NAC domain transcription factor ATAF1 interacts with SNF1-related kinases and silencing of its subfamily causes severe developmental defects in Arabidopsis Tatjana Kleinow a, *, Sarah Himbert a,1 , Bjo ¨ rn Krenz a , Holger Jeske a , Csaba Koncz b,c a Institute of Biology, Department of Molecular Biology and Plant Virology, Universita ¨t Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany b Max Planck Institute for Plant Breeding Research, Carl-von-Linne ´ Weg 10, 50829 Ko ¨ln, Germany c Institute of Plant Biology, Biological Research Center of the Hungarian Academy of Sciences, Temesva ´ri krt. 62, H6701 Szeged, Hungary 1. Introduction Plants respond to various stress stimuli, causing disturbance in the cellular energy status, by complex regulatory changes in their carbohydrate metabolism, which is required for proper optimiza- tion of growth and development under limiting environmental conditions. Sugar signaling plays a pivotal role in the regulation of metabolism and is tightly linked to modulation of development, switch from vegetative to reproductive phase, control of senes- cence, and responses to abiotic and biotic stresses [1–5]. There is accumulating evidence for an extensive cross-talk between sugar, hormone and light signal transduction networks in plants [1–3,6– 8]. Members of the sucrose non-fermenting 1-related (SnRK1)/ AMP-activated protein kinase (AMPK) family are important regulators of sugar signal transduction and energy/carbon metabolism [8–11]. SnRK1s occur in heterotrimeric complexes consisting of a catalytic a-subunit, an activating g-subunit, and a target selective adaptor b-subunit that anchors the a- and g- subunits [9,10]. Because in Arabidopsis and maize the g-subunit (i.e. termed also bg-subunit) carries a domain characteristic of the b-subunits in other organisms, it has been suggested that plant SnRK1 enzymes may also be active as heterodimers of a- and bg- subunits [4,12,13]. Remarkable conservation of biological func- tions of plant SnRK1 kinases is indicated by the fact that the a, and g proteins can suppress the sucrose non-fermenting defects of yeast snf1/a and snf4/g mutants [9,12–15]. Although plants carry three different subfamilies of yeast Snf1-related SnRK kinases, only the SnRK1 family shows close functional and structural relation- ship with yeast Snf1 and animal AMPKs [9,10,16]. Analysis of various members of the SnRK1 family in different plant species documents that they are responsible for the regulation of many downstream targets of glucose signal transduction, implicated in e.g. starch biosynthesis, salt stress tolerance, pathogen responses, development and senescence. Biochemical studies indicate that SnRK1 kinases modulate the functions of key metabolic enzymes either directly by phosphorylation or indirectly by controlling gene expression [4,8–10]. Although SnRK1 signaling in Arabi- dopsis is reported to control transcription of over 1200 genes, thus far only few transcription factors are known, which may represent potential downstream targets of SnRK1 kinase regulation [9–11,17]. Here we describe the identification of a novel SnRK1-binding transcription factor, ATAF1, which belongs to the NAC (NAM [no apical meristem], ATAF, CUC2 [cup-shaped cotyledon]) family, one Plant Science 177 (2009) 360–370 ARTICLE INFO Article history: Received 3 April 2009 Received in revised form 23 June 2009 Accepted 24 June 2009 Available online 3 July 2009 Keywords: NAC transcription factor family Yeast two-hybrid system Protein interaction Silencing Sugar signaling ABSTRACT ATAF1, a member of the plant-specific NAC transcription factor family in Arabidopsis thaliana, was identified in two-hybrid and in vitro binding assays as interacting partner of SNF1-related protein kinase (SnRK1) catalytic subunits. SnRK1s represent essential factors in stress and glucose signal transduction, and are involved in coordinate regulation of metabolic, hormonal and developmental signaling pathways. Transcription profiles of ATAF1 and closely related NACs indicate that their expression is co- regulated in various organs and by wounding, methyl jasmonate, hydrogen peroxide, pathogen infection, abscisic acid, cold, drought, salt and osmotic stress. Transgenic Arabidopsis carrying a 35S::ATAF1 construct developed fast senescing curly leaves and showed various grades of dwarfism leading to growth arrest and subsequent seedling death. RT-PCR analysis exhibited a silencing effect of the overexpression construct that down-regulated transcription of endogenous ATAF family members in plants showing severe developmental defects. These results together with the analysis of T-DNA insertion mutants suggest that the ATAF subfamily members perform redundant functions and act as positive regulators of plant development. ß 2009 Elsevier Ireland Ltd. All rights reserved. * Corresponding author. Tel.: +49 711 685 65075; fax: +49 711 685 65096. E-mail address: tatjana.kleinow@bio.uni-stuttgart.de (T. Kleinow). 1 Present address: Department of Plant Molecular Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria. Contents lists available at ScienceDirect Plant Science journal homepage: www.elsevier.com/locate/plantsci 0168-9452/$ – see front matter ß 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2009.06.011