Spatial accumulation of salicylic acid is regulated by RBOHD in potato immunity against viruses

Abstract

Corresponding author: Tjaša Lukan (tjasa.lukan@nib.si). SIGNIFICANCETo get towards sustainable resistance in the field, it is important to understand mechanisms of immune signaling. We here show novel aspects of spatial regulation in effector-triggered immunity (ETI) against potato virus Y. A detailed spatiotemporal analysis in and surrounding the foci of viral infection, on ultrastructural, biochemical and gene expression levels revealed that redox state maintenance is tightly spatiotemporally regulated. We also show the interconnection of salicylic acid and RBOHD through a feedback loop, regulated through UDP-glucosyltransferase, revealing the mechanism of this spatial regulation. The proper function of this loop is essential for successful ETI leading to viral arrest. ABSTRACTWhile activation of resistance (R) proteins has been intensively studied, the mechanisms acting downstream of R protein activation remain elusive. We studied effector-triggered immunity (ETI) conditioned by the potato Ny-1 gene against potato virus Y. Transcriptomic, ultrastructural and biochemical analyses of four consecutive tissue sections in and surrounding the foci of viral infection at three different lesion developmental stages revealed processes that are spatiotemporally regulated.The transcriptional response in the cell death zone and surrounding tissue is dependent on SA. For 2 some of the genes, spatiotemporal regulation is completely lost while for others, the regulation is different in SA-deficient line indicating multiple connections between hormonal signaling modules. The induction of RBOHD NADPH oxidase expression, together with expression of Thioredoxin H gene, occurs specifically in the border region of the lesion during ETI. In plants with silenced RBOHD, ETI is perturbed and virus spread is not arrested at the site of infection. Expression of RBOHD is under the control of SA. On the other hand, RBOHD activity is required for spatial regulation of SA accumulation.We identified an UDP-glucosyltransferase, encoding an enzyme involved in feedback activation of SA biosynthesis, that is derepressed at the border of the lesion in RBOHD silenced plants. Altogether, we revealed a novel aspect of viral ETI, the RBOHD-SA feedback loop required for its spatial regulation.

Plant Molecular Responses to Potato Virus Y: A Continuum of Outcomes from Sensitivity and Tolerance to Resistance

“…Early induction of photosynthesis-related genes, that could be related to increased energy demands for efficient defense response, was observed in HR of potato with PVY [58,65] (Figure 2). Similarly, granule bound starch synthase gene was induced only in the tissue surrounding viral foci in incompatible interaction [20].…”

“…Rywal, detection of large amounts of hydrogen peroxide and upregulation of several genes involved in redox state regulation from 1 day post-inoculation (dpi) indicated the importance of ROS signalling in an efficient HR ( [58], Figure 2). Recent spatiotemporal analysis of responses in and surrounding the foci of viral infection, on ultrastructural, biochemical, and gene expression levels revealed that tight spatiotemporal regulation of redox state maintenance is required for the successful arrest of the virus [20]. Respiratory Burst Oxidase Homolog D (RBOHD) regulates spatial distribution of SA accumulation and is indispensable for viral arrest [20].…”

“…Recent spatiotemporal analysis of responses in and surrounding the foci of viral infection, on ultrastructural, biochemical, and gene expression levels revealed that tight spatiotemporal regulation of redox state maintenance is required for the successful arrest of the virus [20]. Respiratory Burst Oxidase Homolog D (RBOHD) regulates spatial distribution of SA accumulation and is indispensable for viral arrest [20]. RBOHD protein accumulation and distribution were also different in HR-mediated resistance and sensitive response in cv.…”

“…On the other hand, in SA-deficient genotype, expressing salicylate hydroxylase (NahG), NahG-Rywal, the SA biosynthesis induction responded in narrower timespan and JA and ethylene biosynthesis were induced faster compared to nontransgenic genotype [58]. SA was also shown to regulate the transcriptional events in and around the foci of viral amplification as, for some genes, spatiotemporal regulation was lost or, for some, altered in SA-depleted plants [20].…”

“…On the other hand, the appearance of symptoms did not differ in HR response to PVY N605 -GFP, PVY NTN , and PVY N-Wilga in cv. Rywal [20]. There are also many examples that the outcome of the interaction is affected by abiotic environmental factors [21] and in mixed infections with other viruses ( [22][23][24], see also review [25]).…”