NtTPN1: a RPP8‐like R gene required for Potato virus Y‐induced veinal necrosis in tobacco

Abstract

Potato virus Y (PVY) is one of the most damaging viruses of tobacco. In particular, aggressive necrotic strains (PVY ) lead to considerable losses in yield. The main source of resistance against PVY is linked to the va locus. However, va-overcoming PVY isolates inducing necrotic symptoms were observed in several countries. In this context, it is important to find va-independent protection strategies. In a previous study, the phenotyping of 162 tobacco varieties revealed 10 accessions that do not carry the va allele and do not exhibit typical PVY -induced veinal necrosis. Despite the absence of necrotic symptoms, normal viral accumulation in these plants suggests a va-independent mechanism of tolerance to PVY -induced systemic veinal necrosis. Fine mapping of the genetic determinant(s) was performed in a segregating F2 population. The tolerance trait is inherited as a single recessive gene, and allelism tests demonstrated that eight of the 10 tolerant varieties carry the same determinant. Anchoring the linkage map to the tobacco genome physical map allowed the identification of a RPP8-like R gene, called NtTPN1 (for Nicotiana tabacum Tolerance to PVY-induced Necrosis1), with the same single-nucleotide polymorphism in the eight tolerant accessions. Functional assays using homozygous NtTPN1 EMS mutants confirmed the role of NtTPN1 in the tolerance phenotype. PVY -induced systemic veinal necrosis in tobacco likely represents an inefficient defense response with hypersensitive response-like characteristics. The identification of NtTPN1 opens breeding options to minimize the impact of emerging and so far uncontrolled va-breaking necrotic PVY isolates.

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

“…Genes for proteases with caspase-like activity that are markers of cell death were induced, as were also endoplasmic reticulum chaperones, markers of the endoplasmic reticulum stress response [105] (Figure 2), which is a known consequence of intensive viral multiplication [101]. Similarly, in the symptomatic part of tobacco leaves infected with PVY, the concentrations of ROS and PR gene induction was the strongest and correlated with detected high concentrations of the virus [14].…”

“…PVY is recognized by the plant by receptor proteins also in susceptible interaction [14], triggering the immune response, but the response is not able to restrict the virus (Figure 2). Several studies comparing sensitive and resistant interaction showed the importance of timing for efficient defense response.…”

“…On the molecular level, tolerant responses to PVY included attenuated expression of defense response genes (such as PR-1, PR-2, Figure 2) [14,107,109]. In the interaction of tolerant cv.…”

“…Potato cultivars have different genetic backgrounds, resulting in different responses to the virus. It was shown that a single mutation can shift the outcome [14]. On the other hand, studies of PVY strains showed an exceptional diversification via nucleotide mutation and genome recombination resulting in new strains and isolates with different degrees of pathogenicity [1,[15][16][17].…”

A complex eIF4E locus impacts the durability of va resistance to Potato virus Y in tobacco

“…The total RNA was adjusted to 50 mg/mL and was reverse transcribed according to the manufacturer’s instructions using the RevertAid H Minus enzyme (Thermo Scientific) and oligo(dT) primers. The cDNA was used to perform the real‐time Q‐RT‐PCR on the Light Cycler 480 Instrument II (Roche, Bâle, Switzerland), using the Light Cycler ® 480 SYBR Green I MASTER Kit (Roche, Bâle, Switzerland) following the protocol described in Michel et al (). The PCR mix per well included 10 µL of Master mix, 0.6 µL of each primer (0.3 mM) eIF4E‐2 Fwd and eIF4E‐2 Rev (Table ), and 5 µL of cDNA.…”