Rsv1-Mediated Resistance Against Soybean mosaic virus-N Is Hypersensitive Response-Independent at Inoculation Site, but Has the Potential to Initiate a Hypersensitive Response-like Mechanism

Abstract

Rsv1, a single dominant gene in soybean PI 96983, confers resistance to most strains of Soybean mosaic virus (SMV), including strain G2. The phenotypic response includes the lack of symptoms and virus recovery from mechanically inoculated leaves. To study the resistance mechanism, SMV-N (an isolate of strain G2) was introduced into PI 96983 by grafting. Hypersensitive response (HR)-like lesions occurred on the stems, petioles, and leaf veins, and virus was recovered from these lesions. The response demonstrated the cytological and histological characteristics of HR as well as elevated transcription of a soybean salicylic acid-inducible, pathogenesis-related (PR-1) protein gene. Mechanical inoculation of PI 96983 primary leaves with a high level of SMV-N virions caused no symptoms or up regulation of the PR-1 protein gene transcript. Furthermore, inoculation with infectious viral RNA did not alter the resistance phenotype. The data suggest that interaction of SMV-N with Rsv1 has the potential to induce an HR-like defense reaction. Rsv1-mediated resistance in the inoculated leaf, however, is HR-independent and operates after virion disassembly.

Plant Pathogen Forensics: Capabilities, Needs, and Recommendations

“…In some cases, plant host cells have the ability to recognize and silence double-stranded forms of virus transcripts. In fact, viral infection often activates or inactivates transcription or translation of a number of host plant genes in both the susceptible and the resistant reactions (71). This reaction has been studied in the SMV system, in which variability in any of the viral or virus-specific host gene products could be targets for forensic exploration.…”

Loss and Gain of Elicitor Function of Soybean Mosaic Virus G7 Provoking Rsv1 -Mediated Lethal Systemic Hypersensitive Response Maps to P3

“…The arrest of an avirulent virus in ERexpressing tissues is not associated with any visible symptoms or virus accumulation (5,28). However, in HR-expressing tissues, the arrest is associated with rapid, localized death of infected and neighboring cells; induction of a variety of defense-related genes including pathogenesis-related (PR) proteins; and a wide range of physiological changes (32).…”

“…Perturbation of Avr or R genes (15,20,41), graft inoculation instead of mechanical inoculation (6,28,69,72), change in genetic background of the R gene-carrying plant (45), heterozygosity rather than homozygosity of the R-genotype plant (10,52,56), prevention of salicylic acid accumulation in the R-genotype plant (19,42), or temperature shift (30,70) can result in virus escape to distant tissues, provoking systemic HR (SHR) in resistant genotypes. Occasionally, SHR will result in the death of the infected plant, a condition termed lethal SHR (LSHR) (28,29).…”

“…Occasionally, SHR will result in the death of the infected plant, a condition termed lethal SHR (LSHR) (28,29). Elicitation of SHR, instead of localized HR, is not unique to the interactions involving avirulent viruses and resistant plants.…”

“…However, an isolate belonging to the G2 group of SMV strains (11), SMV-N (68), has the potential to induce Rsv1-mediated restricted SHR when the virus is introduced continuously into Rsv1-bearing scions from infected rootstocks (28). SMV-G7 overcomes Rsv1-mediated ER and spreads systemically in infected PI 96983 (Rsv1) tissues, where it provokes SHR, which eventually progresses to LSHR (28,29). Induction of LSHR by pSMV-G7 is consistently associated with up regulation of a soybean PR-1 gene transcript (28,29), which is considered a universal molecular marker of HR (17).…”