Transcriptomic Analysis of Lr34 Action in Transgenic Barley

The wheat Lr34 (Yr18/Pm38/Sr57) gene has been used effectively in agriculture for over 100 years. It encodes an ABCG type, ATP-binding cassette transporter, which provides durable and adult plant resistance against multiple biotrophic pathogens.  We have successfully over-expressed Lr34 in barley. The transgene expression is associated with a premature leaf tip necrosis and provides resistance against barley leaf rust and powdery mildew in transgenic plants. We used the Affymetrix Barley Genome array to study the transcriptome of transgenic barley expressing Lr34. The transcriptomic analysis in the mature leaf of transgenic barley revealed major changes in the metabolism as compared to wild type. Genes related to plant response to pathogen attack and secondary metabolisms are highly up-regulated even in the absence of pathogen and any other biotic or abiotic stress. Additionally, genes related to protein break down and senescence are also up-regulated. On the other hand genes involved in normal plant growth and development such as protein and cell wall biosynthesis, photosynthesis and oxidative respiration are down-regulated.

To identify early transcriptional changes in the transgenic barley plants, micro-array analysis was also done in very young, green leaves from two-weeks-old wild type and transgenic barley plants, before the onset of leaf tip necrosis. Here also, genes related to pathogen/disease response are up-regulated along with the genes involved in secondary metabolism, suggesting that the action of wheat Lr34 starts very early in the transgenic barley plants.