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The phytohormone abscisic acid (ABA) regulates plant growth and development and stress resistance through the ABA receptor PYLs. To date, no interaction between CPK and PYL has been reported, even in Arabidopsis and rice. In this study, we found that MdCPK4 from Malus domestica (Md for short) interacts with two MdPYLs, MdPYL2/12, in the nucleus and the cytoplasm in vivo and phosphorylates the latter in vitro as well. Compared with the wild type (WT), the MdCPK4- or MdPYL2/12 -overexpressing Arabidopsis lines showed more sensitivity to ABA, and therefore stronger drought resistance. The ABA-related genes (ABF1 , ABF2 , ABF4 , RD29A and SnRK2.2) were significantly upregulated in the overexpressing (OE) lines after ABA treatment. These results indicate that MdCPK4 and MdPYL2/12 act as positive regulators in response to ABA-mediated drought resistance in apple. Our results reveal the relationship between MdCPK4 and MdPYL2/12 in ABA signaling, which will further enrich the molecular mechanism of drought resistance in plants. [ABSTRACT FROM AUTHOR]

Uridine diphosphate‐glucosyltransferases (UGTs) maintain abscisic acid (ABA) homeostasis in Arabidopsis thaliana by converting ABA to abscisic acid‐glucose ester (ABA‐GE). UGT71C5 plays an important role in the generation of ABA‐GE. Abscisic acid receptors are crucial upstream components of the ABA signaling pathway, but how UGTs and ABA receptors function together to modulate ABA levels is unknown. Here, we demonstrated that the ABA receptors RCAR12/13 and UGT71C5 maintain ABA homeostasis in Arabidopsis following rehydration under drought stress. Biochemical analyses show that UGT71C5 directly interacted with RCAR8/12/13 in yeast cells, and the interactions between UGT71C5 and RCAR12/13 were enhanced by ABA treatment. Enzyme activity analysis showed that ABA‐GE contents were significantly elevated in the presence of RCAR12 or RCAR13, suggesting that these ABA receptors enhance the activity of UGT71C5. Determination of the content of ABA and ABA‐GE in Arabidopsis following rehydration under drought stress revealed that ABA‐GE contents were significantly higher in Arabidopsis plants overexpressing RCAR12 and RCAR13 than in non‐transformed plants and plants overexpressing RCAR11 following rehydration under drought stress. These observations suggest that RCAR12 and RCAR13 enhance the activity of UGT71C5 to glycosylate excess ABA into ABA‐GE following rehydration under drought stress, representing a rapid mechanism for regulating plant growth and development. [ABSTRACT FROM AUTHOR]

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/REGULATORY 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. [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]