**1. Introduction**

Soybean (*Glycine max* (L.) Merrill) is a model legume crop, widely grown in the world for hu‐ man consumption or animal fodder. Moreover, soybeans have gained worldwide research in‐ terest in many public laboratories and industrial sectors. Soybean seeds contain protein, oil, carbohydrates, dietary fibers, vitamins, and minerals. For the last few decades the majority of research laboratories have been investigating genetic traits to improve the yield of protein or oil in soybean seeds through genetic engineering, thereby achieving improved quantity and quality of soybean seeds. Until now, most of the transformation experiments have implement‐ ed a single functional gene not multiple genes. Those agronomically and economically impor‐ tant traits affect the enhancement of grain quantity and quality [1]. However, the majority of agronomic and genetic traits such as complex metabolic, biological, and pharmaceutical path‐ ways are polygenetic traits and are produced in a complex pathway. Therefore, those traits are encoded and regulated by a number of genes. In an attempt to study and manipulate those pathways, the transfer of multigene or large inserts into plants have been developed by multi‐ gene engineering technology and have also been involved in metabolic engineering. Several examples of multigene or large insert transfers have been reported such as the application of carotenogenic genes in rice, canola, and maize [2-4], and of polyunsaturated fatty acid and vi‐ tamin E genes in soybean and *Arabidopsis* [5-7]. Therefore, reliable systems for transforming large DNA fragments into plants make it feasible to introduce a natural gene cluster or a series of previously unlinked foreign genes into a single locus.

Over the last two decades, the transfer of DNA into plant cells has been achieved by using several methods. In soybeans, the most frequently employed plant genetic engineering methods are *Agrobacterium*-mediated transformation and particle bombardment. Both sys‐ tems have successfully been used in genetic transformation of soybean. Since the initial re‐ ports of fertile transgenic soybean production [8-9], various efforts have been made to improve the transformation efficiency and to produce transgenic soybean. Particularly, the

© 2013 Lee et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Lee et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

preferred and reproducible transformation is the use of the cotyledonary node as a plant material, which is based on *Agrobacterium*-mediated gene transfer [10-12]. Nevertheless, new methods have been developed for more efficient soybean transformation. There still remain, however, many challenges for genotype- and tissue- specific independent transformation of soybean. This review provides an overview of historical efforts in developing and advanc‐ ing soybean regeneration and transformation systems. In addition, recent advances and challenges in soybean transformation are discussed.
