The role of karrikin in regulating photo- and thermomorphogenesis

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Smoke derived karrikins have recently been shown to induce germination and inhibit hypocotyl elongation in Arabidopsis. Although relatively little is known about how karrikin regulates these responses at the molecular level, it is clear that the signalling pathway is closely connected to light signalling. Besides the fact that seedlings of the karrikin signalling mutants kai2 and smax1smxl2 show altered light responsiveness, also the central regulator of light signalling, HY5, is required for karrikin dependent inhibition of hypocotyl elongation. Also plant’s responses to an elevation in the ambient temperature (thermomorphogenesis) show a close connection to light signalling. Elevated temperatures result in an elongated hypocotyl, hyponastic leaf growth and petiole elongation, responses all ameliorated in the pif4 mutant that was first described for its role in the light signalling pathways. Furthermore, HY5 has also been shown to play important roles in thermomorphogenesis, antagonising the effects of PIF4. Here, we aim to delineate the connections between the newly described karrikin signalling network with light signalling pathways focusing on the role of Arabidopsis B-box proteins and HY5. Furthermore, we will explore how these interactions ultimately might regulate the plants responses to elevated temperatures.