Genome-Wide Identification of the Argonaute Protein Family and Its Expression Analysis under PEG6000, ABA and Heat Treatments in Populus alba x P. glandulosa

The argonaute (AGO) protein, as an important member of the small RNA (sRNA) regulatory pathway gene-silencing complex (RNA-induced silencing complex, RISC), is a key protein that mediates gene silencing and plays a key role in the recruitment of sRNAs. In this study, bioinformatics was used to identify the AGO gene family in poplar and study its expression in various tissues and in response to abiotic stress treatments. A total of 15 PtAGO genes were identified in poplar, which were unevenly distributed in 9 chromosomes. Most proteins were predicted to be located in the nucleus and chloroplast. The PtAGOs had similar motif structures and conserved motifs, except for PtAGO3. All the PtAGO genes could be clustered into 3 groups, and Group II, including PtAGO2/3/7, had the smallest number of exons, while the others had more than 20 exons. Cis-regulatory elements involved in light response, growth and development, abiotic stress and hormone-induced responses were found in the promoters of PtAGO members. Further expression analysis found that the PtAGO genes had tissue-specific expression patterns. For example, PtAGO7 and PtAGO10b were mainly expressed in the xylem and might be involved in secondary xylem development. Furthermore, abiotic stress tests, including heat, ABA and PEG treatments, showed that most PtAGO genes could respond quickly to ABA treatment, and multiple PtAGO genes were constantly regulated under heat-shock stress. These results provide a basis for the elucidation mechanism of PtAGO genes and further molecular breeding in poplar.