The Arabidopsis F‐box E3 ligase RIFP1 plays a negative role in abscisic acid signalling by facilitating ABA receptor RCAR3 degradation

Abstract

The phytohormone abscisic acid (ABA) plays a vital role in plant growth and development. The function of ABA is mediated by a group of newly discovered ABA receptors, named PYRABACTIN RESISTANCE 1/PYR-LIKE/REGULA-TORY COMPONENTS OF ABA RECEPTORs (PYR1/ PYLs/RCARs). Here, we report that an Arabidopsis thaliana F-box protein RCAR3 INTERACTING F-BOX PROTEIN 1 (RIFP1) interacts with ABA receptor (RCAR3) and SCF E3 ligase complex subunits Arabidopsis SKP1-LIKE PROTEINs (ASKs) in vitro and in vivo. The rifp1 mutant plants displayed increased ABA-mediated inhibition of seed germination and water loss of detached leaves, while the overexpression of RIFP1 in Arabidopsis led to plants being insensitive to ABA. Meanwhile, the rifp1 mutant plants showed greater tolerance to water deficit. In addition, the RCAR3 protein level was more stable in the rifp1 mutant plants than in the wild-type plants, indicating that RIFP1 facilitates the proteasome degradation of RCAR3. Accordingly, the loss of RIFP1 increased the transcript levels of several ABA-responsive genes. Taken together, these data indicate that RIFP1 plays a negative role in the RCAR3-mediated ABA signalling pathway and likely functions as an adaptor subunit of the SCF ubiquitin ligase complex to regulate ABA receptor RCAR3 stability.

EAR1 Negatively Regulates ABA Signaling by Enhancing 2C Protein Phosphatase Activity

“…The expression of EAR1 and its protein levels were not altered by ABA treatment (Figure 7E), but ABA treatment led to the accumulation of EAR1 in the nucleus (Figure 7). Given that ABA treatment induces the expression of PP2Cs (Kong et al, 2015), that PYR1/PYLs in turn inhibit PP2C activity in the presence of ABA, and that PP2Cs and PYLs are dynamically regulated by the 26S proteasome (Bueso et al, 2014;Irigoyen et al, 2014;Li et al, 2016), the complexity of this ABA signaling pathway makes it difficult to determine exactly how EAR1 affects PP2C activity during ABA treatment in vivo. In the in vivo assays, we mainly detected changes in total PP2C activity in the presence or absence of EAR1.…”

Diverse and dynamic roles of F-box proteins in plant biology

“…This phenomenon results in phosphorylation and activation of SnRK2 kinases and further phosphorylation of transcription factors that regulate the transcription of ABA-responsive genes (Kline et al 2010;Ng 2016;Yoshida et al 2019). The receptor of ABA, RCAR3/PYL8, had been characterized as the target for FBP, RCAR3 INTERACT-ING F-BOX PROTEIN 1 (RIFP1), which was identified as a negative regulator in ABA signalling (Li et al 2016c). Another FBP that also acts as a negative regulator of ABA signalling, known as AtPP2-B11, was reported by Cheng et al (2017) to regulate SnRK2, specifically SnRK2.3.…”

Novel Pathway Regulates ABA Perception: How ESCRTs Regulate Stability of ABA Receptors

“…Recent studies have described different types of E3 ligases that regulate ABA receptors stability in nucleus and plasma membrane. In nucleus, both the substrate adapter of Cullin4-RING E3 ubiquitin Ligases (CRL4s), Deetiolated1 (DET1)-and Damaged DNA Binding protein1 (DDB1)-Associated1 (DDA1), and the F-box protein of the Skp1-Cullin1-F-box (SCF) complex, the RCAR3 Interacting F-box Protein 1 (RIFP1), can recognize the ABA receptor PYL8 (also named RCAR3), and then accelerate PYL8 degradation via the 26S proteasome [10,11]. Different from the multiunit E3 ubiquitin ligases CRL4s and SCF complex in nucleus, the single unit RING-type E3 ligase Ring finger of Seed Longevity1 (RSL1) mediates ubiquitination of the ABA receptors PYR1/PYL4 on the plasma membrane [12].…”