half of the world population and widely cultivated mostly in Asian countries. Environmental factors such as drought and high salinity are the major yield constraints for the high productivity of rice. The recent advancements in genetic engineering has provided new opportunities to enhance yield potential and tolerance to drought and other stresses by manipulating some of the regulatory genes involved in complex physiological and biochemical processes such as osmotic adjustment under water deficit environment.The Target of Rapamycin (TOR) is one of such genes, which encodes a protein that is involved in the regulation of diverse cellular and metabolic processes, distributed in all eukaryotes including plants, yeast, animals and human. It has important functions in growth, development and metabolism. TOR is a conserved 280 kDa serine/threonine protein kinase belonging to a phosphatidylinositol-3-kinase family possessing five conserved domains represented by HEAT repeat, FAT (Focal adhesive Target), FRB (FKBP12, FK506 drug binding protein 12/Rapamycin Binding), Kinase and FATC domains from N to C-terminus, respectively. HEAT repeats bind directly to the promoter and 5′ UTR regions of 45S rRNA via its Leucine zipper domain and regulates 45S rRNA synthesis 1 . Inducible TOR knockout Arabidopsis plants displayed growth arrest via a reduction in polysome accumulation, which ultimately resulted in a severe reduction in plant biomass, organ and cell size 2 . FAT domain is involved in protein-protein interactions, while FRB is sensitive and specifically binds to an anti-inflammatory...

The PP2A‐interactor TIP41 modulates ABA responses in Arabidopsis thaliana

“…Mutations in the LETHAL WITH SEC THIRTEEN8 (LST8), a member of the TOR complex, resulted in reduced vegetative growth (Moreau et al ., ), while silencing of Arabidopsis TOR kinase led to reduced shoot and root growth (Deprost et al ., ). Vice versa, over‐expression of Arabidopsis TOR in rice led to an increase in the number of lateral roots (Bakshi et al ., ).…”

“…In plants, links between key components of the TOR pathway and ABA responses have been reported. In a recent study, ectopic expression of the Arabidopsis TOR kinase in rice was shown to induce insensitivity to ABA at the seed germination stage (Bakshi et al ., ). Over‐expression of TAP46 (the plant counterpart of TAP42; Ahn et al ., ) caused hypersensitivity to ABA and decreased PP2A activity when over‐expressed in Arabidopsis.…”

Sugar sensing responses to low and high light in leaves of the C4 model grass Setaria viridis

“…6, Table S2). Although the ectopic overexpression of AtTOR improved rice photosynthesis and water use efficiency, especially under water limitation (Bakshi et al, 2017), most studies conducted on Arabidopsis showed that the TOR signalling pathway plays a critical role in young developing sink tissues rather than in source leaves (Anderson et al, 2005;Deprost et al, 2005Deprost et al, , 2007Leiber et al, 2010;Xiong et al, 2013;Montané and Menand, 2013). This could explain why TOR was not activated by HL and glucose accumulation in the source leaves of S. viridis.…”

“…TOR promotes plant development and growth under favourable environmental conditions (Dobrenel et al, 2011;Henriques et al, 2014;Rexin et al, 2015;Xiong and Sheen, 2015). Studies using TOR-specific inhibitors, mutants and transgenic plants showed that the TOR complex is involved in the glucose-dependent induction of photosynthesis, water use efficiency, chlorophyll metabolism, photosynthetic gene expression, stress tolerance, growth and yield A c c e p t e d M a n u s c r i p t 5 (Xiong et al, 2013;Dong et al, 2015;Li et al, 2015b;Xiong et al, 2017;Bakshi et al, 2017).…”

Target of rapamycin signaling orchestrates growth–defense trade‐offs in plants

“…Recent work in the model plant Arabidopsis thaliana has revealed that TORC1, which consists of TOR, Raptor (regulatory-associated protein of mTOR) and LST8 (lethal with SEC13 protein 8), promotes plant growth and cell proliferation by modulating a myriad of biological processes, including transcription, translation, ribosome biogenesis, autophagy, and primary and secondary metabolism (Dobrenel et al, 2011(Dobrenel et al, , 2016Henriques et al, 2014;Xiong & Sheen, 2014Rexin et al, 2015;Xiong et al, 2016;Zhang et al, 2016). Ectopic expression of Arabidopsis TOR improves water use efficiency and yield potential in transgenic rice (Bakshi et al, 2017). However, whether TORC1-steered growth affects plant immunity and, hence, whether TOR orchestrates growth-defense trade-offs in plants remains to be tested.…”