Nuclear body formation by Arabidopsis CPL1-RCF3 complex requires single-stranded RNA-binding domains

Abstract Arabidopsis thaliana CARBOXYL-TERMINAL DOMAIN (CTD) PHOSPHATASE-LIKE 1 (CPL1) and REGULATOR OF CBF GENE EXPRESSION 3 (RCF3) form a complex that function in RNA quality control under various abiotic and biotic stresses. Amino acid sequences show double-stranded RNA-binding motif 1(DRM1) and multiple K-homology (KH) domains in CPL1 and RCF3, respectively. Here we showed that both CPL1 and RCF3 specifically binds to single-stranded poly(C) RNA at DRM1 and multiple KH domains. We also showed that in planta, more than 3 KH domains are sufficient for RCF3 to form a complex with CPL1 in nuclear bodies. However, larger RCF3 fragments were necessary to form speckle structures, suggesting that polyvalent molecular interactions around RCF3 are essential for forming the nuclear structures necessary to process various precursor transcripts.