Agrobacterium-mediated cassava transformation for the Asian elite variety KU50.

Yoshinori Utsumi,Satoshi Takahashi,Maho Tanaka,Nguyen Van Dong,Tong Thi Huong,Anh Vu Nguyen,Yoshie Okamoto,Motoaki Seki,Hiroki Tokunaga,Chikako Utsumi,Nigel Taylor

doi:10.1007/s11103-021-01212-1

Abstract

Cassava genetic transformation has mostly been reported for African cassava varieties, but not for Asian varieties. This is the first report of cassava transformation in Asian elite varieties using friable embryogenic calli. Agrobacterium-mediated cassava transformation via friable embryogenic calli (FEC) has enabled the robust production of transgenic cassava. So far, mostly the model cassava variety 60444 and African varieties have been transformed because of their good production and regeneration from embryogenic tissues. It is important to develop transformation methods for elite Asian cassava varieties to meet the changing needs in one of the world's major cassava production areas. 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 using 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%, approximately half that of 60444 at 45%. Transcriptome analysis indicated that the expression of genes related to cell-wall loosening was upregulated in FEC from KU50 compared with 60444, indicating that cell-wall production and assembly were disproportionate in the Asian variety. The transformation system for KU50 reported here will contribute to the molecular breeding of cassava plants for Asian farmers using transgenic and genome-editing technologies.

Highlights

Cassava (Manihot esculenta Crantz) is grown across the tropics and sub-tropical regions for production of its starchy tuberous roots
organized embryogenic calli (OEC) were induced from axillary buds (AB) of KU50 within 2 weeks culture on MS medium supplemented with 12 mg/L picloram (CIM)
We developed a system for Agrobacterium-mediated transformation of the Asian elite variety KU50

Summary

Introduction

Cassava (Manihot esculenta Crantz) is grown across the tropics and sub-tropical regions for production of its starchy tuberous roots. It provides an important source of daily calories for 100s of millions for people and plays a critical role in global food security and rural economies (Balat and Balat 2009). Genome editing by CRISPR-Cas technology has been reported in cassava (Hummel et al 2018; Odipio et al 2017; Seki et al 2018) For both gene editing and conventional transformation, the preferred methods involve Agrobacterium-mediated delivery of molecular sequences into disorganised embryogenic callus with subsequent regeneration of somatic embryos and their germination to produce plants

Methods

Results

Conclusion