Die Bedeutung von Karrikin in der Regulation der Photo- und Thermomorphogenese
Pflanzenphysiologie
Zusammenfassung der Projektergebnisse
Karrikins (KARs) emerging from burned plant material have been shown to promote seedling responses related to light signalling. In particular, KAR treatment of Arabidopsis seedlings inhibits hypocotyl elongation. However, the molecular connections between light and KAR signalling remains poorly understood. The initial signalling events after KAR perception are relatively well defined where KAI2 act as the KAR receptor that interacts with MAX2 after its activation. The KAI2-MAX2 complex then targets two negative regulators, SMAX1 and SMXL2, for degradation. However, how transcriptional regulation occurs downstream of SMAX1 and SMXL2 remains unknown. In this project, we analysed the role the light signalling component BBX20, which is well known to be strongly transcriptionally up-regulated in response to KAR treatment. Consistent with the transcriptional regulation, bbx20 mutants displayed a reduced sensitivity to KAR treatment. We found that mutants of the close homologue bbx21 also showed a reduced KAR sensitivity, while the hypocotyl elongation of the bbx20bbx21 double mutant was completely KAR insensitive. Concurrently, we have shown that the bZIP transcription factor HY5, which acts as a major positive regulator of refphotomorphogenesis, requires BBX20, BBX21 and BBX22 for its ability to regulate transcription. As it previously had been reported that mutants of hy5 also are KAR insensitive, we speculated that at least some KAR responses are dependent on a HY5-BBX transcriptional module. By analysing a set of higher order mutants, we could show that at least for the KAR induced anthocyanin accumulation, HY5 acts together with BBX20 and BBX21 to regulate transcription of anthocyanin biosynthetic genes. In summary, by utilizing an extensive list of higher order mutants, our results support a model where BBX20 and BBX21 are acting together with HY5 to regulate anthocyanin accumulation and hypocotyl elongation downstream of SMAX1 and SMXL2. However, transcriptomic data also suggests that the HY5- BBX transcriptional module is only responsible for a subset of the transcriptional regulation downstream of SMAX1 and SMXL2. Overall, the work conducted during this project represents significant progress in our understanding of the crosstalk between light and KAR signalling and reveals a part of the events taking place downstream of SMAX1 and SMXL2. In addition, this work extends our knowledge about processes regulated by the HY5-BBX transcriptional module which further extends our understanding of the master regulator HY5.
Projektbezogene Publikationen (Auswahl)
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Karrikins control seedling photomorphogenesis and anthocyanin biosynthesis through a HY5‐BBX transcriptional module. The Plant Journal, 107(5), 1346-1362.
Bursch, Katharina; Niemann, Ella T.; Nelson, David C. & Johansson, Henrik
