Cloning and characterization of two Argonaute genes in wheat (Triticum aestivum L.)

Background: Argonaute proteins are key components of RNA interference (RNAi), playing important roles in RNA-directed gene silencing. Various classes of Argonaute genes have been identified from plants and might be involved in developmental regulation. However, little is known about these genes in wheat (Triticum aestivum). Results: In this study, two full-length cDNAs of Argonaute were cloned from wheat, designated as TaAGO1b and TaAGO4. The cDNA of TaAGO1b is 3273 bp long and encodes 868 amino acids, with a predicted molecular weight of similar to 97.78 kDa and pI of 9.29. The 3157-bp TaAGO4 encodes 916 amino acids, with a molecular mass of 102.10 kDa and pI of 9.12. Genomics analysis showed that TaAGO1b and TaAGO4 contain 20 and 18 introns, respectively. Protein structural analysis demonstrated that typical PAZ and PIWI domains were found in both TaAGO1b and TaAGO4. From the highly conserved PIWI domains, we detected conserved Asp-Asp-His (DDH) motifs that function as a catalytic triad and have critical roles during the process of sequence-specific cleavage in the RNAi machinery. Structural modelling indicated that both TaAGOs can fold to a specific alpha/beta structure. Moreover, the three aligned DDH residues are spatially close to each other at the "slicer" site of the PIWI domain. Expression analysis indicated that both genes are ubiquitously expressed in vegetative and reproductive organs, including the root, stem, leaf, anther, ovule, and seed. However, they are differentially expressed in germinating endosperm tissues. We were interested to learn that the two TaAGOs are also differentially expressed in developing wheat plants and that their expression patterns are variously affected by vernalization treatment. Further investigation revealed that they can be induced by cold accumulation during vernalization. Conclusions: Two putative wheat Argonaute genes, TaAGO1b and TaAGO4, were cloned. Phylogenetic analysis, prediction of conserved domains and catalytic motifs, and modelling of their protein structures suggested that they encode functional Argonaute proteins. Temporal and spatial expression analyses indicated that these genes are potentially involved in developmental regulation of wheat plants.