Searching for genes determining the APR phenotype in rye

Adult-plant resistance (APR) is a type of genetic resistance of cereals against a range of disease-causing pathogens including leaf rust (LR). In rye, APR to LR although known, is poorly understood, especially at the molecular level. Recently, numerous variants of genes encoding ATP-binding cassette (ABC) and sugar transporters, have been identified in the rye transcriptome. In these two pools of genes, we decided to find genes determining APR using both nucleotide and amino acid sequence similarity to the Lr34 and Lr67 genes carrying the APR to LR in wheat as the main selection criterion and as an additional criterion - expression profiles of chosen variants in seedlings infected with LR.

The phylogenetic analysis of chosen genes ScLr_ABC and ScLr_SUG encoding, respectively, ABC and sugar transporters revealed that a lack of polymorphisms responsible for APR in wheat. However, ScLr_SUG1, a putative ortholog of Lr67, and ScLr_ABC25, which shows high 3D structural similarity to Lr34, could potentially be involved in APR of rye. The analysis of the expression of selected ScLr_ABC and ScLr_SUG genes carried out on plants infected with fungal spores collected from locations where phenotypic assessments were performed. Most of the analyzed genes did not show any clear association between APR to LR. Only ScLr_ABC25 gene seems to determine APR-type immunity against LR.

This work is the first attempt to find genetic determinants of APR resistance to LR in common rye. Our studies show that the mechanism of this type of resistance is different in rye than in other cereals studied in this respect (mainly wheat and barley). However, our findings are a good starting point for further research, and, as in the case of the ScLr_ABC25 gene - they can be the basis for creating a molecular resistance breeding program focused on selecting forms characterized by APR to LR.