The Solanum demissum R8 late blight resistance gene is an Sw-5 homologue that has been deployed worldwide in late blight resistant varieties
Theor Appl Genet
The Solanum demissum R8 late blight resistance gene is an Sw‑5 homologue that has been deployed worldwide in late blight resistant varieties
Jack H. Vossen 0
Gert van Arkel 0
Marjan Bergervoet 0
Kwang‑Ryong Jo 0
Evert Jacobsen 0
Richard G. F. Visser 0
0 Wageningen UR Plant Breeding, Wageningen University and Research , P.O. Box 386, 6700 AJ Wageningen , The Netherlands
The broad spectrum late blight resistance gene R8 from Solanum demissum was cloned based on a previously published coarse map position on the lower arm of chromosome IX. Fine mapping in a recombinant population and bacterial artificial chromosome (BAC) library screening resulted in a BAC contig spanning 170 kb of the R8 haplotype. Sequencing revealed a cluster of at least ten R gene analogues (RGAs). The seven RGAs in the genetic window were subcloned for complementation analysis. Only one RGA provided late blight resistance and caused recognition of Avr8. From these results, it was concluded that the newly cloned resistance gene was indeed R8. R8 encodes a typical intracellular immune receptor with an N-terminal coiled coil, a central nucleotide binding site and 13 C-terminal leucine rich repeats. Phylogenetic analysis of a set of representative Solanaceae R proteins shows that R8 resides in a clearly distinct clade together with the Sw-5
Phytophthora infestans; Potato late blight; Disease resistance gene; Cisgenesis; NB-LRR
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tospovirus R protein from tomato. It was found that the R8
gene is present in late blight resistant potato varieties from
Europe (Sarpo Mira), USA (Jacqueline Lee, Missaukee)
and China (PB-06, S-60). Indeed, when tested under field
conditions, R8 transgenic potato plants showed broad
spectrum resistance to the current late blight population in the
Netherlands, similar to Sarpo Mira.
Genetic resistance against pests and diseases is the most
sustainable crop protection strategy (Michelmore et al. 2013)
and has already provided durable solutions in many different
agrosystems. Potato late blight, caused by the oomycete
Phytophthora infestans, is still a serious problem for one of the
major food crops in this world. Despite the fact that genetic
resistance to late blight is amply available in the potato
germplasm (Vleeshouwers et al. 2011; Vossen et al. 2014), it is
deployed in potato varieties only to a limited extent. Limiting
factors in late blight resistance breeding are the long
breeding cycles and the highly heterozygous tetraploid genome.
Also, P. infestans is notorious for its short asexual spore
cycles, allowing mitotic mutations, and sexual generation
which allows rapid genetic recombination in many regions
of the world. To achieve durable resistance to late blight,
multiple resistance (R) genes must be introduced in
varieties to provide incremental and insurmountable hurdles for P.
infestans, thereby further delaying the breeding process. So,
the rigidity of the potato genome and the flexibility of the P.
infestans genome have so far prevented the large-scale use of
resistant varieties. Sarpo Mira is a variety that shows durable
resistance to the current P. infestans population (Lees et al.
2012), but this variety is not widely grown because
agricultural and industrial processing characteristics of late blight
susceptible varieties like Bintje and Russet Burbank are
preferred. Improvement of established varieties through genetic
modification is therefore an obvious approach; especially the
introduction of natural genes from crossable species, known
as cisgenes, is associated with low risks and is preferred by
consumers (Eurobarometer 2010; Devos et al. 2014). In the
last 10 years, the cloning of at least eight cisgenic late blight
R genes has been reported and many more are available from
the germplasm (Rodewald and Trognitz 2013). The
simultaneous introduction of multiple cisgenes causing late blight
resistance has been shown to be a feasible and highly
efficient approach (Zhu et al. 2012; Jo et al. 2014). For a viable
cisgenic late blight breeding approach, many cloned
broadspectrum R genes must be available. The potato late blight
differential MaR8 is considered a valuable late blight
resistance source, because virulence towards MaR8 is found only
with low frequency. The gene responsible for MaR8
resistance is referred to as R8 (Jo et al. 2011; Kim et al. 2012).
R8 has the same map position and recognition specificity as
Rpi-smira2 (Jo 2013), the main determinant of the resistance
in the potato variety Sarpo Mira (Rietman et al. 2012) that
has remained resistant already for several years. Also, the
late blight R gene from the variety Jacqueline Lee is located
at a similar genetic position (Massa et al. 2015). Here, we
report the cloning of the R8 gene through a map-based
cloning approach which includes a fine mapping, BAC landing,
BAC walking, candidate cloning and complementation
analysis. We show that R8 encodes a CC-NB-LRR protein with
89 % identity to Sw-5, a tomato spotted wilt vir (...truncated)