Incidence of GLMD-Like Symptoms on Grapevines Naturally Infected by Grapevine Pinot gris virus, Boron Content and Gene Expression Analysis of Boron Metabolism Genes

Abstract

Grapevine Pinot gris virus (GPGV) is considered to be a causal agent of Grapevine Leaf Mottling and Deformation (GLMD) disease that has been reported worldwide through the grapevine-growing regions. Seven grapevines that were collected from a vineyard in the Czech Republic were tested for the presence of GPGV in leaf and phloem tissues. Each of the seven grapevines was infected by GPGV, from which sic symptoms were mostly shown without a typical mottling. The phylogeny based on RNA-dependent RNA polymerase and movement/coat protein sequences indicated the same origin of the GPGV isolates. The GPGV titer was the highest in the grapevines with the highest GLMD-like symptoms; however, some of the grapevines with milder GLMD-like symptoms had a lower GPGV titer than the asymptomatic grapevine. Soil analysis showed uneven boron content in the direct vicinity of the grapevines, while the boron content in the grapevines was more, even showing no boron deficiency. The quantitative analysis of selected gene expressions associated with boron efflux and transport only partially explained the boron content in the soil and grapevines and only in the grapevines growing in soils with the highest or lowest boron contents. The VvBor2 and VvNIP5 genes had a higher expression and VvNIP6 had a lower expression in the grapevine growing in the soil with the lowest boron content, while a low expression of VvBor1 and VvBor2 was observed in the grapevine that was grown in the soil with the highest boron content.

The conundrum of the connection of grapevine Pinot gris virus with the grapevine leaf mottling and deformation syndrome

“…We hypothesize that GLMD symptoms could be primarily related to the activation and suppression of antiviral RNA silencing, which in turn is affected by the occurrence of mixed infections by distinct strains of the virus with variable virulence. Moreover, suppression of antiviral defence by GPGV CP may directly or indirectly interfere with unrelated physiological pathways, such as those mediating boron homoeostasis (Buoso et al, 2020; Ermacora et al, 2018; Kiss et al, 2021), further affecting symptom expression and severity (Senda, 2004). Unquestionably, further studies are necessary to clarify the picture.…”

“…However, analysis carried out on field-grown plants did not corroborate the results obtained in hydroponics systems. Other studies (Kiss et al, 2021; have reported alterations to gene expression associated with boron efflux and transport that, independent of symptom display, may prove useful as a marker of the disease.…”