Small RNAs in Arabidopsis hyl1 and hyl1 suppressor mutants

DCL1 and HYL1 are the core components of miRNA biogenesis machinery. hyl1-null mutants accumulate low levels of miRNAs and cause pleiotropic morphological phenotypes. Here, we reported that we identified 5 new alleles of DCL1 which are able to suppress the hyl1 morphological phenotypes and restore the miRNA accumulation level in hyl1 plants. These new alleles are located in the helicase and RNaseIIIa domains of DCL1, highlighting the critical functions of these domains. Biochemical analyses of these suppressors indicated that they process pri-miRNA more efficiently, with both higher Kcat and lower Km values. In addition, we investigated the functions of the DCL1 helicase domain. Our results indicated that the helicase domain is able to modulate the DCL1 processing activities. Based on these results, we proposed that HYL1 might exert its function through interaction with the DCL1 helicase domain. Small RNA sequencing from hyl1 and select hyl1/dcl1 suppressor mutants confirms thats suppression of the hyl1 phenotype is due to an increase in the accumulation, but not the precision, of miRNAs in the suppressor mutants. Wild-type, hyl1-2, hyl1-2/dcl1-20, and hyl1-2/dcl1-21 plants were sampled from both rosette leaves and flowers.