Research Highlights

Research Highlights
Genomic Tools to Enable Trait Discovery and Deployment - Genome Editing Pipeline Acceleration

Transformed soybean plant with leaf discs removed for genetic analysis.

By Heidi Kaeppler, University of Wisconsin

Two main methods can be used to modify traits in soybean seeds, genetic engineering (also referred to as “transformation”) and genome editing.

Soybean transformation involves inserting gene sequences encoding a specific trait into a chromosome of a target cell and regenerating a plant in which all of the cells contain the gene insertion. The inserted genes can encode novel traits (for example, herbicide resistance), increase or alter expression of native traits (for example, grain quality), or reduce or eliminate expression of negative traits (such as trypsin inhibitor production).

In genome editing, gene sequences encoding the DNA-cutting enzyme, Cas9, and RNA “guide” sequences are transformed into soybean cells. As part of the cell’s natural DNA repair processes, mutations in the target sequence can occur, resulting in shutting down expression of that gene, also called “knockout”. More recently, genome editing has been used to cut DNA sequences in specific locations and insert new sequences into that location, which is useful for adding new genes/traits or for replacing the current gene sequence with an improved version.

Imbibed soybean seed, embryo with attached cotyledon, and isolated meristem-containing embryonic axis explants.

Current public soybean transformation and editing systems are limited by genotype specificity, where only a few soybean lines or varieties can be successfully transformed and edited low efficiency and high cost, and the specialized expertise and precision required. This $105,000 project aims to develop and optimize novel soybean transformation and editing systems.

The initial focus was to develop a transformation system targeting transgene DNA delivery into soybean meristems (stem cell-containing growing points inside the shoot apex of the seedling within a soybean seed), and regenerating transgenic, clonal plants from the transformed cells. Using meristems allows regeneration of transgenic plants in almost any soybean variety and is much faster than traditional methods. The new system has been used to genetically engineer several soybean lines and varieties, as well as to deliver gene-editing components into soybean for editing applications. Initial results are positive, but further improvement in efficiency and breadth, to reduce both costs and complexity, are needed.

A family of soybean seedlings segregating for herbicide resistance following herbicide application. Green plants contain the herbicide resistance transgene. Bleached plants do not contain the transgene.

A second goal is investigating novel systems to make targeted DNA sequence changes, without integration of editing machinery into the soybean cell, by delivering the Cas9 protein and guide RNAs (and not their DNA sequences) into the target cells. The idea is to encapsulate the Cas9 protein and guide RNAs within extremely small, synthetic “nanoparticles” for delivery into cells. Work is underway to adapt existing nanoparticle-based systems from mammal to plant systems. If successful, this system would work with any soybean genotype, would provide efficient, rapid editing, and would be a “nonintegrating” method, meaning the resulting soybean germplasm would potentially have less regulatory and cost hurdles than traditional genetic engineering methods.

This project is part of the “Genomic Tools to Enable Trait Discovery” iPOP funded by USB in 2019. Overall, development and optimization of soybean transformation and editing systems should result in rapid advancement of soybean genetics and breeding efforts, through greater efficiency, access, and potential reduction of regulatory hurdles for the engineered/edited soybean lines. The Wisconsin Crop Innovation Center is a public fee for service transformation facility, and the knowledge gained will benefit all soybean researchers who use the facility.

Published: May 8, 2020

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.