A novel nucleus-targeted protein is expressed in barley leaves during senescence and pathogen infection

The barley (Hordeum vulgare) cDNA HvS40 represents a gene with enhanced mRNA level during leaf senescence. Biolistic transformation of onion (Allium cepa) epidermal cell layers with a glucuronidase fusion protein construct provided evidence that the 15.4-kD protein encoded by HvS40 is localized to the nucleus. Expression of the gene is induced by jasmonate and salicylic acid; both are known to act as signaling compounds during senescence and defense toward pathogens. Transcript levels of HvS40 were observed to be particularly high in leaf sectors that undergo necrosis and chlorosis after infection with Pyrenophora teres. This pathogen-related expression is, in contrast, clearly reduced in transgenic barley plants expressing a stilbene synthase from grape (Vitis vinifera), whereas the mRNA level of a gene encoding the pathogen-related protein HvPR1 is unaffected. In situ hybridization with HvS40 antisense RNA revealed that during leaf senescence, the HvS40 transcript predominantly accumulates in the mesophyll. Taken together, the findings suggest a connection between the nuclear protein encoded by HvS40 and the degeneration of chloroplasts occurring during senescence and during infection of barley wild-type plants with P. teres.