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Highlight Transgenic barley plants with an RNAi-mediated knockdown of the gene encoding the plastid–nucleus-located DNA/RNA-binding protein WHIRLY1 display a stay-green phenotype at high light intensity, but not at low light., WHIRLY1 in barley was isolated as a potential regulator of the senescence-associated gene HvS40. In order to investigate whether the plastid–nucleus-located DNA/RNA-binding protein WHIRLY1 plays a role in regulation of leaf senescence, primary foliage leaves from transgenic barley plants with an RNAi-mediated knockdown of the WHIRLY1 gene were characterized by typical senescence parameters, namely pigment contents, function and composition of the photosynthetic apparatus, as well as expression of selected genes known to be either down- or up-regulated during leaf senescence. When the plants were grown at low light intensity, senescence progression was similar between wild-type and RNAi-W1 plants. Likewise, dark-induced senescence of detached leaves was not affected by reduction of WHIRLY1. When plants were grown at high light intensity, however, senescence was induced prematurely in wild-type plants but was delayed in RNAi-W1 plants. This result suggests that WHIRLY1 plays a role in light sensing and/or stress communication between chloroplasts and the nucleus.

HvS40 is a marker gene for leaf senescence in barley. It is expressed during dark-induced as well as age-dependent senescence and in response to biotic and abiotic stress factors. Its expression is also induced by hormones involved in the control of stress responses and senescence processes. Run-on-transcription assays with isolated nuclei showed that its expression during dark-induced senescence is regulated at the transcriptional level. Its promoter contains two elicitor response elements (ERE) consisting of two W-boxes. Binding of proteins to these motifs changed during senescence. A 24-kDa protein binding to ERE2 of nonsenescent leaves was identified as WHIRLY1.