The Sw-5b NLR Immune Receptor Induces Early Transcriptional Changes in Response to Thrips and Mechanical Modes of Inoculation of Tomato spotted wilt orthotospovirus

Abstract

The nucleotide-binding leucine-rich repeat (NLR) class of immune receptor, Sw-5b confers resistance to Tomato spotted wilt orthotospovirus (TSWV). Although Sw-5b is known to activate immunity upon recognition of the TSWV movement protein NSm, we know very little about the downstream events that lead to resistance. Here, we investigated the Sw-5b-mediated early transcriptomic changes that occur in response to mechanical and thrips-mediated inoculation of TSWV using near-isogenic tomato lines, CNPH-LAM 147 (Sw5b+/+) and Santa Clara (Sw-5b-/-). We observed earlier Sw-5b-mediated transcriptional changes in response to thrips-mediated inoculation compared to mechanical inoculation of TSWV. With thrips-mediated inoculation, differentially expressed genes (DEGs) were observed at 12, 24 and 72 hours post-inoculation (hpi). Whereas, with mechanical inoculation, DEGs were observed only at 72 hpi. Although some DEGs were shared between the two methods of inoculation, many DEGs were specific to either thrips-mediated or mechanical inoculation of TSWV. In response to thrips-mediated inoculation, an NLR immune receptor, cysteine-rich receptor-like kinase, G-type lectin S-receptor-like kinases, the ethylene response factor 1 and the calmodulin-binding protein 60 were induced. Fatty acid desaturase 2-9, cell death genes, DCL2b, RIPK/PBL14-like, ERF017 and WRKY75 were differentially expressed in response to mechanical inoculation. Our findings reveal Sw-5b responses specific to the method of TSWV inoculation. Although TSWV is transmitted in nature primarily by the thrips, Sw-5b responses to thrips inoculation have not been previously studied. Therefore, the DEGs we have identified in response to thrips-mediated inoculation provide a new foundation for understanding the mechanistic roles of these genes in the Sw-5b-mediated resistance.

The genome of a bunyavirus cannot be defined at the level of the viral particle but only at the scale of the viral population

“…All plants were seeded and maintained in a growth chamber with a 16/8-h day/night photoperiod, a constant temperature of 20 °C, and 70% hygrometry. The TSWV isolate used in this study is the TSWV MR-01 ( 47 ), maintained as a −80 °C frozen stock of Datura stramonium (L.) leaves collected from plants initially infected through transmission by the natural thrips vector Frankliniella occidentalis (Pergande). Nicotiana rustica (L.) plantlets at the sixth leaf stage were mechanically inoculated on their fourth leaf, by rubbing a virus suspension prepared from the frozen stock with 1 g of infected leaves ground in 3 mL of 0.01 M phosphate buffer (pH 7.5) with the addition of Carborundum or Celite abrasive powder.…”

Novel sources of resistance/tolerance to orthotospoviruses in Lactuca germplasm identified via field exposure to viruliferous vectors and in greenhouse mechanical transmission assays

“…Three weeks after inoculation, the disease incidence was assessed by collecting new emerged leaves for the NCM-ELISA test. Plants of D. stramonium and N. rustica were the positive controls to monitor the viability of the virus inoculum, and plants of the tomato inbred line 'LAM 147' with the Sw-5b gene in homozygous condition(Ordaz et al 2023) were the negative controls. Air temperatures were…”