Search

Ubiquitination is one of the most common posttranslational modifications. A series of E3 ligases are implicated in plant abiotic stress signaling, regulating the degradation of multiple specific target proteins. Here, we showed that a novel gene ABA- RESPONSE KELCH PROTEIN 1 ( AtARKP1), which encodes an F-box subunit of Skp-cullin-F-box (SCF) ubiquitin ligase complex, was localized in the nucleus and could be induced by phytohormone abscisic acid (ABA) in Arabidopsis. ARKP1 interacted with ASK1 and ASK2, which tethered the rest of the complex to an F-box protein, suggesting that they might form an SCF ubiquitin ligase complex. Further analysis revealed that ARKP1 was exclusively expressed in the seed, rosette leaf, and root. arkp1 T-DNA insertion mutant plants were insensitive to ABA, displaying reduced ABA-mediated inhibition of seed germination, root elongation, and water loss rate of detached leaves. In contrast, transgenic plants showed enhanced sensitivity to ABA and tolerance to water deficit. Accordingly, the expressions of ABA and drought responsive marker genes were markedly upregulated in ARKP1 overexpressing plants than the wild-type and arkp1 mutant plants. Taken together, our findings suggest that AtARKP1 plays a positive role in ABA signaling network. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) plays a fundamental role in plant growth and development, as well as in the responses to abiotic stresses. Previous studies have revealed that many components in ABA and drought stress signaling pathways are ubiquitinated by E3 ligases. In this study, AtPPRT1, a putative C3HC4 zinc-finger ubiquitin E3 ligase, was explored for its role in abiotic stress response in Arabidopsis thaliana. The expression of AtPPRT1 was induced by ABA. In addition, the β-glucuronidase (GUS) gene driven by the AtPPRT1 promoter was more active in the root hair zone and root tips of primary and major lateral roots of young seedlings in the presence of ABA. The assays for seed germination, stomatal aperture, root length, and water deficit demonstrated that the AtPPRT1-overexpressing Arabidopsis was insensitive to ABA and sensitive to drought stress compared with wild-type (WT) plants. The analysis by quantitative real-time PCR (qRT-PCR) revealed that the expression of three stress-inducible genes (AtRAB18, AtERD10, and AtKIN1) were upregulated in the atpprt1 mutant and downregulated in AtPPRT1-overexpressing plants, while two ABA hydrolysis genes (AtCYP707A1 and AtCYP707A3) were downregulated in the atpprt1 mutant and upregulated in AtPPRT1-overexpressing plants in the presence of ABA. AtPPRT1 was localized in the mitochondria. Our findings indicate that AtPPRT1 plays a negative role in ABA and drought stress responses. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) is an important plant hormone that mediates abiotic stresses in plant growth and development. A number of E3 ligases have been reported to be involved in ABA signaling pathway. In this study, we identified a C3H2C3 RING-type E3 ligase, Arabidopsis thaliana Tόxicos en Levadura 61 (ATL61), which regulated drought stress in planta. Enzyme assay in vitro demonstrated that ATL61 had E3 ubiquitin ligase activity, while point mutation of ATL61H109A, H122A (mATL61) abolished its E3 ubiquitin ligase activity. ATL61 overexpression plants exhibited ABA hypersensitivity and were more tolerant to drought, while the atl61 mutant plants were insensitive to ABA. Moreover, mATL61 overexpression lines exhibited similar ABA-related phenotypes with wild type (WT) plants. The transcript abundances of ABA-mediated drought stress-related genes RD20 and RD22 were higher in ATL61 overexpression plants than those in WT, atl61, and mATL61 plants. Our results indicated that ATL61 acted as a positive regulator in the ABA-mediated drought stress response. • ATL61 is a C3H2C3 RING type E3 ligase with necessary H109 and H122 residues. • ATL61 is induced by ABA and other abiotic stresses and involved in ABA-mediated plants tolerance to drought. • E3 ligase activity of ATL61 was critical to the function of ATL61 in ABA signaling pathway. [ABSTRACT FROM AUTHOR]