Overexpression of a nascent polypeptide associated complex gene (SabNAC) of Spartina alterniflora improves tolerance to salinity and drought in transgenic Arabidopsis Ratna Karan, Prasanta K. Subudhi ⇑ School of Plant, Environmental, and Soil Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA article info Article history: Received 20 June 2012 Available online 15 July 2012 Keywords: Abiotic stress Drought Halophyte Nascent polypeptide associated complex (NAC) Salinity Spartina alterniflora abstract Salinity and drought are the most important environmental constraints limiting crop growth and produc- tivity. Here, we have characterized a gene ‘SabNAC’ encoding the b subunit of nascent polypeptide asso- ciated complex from a halophyte Spartina alterniflora and investigated its role toward abiotic stress regulation. Expression of SabNAC was differentially regulated by abiotic stresses, including salinity, drought, cold, and ABA in leaves and roots of S. alterniflora. Constitutive over-expression of SabNAC in Arabidopsis exhibited normal growth under non-stress conditions but enhanced tolerance to salt and drought stresses. Transgenic SabNAC Arabidopsis retained more chlorophyll, proline, and showed improved ionic homeostasis with less damage under stress conditions compared to WT plants. This is a first report to demonstrate the involvement of bNAC in imparting abiotic stress tolerance which might be due to protection of the newly synthesized polypeptides involved in various stress tolerance mecha- nisms from abiotic stress induced damage and inhibition of cell death in plant. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Abiotic stresses severely affect the growth, development, and metabolism of plants. Plants have developed an extensive frame- work of regulatory pathways at each level of cellular hierarchy and a network of genes are co-expressed at a particular time of stress to cope with the environmental stresses. Ribosomes are molecular machines inside the cytosol that syn- thesize polypeptides under different environmental conditions. Newly synthesized polypeptides on ribosome get attached with nascent polypeptide associated complex (NAC), also known as basal transcription factor 3 (Btf3), which plays an important role in pro- tecting newly formed proteins from interaction with inappropriate cytosolic factors [1–3]. The nascent polypeptide associated complex directly interacts with signal recognition particle and reported to be involved in translocation of newly synthesized proteins to the endoplasmic reticulum to prevent the mistargeting of nonsecretory proteins [4,5]. It is a highly conserved heterodimeric complex com- posed of a and b subunits [3]. Unequal expression of either NAC subunit has been reported to be associated with transcription reg- ulation and cell differentiation, suggests subunit specific functions of a and b subunits [6–8]. a-NAC has transcriptional activating activity and bind to DNA, rRNA, and tRNA, whereas bNAC can bind to RNA polymerase II, although it does not activate transcription [3,9]. In Saccharomyces cerevisiae, both a and b subunits of NAC associates with nascent polypeptide directly, however only bNAC is responsible for binding to the ribosome [9]. bNAC of Arabidopsis interacts with eIF4E, a major component of the translational initia- tion complex and might be associated with the regulation of trans- lation initiation [10]. All NAC proteins contain a NAC domain, which is suggested to be responsible for their dimerization [1]. NAC has several important functions in the cellular environment: (a) it pro- motes interaction of ribosomes with the mitochondrial surface and maintain efficient targeting of mitochondrial proteins such as fumarase and malate dehydrogenase [11], (b) it provides a protec- tive environment for newly synthesized polypeptides destined for endoplasmic reticulum and mitochondria [11–13], and (c) it inter- acts with unfolded polypeptide chains independent of their amino acid sequence like a typical chaperone and aids in folding of nascent polypeptide chains [14,15]. Inhibitor of cell death-1 gene (ICD-1) of Caenorhabditis elegans encodes for bNAC and its overexpression pre- vents apoptosis, while RNAi mediated underexpression of ICD-1 in- duces inappropriate apoptosis [16]. In Nicotiana benthamiana, virus induced silencing of NbBTF3, a homolog of bNAC caused leaf yellow- ing, abnormal leaf morphology, and simultaneously reduced the chloroplast sizes and chlorophyll content [17]. Recently, Huh et al. [18] reported involvement of bNAC (CaBtf3) isolated from Cap- sicum annuum in regulation of transcription for pathogenesis re- 0006-291X/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.bbrc.2012.07.023 ⇑ Corresponding author. Address: School of Plant, Environmental, and Soil Sciences, Louisiana State University Agricultural Center, 104 Sturgis Hall, Baton Rouge, LA 70803, USA. Fax: +1 225 578 1403. E-mail address: psubudhi@agcenter.lsu.edu (P.K. Subudhi). Biochemical and Biophysical Research Communications 424 (2012) 747–752 Contents lists available at SciVerse ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc