Genetic Background-Dependent Expression of Lr34, Lr67 and the Lr46-Associated Candidate Gene Lr46-Glu2 in Wheat (Triticum aestivum L.) Highlights Contrasting Transcriptional Responses Following Puccinia triticina Infection

Adult plant resistance (APR) is widely used in wheat breeding, but its behaviour across genetic backgrounds remains poorly understood. In this study, we analysed the expression of three APR loci (Lr34, Lr46, Lr67) following their introgression into elite winter wheat cultivars. BC2F1 populations derived from crosses between donor lines and commercial cultivars were evaluated under controlled infection with Puccinia triticina (Pt). Gene expression was assessed using RT-qPCR, and miRNA abundance was quantified by ddPCR at five time points (0–48 hours post-inoculation, hpi). Expression patterns differed markedly between genetic backgrounds, affecting both the magnitude and timing of gene activity. Lr34 and Lr67 showed the highest expression prior to inoculation, with no consistent or sustained induction following infection. In contrast, the candidate gene Lr46-Glu2 displayed a clear tendency towards early induction, with peak expression typically observed at 6–12 hours post-inoculation, although the amplitude of this response varied among genotypes. Levels of miRNA varied across genotypes and time points and did not consistently reflect mRNA expression. The results suggest that the expression of APR-associated loci is influenced by genetic background. Lr34 and Lr67 showed predominantly baseline-associated expression, whereas the Lr46-associated candidate gene Lr46-Glu2 displayed a more infection-responsive transcriptional profile following inoculation. These patterns are consistent with different transcriptional behaviours of the analysed genes but do not establish their functional contribution to resistance. Further phenotypic and functional validation will be required to determine the biological significance of these expression patterns.