Supplementation of mineral nutrients limits the viral RNA accumulation and systemic spread in Vigna unguiculata infected with Groundnut bud necrosis virus

Abstract

Groundnut bud necrosis virus (GBNV), a tripartite ambisense RNA genome containing plant virus fall under the family Bunyaviridae and genus Tospovirus. It infects majorly the crops belonging to the leguminosae and solanaceae families, causing characteristic symptoms such as chlorotic and necrotic spots on the leaves. Previously we reported that GBNV infection cycle induces the necrotic cell death at inoculated site and early senescence at the systemic site in the GBNV inoculated plants. In the current study we tried to understand the effect of macro and micro-nutrient supplementation on the viral disease development during GBNV infection in cowpea plant. We found that supplementation of macro-nutrients P (Phosphorus) and K (Potassium), and micro-nutrient Zn (Zinc) reduced the viral accumulation and inhibits the viral spread to systemic site. Whereas the supplementation of micro-nutrient Mn (Manganese) did not show any effect on disease development. Infected plants showed the chlorotic spots at inoculated site, those turned to necrotic as the infection progressed. Occurrence of oxidative stress was judged by the increased concentration of H2O2 (ROS) both at inoculated and systemic sites. ROS concentration was lower in the plants supplemented with nutrients P, K and Zn than the Mn supplemented and non-supplemented plants. We also we conducted a comparative analysis of antioxidants enzymes activities and examined oxidative stress responsive micro RNAs (miRNAs) along with their corresponding target transcripts in cowpea plants infected with GBNV at both inoculated and systemic sites. Antioxidants enzymes activities such as catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX), were more induced in the plants supplemented with nutrients P, K and Zn than the supplemented with Mn and non-supplemented plants during viral infection. We also found the up-regulation of miR319 controlling metacaspase, responsible for initiation of cell death and down-regulation of miR398 and mir482 controlling COX-5b (Cytochrome C oxidase subunit 5b) and NBS-LRR genes, respectively in the plants supplemented with nutrients P, K and Zn than the supplemented with Mn and non-supplemented plants. Production of stress signals in plant induced with supplementation of macro and micro-nutrients with reduction in viral symptoms both at inoculation and systemic sites are also discussed.