Primary Metabolism, Phenylpropanoids and Antioxidant Pathways Are Regulated in Potato as a Response to Potato virus Y Infection

Abstract

Potato production is one of the most important agricultural sectors, and it is challenged by various detrimental factors, including virus infections. To control losses in potato production, knowledge about the virus-plant interactions is crucial. Here, we investigated the molecular processes in potato plants as a result of Potato virus Y (PVY) infection, the most economically important potato viral pathogen. We performed an integrative study that links changes in the metabolome and gene expression in potato leaves inoculated with the mild PVYN and aggressive PVYNTN isolates, for different times through disease development. At the beginning of infection (1 day post-inoculation), virus-infected plants showed an initial decrease in the concentrations of metabolites connected to sugar and amino-acid metabolism, the TCA cycle, the GABA shunt, ROS scavangers, and phenylpropanoids, relative to the control plants. A pronounced increase in those metabolites was detected at the start of the strong viral multiplication in infected leaves. The alterations in these metabolic pathways were also seen at the gene expression level, as analysed by quantitative PCR. In addition, the systemic response in the metabolome to PVY infection was analysed. Systemic leaves showed a less-pronounced response with fewer metabolites altered, while phenylpropanoid-associated metabolites were strongly accumulated. There was a more rapid onset of accumulation of ROS scavengers in leaves inoculated with PVYN than those inoculated with PVYNTN. This appears to be related to the lower damage observed for leaves of potato infected with the milder PVYN strain, and at least partially explains the differences between the phenotypes observed.

Fig 1. Overview of the response of individual leaf sample and changes of metabolites in inoculated leaves.

Mock-inoculated (S, 1 to 6), PVY^N-inoculated (N, 1 to 6), and PVY^NTN-inoculated (NTN, 1 to 6) leaves, collected at 1, 3 and 6 dpi, are shown. Distance matrix (A) shows more similar responses between samples collected at 1 dpi and at 6 dpi, while less uniform response is observed in samples collected at 3 dpi. Hierarchical clustering (B) was done on a set of identified metabolites to which metabolite ontology (metabolic pathway) was assigned. Clusters of metabolites linked to amino-acid synthesis and those linked to secondary metabolism and cell wall clustered together.

Fig 2. Venn diagrams showing the numbers of statistically significantly differentially accumulated metabolites at the different times in the inoculated leaves (A) and non-inoculated leaves (B).

Diagrams are showing the number of metabolites in PVY^N-inoculated and PVY^NTN-inoculated leaves, relative to the mock-inoculated leaves (N/mock, NTN/mock, respectively). The intercept areas show the numbers of metabolites that were common to both of the plant responses in the comparisons.

Fig 3. Integration of the changes in the metabolites and transcripts associated with selected metabolic pathways in the PVY^N-inoculated and PVY^NTN-inoculated leaves, relative to the mock-inoculated leaves.

The metabolites identified and the genes analysed from the primary and secondary metabolism and from redox reactions are shown. Each coloured square represents the log2 ratios of the expression or abundance (red, high; green, low) at 1, 3 and 6 dpi in the PVY^N-inoculated (N:m) and PVY^NTN-inoculated (NTN:m) leaves, relative to the mock-inoculated leaves (as indicated). MapMan BINs linked to primary metabolism: 2.1.1 major CHO metabolism, sucrose synthesis; 2.2.1 major CHO metabolism, sucrose degradation; 2.2.2 major CHO metabolism, starch degradation. MapMan BINs linked to the GABA shunt: 13.1.1.1 amino-acid metabolism, GABA synthesis; 8.1. TCA; 22. polyamine metabolism; 12.2.1002 N-metabolism, ammonia. MapMan BINs linked to secondary metabolism: 16.2.1 secondary metabolism, phenylpropanoids biosynthesis; 13.1. amino-acid synthesis.

Fig 4. Integration of the changes in the metabolites associated with selected metabolic pathways in the upper non-inoculated leaves from the PVY^N-inoculated and PVY^NTN-inoculated plants, relative to the mock-inoculated plants.

The metabolites identified from the primary and secondary metabolism and from redox reactions are shown. Each coloured square represents the log2 ratios of the concentration (red, high; green, low) at 3 and 6 dpi in the upper non-inoculated leaves of the PVY^N-inoculated (N:m) and PVY^NTM-inoculated (NTN:m) plants, relative to the mock-inoculated plants (as indicated). MapMan BINs linked to primary metabolism: 2.1.1 major CHO metabolism, sucrose synthesis; 2.2.1 major CHO metabolism, sucrose degradation; 2.2.2 major CHO metabolism, starch degradation. MapMan BINs linked to the GABA shunt: 13.1.1.1 amino-acid metabolism, GABA synthesis; 8.1. TCA; 22. polyamine metabolism; 12.2.1002 N-metabolism, ammonia. MapMan BINs linked to secondary metabolism: 16.2.1 secondary metabolism, phenylpropanoids biosynthesis; 13.1. amino-acid synthesis.