Research review paper Suitability of non-lethal marker and marker-free systems for development of transgenic crop plants: Present status and future prospects P. Manimaran a , G. Ramkumar a , K. Sakthivel b , R.M. Sundaram a , M.S. Madhav a , S.M. Balachandran a, ⁎ a Biotechnology Laboratory, Crop Improvement Section, Directorate of Rice Research, Rajendranagar, Hyderabad 500030, India b Vegetable Research Station, Tamilnadu Agricultural University, Palur 607102, India abstract article info Article history: Received 23 December 2010 Received in revised form 30 May 2011 Accepted 31 May 2011 Available online 7 June 2011 Keywords: Selectable marker genes Marker gene elimination Plant transformation Transgenics Genetically modified crops are one of the prudent options for enhancing the production and productivity of crop plants by safeguarding from the losses due to biotic and abiotic stresses. Agrobacterium-mediated and biolistic transformation methods are used to develop transgenic crop plants in which selectable marker genes (SMG) are generally deployed to identify ‘true’ transformants. The commonly used SMG obtained from prokaryotic sources when employed in transgenic plants pose risks due to their lethal nature during selection process. In the recent past, some non-lethal SMGs have been identified and used for selection of transformants with increased precision and high selection efficiency. Considering the concerns related to bio-safety of the environment, it is desirable to remove the SMG in order to maximize the commercial success through wide adoption and public acceptance of genetically modified (GM) food crops. In this review, we examine the availability, and the suitability of wide range of non-lethal selection markers and elimination of SMG methods to develop marker-free transgenics for achieving global food security. As the strategies for marker-free plants are still in proof-of-concept stage, adaptation of new genomics tools for identification of novel non-lethal marker systems and its application for developing marker-free transgenics would further strengthen the crop improvement program. © 2011 Elsevier Inc. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704 2. Selectable marker gene (SMG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704 2.1. Non-plant based positive SMGs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705 2.1.1. Aminoglycoside-3′-adenyl transferase (aadA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705 2.1.2. D-amino acid oxidase (dao1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705 2.1.3. Mannose A (manA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705 2.1.4. Green fluorescent protein (GFP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706 2.1.5. Yeast proline analogue resistance (MPR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706 2.2. Plant based positive SMGs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706 2.2.1. Mannose 6 phosphate reductase (M6PR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706 2.2.2. Maize knotted 1 (kn1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 2.2.3. Trehalose 6 phosphate synthase 1 (TPS1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 2.2.4. Anthranilate synthase (ASA2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 2.2.5. Plant α-tubulin (Tub1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 2.2.6. Nitrite reductase (NiR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 3. Elimination of selection marker gene from transgenic plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 3.1. Marker elimination by co-transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708 3.2. Marker elimination by site-specific recombination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708 3.2.1. Cre/loxP site specific recombination system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709 3.2.2. FLP/FRT system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709 3.2.3. R/RS system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709 Biotechnology Advances 29 (2011) 703–714 ⁎ Corresponding author. Tel.: + 91 40 24591228; fax: + 91 40 24591217. E-mail address: balasena@yahoo.com (S.M. Balachandran). 0734-9750/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.biotechadv.2011.05.019 Contents lists available at ScienceDirect Biotechnology Advances journal homepage: www.elsevier.com/locate/biotechadv