The wheat gene Lr34 confers durable resistance against multiple fungal pathogens, including the three wheat rusts and powdery mildew. Lr34 encodes an ATP-binding cassette (ABC) transporter. Only one resistance-conferring Lr34 allele named Lr34res has been identified so far. Most susceptible wheat cultivars carry the Lr34sus allele that differs from Lr34res by two critical nucleotide polymorphisms. Lr34res is functionally transferrable as a transgene into all major cereals, including rice, barley, maize, and sorghum. In rice for example, Lr34res confers partial resistance against the rice blast pathogen.

Lr34res results in a constitutive induction of transcripts reminiscent of an abscisic acid (ABA)-regulated response in transgenic rice, even in the absence of pathogens. A similar constitutive defense response had previously been observed in Lr34res expressing wheat and barley plants, indicating a common molecular mechanism across different cereals. Lr34expressing rice was altered in biological processes that are controlled by ABA, including dehydration tolerance, transpiration and seedling growth. In planta seedling and in vitro yeast accumulation assays revealed that both LR34res and LR34sus act as ABA transporters. However, only the LR34res protein was detected in planta while the LR34sus version was not, suggesting a post-transcriptional regulatory mechanism.

Our results identify ABA as a substrate of the LR34 ABC transporter. We conclude that LR34res-mediated ABA redistribution has a major effect on the transcriptional response and physiology of Lr34res-expressing plants and that ABA is a candidate molecule that contributes to Lr34res-mediated disease resistance.