The Arabidopsis Kelch Repeat F-box E3 Ligase ARKP1 Plays a Positive Role for the Regulation of Abscisic Acid Signaling

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.