ABA inhibits myristoylation and induces shuttling of the RGLG1 E3 ligase to promote nuclear degradation of PP2CA

• Published in: The Plant journal : for cell and molecular biology 2019-06, Vol.98 (5), p.813-825
• Main Authors: Belda‐Palazon, Borja, Julian, Jose, Coego, Alberto, Wu, Qian, Zhang, Xu, Batistic, Oliver, Alquraishi, Saleh A., Kudla, Joerg, An, Chengcai, Rodriguez, Pedro L.
• Format: Article
• Language: English
• Subjects: Abscisic acid; Abscisic Acid - pharmacology; abscisic acid signaling; Active Transport, Cell Nucleus - drug effects; Acyltransferases - metabolism; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis thaliana; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cycloheximide; Degradation; Down-Regulation - drug effects; E3 ligase; Localization; Myristic Acid - metabolism; Myristoylation; Nuclear interactions; Nuclear transport; Osmotic stress; Plant Growth Regulators - pharmacology; Plants, Genetically Modified; Protein Binding - drug effects; Protein Phosphatase 2C - metabolism; protein phosphatase type 2C; Proteins; Proteolysis - drug effects; Receptors; Regulators; Regulatory proteins; RGLG1; shuttling; Signaling; Stress; Translocation; Ubiquitin-protein ligase; Ubiquitin-Protein Ligases - metabolism; Ubiquitination; Ubiquitination - drug effects
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.14274

Summary Hormone‐ and stress‐induced shuttling of signaling or regulatory proteins is an important cellular mechanism to modulate hormone signaling and cope with abiotic stress. Hormone‐induced ubiquitination plays a crucial role to determine the half‐life of key negative regulators of hormone signaling. For ABA signaling, the degradation of clade‐A PP2Cs, such as PP2CA or ABI1, is a complementary mechanism to PYR/PYL/RCAR‐mediated inhibition of PP2C activity. ABA promotes the degradation of PP2CA through the RGLG1 E3 ligase, although it is not known how ABA enhances the interaction of RGLG1 with PP2CA given that they are predominantly found in the plasma membrane and the nucleus, respectively. We demonstrate that ABA modifies the subcellular localization of RGLG1 and promotes nuclear interaction with PP2CA. We found RGLG1 is myristoylated in vivo, which facilitates its attachment to the plasma membrane. ABA inhibits the myristoylation of RGLG1 through the downregulation of N‐myristoyltransferase 1 (NMT1) and promotes nuclear translocation of RGLG1 in a cycloheximide‐insensitive manner. Enhanced nuclear recruitment of the E3 ligase was also promoted by increasing PP2CA protein levels and the formation of RGLG1–receptor–phosphatase complexes. We show that RGLG1Gly2Ala mutated at the N‐terminal myristoylation site shows constitutive nuclear localization and causes an enhanced response to ABA and salt or osmotic stress. RGLG1/5 can interact with certain monomeric ABA receptors, which facilitates the formation of nuclear complexes such as RGLG1–PP2CA–PYL8. In summary, we provide evidence that an E3 ligase can dynamically relocalize in response to both ABA and increased levels of its target, which reveals a mechanism to explain how ABA enhances RGLG1–PP2CA interaction and hence PP2CA degradation. Significance Statement The degradation of negative regulators is crucial for hormone signaling. ABA promotes the degradation of PP2CA through the RGLG1/5 E3 ligases and enhances the interaction of RGLG1/5 with PP2CA through an unknown mechanism. We show that ABA modifies the plasma membrane localization of RGLG1 by inhibiting its myristoylation and promoting cycloheximide‐insensitive nuclear translocation, which allows interaction with nuclear PP2CA‐receptor complexes. We explain how a hormone can modulate the interaction of an E3 ligase with its target.