Research and analysis

Advice on the regulatory status of potato transformants

Updated 8 September 2023

Applies to England

Advice of the Advisory Committee on Releases to the Environment to the Secretary of State under section 124 of the Environmental Protection Act 1990

Summary advice

Based on current evidence, the Advisory Committee on Releases to the Environment (ACRE) does not consider the potato lines in question to be ‘qualifying higher plants’ as defined in the Genetically Modified Organisms (Deliberate Release) (Amendment) (England) Regulations 2022.

Whilst the genetic elements inserted to alter the potato phenotype all originate from within the Solanum genus, ACRE considered that using traditional processes, it would be unlikely that the acetolactate synthase (ALS) gene from tomato (S. lycopersicon) could be successfully introgressed into elite potato germplasm, noting that attempts to do so using protoplast fusion have been made in the past1.

ACRE noted that one of the inserted genes (Rpi-vnt-1) had already been introgressed into potato following interspecific crossing (S. phureja × S. stenotomum) back to a diploid potato (S. tuberosum) demonstrating it to be cisgenic.

ACRE also considered that although there is some evidence that allotetraploid hybrids between S. americanum and potato are possible, there is currently little evidence that genetically stable cultivated potato plants have been generated by back crossing although this is technically feasible.

Furthermore, although gene regulation in plants is known to be mediated by naturally occurring antisense transcripts, ACRE concluded that the likelihood of achieving the precise arrangement of sense and antisense sequences of the potato Ppo and Vlnv genes (plus the small hairpin spacer sequence) through traditional processes would be very low.

ACRE also concluded that the inserted potato virus Y resistance gene from S. stoloniferum may be considered a cisgene on the basis that S. stoloniferum and potato are fully sexually compatible.

Introduction

The Genetically Modified Organisms (Deliberate Release) (Amendment) (England) Regulations 2022 includes provisions which facilitate research trials of certain types of GMOs described as ‘qualifying higher plants’.

ACRE has published guidance to assist developers in determining whether an organism is a ‘qualifying higher plant’ and may therefore be cultivated in research trials without needing Defra Ministerial consent.

ACRE was asked whether three different potato lines resulting from Agrobacterium-mediated transformation could be considered as ‘qualifying higher plants’ on the basis that the introduced DNA sequences that they contain all originate from within the same genus (Solanum) as potato (Solanum tuberosum)

The lines in question contain T-DNA constructs comprising these sequences organised into expression cassettes of different types. Many species within the Solanum genus are sexually compatibility and so these plants have the potential to be classed as cisgenic.

ACRE is familiar with the genes and cassettes within these T-DNA constructs as they appear in the relevant sections of the environmental risk assessments of ‘Part B’ applications 19/R29/01 and 22/R29/01. Their identities, functions and origins are summarised in the relevant environmental risk assessments.2,3

Late blight resistance genes (Rpi genes) from wild potato varieties S. venturii and S. americanum

Two of the Rpi genes were derived from S. americanum and one from S. venturii. ACRE discussed the level of sexual compatibility between potato and these different species, including whether there was existing evidence that successful crosses had been made. It was important to take into account the range of traditional processes that exist for achieving genetically stable potato plants containing Rpi genes. With regard to the Rpi-vnt1 gene from S. venturii, ACRE noted that an identical gene (Rpi-phu1), had already been bred into some Polish potato varieties via interspecific crossing between S. phureja and S. stenotomum back into diploid potato4. This demonstrates that the Rpi-vnt1 gene in the present potato transformants may be considered cisgenic.

With regard to S. americanum, ACRE noted that somatic fusion had been used to generate flowering hybrids of S. americanum and potato but that introgression of resistance traits after recurrent backcrossing had yet to be demonstrated. ACRE concluded that there is some evidence that genetically stable cultivated potato plants containing the Rpi genes from S. americanum could potentially be produced using traditional processes. On this basis it is likely that the Rpi genes from S. americanum could be considered cisgenic even though there is little evidence that successful introgression into potato has yet been achieved.

The tomato acetolactate synthase (ALS) gene from S. lycopersicon

All three lines under discussion contain the ALS gene from tomato which confers resistance to chlorsulfuron based herbicides. ACRE was unable to find evidence to support the hypothesis that traditional processes could be used to make genetically stable cultivated potato plants containing the ALS gene from tomato. ACRE noted early attempts to make intermediate hybrids between tomato and potato using protoplast fusion5 had been made but concluded that the results did not represent convincing evidence that genetically stable cultivated potato plants could be produced with this approach.

Sense and antisense Ppo and Vlvn genes from potato

In two of the potato lines discussed here, a pair of Vlnv genes and a pair of PPo genes (both from potato) are specifically arranged in an inverted and outward facing orientation with respect to the T-DNA construct. Furthermore, the two different genes are inverted with respect to each other and linked to cause the formation of a hairpin loop as a result of cloning a short spacer fragment of DNA (also from potato) between the 3’ end of the antisense Ppo gene and the 5’ end of the sense Ppo gene. Whilst ACRE is aware of the potential role in traditional breeding of naturally occurring antisense transcripts, it concluded that the specific arrangement of genes in these potato lines is unlikely to be one that breeders could select for using traditional processes. Therefore, they are unlikely to be considered as cisgenic.

Potato virus Y resistance gene (Ry^sto) from a wild potato variety S. stoloniferum

The origin of the potato virus Y resistance gene (Ry^sto) in one of the potato lines under discussion is the wild potato species S. stoloniferum. Native to North and South America, it has been used often in potato breeding and can result in both tetraploid and hexaploid hybrid progeny when crossed with S. tuberosum. Introgression of wild traits (including resistance to potato virus Y) has been achieved in many cases in breeding programmes. Given such sexual compatibility between the two species, the presence of the Ry gene from S. stoloniferum within the S. tuberosum background should be considered as evidence for the cisgenic nature of this insertion.

Other inserted sequences

In addition to the genes/cassettes described above, the lines under discussion contain small, synthetic polylinkers and T-DNA borders which have no effect on plant phenotype. As such, ACRE did not consider these elements as having any relevance to the discussion of whether the lines may or may not be qualifying higher plants.