Infection with Jujube Witches’ Broom Phytoplasma Alters the Expression Pattern of the Argonaute Gene Family in Ziziphus jujuba

The cultivation of jujube (<i>Ziziphus jujuba</i>) in China is threatened by jujube witches' broom (JWB) disease, a devastating infectious disease associated with JWB phytoplasma ('<i>Candidatus</i> Phytoplasma ziziphi'). In many plants, proteins in the Argonaute (AGO) family, as main components of the RNA-induced silencing complex (RISC), play important roles in RNA silencing and pathogen resistance. The jujube telomere-to-telomere genome was searched by BLAST using Arabidopsis AGOs as probes. A total of nine jujube AGO gene members were identified, with each containing the conserved N-terminal, PZA, and PIWI domains. Phylogenetic analysis revealed that the nine jujube AGOs scattered into all three <i>Arabidopsis</i> AGO clades. Expression patterns of the <i>ZjAGO</i> genes were analyzed in response to phytoplasma in transcriptome data and by qRT-PCR. The jujube-phytoplasma interaction altered the expression of jujube <i>AGO</i> genes. <i>ZjAGO1</i> and <i>ZjAGO8</i> were up-regulated in the majority of the eight sampling periods subjected to qRT-PCR analysis. In the transcriptome data, <i>ZjAGO1</i> and <i>ZjAGO8</i> were also up-regulated during the key stages 37 and 39 weeks after grafting (WAG) with phytoplasma-infected material. These two jujube <i>Argonaute</i> genes may play important roles in response to JWB phytoplasma infection.