Oxylipin Biosynthesis Genes Positively Regulate Programmed Cell Death during Compatible Infections with the Synergistic Pair Potato Virus X-Potato Virus Y and Tomato Spotted Wilt Virus

Abstract

One of the most severe symptoms caused by compatible plant-virus interactions is systemic necrosis, which shares common attributes with the hypersensitive response to incompatible pathogens. Although several studies have identified viral symptom determinants responsible for systemic necrosis, mechanistic models of how they contribute to necrosis in infected plants remain scarce. Here, we examined the involvement of different branches of the oxylipin biosynthesis pathway in the systemic necrosis response caused either by the synergistic interaction of Potato virus X with Potato virus Y (PVX-PVY) or by Tomato spotted wilt virus (TSWV) in Nicotiana benthamiana. Silencing either 9-lipoxygenase (LOX), 13-LOX, or ␣-dioxygenase-1 (␣-DOX-1) attenuated the programmed cell death (PCD)-associated symptoms caused by infection with either PVX-PVY or TSWV. In contrast, silencing of the jasmonic acid perception gene, COI1 (Coronatine insensitive 1), expedited cell death during infection with compatible viruses. This correlated with an enhanced expression of oxylipin biosynthesis genes and dioxygenase activity in PVX-PVY-infected plants. Moreover, the Arabidopsis thaliana double lox1 ␣-dox-1 mutant became less susceptible to TSWV infection. We conclude that oxylipin metabolism is a critical component that positively regulates the process of PCD during compatible plant-virus interactions but does not play a role in restraining virus accumulation in planta.

The P25 Protein of Potato Virus X (PVX) Is the Main Pathogenicity Determinant Responsible for Systemic Necrosis in PVX-Associated Synergisms

“…LOX activity in soluble fractions was spectrophotometrically measured by monitoring the increase of the conjugated diene hydroperoxide at A 234 , as described previously (29). The assay was performed in the presence of 0.6 mM KCN to verify that the enzymatic activity was cyanide resistant.…”

“…Silencing of NbRAR1 and NbSGT1 mRNA was detected from upper, noninoculated leaf tissue by reverse transcriptase PCR at 14 dpa (29). To ensure that similar amounts of cDNA were used for silenced and nonsilenced plants, amplification of Actin was used as the internal control.…”

“…RT-PCR for the analysis of threonine deaminase (TD) and proteinase inhibitor I (PI-I) gene expression was performed as described by García-Marcos et al (29). The Actin gene transcripts were amplified as an internal control.…”

“…Real-time quantitative reverse transcriptase PCR (qRT-PCR) for virus detection was performed as described by García-Marcos and associates (29). The relative quantification of PCR products was calculated by the comparative cycle threshold (⌬⌬C T ) method.…”

“…Recently, we have shown that SN was correlated with an enhanced expression of lipoxygenase (LOX) activity in PVX-Potato virus Y (PVY)-infected plants (29). LOX action on polyunsaturated fatty acid substrates is the first step in the jasmonic acid (JA) biosynthesis pathway, a hormone involved in the execution of HR cell death in tobacco (30).…”