RESEARCH ARTICLE DRACULA2 is a dynamic nucleoporin with a role in regulating the shade avoidance syndrome in Arabidopsis Marçal Gallemı ́ 1, * , **, Anahit Galstyan 1, ‡, **, Sandi Pauliš ić 1 , Christiane Then 1,§ , Almudena Ferrá ndez-Ayela 2 , Laura Lorenzo-Orts 1 , Irma Roig-Villanova 1 , Xuewen Wang 3,¶ , Jose Luis Micol 2 , Maria Rosa Ponce 2 , Paul F. Devlin 3 and Jaime F. Martı ́ nez-Garcı ́ a 1,4, ‡‡ ABSTRACT When plants grow in close proximity basic resources such as light can become limiting. Under such conditions plants respond to anticipate and/or adapt to the light shortage, a process known as the shade avoidance syndrome (SAS). Following genetic screening using a shade-responsive luciferase reporter line (PHYB:LUC), we identified DRACULA2 (DRA2), which encodes an Arabidopsis homolog of mammalian nucleoporin 98, a component of the nuclear pore complex (NPC). DRA2, together with other nucleoporins, participates positively in the control of the hypocotyl elongation response to plant proximity, a role that can be considered dependent on the nucleocytoplasmic transport of macromolecules (i.e. is transport dependent). In addition, our results reveal a specific role for DRA2 in controlling shade-induced gene expression. We suggest that this novel regulatory role of DRA2 is transport independent and that it might rely on its dynamic localization within and outside of the NPC. These results provide mechanistic insights in to how SAS responses are rapidly established by light conditions. They also indicate that nucleoporins have an active role in plant signaling. KEY WORDS: Arabidopsis thaliana, Nucleoporin, Nup98, Hypocotyl elongation, Shade avoidance syndrome, Shade-induced gene expression INTRODUCTION As sessile organisms, plants cannot move to the best places to grow: therefore, they either adapt or die. One unfavorable situation is to grow in crowded conditions (e.g. those found in forests, prairies or agricultural communities), since the close proximity of neighboring plants can result in competition for limited resources, such as light. The shade avoidance syndrome (SAS) comprises the set of plant responses aimed to adapt growth and development to high plant density environments. Neighboring plants selectively absorb red light (R) and reflect far-red light (FR), resulting in a moderate reduction in the R to FR ratio (R:FR). Under plant canopy shade, the concomitant reduction in light intensities results in even lower R:FR ratios. In either case, these changes become a signal perceived by the R- and FR-absorbing phytochrome photoreceptors (Smith, 1982; Smith and Whitelam, 1997; Keuskamp et al., 2010; Martínez- García et al., 2010). In Arabidopsis thaliana (hereafter Arabidopsis), a gene family of five members (PHYA-PHYE) encodes the phytochromes (Bae and Choi, 2008), which have positive (phyB-phyE) and negative (phyA) roles in controlling SAS-driven development (Franklin, 2008; Martínez-García et al., 2010, 2014). Phytochromes exist in two photoconvertible forms: an inactive R-absorbing Pr form and an active FR-absorbing Pfr form. Under sunlight (i.e. a high R:FR ratio), the photo-equilibrium is displaced towards the active Pfr forms, and SAS is suppressed. Under a low R:FR ratio, the phytochrome photo-equilibrium is displaced towards the inactive Pr forms, and SAS is induced by affecting the interaction with PHYTOCHROME INTERACTING FACTORs (PIFs) and altering their stability and/or activity (Smith and Whitelam, 1997; Martínez- García et al., 2000; Lorrain et al., 2008; Leivar and Quail, 2011), which results in rapid changes in the expression of dozens of PHYTOCHROME RAPIDLY REGULATED (PAR) genes (Salter et al., 2003; Roig-Villanova et al., 2006, 2007; Lorrain et al., 2008). Because most of these PAR genes encode transcriptional regulators, it is assumed that SAS responses are a consequence of the regulation of a complex transcriptional network by phytochromes (Bou-Torrent et al., 2008; Josse et al., 2008). Indeed, genetic approaches have demonstrated regulatory roles in SAS for a large number of PAR genes encoding transcriptional regulators, including members of at least three different families: basic helix-loop-helix (HFR1, PAR1, PAR2, BIMs and BEEs), homeodomain-leucine zipper (HD-ZIP) class II (ATHB2, ATHB4, HAT1, HAT2 and HAT3), and B-BOX- CONTAINING (BBX). PIF stability and/or activity was also shown to be increased by low R:FR perception (Lorrain et al., 2008; Li et al., 2012). Genetic analyses unraveled roles for these factors in the negative (including BBX21, BBX22, HFR1, PAR1, PAR2 and PIL1) or positive (including BBX24, BBX25, PIFs, BIMs and BEEs) regulation of SAS (Sessa et al., 2005; Roig-Villanova et al., 2006, 2007; Crocco et al., 2010; Cifuentes-Esquivel et al., 2013; Gangappa et al., 2013; Bou-Torrent et al., 2015). Therefore, the low R:FR perception rapidly changes the balance of positive and negative factors, resulting in the appropriate SAS responses. Phytochromes are known to partition between the cytoplasm and nucleus (and even within the nucleus) in a light-dependent manner; similarly, after low R:FR exposure, newly formed and shade- stabilized PIFs rapidly reach the nucleus. To do so these proteins have to cross the nuclear envelope, a physical barrier that separates both cell compartments. The nuclear pore complex (NPC) is a large multiprotein complex that is the sole gateway of macromolecular Received 26 August 2015; Accepted 3 March 2016 1 Centre for Research in Agricultural Genomics (CRAG), CSIC-IRTA-UAB-UB, Campus UAB, 08193 Barcelona, Spain. 2 Instituto de Bioingenierı ́ a, Universidad Miguel Herná ndez, Campus de Elche, 03202 Elche, Spain. 3 School of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK. 4 Institució Catalana de Recerca i Estudis Avançats (ICREA), Ps. Lluı ́ s Companys 10, 08010 Barcelona, Spain. *Present address: Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria. ‡ Present address: Department of Comparative Development and Genetics, Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany. § Present address: INRA, Joint Research Unit ‘Biology and Genetics of Plant-Pathogen Interactions’, Campus International de Baillarguet, 34398 Montpellier Cedex 5, France. ¶ Present address: Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China. **These authors contributed equally to this work ‡‡ Author for correspondence ( jaume.martinez@cragenomica.es) 1623 © 2016. Published by The Company of Biologists Ltd | Development (2016) 143, 1623-1631 doi:10.1242/dev.130211 DEVELOPMENT