SlCPK27 cross-links SlHY5 and SlPIF4 in brassinosteroid-dependent photo-and thermo-morphogenesis in tomato
Changan Zhu, Zhangjian Hu, Chaoyi Hu, Hongxue Ma , Jie Zhou, Xiaojian Xia , Kai Shi, Christine H. Foyer, Jingquan Yu, and Yanhong Zhoua
ABSTRACT
ELONGATED HYPOCOTOYL5 (HY5) and PHYTOCHROME INTERACTING FACTORs (PIFs) are two types of important light-related regulators of plant growth, however, their interplay remains elusive. Here, we report that the activated tomato (Solanum lycopersicum) HY5 (SlHY5) triggers the transcription of a Calcium-dependent Protein Kinase SlCPK27. SlCPK27 interacts with and phosphorylates SlPIF4 at Ser-252 and Ser-308 phosphosites to promote its degradation. SlPIF4 promotes hypocotyl elongation mainly by activating the transcription of SlDWF, a key gene in brassinosteroid (BR) biosynthesis. Such a SlHY5-SlCPK27-SlPIF4-BR cascade not only plays a crucial role in photomorphogenesis but also regulates thermomorphogenesis. Our results uncover a previously unidentified mechanism that integrates Ca2+ signaling with the light signaling pathways to regulate plant growth by modulating BR biosynthesis in response to changes in ambient light and temperature.
GST pull-down assay of the interaction between SlCPK27 and SlPIF4 in vitro. GST or GST-SlPIF4 fusion proteins coupled with glutathione beads were used to pull down His-SlCPK27.
Co-IP assays showing the interaction of SlCPK27 with SlPIF4 in N. benthamiana leaves. CaCl2 was supplied at 15 mM. The relative levels of SlCPK27-Flag, normalized to GFP or SlPIF4-GFP, were shown above the SlCPK27-Flag immunoblots.
