Plant & Animal Genome IX Conference

Poster: Large Insert Libraries, Gene Isolation, Etc.
P02_44.html

PHYSICAL ARRANGEMENT AND SEQUENCE ANALYSIS OF HOMOLOGS OF THE NEMATODE AND APHID RESISTANCE GENE MI-1.2 IN RESISTANT TOMATO.

Center for Engineering Plants for Resistance against Pathogens (CEPRAP), UC Davis, One Shields Avenue, Davis, CA, 95616, USA

The resistance (R) gene Mi-1, introgressed into cultivated tomato (L. esculentum), from its wild relative L. peruvianum, confers effective resistance against 3 species of root-knot nematode (Meloidogyne spp.) and certain isolates of the potato aphid (Macrosiphum euphorbiae). The isolated Mi-1 gene belongs to the NBS-LRR class of R-genes as it contains a putative nucleotide-binding site (NBS) and a leucine-rich repeat domain (LRR). The Mi-1 region of the tomato genome carries 2 distinct clusters of Mi-1 homologs on chromosome 6 separated by ~230 kb. One cluster (Mi-1') 60 kb in size, consists of at least 4 homologs, whereas the other cluster (Mi-1) carrying the functional gene member, Mi-1.2, contains 3 homologs within a 50 kb region. Three out of the 7 homologs contain large deletions and/or rearrangements within the open reading frame (ORF). One of the homologs (Mi-1.6) contain a 1 bp deletion resulting in a loss of the ORF. The 4 homologs (including Mi-1.2) with complete or near complete ORFs (most of which are expressed), share 94-95% similarity in nucleic acid sequence. Sequence analysis of the remaining 50 kb non-coding region spanning the Mi-1 cluster provide early evidence of genetic duplication and recombination events as keys contributors to the diversification of the homologs in tomato. There are at least 8 Mi-1 homologs in the corresponding chromosomal region in susceptible tomato. The Mi-1 homologs belong to a large gene family in tomato and in other solanaceous plant species.