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Hydrogen Peroxide Accumulation and Transcriptional Changes in Grapevines Recovered from Flavescence Dorée Disease

First, second, and fifth authors: Plant Virology Institute, National Research Council (IVV-CNR), Grugliasco Unit, Via L. da Vinci 44, 10095 Grugliasco-TO, Italy; and third and fourth authors: Plant Virology Institute, National Research Council (IVV-CNR), Torino, Strada delle Cacce 73, 10135 Torino, Italy.

Flavescence dorée (FD) is considered one of the most severe phytoplasma diseases affecting grapevine. The spontaneous, complete, and stable remission of the symptoms of FD (recovery) is a phenomenon that may occur in infected grapevines. The molecular bases of this phenomenon are still unclear, although some works suggest that recovery could be linked to the accumulation of hydrogen peroxide (H₂O₂). Several genes coding for enzymes involved in H₂O₂ metabolism, in the ascorbate-glutathione cycle, defense responses, and the biosynthesis of hormones were identified. The H₂O₂ content was biochemically determined and the expression levels of 44 genes were analyzed through quantitative real-time reverse-transcription polymerase chain reaction in healthy (H), infected by FD-associated phytoplasma (I), and 2-years-recovered (R) plants of Vitis vinifera ‘Barbera’. In tissues of R plants, large amounts of H₂O₂ were detected, essentially linked to an upregulation of genes involved in the production of H₂O₂ (germin-like protein and glycolate oxidase); whereas, in I grapevines, the overexpression of some scavenging genes reduced the quantity of H₂O₂. The recovery state was characterized by the activation of ethylene biosynthesis and of defense genes not linked to salicylic acid (SA) signaling, such as the WRKY2 transcription factor. Conversely, I plants reacted to phytoplasma with SA-mediated signaling, even though this response does not appear to be effective against the pathogen.

Additional keywords: reactive oxygen species.