Transcriptional profiling of summer wheat, grown under different realistic UV-B irradiation regimes.

There is limited information on the impact of present-day ultraviolet-B (UV-B) radiation on a reprogramming of gene expression in crops. Summer wheat was cultivated in controlled environmental facilities under simulated realistic climatic conditions. We investigated the effect of different regimes of UV-B radiation on summer wheat (Triticum aestivum L.) cultivars Nandu, Star and Turbo. Until recently, these were most important in Bavaria. Different cultivars of crops often show great differences in their sensitivity towards UV-B radiation. To identify genes that might be involved in UV-B defence mechanisms, we first analyzed selected genes known to be involved in plant defence mechanisms. RNA gel blot analysis of RNA isolated from the flag leaf of 84-day-old plants showed differences in transcript levels among the cultivars. Flag leaves are known to be important for grain development, which was completed at 84 days post-anthesis. Catalase 2 (Cat2) transcripts were elevated by increased UV irradiation in all cultivars with highest levels in cv. Nandu. Pathogenesis-related protein 1 (PR1) transcripts were elevated only in cv. Star. A minor influence on transcripts for phenylalanine ammonia-lyase (PAL) was observed in all three cultivars. This indicates different levels of acclimation to UV-B radiation in the wheat cultivars studied. To analyze these responses in more detail, UV-B-exposed flag leaves of 84-day-old wheat (cv. Nandu) were pooled to isolate cDNAs of induced genes by suppression-subtractive hybridization (SSH). Among the initially isolated cDNA clones, 13 were verified by RNA gel blot analysis showing an up-regulation at elevated levels of UV-B radiation. Functional classification revealed genes encoding proteins associated with protein assembly, chaperonins, programmed cell death and signal transduction. We also studied growth, flowering time, ear development and yield as more typical agricultural parameters. Plant growth of young plants was reduced at increased UV-B radiation. Flowering and ear development were delayed concomitantly, whereas total grain weight was not influenced at any of the UV-B irradiation regimes.