The Phenotypes conferred by Wheat Multiple Pathogen Resistance Locus, Sr2, include Cell Death in Response to Biotic and Abiotic Stresses

The wheat Sr2 locus confers partial resistance to four biotrophic pathogens: wheat stem rust (Puccinia graminis f. sp. tritici), leaf rust (Puccinia triticina), stripe rust (Puccinia striiformis f. sp. tritici) and powdery mildew (Blumeria graminins f. sp. tritici). In addition, it is linked with a brown coloration of ears and stems, termed pseudo black chaff (PBC). PBC, initially believed to be elicited by stem rust infection, was subsequently recognized to occur in the absence of pathogen infection. In the current study, it is demonstrated that the resistance response to stem rust was associated with death of photosynthetic cells around rust infection sites in inoculated leaf sheath. Similarly, Sr2-dependent resistance to powdery mildew was associated with death of leaf mesophyll cells around mildew infection sites. We demonstrate that the PBC occurring in the absence of pathogen inoculation also corresponds with death and collapse of photosynthetic cells in the affected parts of stems and ears. In addition, Sr2-dependent necrosis was inducible in leaves by application of petroleum jelly, or by heat treatments. Thus Sr2 was found to be associated with cell death, which could be triggered by either biotic or abiotic stresses. Our results suggest a role for the Sr2 locus in controlling cell death in response to stress.