DWA3, an Arabidopsis DWD protein, acts as a negative regulator in ABA signal transduction

DWD (DDB1 binding WD40) proteins have been reported as substrate receptors for cullin-RING ubiquitin ligase 4 complexes (CRL4), a family of E3 ligases. Abscisic acid (ABA) plays an important role in plant responses to abiotic stresses, such as drought and salinity. Upon screening T-DNA mutants of DWD genes for ABA responses we obtained several candidates that exhibited ABA-hypersensitivity, and one was named DWA3 (DWD hypersensitive to ABA 3). DWA3 interacted with DDB1, which has been proposed to be an adaptor protein of the CUL4 E3 ligase complex, in yeast two-hybrid assays. Also, association between DWA3 and the DDB1-CUL4 machinery was detected in vivo by co-immunoprecipitation assays, indicating that DWA3 may function as a substrate receptor for CRL4. ABA-inducible transcription factors (ABI5 and AtMYC2) and their downstream genes were hyper-induced by ABA in dwa3. Taken together, we suggest that DWA3 is a negative regulator of ABA responses and may be involved in protein degradation mediated by CRL4.