Genetic transformation of wheat: current status and future prospects

Genetic transformation is a reverse genetics tool for validation of target genes and crop improvement. However, due to its low efficiency and genotype dependency, wheat is considered a recalcitrant plant for genetic transformation. During the last 20 years, various in vitro and in planta transformation methods have been reported in wheat. Until now, biolistic particle and Agrobacterium-mediated wheat transformation methods using immature embryos as explants have been the two major transformation approaches. In addition to immature embryos, other explant types, such as mature embryos, anther-derived calli, inflorescences, apical meristems, and other floral organs, have been employed; however, they need further optimization. In addition to the common marker genes, such as bar, hpt and gus, other effective markers, ALS, AtMYB12 and pmi, have been successfully used for selection of positive transgenic plants. Numerous agronomic trait genes such as biotic stress resistance or tolerance genes have been transferred into wheat plants. Future prospects, such as recipient wheat cultivars and explants, marker free issues, and transgene silencing, are discussed. The objective of this review is to summarize current successful techniques for wheat transformation and stimulate further research into long-term wheat improvement by genetic engineering approaches.