Identification and Characterization of NPR1 and PR1 Homologs in Cymbidium orchids in Response to Multiple Hormones, Salinity and Viral Stresses

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.

De novo transcriptome sequencing and analysis of salt-, alkali-, and drought-responsive genes in Sophora alopecuroides

“…The SaNPR1 gene was annotated as a regulatory protein NPR1-like, which is a positive regulatory gene in the salicylic acid signal pathway. Studies have shown that NRP1 participates in abiotic stresses including low temperature and salt stress through the salicylic acid signaling pathway [36][37][38][39][40], and that salicylic acid, as a plant stress signal, plays an important role under high pH stress conditions [41]. In the ethylene signaling pathway, 17 genes related to serine/threonine-protein kinase CTR1 were upregulated.…”

AhNPR3 regulates the expression of WRKY and PR genes, and mediates the immune response of the peanut (Arachis hypogaea L.)

“…In Madagascar periwinkle ( Catharanthus roseus ), silencing of CrNPR1 and CrNPR3 alters plant susceptibility to periwinkle leaf yellowing phytoplasma (Sung et al., 2019). Similarly, the CsNPR1‐2 gene of Cymbidium orchids could also mediate the SA signaling pathway independently, and confers the ability to resist Cymbidium mosaic virus infection (Ren et al., 2020). In Arabidopsis, there are six AtNPR genes namely AtNPR1 to AtNPR6 (Liu et al., 2005).…”

Salicylic Acid and Nitric Oxide: Insight Into the Transcriptional Regulation of Their Metabolism and Regulatory Functions in Plants

“…These SINCs are rich in stress proteins that trigger ETI by facilitating programmed cell death and SAR (Li et al, 2021). The fundamental role of NPR1 and NPR2 homologs in conferring viral resistance have also been identified and characterized in Cymbidium orchids (Ren et al, 2020), thus indicating SA-induced NPR proteins act as a central hub for modulating the expression of defense-related genes.…”