OVATE Family Protein 8 Positively Mediates Brassinosteroid Signaling through Interacting with the GSK3-like Kinase in Rice

Abstract

OVATE gene was first identified as a key regulator of fruit shape in tomato. OVATE family proteins (OFPs) are characterized as plant-specific transcription factors and conserved in Arabidopsis, tomato, and rice. Roles of OFPs involved in plant development and growth are largely unknown. Brassinosteroids (BRs) are a class of steroid hormones involved in diverse biological functions. OsGKS2 plays a critical role in BR signaling by phosphorylating downstream components such as OsBZR1 and DLT. Here we report in rice that OsOFP8 plays a positive role in BR signaling pathway. BL treatment induced the expression of OsOFP8 and led to enhanced accumulation of OsOFP8 protein. The gain-of-function mutant Osofp8 and OsOFP8 overexpression lines showed enhanced lamina joint inclination, whereas OsOFP8 RNAi transgenic lines showed more upright leaf phenotype, which suggest that OsOFP8 is involved in BR responses. Further analyses indicated that OsGSK2 interacts with and phosphorylates OsOFP8. BRZ treatment resulted in the cytoplasmic distribution of OsOFP8, and bikinin treatment reduced the cytoplasmic accumulation of OsOFP8. Phosphorylation of OsOFP8 by OsGSK2 is needed for its nuclear export. The phospphorylated OsOFP8 shuttles to the cytoplasm and is targeted for proteasomal degradation. These results indicate that OsOFP8 is a substrate of OsGSK2 and the function of OsOFP8 in plant growth and development is at least partly through the BR signaling pathway.

Exploring the Brassinosteroid Signaling in Monocots Reveals Novel Components of the Pathway and Implications for Plant Breeding

“…The OsGSK1 protein may control the abiotic stress tolerance through suppression of stress responsive genes [42]. However, in the BR signaling pathway the major role of the OsGSK2 kinase is phosphorylation and inhibition of activity of the following transcription factors (described below): OsBZR1, OsLIC, OsDLT, OsRLA1/SMOS1, OsOFP1, and OsOFP8 ( Figure 1) which are crucial for the regulation of the BR-dependent gene expression [24,37,38,48,49,82,83]. In rice (and Arabidopsis) the GSK proteins regulate in the phosphorylation-dependent manner various substrate proteins which represent different signaling and developmental processes.…”

OsOFP19 modulates plant architecture by integrating the cell division pattern and brassinosteroid signaling

“…It has also been reported that AtOFP1 and AtOFP4 interact with KNAT7 to enhance KNAT7‐mediated transcriptional repression of target genes, and the interaction is of particular importance in the determination of secondary cell wall formation (Li et al ., ). In addition to interaction with TALE proteins, OsOFP8 (LOC_Os01 g64430) has been shown to interact with OsGSK2, a key negative player in the brassinosteroid (BR) response in rice, and acts as a substrate for OsGSK2, suggesting that OsOFP8 is involved in BR signaling (Yang et al ., ).…”

OsmiR396d Affects Gibberellin and Brassinosteroid Signaling to Regulate Plant Architecture in Rice

“…Then, the signal is passed along to a key negative regulator, BRASSINOSTEROID-INSENSITIVE 2 (BIN2), which is dephosphorylated by BRI1 SUPPRESSOR 1 (Li et al, 2001;Mora-Garciá et al, 2004;Kim et al, 2011). In rice, the dephosphorylation of GSK3/SHAGGY-like Kinase (OsGSK2, a rice homolog of Arabidopsis BIN2) releases its suppression on BRASSINAZOLE-RESISTANT1 (OsBZR1), LEAF AND TILLER ANGLE INCREASED CONTROLLER (OsLIC), DWARF AND LOW-TILLERING (OsDLT), OVATE Family Protein 8, and REDUCED LEAF ANGLE1 to activate BR response and increase leaf angle (Bai et al, 2007;Wang, L et al, 2008;Tong et al, , 2012Zhang et al, 2012;Yang et al, 2016, Qiao et al, 2017. The kinase activity of OsGSK2 can also be directly inhibited by membrane protein GW5 (quantitative trait locus for grain width and weight on chromosome 5), which is a calmodulin-binding protein (Liu et al, 2017).…”