CPL phosphatases as plant miRNA-processing regulators - mRNA reads

MicroRNAs (miRNAs) are processed from primary transcripts that contain partially self- complementary foldbacks. As in animals, the core microprocessor in plants is a Dicer protein, DICER- LIKE1 (DCL1). Processing accuracy is greatly enhanced through the RNA binding protein HYPONASTIC LEAVES 1 (HYL1) and the zinc finger protein SERRATE (SE). Here, we present results of a luciferase- based genetic screen, which we combined with whole-genome sequencing for rapid identification of new miRNA biogenesis factors. Among the first six mutants analyzed were three alleles of C-TERMINAL DOMAIN PHOSPHATASE-LIKE 1 (CPL1)/FIERY2 (FRY2). In the miRNA processing complex, SE functions as a scaffold to mediate CPL1 interaction with HYL1, which needs to be dephosphorylated for optimal activity. In the absence of CPL1, HYL1 dephosphorylation and hence accurate processing of miRNAs are compromised. Our findings thus define a new regulatory step in plant miRNA biogenesis.