Abstract
Genetic gain in potato is hampered by the heterozygous tetraploid genome of cultivated potato. Converting potato into a diploid inbred-line based F1-hybrid crop provides a promising route towards increased genetic gain. The introduction of a dominant S-locus inhibitor (Sli) gene into diploid potato germplasm allows efficient generation of self-fertilized seeds and thus the development of potato inbred lines. Little is known about the structure and function of the Sli locus. Here we describe the mapping of Sli to a 12.6 kb interval on chromosome 12 using a recombinant screen approach. One of two candidate genes present in this interval shows a unique sequence that is exclusively present in self-compatible lines. We describe an expression vector that converts self-incompatible genotypes into self-compatible and a CRISPR-Cas9 vector that converts SC genotypes into SI. The Sli gene encodes an F-box protein that is specifically expressed in pollen from self-compatible plants. A 533 bp insertion in the promotor of that gene leads to a gain of function mutation, which overcomes self-pollen rejection.
Highlights
Genetic gain in potato is hampered by the heterozygous tetraploid genome of cultivated potato
In one F2 population derived from a cross between the S-locus inhibitor (Sli) donor and a diploid S. tuberosum (D2) we observed a modest effect QTL for self-berry set on chromosome 2, but a subsequent recombinant screening was not successful
Based on this skewness and the mapping of Sli on chromosome 12, we hypothesized that Sli is gametophytically expressed, meaning that in a self-pollination of a plant heterozygous for Sli (Sli/sli), only pollen containing the dominant Sli allele can participate in self-fertilization
Summary
Genetic gain in potato is hampered by the heterozygous tetraploid genome of cultivated potato. Targeted introduction of new traits into elite cultivars while maintaining the genetic integrity via backcrossing schemes is impossible without homozygous parental lines To overcome these problems, several groups have started inbred-line-based diploid potato breeding programs[2,3,4,5]. Hosaka and Hanneman mapped a dominant Slocus inhibitor (Sli) gene from a Solanum chacoense accession at the distal end of chromosome 12 and used it to generate potato inbred lines[13,14] Based on their results, Hosaka and Hanneman suggested that Sli is a pollen-expressed gene with sporophytic action and that homozygosity for Sli is lethal since homozygous SliSli genotypes were absent in the F8 population of S. chacoense. We describe the identification of the causal gene of selfcompatibility to gain further insight into the biology of selfcompatibility in diploid potato
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