The role of enzymatic activities of antiviral proteins from plants for action against plant pathogens

Comparative antiviral resistance induction by CIP-29, a ribosome-inactivating protein from Clerodendrum inerme, and salicylic acid, a chemical

CIP-29, a basic glycoprotein purified from the leaves of Clerodendrum inerme, induces resistance against viruses in plants. It is a type-I ribosome-inactivating protein (RIP) with polynucleotide:adenosine glycosidase activity. Present study was made to compare the resistance induced against TMV by CIP-29 and salicylic acid (SA), a chemical elicitor of systemic acquired resistance (SAR). Foliar treatments with CIP-29 (20 µg mL-1) and SA (2.5 mM) on Nicotiana tabacum cv. Xanthi-nc resulted in a percent reduction of TMV lesion number by 99 and 64 on remote leaves and decrease in lesion diameter by 2.67- and 1.97-fold, respectively. CIP-29-treated (resistant) tobacco leaf extract inhibited TMV by 93%, as against 25% by SA, suggesting induction of a virus inhibitory agent (VIA) in the former. In semi-quantitative gene expression analysis of treated and inoculated (+V) sets of tobacco Xanthi-nc, PR1a (PR-1) and Osmotin (PR-5) gene transcripts were significantly enhanced only in SA-treated set, and showed pronounced accumulation in both CIP-29+V and SA+V. Acidic chitinase (PR-3) transcripts were detectable only in SA and SA+V. Expression of allene oxide cyclase (AOC) gene was prominent in CIP-29+V and DW+V, while 1-aminocyclopropane-1-carboxylate oxidase (ACO) and ethylene responsive factor 1 (ERF1) genes were expressed in greater intensity in CIP-29+V. In qPCR analysis of ACO and ERF1 genes, a respective fold increase of 377.4 and 25.1 was observed in the post-inoculated CIP-29-treated sets compared to an increase by 22.5- and 10.2-fold in SA-treated sets. Between 14 and 28 days post-inoculation with TMV, symptomatic plants of Solanum lycopersicum increased from 0 to 20% in the CIP-29 treated set, compared to an increase from 30 to 90% in SA-treated set. Greater delay in symptom progression and accumulation of TMV was noted in CIP-29 compared to SA-treated sets, while growth parameters were significantly higher following SA treatment. This study clearly points to different mechanisms governing phytoprotein and chemical induced resistance.

Antiviral agent fTDP stimulates the SA signaling pathway and enhances tobacco defense against tobacco mosaic virus

TEER-decreasing protein (TDP) from Flammulina velutipes was antiviral resource against tobacco mosaic virus (TMV). However, the resistance mechanisms have not been clarified. In this study, the fTDP (fusion teer-decreasing protein), obtained by prokaryotic fusion expression system, exhibited obvious protective efficacy against TMV and significantly suppressed the reproduction of TMV in tobacco. Transcriptomics and proteomics analysis showed that fTDP may interact with a receptor, activate the mitogen-activated protein kinase (MAPK) pathway and NB-ARC and increase the content of reactive oxygen species (ROS) and salicylic acid (SA), which promoted the hypersensitive response (HR) and system acquired resistance (SAR). SAR caused increased expression of catalase (CAT), pathogenesis-related protein 1 (PR1), phenylalanine ammonia lyase (PAL) and other proteins involved in pathogen defense, such as chalcone-dihydroflavone isomerase (CHI) and cytochrome P450. In conclusion, SAR was induced by fTDP to protect tobacco from TMV infection and alleviate the symptoms caused by the virus. The study provided a theoretical basis for the application of the TDP protein, which may represent a potential biopesticide.