Abstract
The plant nonexpressor of pathogenesis-related 1 (NPR1) and pathogenesis-associated 1 (PR1) genes play fundamental roles in plant immunity response, as well as abiotic-stress tolerance. Nevertheless, comprehensive identification and characterization of NPR1 and PR1 homologs has not been conducted to date in Cymbidium orchids, a valuable industrial crop cultivated as ornamental and medicinal plants worldwide. Herein, three NPR1-like (referred to as CsNPR1-1, CsNPR1-2, and CsNPR1-3) and two PR1-like (CsPR1-1 and CsPR1-2) genes were genome-widely identified from Cymbidium orchids. Sequence and phylogenetic analysis revealed that CsNPR1-1 and CsNPR1-2 were grouped closest to NPR1 homologs in Zea mays (sharing 81.98% identity) and Phalaenopsis (64.14%), while CsNPR1-3 was classified into a distinct group with Oryza sativa NPR 3 (57.72%). CsPR1-1 and CsPR1-2 were both grouped closest to Phalaenopsis PR1 and other monocot plants. Expression profiling showed that CsNPR1 and CsPR1 were highly expressed in stem/pseudobulb and/or flower. Salicylic acid (SA) and hydrogen peroxide (H2O2) significantly up-regulated expressions of CsNPR1-2, CsPR1-1 and CsPR1-2, while CsNPR1-3, CsPR1-1 and CsPR1-2 were significantly up-regulated by abscisic acid (ABA) or salinity (NaCl) stress. In vitro transcripts of entire Cymbidium mosaic virus (CymMV) genomic RNA were successfully transfected into Cymbidium protoplasts, and the CymMV infection up-regulated the expression of CsNPR1-2, CsPR1-1 and CsPR1-2. Additionally, these genes were transiently expressed in Cymbidium protoplasts for subcellular localization analysis, and the presence of SA led to the nuclear translocation of the CsNPR1-2 protein, and the transient expression of CsNPR1-2 greatly enhanced the expression of CsPR1-1 and CsPR1-2. Collectively, the CsNPR1-2-mediated signaling pathway is SA-dependent, and confers to the defense against CymMV infection in Cymbidium orchids.
Highlights
The Orchidaceae is one of the largest and the most evolved families of monocot plants [1]
Genome-wide identification resulted in three CsNPR1-like and two CsPR1-like genes (CsPR1-1 and CsPR1-2) being identified from Cymbidium sinense
Based on a genome-widely identification, three CsNPR1-like (CsNPR1-1, CsNPR1-2 and CsNPR1-3) and two CsPR1-like (CsPR1-1 and CsPR1-2) genes were isolated from Cymbidium orchids
Summary
The Orchidaceae is one of the largest and the most evolved families of monocot plants [1]. The nonexpressor of pathogenesis-related 1 (NPR1) plays a key role in multiple signaling pathways in plant immunity [12] and abiotic-stress tolerance [13,14,15]. The NPR1 protein has been demonstrated as an essential regulator of long-lasting and broad-spectrum systemic acquired resistance (SAR) contributing to resistance against fungal, bacterial and viral pathogens [16,17]. When SAR occurs, several pathogenesis-related (PR) genes are active locally at the site of infection and systemically in distal plant tissues [20,21]. To investigate the involvement of the NPR1-mediated signaling pathway in Cymbidium orchids, the expression of CsNPR1 and CsPR1 genes in response to phytohormones, abiotic salinity stresses and CymMV infection were examined. We figured out the NPR1-mediated signaling pathway, which is Salicylic acid-dependent and triggered by CymMV infection in Cymbidium orchids
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