Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 2.44

MUTATION HOTSPOTS IN GENES INVOLVED IN RESISTANCE IN NICOTIANA TABACUM

M.C. INTRIERI*^,**, A. SABATINI**, M. GORI**, R. MULEO*^,**, M. BUIATTI**

*) Università della Tuscia, Dipartimento di Produzione Vegetale, via San C. de Lellis, 01100 Viterbo

**) Università di Firenze, Dipartimento di Biologia animale e Genetica, via Romana 17-19, 50125 FI

Nicotina, gene resistance, polymorphism, SSR

Many biodiversity studies within species to date have focused on “neutral” molecular markers, such as RAPD, ISSR and microsatellites. The breeding structure of populations, population bottlenecks and the biogeographical history of a species are expected to affect all markers in similar ways. By contrast, variation in functional regions (expressed or regulatory sequences) might reflect the past influences of selection, which can be different for each gene. Traits of interest include disease resistance, stress tolerance, growth rate, morphology and life-history, which are often quantitative traits that are likely to be affected by many genes. New marker systems for functional genes are now being developed, and previous work from our laboratory, demonstrated the utility of such markers in phylogenetic studies and for the analysis of agronomical traits. Existing sequence information is being used to develop markers that tag variation within the gene or in a flanking region. In this work microsatellites located in functional regions have been developed and studied in Nicotiana tabacum.

Among all the sequences of N. tabacum present in GeneBank, those including complete genes have been analysed for the presence of simple repeats of two and three nucleotides of at least 5 units. From this analysis, SSRs are located preferentially in promoters, introns and UTR of the analysed genes. The classes of genes in which the SSRs are preferencially found are those involved in resistance, and in particular resistance against biotic stress, even if SSRs have been found in other classes of genes, e.g. in phyA third intron or genes involved in metabolic traits. Of 11 primers tested 8 were able to produce simple and reproducible bands, and among those 8 correspond to polymorphic loci.

Genes involved in stress response are the most variable, among the markers analised. These results could suggest the selective advantage of hypervariable sequences in genes involved in defense against pathogens. Further studies on the phenotipic expression of the genes analysed will be necessary for a definitive conclusion. The association between a marker and the phenotypic expression tagged by that marker will depend on the frequency of recombination and presence of recombinational hotspots, the breeding and population structure and the genealogical history of the genomic region. Probably, evolution favoured the presence of mutation hotspots in genes involved in resistance.