An ANNEXIN-Like Protein from the Cereal Cyst Nematode <i>Heterodera avenae</i> Suppresses Plant Defense

<div><p>Parasitism genes encoding secreted effector proteins of plant-parasitic nematodes play important roles in facilitating parasitism. An annexin-like gene was isolated from the cereal cyst nematode <i>Heterodera avenae</i> (termed <i>Ha-annexin</i>) and had high similarity to <i>annexin 2</i>, which encodes a secreted protein of <i>Globodera pallida</i>. <i>Ha-annexin</i> encodes a predicted 326 amino acid protein containing four conserved annexin domains. Southern blotting revealed that there are at least two homologies in the <i>H</i>. <i>avenae</i> genome. <i>Ha-annexin</i> transcripts were expressed within the subventral gland cells of the pre-parasitic second-stage juveniles by <i>in situ</i> hybridization. Additionally, expression of these transcripts were relatively higher in the parasitic second-stage juveniles by quantitative real-time RT-PCR analysis, coinciding with the time when feeding cell formation is initiated. Knockdown of <i>Ha-annexin</i> by method of barley stripe mosaic virus-based host-induced gene silencing (BSMV-HIGS) caused impaired nematode infections at 7 dpi and reduced females at 40 dpi, indicating important roles of the gene in parasitism at least in early stage <i>in vivo</i>. Transiently expression of Ha-ANNEXIN in onion epidermal cells and <i>Nicotiana benthamiana</i> leaf cells showed the whole cell-localization. Using transient expression assays in <i>N</i>. <i>benthamiana</i>, we found that Ha-ANNEXIN could suppress programmed cell death triggered by the pro-apoptotic mouse protein BAX and the induction of marker genes of PAMP-triggered immunity (PTI) in <i>N</i>. <i>benthamiana</i>. In addition, Ha-ANNEXIN targeted a point in the mitogen-activated protein kinase (MAPK) signaling pathway downstream of two kinases MKK1 and NPK1 in <i>N</i>. <i>benthamiana</i>.</p>