Agrobacterium-Mediated Cassava Transformation For The Asian-elite Variety KU50

Abstract Agrobacterium-mediated cassava transformation via friable embryogenic calli (FEC) has allowed the robust production of transgenic cassava. So far, transformation has been performed mostly for the model cassava variety 60444 and African varieties due to their good production of, and regeneration from, embryogenic tissues. It is important to develop transformation methods for elite Asian cassava varieties to meet changing needs within one of the world’s major cassava production areas. To date, however, a suitable transformation method for the Asian elite variety Kasetsart 50 (KU50) has not been developed. Here, we report a transformation method for KU50, the cultivar with the highest planting area in Thailand and Vietnam. In cassava transformation, the preparation of FEC as the target tissue for transgene integration is a key step. FEC induction from KU50 was improved by the use of media with reduced nutrients and excess vitamin B1, and somatic embryo and plant regeneration optimized by manipulation of naphthalene acetic acid (NAA) and benzylamino purine (BAP). The transformation efficiency for KU50 was 22%, at approximately half of that of 60444 (45%). Transcriptome analysis indicated that expression of genes related to cell wall loosing was upregulated in FEC from KU50 compared with 60444, indicating cell wall production and assembly was out of balance in the Asian variety. The transformation system for KU50 reported here will contribute to molecular breeding of cassava plants for Asian farmers by transgenic and genome-editing technologies.