ORIGINAL PAPER Effect of Agrobacterium strain and plasmid copy number on transformation frequency, event quality and usable event quality in an elite maize cultivar Li Zhi • Susan TeRonde • Sandra Meyer • Maren L. Arling • James C. Register III • Zuo-Yu Zhao • Todd J. Jones • Ajith Anand Received: 24 October 2014 / Revised: 17 December 2014 / Accepted: 19 December 2014 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract Key message Improving Agrobacterium-mediated transformation frequency and event quality by increasing binary plasmid copy number and appropri- ate strain selection is reported in an elite maize cultivar. Abstract Agrobacterium-mediated maize transformation is a well-established method for gene testing and for introducing useful traits in a commercial biotech product pipeline. To develop a highly efficient maize transforma- tion system, we investigated the effect of two Agrobacte- rium tumefaciens strains and three different binary plasmid origins of replication (ORI) on transformation frequency, vector backbone insertion, single copy event frequency (percentage of events which are single copy for all trans- genes), quality event frequency (percentage of single copy events with no vector backbone insertions among all events generated; QE) and usable event quality frequency (trans- formation frequency times QE frequency; UE) in an elite maize cultivar PHR03. Agrobacterium strain AGL0 gave a higher transformation frequency, but a reduced QE fre- quency than LBA4404 due to a higher number of vector backbone insertions. Higher binary plasmid copy number positively correlated with transformation frequency and usable event recovery. The above findings can be exploited to develop high-throughput transformation protocols, improve the quality of transgenic events in maize and other plants. Keywords Agrobacterium  Maize inbred  Plasmid copy number  Origins of replication  Transformation  Quality events Abbreviations SC % Single copy frequency (percentage of events which are single copy for all transgenes) BB % Backbone minus frequency (percentage of events which no vector backbone insertions among all the events analyzed transgenes) QE % Quality event frequency (percentage of single copy events with no vector backbone insertions among all events analyzed) UE Usable event quality frequency (transformation frequency times QE frequency) Introduction Agrobacterium-mediated plant transformation is a pre- ferred method for introducing genes in model, and crop plants for basic and applied research. The unique ability of the bacterium to transfer a fragment of DNA within the transferred DNA (T-DNA) on the tumor inducing (Ti) plasmid to a recipient plant cell has made it an attractive tool for transgenesis (Anand et al. 2010; Gelvin 2003). The commercial biotech industry has taken advantage of this unique feature of Agrobacterium for gene testing, gene Communicated by Prakash P. Kumar. L. Zhi and S. TeRonde contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s00299-014-1734-0) contains supplementary material, which is available to authorized users. L. Zhi  S. TeRonde  S. Meyer  M. L. Arling  J. C. Register III  Z.-Y. Zhao  T. J. Jones  A. Anand (&) DuPont Agricultural Biotechnology, DuPont-Pioneer, 8305 NW 62nd Avenue, P. O. Box 7060, Johnston, IA 50131, USA e-mail: ajith.anand@pioneer.com 123 Plant Cell Rep DOI 10.1007/s00299-014-1734-0