ZmCOI6.1, a novel, alternatively spliced maize gene, whose transcript level changes under abiotic stress Orlene Guerra-Peraza, Ha Thuy Nguyen, Peter Stamp, Jo ¨ rg Leipner * ETH Zurich, Institute of Plant Sciences, Universita ¨tstrasse 2, 8092 Zu ¨rich, Switzerland 1. Introduction Maize (Zea mays L.) originates from subtropical mid-altitudes of Mexico and is adapted to a semi-arid climate with high light intensity and high temperature during the day and moderate temperature at night [1]. The cultivation of maize has been extended to colder regions where damage caused by low temperature is a frequent problem. In particular, temperatures below 15 8C retard germination and seedling growth [2,3]. Low temperature affects a wide range of processes in the maize seedling; however, the primary cause of this sensitivity to chilling stress is still unknown [4]. Damage caused to maize seedlings by low temperature is primarily to the chloroplasts, leading to inhibition of photo- synthesis [5]. Furthermore, development of maize leaves at low temperature leads to a reduction in the activity of the carbon cycle [6,7] and changes in the antioxidative defences [8]. An important role in this response to low temperature may be played by signaling molecules, such as the plant hormones salicylic acid (SA), abscisic acid (ABA) and jasmonic acid (JA). These plant hormones induce acclimation to cold, resulting in improved tolerance to low temperature [9–11]. Furthermore, hydrogen peroxide (H 2 O 2 ) is regarded as another important signaling molecule and a regulator of expression of some genes in response to stress [12]. The response to chilling is accompanied by changes in specific gene transcripts. Some cold- induced genes have been identified in maize, among them genes involved in transcriptional regulation [13,14] and in lipid metabolism [15]. The wide functional range of maize genes, which respond to cold was also shown by the identification of cold-induced genes by suppression subtractive hybridization [16]. However, the exact molecular function of these genes and encoded proteins in the cold response of maize is still not understood. Most of our knowledge of the molecular response to cold is based on studies of Arabidopsis. In particular, the transcriptional regulation by the C-repeat (CRT)/dehydration- responsive element (DRE) binding factors (CBF) has received considerable attention [17]. The identification of the CBF-type transcription factors in other plant species suggests that this transcriptional regulation mechanism is conserved in several plant species, see, e.g., [18,19]. However, there are indications that cold acclimation can also be CBF-independent [20]. Beside the regulation on the transcriptional level, gene expression is also regulated by post-transcriptional and post-translational modifica- tions, which seem to be of particular importance during the response to stress [21]. Among the post-transcriptional modifica- tions, alternative splicing, by which different forms of mature mRNA are produced from a single transcript, seems to play an important role during abiotic stress [22]. Plant Science 176 (2009) 783–791 ARTICLE INFO Article history: Received 23 December 2008 Received in revised form 2 March 2009 Accepted 4 March 2009 Available online 21 March 2009 Keywords: Cold acclimation Intron retention Maize Stress-regulated gene expression ABSTRACT Maize (Zea mays L.) is an important crop that is poorly adapted to cold stress; very little is known about the components of the response to stress. By means of the cDNA subtraction technique, several novel genes, responsive to cold stress, have been identified, including ZmCOI6.1, the function of which is unknown. The predicted ZmCOI6.1 amino acid sequence and its homologue are very similar to proteins in rice and Arabidopsis, suggesting that it belongs to a conserved group of plant proteins. Analysis of the ZmCOI6.1 promoter sequence revealed several conserved stress-responsive cis-acting elements. Further characterization of expression showed that ZmCOI6.1 was induced not only by cold, but also by drought and salinity as well as by the signaling molecules abscisic acid and salicylic acid, indicating that ZmCOI6.1 is a stress-responsive gene. ZmCOI6.1 is alternatively spliced and yields two transcripts, the level of which change depending on the stress, indicating a possible mechanism of regulation at the splicing level. Constitutive expression of ZmCOI6.1 in Arabidopsis yielded plants that were less tolerant to abiotic stress, providing evidence that ZmCOI6.1 may be a negative regulator. ß 2009 Elsevier Ireland Ltd. All rights reserved. * Corresponding author. Tel.: +41 44 6328334; fax: +41 44 6321143. E-mail address: joerg.leipner@ipw.agrl.ethz.ch (J. Leipner). 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.2009.03.004