BIOLOGIA PLANTARUM 53 (1): 37-44, 2009 37 Molecular characterization of two genes encoding plastidic ATP/ADP transport proteins in cassava C.Y.L. YUEN 1,2 , O. LEELAPON 1 , Y. CHANVIVATTANA 1 , J. WARAKANONT 3 and J. NARANGAJAVANA 3,4 * National Center for Genetic Engineering and Biotechnology, Klong 1, Klong Luang, 113 Paholyothin Rd., Pathumthani 12120, Thailand 1 Department of Molecular Biosciences & Bioengineering, University of Hawaii, 1955 East-West Road, Manoa, HI 96822, USA 2 Department of Biotechnology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand 3 Center for Cassava Molecular Biotechnology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand 4 Abstract The import of ATP into plastids is facilitated by members of the plastidic ATP/ADP transporter (AATP) family. Our results indicate that the cassava (Manihot esculenta Crantz) genome possesses two genes encoding for putative ATP/ADP translocases, which we have designated as MeAATP1 and MeAATP2. Their deduced products are 92 % identical, and phylogenetic reconstructions of plant AATP sequences suggest that MeAATP1 and MeAATP2 are the result of a relatively recent duplication event. Both genes were found to be expressed in a wide range of plant organs via RT-PCR, including young and mature leaves, fibrous and tuberous roots, and green stems. Neither MeAATP1 nor MeAATP2 showed evidence of increased transcription in the presence of exogenous sucrose. Interestingly, the transcriptional activity of MeAATP1 in leaves appeared to be upregulated after wounding, potentially indicating its involvement in the wound response mechanism of cassava. Additional key words: amyloplasts, Manihot esculenta, starch biosynthesis, wounding. Introduction Plastids are a set of developmentally-interrelated orga- nelles which host several metabolic processes essential for the proper growth and development of plants, including carbon and nitrogen assimilation, and the synthesis of amino acids, fatty acids and starch. Though possessing their own genome, most plastid proteins are encoded by nuclear genes and are targeted to plastids posttranslationally. These include nuclear-encoded trans- membrane proteins involved in the movement of metabo- lites across the plastidic double-membrane system. The outer membrane is freely permeable to molecules of 10 kDa or less via porins (Flügge and Benz 1983, Fischer et al. 1994), while the movement of specific molecules across the inner membrane is facilitated by specialized transporters (reviewed in Emes and Neuhaus 1997). ATP is the principle energy carrier of living organisms. Although chloroplasts are capable of genera- ting ATP via photosynthesis, non-photosynthetic plastids must rely upon the import of ATP from the cytosol. Movement of ATP across the plastid inner membrane is mediated by the members of at least two distinct transport protein families. Members of the plastidic ATP/ADP transport protein (AATP) family share significant sequence homology to a class of nucleotide transporters ⎯⎯⎯⎯ Received 16 April 2007, accepted 6 December 2007. Abbreviations: AATP - ATP/ADP transporter; ADP-Glc - ADP-glucose; AGPase - ADP-glucose pyrophosphorylase; CS - transit peptide cleavage sites; RACE - rapid amplification of cDNA ends; TM - transmembrane. Acknowledgements: Cassava samples were graciously provided by Dr. Opas Boonseng of the Rayong Field Crops Research Center (Rayong, Thailand). We are grateful to Dr. Malinee Suksangpanomrung and Ms. Apaporn Rattanakitti for establishing and maintaining cassava plants at Thailand Science Park (Pathumthani, Thailand), and for advice and assistance with cassava nucleic acid extraction. We are also thankful to the members of the Starch Biosynthesis laboratory (BIOTEC Central Research Unit) and the Center for Cassava Molecular Biotechnology, Faculty of Science, Mahidol University for their helpful comments and suggestions. This research was supported by National Center for Genetic Engineering and Biotechnology grant BT-B-02-PM-BC-4706. C.Y.L. Yuen and O. Leelapon contributed equally to the paper. * Corresponding author: fax: (+66) 2 354 7160, e-mail: scjnr@mahidol.ac.th