TRA1: A Locus Responsible for Controlling Agrobacterium-Mediated Transformability in Barley.

Pete E Hedley,Wendy Harwood,Malcolm Macaulay,Alison Hinchcliffe,Kay Trafford,Beata Orman-Ligeza,Cristobal Uauy

doi:10.3389/fpls.2020.00355

Abstract

In barley (Hordeum vulgare L.), Agrobacterium-mediated transformation efficiency is highly dependent on genotype with very few cultivars being amenable to transformation. Golden Promise is the cultivar most widely used for barley transformation and developing embryos are the most common donor tissue. We tested whether barley mutants with abnormally large embryos were more or less amenable to transformation and discovered that mutant M1460 had a transformation efficiency similar to that of Golden Promise. The large-embryo phenotype of M1460 is due to mutation at the LYS3 locus. There are three other barley lines with independent mutations at the same LYS3 locus, and one of these, Risø1508 has an identical missense mutation to that in M1460. However, none of the lys3 mutants except M1460 were transformable showing that the locus responsible for transformation efficiency, TRA1, was not LYS3 but another locus unique to M1460. To identify TRA1, we generated a segregating population by crossing M1460 to the cultivar Optic, which is recalcitrant to transformation. After four rounds of backcrossing to Optic, plants were genotyped and their progeny were tested for transformability. Some of the progeny lines were transformable at high efficiencies similar to those seen for the parent M1460 and some were not transformable, like Optic. A region on chromosome 2H inherited from M1460 is present in transformable lines only. We propose that one of the 225 genes in this region is TRA1.

Highlights

Agrobacterium-mediated transformation of immature barley embryos was first reported in 1997 using the cultivar Golden Promise (Tingay et al, 1997) and most barley transformation since has used this cultivar
In Arabidopsis, progress has been made in identifying the molecular mechanisms governing Agrobacterium-mediated transformation
The methods used to transform Arabidopsis differ from that used to transform barley, we looked to see if any of the Arabidopsis transformation genes were TRA1 candidates

Summary

Introduction

Agrobacterium-mediated transformation of immature barley embryos was first reported in 1997 using the cultivar Golden Promise (Tingay et al, 1997) and most barley transformation since has used this cultivar. This is because no other cultivar has been found to give a similar or higher transformation efficiency (Bartlett et al, 2008; Harwood et al, 2009; Harwood, 2012). TFA1 is located on chromosome 3H and two others, TFA2, and TFA3, are both on chromosome 2H (Hisano and Sato, 2016; Hisano et al, 2017) This suggests that the transformability trait in Golden Promise is multi-genic in nature which means that it would be technically challenging to transfer the trait to another barley cultivar. There is a need for other, preferably elite, lines of barley that can be transformed with high efficiency

Methods

Results

Conclusion