| Summary: | <p>Abstract</p> <p>Background</p> <p>Smoke released from burning vegetation functions as an important environmental signal promoting the germination of many plant species following a fire. It not only promotes the germination of species from fire-prone habitats, but several species from non-fire-prone areas also respond, including some crops. The germination stimulatory activity can largely be attributed to the presence of a highly active butenolide compound, 3-methyl-2<it>H</it>-furo[2,3-<it>c</it>]pyran-2-one (referred to as karrikin 1 or KAR<sub>1</sub>), that has previously been isolated from plant-derived smoke. Several hypotheses have arisen regarding the molecular background of smoke and KAR<sub>1 </sub>action.</p> <p>Results</p> <p>In this paper we demonstrate that although smoke-water and KAR<sub>1 </sub>treatment of maize kernels result in a similar physiological response, the gene expression and the protein ubiquitination patterns are quite different. Treatment with smoke-water enhanced the ubiquitination of proteins and activated protein-degradation-related genes. This effect was completely absent from KAR<sub>1</sub>-treated kernels, in which a specific aquaporin gene was distinctly upregulated.</p> <p>Conclusions</p> <p>Our findings indicate that the array of bioactive compounds present in smoke-water form an environmental signal that may act together in germination stimulation. It is highly possible that the smoke/KAR<sub>1 </sub>'signal' is perceived by a receptor that is shared with the signal transduction system implied in perceiving environmental cues (especially stresses and light), or some kind of specialized receptor exists in fire-prone plant species which diverged from a more general one present in a common ancestor, and also found in non fire-prone plants allowing for a somewhat weaker but still significant response. Besides their obvious use in agricultural practices, smoke and KAR<sub>1 </sub>can be used in studies to gain further insight into the transcriptional changes during germination.</p>
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