Abstract:Ribonucleic acid interference (RNAi) is a biological process in which small RNAs regulate gene silencing at the transcriptional or post-transcriptional level. The argonaute (AGO) and dicer-like (DCL) proteins are two of the key components in the RNAi machinery of eukaryotes. In order to understand the function of AGO and DCL in sunflower (Helianthus annuus), the sequence of AGO and DCL in Arabidopsis thaliana were used for homology alignment in the sunflower database. The bioinformatics of AGO and DCL family members in sunflower were analysed. The results showed that there were 15 HaAGOs and 5 HaDCLs members obtained, which were unevenly distributed on chromosomes. The HaAGOs members could be cluster into 3 clades, containing conserved domains of N domain, DUF1785, PAZ and PIWI, whereas those of HaDCLs could be cluster into 4 clades, containing conserved domains of PAZ and RIBOc. The expressions of HaDCL3a and HaDCL3b in the steam and peduncle were stronger than those in other tissues. The subcellular localization showed that HaAGO was mostly localized in the nucleus. Therefore, it was suggested that a typical RNAi mechanism might exist in sunflower, and involve in coordinating growth and development in sunflower.