Ubiquitin‐specific protease 24 negatively regulates abscisic acid signalling in Arabidopsis thaliana

Abstract

Abscisic acid (ABA) is an important plant hormone integrating environmental stress and plant growth. Protein ubiquitination and deubiquitination are reversible processes catalysed by E3 ubiquitin ligase and deubiquitinating enzyme, respectively. Lots of E3 ubiquitin ligase and transcriptional factors modified by ubiquitination were reported to modulate ABA signalling. However, no deubiquitinating enzyme has been identified that functions in ABA signalling until now. Here, we isolated an ABA overly sensitive mutant, ubp24, in which the gene encoding ubiquitin-specific protease 24 (UBP24, At4g30890) was disrupted by a T-DNA insertion. The ubp24 mutant was hypersensitive to ABA and salt stress in both post-germinative growth and seedling growth. However, stomata closure in the ubp24 mutant was less sensitive to ABA, and the ubp24 mutant showed drought sensitivity. UBP24 possessed deubiquitinating enzyme activity, and the activity was essential for UBP24 function. Additionally, UBP24 formed homodimer in vivo. UBP24 was genetically upstream of ABI2, and the phosphatase activity of protein phosphatase 2C was decreased in the ubp24 mutant compared with the wild type in the presence of ABA. These results uncover an important regulatory role for the ubiquitin-specific protease in response to ABA and salt stress in plant.

Quantitative Phosphoproteomic Analysis Reveals Shared and Specific Targets of Arabidopsis Mitogen-Activated Protein Kinases (MAPKs) MPK3, MPK4, and MPK6

“…Another interesting factor of our phosphoproteome analysis was the identification of the deubiquitinase UBP24 as MPK3-specific target. UBP24 is an upstream regulator of ABI2 for ABA and salt stress (69) and phosphorylation of UBP24 by MPK3 might influence protein turnover of certain MAPK stress pathway components.…”

Ubiquitin Ligases RGLG1 and RGLG5 Regulate Abscisic Acid Signaling by Controlling the Turnover of Phosphatase PP2CA

“…Whereas inhibition of PP2C activity is a reversible mechanism that regulates ABA signaling according to fluctuating ABA levels in response to environmental cues, degradation of PP2Cs is an irreversible decision that might lead to sustained ABA signaling when a stress situation persists. However, the degradation of PP2Cs or ABA receptors relies on their ubiquitination, which is a reversible process by the action of deubiquitinating enzymes that can further regulate the stability from core ABA signaling components (Zhao et al, 2016). In nature, both transient and sustained forms of stress occur; therefore, a double mechanism to abolish PP2C function seems to be better prepared to cope with different environmental stresses.…”

The Deubiquitinating Enzymes UBP12 and UBP13 Positively Regulate MYC2 Levels in Jasmonate Responses

“…Much more work has been done with the characterization and function of plant ubiquitin E3 ligases compared with DUBs. Since their description by Yan et al (2000), around 10 Arabidopsis UBPs (ubiquitin proteases) have been characterized mainly based on the phenotypes of loss-of-function mutants: UBP1 and UBP2 are needed for resistance to canavanine, an amino acid analog (Yan et al, 2000); UBP14 is implicated in embryogenesis (Doelling et al, 2001); UBP3 and UBP4 play a role in pollen development (Doelling et al, 2007); UBP26 deubiquitinates histone H2B to regulate DNA methylation and heterochromatic silencing (Sridhar et al, 2007); and UBP24 has been recently shown to be a negative regulator of ABA signaling (Zhao et al, 2016). Other than for UBP26, none of the substrates of the USPs have been identified, thus precluding more in-depth mechanistic understanding.…”