Novel Disease Resistance Specificities Result from Sequence Exchange between Tandemly Repeated Genes at the Cf-4/9 Locus of Tomato

Abstract

Tomato Cf genes confer resistance to C. fulvum, reside in complex loci carrying multiple genes, and encode predicted membrane-bound proteins with extracytoplasmic leucine-rich repeats. At least two Cf-9 homologs confer novel C. fulvum resistance specificities. Comparison of 11 genes revealed 7 hypervariable amino acid positions in a motif of the leucine-rich repeats predicted to form a beta-strand/beta-turn in which the hypervariable residues are solvent exposed and potentially contribute to recognition specificity. Higher nonsynonymous than synonymous substitution rates in this region imply selection for sequence diversification. We propose that the level of polymorphism between intergenic regions determines the frequency of sequence exchange between the tandemly repeated genes. This permits sufficient exchange to generate sequence diversity but prevents sequence homogenization.

Guarding the Goods. New Insights into the Central Alarm System of Plants

“…In other proteins, LRRs are known to participate in protein to protein interactions, including binding of peptide ligands by receptors (Kobe and Kajava, 2001). Careful sequence analysis of R gene families revealed that the putative ligand binding surface of LRR domains in many families are undergoing diversifying selection (Parniske et al, 1997;Meyers et al, 1998), meaning that mutations that give rise to amino acid substitutions outnumber silent mutations. This observation is consistent with idea that the LRR domains of R proteins might directly bind pathogen-derived proteins.…”

Evolution of plant resistance at the molecular level: ecological context of species interactions

“…Analyses of diversity at different Rgenes have identified several molecular mechanisms responsible for the generation of diversity at these loci. Adaptive evolution resulting from mutations on the solvent-exposed residues of leucine-rich repeats (LRR) has been shown, presumably enabling detection of variable pathogen-related ligands (Parniske et al, 1997;Meyers et al, 1998;Noel et al, 1999;Dixon et al, 2000;Sun et al, 2001). In addition, recombination plays an important role in generating new LRR configurations (McDowell et al, 1998;Luck et al, 2000) and new paralogues at complex loci (Parniske et al, 1997;Meyers et al, 1998;Sun et al, 2001).…”

“…In addition, recombination plays an important role in generating new LRR configurations (McDowell et al, 1998;Luck et al, 2000) and new paralogues at complex loci (Parniske et al, 1997;Meyers et al, 1998;Sun et al, 2001). However, mutation and recombination seem to differentially affect R-gene families, which vary in their density and positioning along the chromosome (Parniske et al, 1997;Meyers et al, 1998), in their copy numbers Noel et al, 1999), in the proportion of nonfunctional genes (Parniske et al, 1997;Noel et al, 1999;Sun et al, 2001), in divergence levels among paralogues (Wei et al, 1999;Sun et al, 2001), and in relative rates of recombination (Wei et al, 1999;Sun et al, 2001). The cause of these differences among loci is not yet understood.…”

Marcadores moleculares derivados de sequências expressas do genoma café potencialmente envolvidas na resistência à ferrugem

“…De acordo com Parniske et al (1997), o domínio LRR pode facilitar a interação da proteína R com o seu fator Avr (elicitor) relacionado e pode fornecer diferentes especificidades de reconhecimento para fatores Avr alterados. De fato, em vários sistemas planta-patógeno, a variação da sequência na região LRR tem mostrado ser responsável por diferentes especificidades de reconhecimento ou de resistência Thomas et al, 1997;Botella et al, 1998;Wang et al, 1998;Ellis et al, 1999).…”