S. okadae and S. neorossii
Using a combination of AFLP, SSR and CAPS markers derived from sequenced tomato RFLP markers we have determined that Rpi-oka1 and 2 are located in the same region on the long arm of chromosome IX but appear to be on distinct haplotypes, raising the possibility that they may exhibit different recognition specificities. From analysis of recombinants in our Rpi-oka1 mapping population we have established that there are two closely linked genes conferring resistance (Rpi-oka1a and 1b). A third gene from S. okadae, Rpi-oka3 maps slightly South from Rpi-oka1/2.Rpi-nrs1 from S. neorosii also maps to the same position on chromosome IX as Rpi-oka1/2, and, as for Rpi-oka1, it appears that there may also be a second closely linked gene (Rpi-nrs1b). Rpi-nrs2 maps further South from the other Rpi-oka/nrs genes (possible in a similar location to Rpi-oka3). We are currently refining the map position for these genes.Using a BAC library made from a transheterozygote plant containing both Rpi-oka1 and Rpi-oka2 we have established a contig containing Rpi-oka1. Southern blotting and sequencing of candidate BACs has revealed the presence of one candidate resistance gene and we are currently in the process of testing the ability of this gene to confer late blight resistance in a susceptible cultivar. Candidate BACs containing Rpi-oka2 could not be found within the BAC library and so we will PCR the corresponding genes using Rpi-oka1 sequence information. We will also use this approach to obtain candidate sequences for Rpi-nrs1a and 1b. For further information please contact Simon Foster or Tae-Ho Park .
S. berthaultii
Rpi-ber1 and Rpi-ber2 are located on chromosome X and appear to be distinct genes which are both at roughly the same position as the previously identified RPi-ber (Rauscher et al.,2006); indeed Rpi-ber1 may be the same gene that was mapped in the previous study. We are currently mapping these two genes to a higher resolution using CAPS, AFLP and NBS markers. For further information please contact Simon Foster or Tae-Ho Park .
S. mochiquense
Rpi-mcq1 was previously mapped to the bottom of the long arm of chromosome IX (Smilde et al, 2005). Using higher resolution mapping we have been able to delimit a narrow region with a genetic interval of 0.32 cM containing Rpi-mcq1. A BAC library of approximately 9X coverage was constructed from a heterozygote plant with an average insert size of 85 kb. The BAC library was screened by PCR using flanking and co-segregating markers. A contig spanning the candidate gene was constructed with positive BAC clones that were identified from the resistant haplotype. With help from recombinant information, we fine mapped the Rpi-mcq1 to two overlapping BACs which are estimated to cover 100 kb. Based on Southern blotting and sequences of the two BAC clones we have determined that the Rpi-mcq1 region contains three R genes, one of which contains an early stop codon, leaving two candidates for Rpi-mcq1. To enable functional testing of the candidate genes by transformation, the two candidate genes have been subcloned into the binary cosmid vector pCLD04541 for transformation of a susceptible potato cultivar. For further information please contact Chu Zhaohui .
S. brachistotrichum
Rpi-bst1 maps to chromosome IV in a complex region known to contain the previously identified late blight R genes R2, Rpi-blb3 and Rpi-abpt and numerous additional resistance gene homologues. Our collaborators in Wageningen have recently cloned Rpi-blb3. Given the proximity of Rpi-bst1 to this gene there is the possibility that it may be a paralogue, or indeed an orthologue of Rpi-blb3. For further information please contact Chu Zhaohui .
What P infestans genes do these R genes recognize?
We are implementing a collaboration with Sophien Kamoun and Paul Birch to deliver candidate effector proteins of P infestans into our segregating Solanum germplasm using either potato virus X or Erwinia type 3 secretion. The aim is to identify the pathogen molecules that these Rpi genes recognize.
