Genetic and physical localization of an anthracnose resistance gene in <Emphasis Type="Italic">Medicago truncatula</Emphasis>

Anthracnose of alfalfa, caused by the fungal pathogen Colletotrichum trifolii, is one of the most destructive diseases of alfalfa worldwide. An improved understanding of the genetic and molecular mechanisms underlying host resistance will facilitate the development of resistant alfalfa cultivars, thus providing the most efficient and environmentally sound strategy to control alfalfa diseases. Unfortunately, cultivated alfalfa has an intractable genetic system because of its tetrasomic inheritance and out-crossing nature. Nevertheless, the model legume Medicago truncatula, a close relative of alfalfa, has the potential to serve as a surrogate to map and clone the counterparts of agronomically important genes in alfalfa—particularly, disease resistance genes against economically important pathogens. Here we describe the high-resolution genetic and physical mapping of RCT1, a host resistance gene against C. trifolii race 1 in M. truncatula. We have delimited the RCT1 locus within a physical interval spanning ∼200 kb located on the top of M. truncatula linkage group 4. RCT1 is part of a complex locus containing numerous genes homologous to previously characterized TIR-NBS-LRR type resistance genes. The result presented in this paper will facilitate the positional cloning of RCT1 in Medicago.     

Cloning and characterisation of glutathione reductase cDNAs and identification of two genes encoding the tobacco enzyme

We have isolated 4 cDNA clones (GRT1-4) encoding glutathione reductase (GR) from a tobacco (Nicotiana tabacum L.) leaf cDNA library. The cDNAs were almost identical: GRT1, GRT3 and GRT4 represented the same gene, differing only in that GRT4 contained an intron within the C-terminal part of the coding sequence. Failure to splice out this intron resulted in a substitution of the final 13 amino acids of the deduced amino acid sequence. A second gene was represented by GRT2. Southern blots indicated that there were two related GR genes in tobacco. The presence of multiple isoforms of GR in tobacco may be explained in part by the expression of a small gene family. In addition, alternative isoforms may result from translation of different mRNAs derived from the same gene by intron skipping during the splicing of nascent GR mRNAs.