ORIGINAL PAPER Identification of miRNA Targets by AtFT Overexpression in Tobacco Ahamed Khan 1 & Ankita Shrestha 1 & Mukundan Shaju 2 & Kishore C. Panigrahi 2 & Nrisingha Dey 1 # Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract The onset of flowering is regulated by complex gene networks that integrate multiple genetic cues to floral transition in plants. The highly conserved florigen FLOWERING LOCUS T (FT) functions at the core of this process. Here, we demonstrate that overexpression of Arabidopsis FT in tobacco (oxAtFT) leads to precocious flowering in a photoperiod-independent manner. Strikingly altered phenotypes such as stunted growth, increased number of axillary branches, change in leaf morphology, and elongated style were observed in oxAtFT transgenic tobacco plants. In addition, the generation time of oxAtFT tobacco was drastically reduced by 8–10 weeks. We observed defects in lateral root formation in both oxAtFT tobacco and oxFT Arabidopsis lines. Interestingly, oxAtFT tobacco displayed significant heat and drought tolerance as compared to the wild type. Through small RNA profiling, we observed the upregulation of a conserved microRNA (nta-miR393a-5p) of miR393 family that targets the TRANSPORT INHIBITOR RESPONSE 1-like (TIR1) gene. Overall, the heterologous expression of AtFT in tobacco may have potential in imparting abiotic stress tolerance in other plant species through plant biotechnology–based approaches. Keywords FLOWERING LOCUS T . Lateral root . Stress tolerance . Micro-RNA . TIR1 Introduction Floral transition in plants is controlled by various signaling pathways depending on the environmental factors such as light, temperature, and stress (Coupland 1995; Mouradov et al. 2002). The perception of day length in leaves is usually followed by the transmission of a floral signal into the shoot apex where flowering is initiated (Turck et al. 2008; Turnbull 2011). This photoperiodic event eventually triggers the syn- thesis of the FT “florigen” in leaves which are transported over long distances through the phloem to shoot apical meri- stem (SAM) that initiates the flowering bud (Zeevaart 2006; Corbesier et al. 2007). In general, FT is induced in the com- panion cells of the phloem tissue under LD conditions which acts downstream of GIGANTEA and CONSTANS genes (An et al. 2004). The FT protein travels from leaf to SAM through the phloem sieve elements (Suárez-López et al. 2001; Valverde et al. 2004; Yoo et al. 2005; Corbesier et al. 2007) where it interacts with accessory proteins called bZIP tran- scription factor FD which interact with FT. This FT-FD com- plex directs the expression of several floral identity genes such as SOC1, AP1, LEAFY (LFY), and MADS-box TFs for floral induction (Schmid et al. 2003; Teper-Bamnolker and Samach 2005; Corbesier et al. 2007). In various instances, early flowering has been demonstrated to be induced by the Ahamed Khan and Ankita Shrestha contributed equally to this work. Key Message • oxAtFT tobacco leads to early flowering with reduced generation time. • oxAtFT tobacco showed altered morphology and repressed lateral roots. • oxAtFT tobacco lines exhibited tolerance against both heat and drought stresses. • oxAtFT tobacco lines showed the upregulation of nta-miR393a-5p miRNA, which directs the downregulation of TIR1 gene. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11105-019-01180-3) contains supplementary material, which is available to authorized users. * Kishore C. Panigrahi panigrahi@niser.ac.in * Nrisingha Dey nrisinghad@gmail.com Ahamed Khan ahamedbio19@gmail.com Ankita Shrestha ankitashreshta@gmail.com Mukundan Shaju mukundan.kollam@gmail.com 1 Division of Plant and Microbial Biotechnology, Institute of Life Sciences, Bhubaneswar, India 2 National Institute of Science Education and Research, Jatni, Odisha, India Plant Molecular Biology Reporter https://doi.org/10.1007/s11105-019-01180-3